mechanical+ventilation-basics+for+beginners [unlocked by com

Basics for beginners

Mechanical Ventilation

Definition

It is a method to mechanically assist or replace spontaneous breathing when patients can not do so on their own

General Considerations Mechanical ventilation has resulted in profoundly improved survival from acute and chronic respiratory failure

Mechanical ventilation in the intensive care unit (ICU) is delivered under positive pressure in contrast to normal human breathing in which inspiration induces negative pressure in the thorax This makes the complications of barotrauma and hypotension predictable To achieve ventilation rate tidal volume (VT) fraction of inspired oxygen (FIO2) and positive end-expiratory pressure (PEEP) are selected It is useful to track the product of VT and rate the minute ventilation (E) to assess for complications and readiness to wean A normal E is less then 10 Lmin Pressures in ventilators There are two types of pressures used in ventilators

a Negative pressure ventilators The best example is ldquoiron lungrdquo that creates a negative pressure environment around the patientrsquos chest thus sucking air into the lungs This is a large elongated tank which encases the patient up to the neck The neck is sealed with a rubber gasket so that the petientrsquos face and airway are exposed to the room air This was largely used to treat patients with respiratory paralysis due to poliomyelitis

triplehelix Mechanical Ventilation

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b Poistive pressure ventilators This is the main form of ventilators currently used

These ventilators work by increasing the pressure in the patientrsquos airway and thus forcing additional air into the lungs

The fundamental difference between positive pressure and negative pressure is in positive pressure ventilation air is introduced into the lungs forcefully creating positive pressure but in negative pressure ventilation negative pressure is created outside of the lungs that sucks the chest to inflate and creates negative pressure within lungs as a result air flows into the lungs

Ventilation Invasive Vs non-invasive The difference is just use of a tube (ie endotracheal tube tracheostomy tube) If you use endotracheal tube it is invasive ventilation If you do not use it is non-invasive ventilation Non-invasive ventilation can be delivered with the use either of

a Negative pressure ventilators (eg Iron lung) b Positive pressure assistance to the airway by mask (using NIPPV) Non Invasive

Positive Pressure Ventilation (NIPPV) can be delivered by several appliances including face masks nasal masks nasal pillows etc


4

Bi-PAP setting


5

Nasalface mask


6


7


8

Nasotracheal intubation


9

Positive pressure machines


10

Negative-pressure ventilation

Uuml Negative-pressure ventilators support ventilation by lowering the pressure surrounding the chest wall during inspiration and reversing the pressure to atmospheric level during expiration These devices augment the tidal volume by generating negative extrathoracic pressure

Uuml Several of these devices such as body ventilators and iron lungs are available and either cover the whole body below the neck or apply negative pressure to the thorax and abdomen

Noninvasive positive-pressure ventilation (NPPV)

Uuml NPPV is delivered by a nasal or face mask therefore eliminating the need for intubation or tracheostomy NPPV can be given by a volume ventilator a pressure-controlled ventilator a bilevel positive airway pressure (BIPAP or bilevel ventilator) device or a continuous positive airway pressure (CPAP) device Volume ventilators are often not tolerated because they generate high inspiratory pressures that result in discomfort and mouth leaks

Uuml NPPV delivers a set pressure for each breath (with a bilevel or standard ventilator in the pressure-support mode) Although positive-pressure support is usually well tolerated by patients mouth leaks or other difficulties are sometimes encountered BIPAP ventilators provide continuous high-flow positive airway pressure that cycles between a high positive pressure and a lower positive pressure

Uuml NPPV may be used as an intermittent mode of assistance depending on patients clinical situations Instantaneous and continuous support is given to the patients in acute respiratory distress As the underlying condition improves ventilator-free periods are increased as tolerated and support is discontinued when the patient is deemed stable In most studies the duration of NPPV use in patients with acute on chronic respiratory failure averages 6-18 hours

Uuml The total duration of ventilator use varies with the underlying disease approximately 6 hours is used for acute pulmonary edema and more than 2 days is used for COPD exacerbation

Mechanisms of action Uuml NPPV decreases the work of breathing and thereby improves alveolar ventilation

while simultaneously resting the respiratory musculature The improvement in gas exchange with BIPAP occurs because of an increase in alveolar ventilation

Uuml Externally applied expiratory pressure (eg positive end-expiratory pressure [PEEP]) decreases the work of breathing by partially overcoming the auto-PEEP which is frequently present in these patients The patients generate a less negative inspiratory force to initiate a breathing cycle


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Inhalation and exhalation Uuml In spontaneous mode upon detection of inspiration higher pressure is delivered

until the flow rate falls below the threshold level The expiratory pressure with bilevel pressure support is equivalent to the PEEP and the inspiratory pressure is equivalent to the sum of the PEEP and the level of pressure support

Uuml In timed mode biphasic positive airway pressure ventilation alternates between the inspiratory and expiratory pressures at fixed time intervals which allows unrestricted breathing at both pressures This differs from the spontaneous mode of BIPAP which cycles on the basis of the flow rates of the patients own breathing

Uuml Supplemental oxygen can be connected to the device but a higher flow of oxygen therapy is usually required

Uuml NPPV is more effective in a relaxed patient and is not optimal in an anxious uncooperative patient or a patient fighting the ventilator Patients must be adequately prepared with properly fitting masks and the increase of the inspiratory and the expiratory pressures should occur gradually

Uuml Effectiveness should be determined clinically by improved respiratory distress decreased patient discomfort and improved results from arterial blood gas determinations

BIPAP ventilator versus conventional ventilator

The conventional ventilator offers a number of advantages such as the delivery of precise oxygen concentrations and separate inspiratory and expiratory tubing that minimizes carbon dioxide rebreathing Patient disconnection can be readily detected because monitoring and alarm features are more sophisticated in conventional ventilators than in bilevel systems

Nasal mask versus face mask

No randomized trials have compared nasal masks to full face masks in NPPV Most patients in acute respiratory failure are mouth breathers therefore a facial mask may be preferable in some patients These patients should be carefully observed because of the risk of aspiration


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Neurally Adjusted Ventilatory Assist (NAVA)

Uuml NAVA is a new positive pressure mode of mechanical ventilation where the ventilator is controlled directly by the patients own neural control of breathing

Uuml The neural control signal of respiration originates in the respiratory center and are transmitted through the phrenic nerve to excite the diaphragm These signals are monitored by means of electrodes mounted on a nasogastric feeding tube and positioned in the esophagus at the level of the diaphragm As respiration increases and the respiratory center requires the diaphragm for more effort the degree of ventilatory support needed is immediately provided

Uuml This means that the patients respiratory center is in direct control of the mechanical support required on a breath-by-breath basis and any variation in the neural respiratory demand is responded to by the appropriate corresponding change in ventilatory assistance

Choosing amongst ventilator modes

Uuml Assist-control mode minimizes patient effort by providing full mechanical support with every breath This is often the initial mode chosen for adults because it provides the greatest degree of support

Uuml In patients with less severe respiratory failure other modes such as SIMV may be appropriate

Uuml Assist-control mode should not be used in those patients with a potential for respiratory alkalosis in which the patient has an increased respiratory drive Such hyperventilation and hypocapnia (decreased systemic carbon dioxide due to hyperventilation) usually occurs in patients with end-stage liver disease hyperventilatory sepsis and head trauma Respiratory alkalosis will be evident from the initial arterial blood gas obtained and the mode of ventilation can then be changed if so desired

Uuml Positive End Expiratory Pressure may or may not be employed to prevent atelectasis in adult patients It is almost always used for pediatric and neonatal patients due to their increased tendency for atelectasis

Uuml High frequency oscillation is used most frequently in neonates but is also used as an alternative mode in adults with severe ARDS

Uuml Pressure Regulated Volume Control is another option


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Guidelines for the use of NPPV in patients with acute respiratory failure

Uuml Blood gas findings o Partial pressure of carbon dioxide in arterial gas (PaCO2) greater than 45

mm Hg o pH less than 735 but more than 710 o PaO2 and fraction of inspired oxygen (FIO2) less than 200

Uuml Clinical inclusion criteria o Signs or symptoms of acute respiratory distress o Moderate-to-severe dyspnea increased over usual o Respiratory rate greater than 24 breaths per minute o Accessory muscle use o Abdominal paradox o Gas exchange o PaCO2 greater than 45 mm Hg and pH less than 735 o PaCO2-to-FIO2 ratio less than 200 mm Hg

Uuml Diagnosis o COPD exacerbation o Acute pulmonary edema o Pneumonia

Uuml Contraindications o Respiratory arrest o Inability to use mask because of trauma or surgery o Excessive secretions o Hemodynamic instability or life-threatening arrhythmia o High risk of aspiration o Impaired mental status o Uncooperative or agitated patient o Life-threatening refractory hypoxemia (alveolar-arterial difference in

partial pressure of oxygen [PaO2] lt60 mm Hg with FIO2 of 1) Uuml Factors predictive of success

o Younger age o Lower acuity of illness (ie acute physiology and chronic health evaluation

[APACHE] score) o Patient able to cooperate o Ability to coordinate breathing with ventilator o Moderate hypercapnia (PaCO2 gt45 mm Hg but lt92 mm Hg) o Moderate acidemia (pH gt710 but lt735) o Improvement in gas exchange and heart and respiratory rates within first 2

hours


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Protocol for Initiation of NPPV in patients with acute respiratory failure

Uuml Position the head of the bed at a 45deg angle Uuml Choose the correct size of mask and initiate ventilator at CPAP (expiratory

positive airway pressure or EPAP) of 0 cm water with a pressure support of 10 cm water

Uuml Hold the mask gently on the patients face until the patient is comfortable and in full synchrony with the ventilator

Uuml Apply wound care dressing on the patients nasal bridge and other pressure points Uuml Secure the mask with head straps but avoid a tight fit Uuml Slowly increase CPAP to more than 5 cm water Uuml Increase pressure support (ie inspired positive airway pressure or IPAP 10-20 cm

water) to achieve maximal exhaled tidal volume (10-15 mLkg) Uuml Evaluate that ventilatory support is adequate which is indicated by an

improvement in dyspnea a decreased respiratory rate achievement of desired tidal volume and good comfort for the patient

Uuml Oxygen supplementation is achieved through NPPV machine-to-machine oxygen saturation of greater than 90

Uuml A backup rate may be provided in the event the patient becomes apneic Uuml In patients with hypoxemia increase CPAP in increments of 2-3 cm water until

FiO2 is less than 06 Uuml Set the ventilator alarms and backup apnea parameters Uuml Ask the patient to call for needs and provide reassurance and encouragement Uuml Monitor with oximetry and adjust ventilator settings after obtaining arterial blood

gas results

Benefits of NPPV

In acute respiratory failure NPPV offers a number of potential advantages over invasive PPV These advantages include the avoidance of intubation-related trauma a decreased incidence of nosocomial pneumonia enhanced patient comfort a shorter duration of ventilator use a reduction in hospital stay and ultimately reduced cost


15

Guidelines for use of NPPV in chronic respiratory failure resulting from restrictive processes

Uuml Uuml Blood gas and clinical criteria

o PaCO2 greater than 45 mm Hg o Nocturnal hypoventilation and symptoms (eg hypersomnolence morning

headache) Uuml Appropriate diagnosis

o Neuromuscular diseases o Thoracic deformity o Obesity hypoventilation syndrome o Obstructive sleep apnea unresponsive to CPAP

Uuml Exclusions o Inability to clear secretions o Moderate-to-severe bulbar involvement o Uncooperative patients o Patients who need continuous ventilatory support

Indication of mechanical ventilation

Uuml Mechanical ventilation is indicated when the patients spontaneous ventilation is inadequate to maintain life

Uuml It is also indicated as prophylaxis for imminent collapse of other physiologic functions or ineffective gas exchange in the lungs

Uuml Because mechanical ventilation only serves to provide assistance for breathing and does not cure a disease the patients underlying condition should be correctable and should resolve over time

Uuml In addition other factors must be taken into consideration because mechanical ventilation is not without its complications

Common medical indications for use include

Uuml Acute lung injury (including ARDS trauma) Uuml Apnea with respiratory arrest including cases from intoxication Uuml Chronic obstructive pulmonary disease (COPD) Uuml Acute respiratory acidosis with partial pressure of carbon dioxide (pCO2) gt 50

mmHg and pH lt 725 which may be due to paralysis of the diaphragm due to Guillain-Barreacute syndrome Myasthenia Gravis spinal cord injury or the effect of anaesthetic and muscle relaxant drugs

Uuml Increased work of breathing as evidenced by significant tachypnea retractions and other physical signs of respiratory distress

Uuml Hypoxemia with arterial partial pressure of oxygen (PaO2) with supplemental fraction of inspired oxygen (FiO2) lt 55 mm Hg

Uuml Hypotension including sepsis shock congestive heart failure


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Note Mechanical ventilation does not mandate endotracheal intubation nor does intubation require mechanical ventilation For example endotracheal intubation may be life saving in a case of impending upper airway obstruction or high risk for aspiration without need for a ventilator

Types of ventilators

Ventilation can be delivered via

A Hand-controlled ventilation such as Uuml Bag valve mask Uuml Continuous-flow or Anaesthesia (or T-piece) bag

B A mechanical ventilator

Types of mechanical ventilators include

Uuml Transport ventilators These ventilators are small more rugged and can be powered pneumatically or via AC or DC power sources

Uuml ICU ventilators These ventilators are larger and usually run on AC power (though virtually all contain a battery to facilitate intra-facility transport and as a back-up in the event of a power failure) This style of ventilator often provides greater control of a wide variety of ventilation parameters (such as inspiratory rise time) Many ICU ventilators also incorporate graphics to provide visual feedback of each breath

Uuml PAP ventilators These ventilators are specifically designed for non-invasive ventilation This includes ventilators for use at home in order to treat sleep apnea

Modes of mechanical ventilation

A mode of mechanical ventilation refers to the program by which the ventilator interacts with the patient the relationship between the possible types of breaths allowed by the ventilator and the variables that define inspiration

Inspiration is defined by three variables

Uuml trigger

Uuml limit

Uuml cycle


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Trigger is the change detected by the ventilator that causes inspiration to begin

Limit is the value that cannot be exceeded during inspiration (volume pressure or flow)

Cycle is the value that when reached terminates inspiration

Using these definitions three breath types are possible

Uuml Full ventilator control (mandatory) the ventilator controls the breathing

Uuml Partial ventilator control (assisted) ventilator assist with patientrsquos breathing

Uuml Full patient control (spontaneous) patient controls the breathing completely

The most commonly used modes in adults are volume limited

In controlled mechanical ventilation (CMV) there is no patient triggering rather all breaths are ventilator triggered limited and cycled CMV is used in patients who make no respiratory effort such as those with neuromuscular paralysis

In assistcontrol ventilation (ACV) by contrast the clinician sets a minimum rate and tidal volume The patient can trigger the ventilator at a more rapid rate and will receive the set volume each time

In intermittent mandatory ventilation (IMV) ventilator-limited (ie volume or pressure) breaths are similarly delivered at a set (minimum) rate but the patient can breathe spontaneously by triggering a demand valve between machine-limited breaths

In current ventilators IMV is modified to synchronized IMV (SIMV) in which the ventilator synchronizes machine breaths with patient effort

In the patient who does not trigger the ventilator CMV ACV and SIMV are qualitatively identical In assist control there is a greater potential for respiratory alkalosis and intrinsic PEEP (PEEPi) or autoPEEP


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What is auto-PEEP (PEEPi)

This is persistent positive alveolar pressure at end of expiration often with associated hyperinflation due to delivery of full machine breaths for all patient efforts The hyperinflation results from insufficient time for the lungs to empty This causes gas trapping and builds up of positive pressure in the lungs

Is the patient gas trapping ndash Expiratory flow does not return to baseline before inspiration commences (ie gas is trapped in the airways at end-expiration)


19

In principle machine breaths in the assistcontrol or IMV modes can be defined by a set volume or pressure

If volume control is selected the tidal volume is fixed and airway pressure varies with the resistance and compliance of the patients lungs and chest wall

If pressure control is selected a fixed inspiratory pressure level is maintained for a set inspiratory time or inspirationexpiration (IE) ratio and tidal volume and flow vary with patient effort and mechanics

Two additional common modes of ventilation are continuous positive airway pressure (CPAP) and pressure support ventilation (PSV)


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CPAP is spontaneous breathing with no mandatory or assisted breaths a constant level of pressure is applied to the airway throughout the respiratory cycle The mode CPAP is similar to PEEP which is not a mode but is the addition of baseline positive pressure during mechanical ventilation

In PSV breaths are patient triggered pressure limited and flow cycled That is with no machine backup rate the ventilator assists the patients inspiratory effort with a preset pressure Patients determine their own respiratory rate inspiratory time and tidal volume

PSV can be combined with other modes such as SIMV to assist patient efforts between the set machine breaths


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Although the ventilator performs the full work of breathing in CMV and the patient performs the full work of breathing in CPAP two important points should be emphasized

Uuml First the ideal work of breathing for the mechanically ventilated patient remains unclear (ie the ideal amount that prevents muscle atrophy yet permits rest)

Uuml Second patient work of breathing is not necessarily less in ACV or SIMV than in PSV particularly if patientndashventilator synchrony is optimized in PSV

Several newer alternative ventilatory modes have been developed in recent years in an attempt to combine attractive features of pressure and volume ventilation into a single mode that will deliver the minimum necessary ventilator pressure for a tidal volume goal Modes including mandatory minute ventilation (MMV) automatically titrate the amount of ventilator assistance to changing patient mechanics and breathing drive These modes have not yet been shown to improve clinical end points in prospective trials but are increasingly encountered in general practice

Ventilator Settings

The major variables to set for the volume-controlled modes ACV and SIMV are

not respiratory rate

not tidal volume

not flow rate and pattern

not FIO2 (fraction of inspired oxygen) and

not PEEP level

Respiratory rate

Uuml Although a rate of 10ndash20 breathsmin is generally appropriate for most patients with respiratory failure patients with airflow limitation who are at risk fordeveloping PEEPi may benefit from lower rates and patients with a need for highminute ventilation due to metabolic acidosis need higher rates

Uuml In SIMV it is best to initially deliver at least 80 of minute ventilation withmachine breaths

Uuml In ACV setting the rate about 4 breathsmin below the patient rate ensures that thepatient and not the machine is dictating minute ventilation and yet providesadequate backup if the patient becomes apneic


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Tidal Volume

Uuml Although tidal volumes as high as 10 mLkg (and perhaps higher) may beappropriate for patients without lung disease lower volumes are otherwiseindicated

Uuml In acute respiratory distress syndrome (ARDS) the use of a tidal volume of 6 mLkg (ideal body weight) was associated with improved mortality compared with12 mLkg and should be considered the standard of care

Uuml A tidal volume of 6ndash8 mLkg is often used in obstructive lung disease (asthmaCOPD) to avoid high airway pressures and development of PEEPi

Uuml In fact studies of asthma and ARDS suggest that a lung protective ventilatorystrategy termed permissive hypercapnia may lead to improved outcomes This strategy reduces tidal volumes andor rate and allows a respiratory acidosis to a pH as low as 715ndash720

Uuml Generally when increased ventilation is needed it is more effective to adjustminute ventilation by changes in rate rather than tidal volume becauseincreases in tidal volume occasionally have the paradoxical effect of slowing respiratory rate

Uuml Frequent arterial blood sampling to check CO2 tension in the stable patient can be avoided by noting the minute ventilation needed to achieve a given level ofPaCO2

Flow rate and pattern

Uuml The peak flow rate determines the maximal inspiratory flow delivered by theventilator during inspiration Although 60 Lmin is a common initial peak flowsetting higher flows with subsequent higher peak inspiratory pressure are commonly needed for high ventilatory demand or underlying airway obstruction

Uuml Flow is delivered during the inspiratory period via one of three waveforms

not constant (square wave)

not decelerating (ramp wave) or

not sinusoidal


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Uuml Although important differences in clinical outcome have not been demonstratedfor particular flow patterns decelerating flow is most commonly used because itmay achieve better gas exchange (ie lower alveolarndasharterial oxygen gradient and lower dead space) as well as lower peak inspiratory pressure despite higher meanairway pressure

Uuml To improve oxygenation in ARDS mean airway pressure is increased To do thisin volume-controlled modes the peak inspiratory flow rate is decreased In pressure control ventilation inspiratory time is increased (pressure control) to

What is the difference between constant decelerating and sinusoidal flow waveforms

Flow of gas is calculated in liters per minute Flow commences at the beginning of a breath and stops at the end of the breath Gas flows into the lungs in inspiration and out of the lungs in expiration The pattern of expiratory flow is more or less the same for different modes of ventilation as long as the expiratory phase is long enough to prevent gas trapping

The normal flow pattern of gas moving in and out of the lungs is sinusoidal

In volume control ventilation a variety of different wave patterns can be used

In clinical practice constant and decelerating flow patterns are used the latter is preferred In constant decelerating and sinusoidal flow patterns the inspiratory flow rate is equal to the peak flow rate but the mean flow rate is higher in constant flow patterns rather than the other two This suggests that this pattern will cause more shearing injury to the lung parenchyma Therefore a decelerating flow pattern is probably the most effective flow pattern ndash it ensures peak flow early in inspiration while simultaneously minimizing flow during the phase of the inspiratory cycle in which the patient is least likely to need it


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reach an IE ratio greater than 1 a practice termed inverse ratio ventilation (IRV)

Uuml IRV is uncomfortable for the patient often requiring deep sedation or evenparalysis and carries the risk of gas trapping it should be used selectively and byexperienced clinicians

Fraction of inspired osygen (FIO2)

Uuml The FIO2 is typically started at 10 (100 oxygen)

Uuml Although the literature does not stipulate a cutoff for a safe level of inspired oxygen in humans concerns over oxygen radical-mediated lung injury have led to the common practice of decreasing the FIO2 below 05ndash06 as soon as feasible

Uuml Pulse oximetry may be used to titrate FIO2 with one study suggesting that a threshold of 92 in light-skinned patients and 95 in darker-skinned patients ensures adequate oxygenation

Uuml Measurement of partial pressure of arterial oxygen by arterial blood gas (PaO2gt55ndash60 mm Hg is typically acceptable) is recommended at the start of ventilation to verify accuracy of pulse oximetry for each patient

Positive End Expiratory Pressure (PEEP)

Uuml PEEP is selected to improve oxygenation

Uuml It can also be used to improve work of breathing and inspiratory triggering inpatients with PEEPi

Uuml Potential adverse effects of PEEP include elevation of intracranial pressure andhemodynamic compromisehypotension

Uuml PEEP improves oxygenation mostly by recruiting lung units

Uuml Paradoxically PEEP may sometimes worsen oxygenation by

not decreasing cardiac output and thereby the oxygen saturation of mixed venous blood returning to the lungs

not directing pulmonary blood flow to more consolidated airspaces bycompressing alveolar capillaries in nondiseased more compliant airspacesor

not promoting right-to-left interatrial shunting Because high levels of PEEP reduce cardiac output and impair oxygen delivery to tissues measurementof the effect of PEEP on oxygen delivery termed a best PEEP trial maybe helpful

Uuml In patients with airflow limitation (eg COPD) PEEPi increases the work of breathing by increasing the inspiratory effort needed to initiate ventilator flow Insuch patients with dynamic airflow limitation and expiratory airway collapse


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addition of ventilator PEEP up to 85 of the PEEPi level may improve inspiratory triggering and work of breathing However given the potential forworsening of hyperinflation particularly for patients with asthma PEEP for this purpose should be used cautiously A stable inspiratory plateau pressure (Pplat)after addition of ventilator PEEP suggests absence of worsened hyperinflation

PEEP is an adjuvant to the mode of ventilation used to help maintain functional residual capacity (FRC) At the end of expiration the PEEP exerts pressure to oppose passive emptying of the lung and to keep the airway pressure above the atmospheric pressure The presence of PEEP opens up collapsed or unstable alveoli and increases the FRC and surface area for gas exchange thus reducing the size of the shunt For example if a large shunt is found to exist based on the estimation from 100 FiO2 then PEEP can be considered and the FiO2 can be lowered (lt 60) in order to maintain an adequate PaO2 thus reducing the risk of oxygen toxicity

In addition to treating a shunt PEEP may also be useful to decrease the work of breathing In pulmonary physiology compliance is a measure of the stiffness of the lung and chest wall The mathematical formula for compliance (C) = change in volume change in pressure The higher the compliance the more easily the lungs will inflate in response to positive pressure An underinflated lung will have low compliance and PEEP will improve this initially by increasing the FRC since the partially inflated lung takes less energy to inflate further Excessive PEEP can however produce overinflation which will again decrease compliance Therefore it is important to maintain an adequate but not excessive FRC

Indications

PEEP can cause significant haemodynamic consequences through decreasing venous return to the right heart and decreasing right ventricular function As such it should be judiciously used and is indicated for adults in two circumstances

bull If a PaO2 of 60 mmHg cannot be achieved with a FiO2 of 60 bull If the initial shunt estimation is greater than 25

If used PEEP is usually set with the minimal positive pressure to maintain an adequate PaO2 with a safe FiO2 As PEEP increases intrathoracic pressure there can be a resulting decrease in venous return and decrease in cardiac output A PEEP of less than 10 cmH2O is usually safe in adults if intravascular volume depletion is absent Lower levels are used for pediatric patients Older literature recommended routine placement of a Swan-Ganz catheter if the amount of PEEP used is greater than 10 cmH2 for hemodynamic monitoring More recent literature has failed to find outcome benefits with


27

routine PA catheterisation when compared to simple central venous pressure monitoring] If cardiac output measurement is required minimally invasive techniques such as oesophageal doppler monitoring or arterial waveform contour monitoring may be sufficient alternatives PEEP should be withdrawn from a patient until adequate PaO2 can be maintained with a FiO2 lt 40 When withdrawing it is decreased through 1-2 cmH2O decrements while monitoring haemoglobin-oxygen saturations Any unacceptable haemoglobin-oxygen saturation should prompt reinstitution of the last PEEP level that maintained good saturation

Positioning

Prone (face down) positioning has been used in patients with ARDS and severe hypoxemia It improves FRC drainage of secretions and ventilation-perfusion matching (efficiency of gas exchange) It may improve oxygenation in gt 50 of patients but no survival benefit has been documented

Sedation

Most intubated patients receive sedation through a continuous infusion or scheduled dosing to help with anxiety or psychological stress Daily interruption of sedation is commonly helpful to the patient for reorientation and appropriate weaning

Prophylaxis

bull To protect against ventilator-associated pneumonia patients bed is often elevated to about 30deg

bull Deep vein thrombosis prophylaxis with heparin or sequential compression device is important in older children and adults

bull A histamine receptor (H2) blocker or proton-pump inhibitor may be used to prevent gastrointestinal bleeding which has been associated with mechanical ventilation

Modification of settings

Uuml In adults when 100 FiO2 is used initially it is easy to calculate the next FiO2 to be used and easy to estimate the shunt fraction The estimated shunt fraction refers to the amount of oxygen not being absorbed into the circulation In normal physiology gas exchange (oxygencarbon dioxide) occurs at the level of the alveoli in the lungs The existence of a shunt refers to any process that hinders this gas exchange leading to wasted oxygen inspired and the flow of un-oxygenated blood back to the left heart (which ultimately supplies the rest of the body with unoxygenated blood)


28

Uuml When using 100 FiO2 the degree of shunting is estimated by subtracting the measured PaO2 (from an arterial blood gas) from 700 mmHg For each difference of 100 mmHg the shunt is 5 A shunt of more than 25 should prompt a search for the cause of this hypoxemia such as mainstem intubation or pneumothorax and should be treated accordingly If such complications are not present other causes must be sought after and PEEP should be used to treat this intrapulmonary shunt Other such causes of a shunt include

not Alveolar collapse from major atelectasis not Alveolar collection of material other than gas such as pus from pneumonia water

and protein from acute respiratory distress syndrome water from congestive heart failure or blood from haemorrhage

Monitoring the Ventilated Patient Managing a patient on the mechanical ventilator necessitates monitoring respiratory physiological variables These variables track progression and resolution of disease complications of mechanical ventilation patient comfort work of breathing and likelihood of successful patient liberation from the ventilator

RESPIRATORY MECHANICS

Variables indicated on all mechanical ventilators include exhaled tidal volume and airway pressure For the

patient on volume-cycled ventilation for whom breath-to-breath volume is constant airway pressure at any

moment depends on

Uuml the impedance of the respiratory system to air delivery (ie respiratory system compliance and

airflow resistance)

Uuml patient effort and

Uuml patient synchrony with the ventilator

Respiratory system refers to the lung (parenchyma and airways) and its surrounding chest wall (pleura and

thoracoabdominal cage) Although lung and chest wall mechanics may be distinguished with the use of

invasive tools such as the esophageal balloon this is rarely needed Specifically it is important to

remember that pressures caused by changes in compliance of the chest wall such as pneumothorax or even

abdominal distention are transmitted to the lung

Pressure at the airway opening (Pao) will increase with any increase in PEEP PEEPi flow resistance

(eg bronchospasm) or tidal volume and with any decrease in compliance (eg pneumothorax)

Pao increases progressively during inspiration with volume delivery by the ventilator until it reaches its

peak the peak inspiratory pressure (PIP) at the moment the full tidal volume is delivered


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Pao likewise normally decreases to atmospheric (or to PEEP if PEEP is programmed into the ventilator) at

the end of exhalation as the respiratory system empties The downstream pressure in the alveolar

compartment (which includes PEEP and PEEPi) reflecting respiratory system compliance can be

measured at the airway opening in isolation from the additional pressure generated in the airways by

stopping flow (ie making flow zero) and thereby making pressure generated by flow through the airways

zero

In practice the maximum pressure of the alveolar compartment reached at completion of the tidal volume

or plateau pressure (Pplat) can be monitored by programming a 10-s end-inspiratory pause of zero flow

The PIP ndash Pplat difference equals the flow-resistive pressure (ie the pressure generated by flow along the

airways)

These measurements apply best to volume-controlled ventilation in which flow and tidal volume are

programmed By contrast in pressure-controlled ventilation in which a constant pressure is applied to the

airway opening for a prescribed inspiratory time PIP is often equal to Pplat as can be demonstrated by

observing an end-inspiratory period of zero flow on the ventilator flow-time graph

The monitoring variables of static compliance (Cstat) resistance to airflow (R) and intrinsic PEEP (PEEPi)

can be easily derived at the bedside These variables are used to adjust the ventilator follow disease

progression and monitor response to therapy


30

THE MECHANICALLY VENTILATED PATIENT IN ACUTE RESPIRATORY DISTRESS A useful approach to the ventilated patient who develops acute hypoxemia is depicted below By observing PIP and measuring Pplat the problem can often be localized either to the alveolar or the airways compartment and an immediate differential diagnosis can be generated Specifically elevation of PIP with an unchanged Pplat (ie PIPndashPplat increased) may indicate mucus plugging or bronchospasm Elevation of both PIP and Pplat in parallel (ie PIPndashPplat unchanged) may indicate pneumothorax pulmonary edema or pneumonia Alternatively if neither is elevated the possibility of a vascular event altering gas exchange should be considered (ie pulmonary embolism)

Normally at end exhalation (before the next delivered breath) the tidal volume in the alveolar

compartment fully empties and both expiratory airflow and alveolar pressure fall to zero However if

elevated airflow resistance slows alveolar emptying beyond the available expiratory period

particularly in settings of decreased expiratory time (eg elevated respiratory rate) andor decreased

alveolar driving pressure (eg emphysema) positive alveolar pressure or PEEPi may persist at end

exhalation PEEPi is often initially detected by observing the flow graphic on the ventilator for

persistent flow at end-expiration PEEPi is measured by programming a 10-s end-expiratory pause of

zero flow into the ventilator PEEPi may cause hypoventilation hypotension or a false elevation in

pulmonary capillary wedge pressure Strategies to minimize PEEPi include decreasing the respiratory

rate use of bronchodilators or addition of PEEP


31

What is the Peak inspiratory pressure (PIP) and Plateau Pressure (Pplat)

The plateau pressure is the pressure applied (in positive pressure ventilation) to the small airways and alveoli It is believed that control of the plateau pressure is important as excessive stretch of alveoli has been implicated as the cause of ventilator induced lung injury

The peak pressure is the pressure measured by the ventilator in the major airways and it strongly reflects airways resistance For example in acute severe asthma there is a large gradient between the peak pressure (high) and the plateau pressure (normal) In pressure controlled ventilation the pressure limit is (usually) the plateau pressure due to the dispersion of gas in inspiration In volume control the pressure measured (the PAW) by the ventilator is the peak airway pressure which is really the pressure at the level of the major airways To know the real airway pressure the plateau pressure which is applied at alveolar level the volume breath must be made to simulate a pressure breath

An inspiratory hold (05 to 1 second) is applied and the airway pressure from the initial peak drops down to a plateau The hold represents a position of no flow


32


33triplehelix Mechanical Ventilation

33

What is permissive hypercapnia

With acute respiratory distress syndrome (ARDS) a tidal volume of 6-8 mLkg is used with a rate of 10-12minute This reduced tidal volume allows for minimal volutrauma but may result in an elevated pCO2 (due to the relative decreased oxygen delivered) is called permissive hypercapnia but this elevation does not need to be corrected

Sighs

Uuml An adult patient breathing spontaneously will usually sigh about 6-8 timeshr to prevent microatelectasis and this has led some to propose that ventilators should deliver 15-2 times the amount of the preset tidal volume 6-8 timeshr to account for the sighs However such high quantity of volume delivery requires very high peak pressure that predisposes to barotrauma

Uuml Currently accounting for sighs is not recommended if the patient is receiving 10-12 mLkg or is on PEEP If the tidal volume used is lower the sigh adjustment can be used as long as the peak and plateau pressures are acceptable

Uuml Sighs are not generally used with ventilation of infants and young children

Connection to ventilators

There are various procedures and mechanical devices that provide protection against airway collapse air leakage and aspiration

Uuml Face mask - In resuscitation and for minor procedures under anaesthesia a face mask is often sufficient to achieve a seal against air leakage Airway patency of the unconscious patient is maintained either by manipulation of the jaw or by the use of nasopharyngeal or oropharyngeal airway These are designed to provide a passage of air to the pharynx through the nose or mouth respectively Poorly fitted masks often cause nasal bridge ulcers a problem for some patients Face masks are also used for non-invasive ventilation in conscious patients A full face mask does not however provide protection against aspiration

Uuml Laryngeal mask airway - The laryngeal mask airway (LMA) causes less pain and coughing than a tracheal tube However unlike tracheal tubes it does not seal


34

against aspiration making careful individualised evaluation and patient selection mandatory

Uuml Tracheal intubation is often performed for mechanical ventilation of hours to weeks duration A tube is inserted through the nose (nasotracheal intubation) or mouth (orotracheal intubation) and advanced into the trachea In most cases tubes with inflatable cuffs are used for protection against leakage and aspiration Intubation with a cuffed tube is thought to provide the best protection against aspiration Tracheal tubes inevitably cause pain and coughing Therefore unless a patient is unconscious or anaesthetized for other reasons sedative drugs are usually given to provide tolerance of the tube Other disadvantages of tracheal intubation include damage to the mucosal lining of the nasopharynx or oropharynx and subglottic stenosis

Uuml Oesophageal obturator airway - commonly used by emergency medical technicians if they are not authorized to intubate It is a tube which is inserted into the oesophagus past the epiglottis Once it is inserted a bladder at the tip of the airway is inflated to block (obturate) the oesophagus and air or oxygen is delivered through a series of holes in the side of the tube

Uuml Cricothyrotomy - Patients who require emergency airway management in whom tracheal intubation has been unsuccessful may require an airway inserted through a surgical opening in the cricothyroid membrane This is similar to a tracheostomy but a cricothyrotomy is reserved for emergency access

Uuml Tracheostomy - When patients require mechanical ventilation for several weeks a tracheostomy may provide the most suitable access to the trachea A tracheostomy is a surgically created passage into the trachea Tracheostomy tubes are well tolerated and often do not necessitate any use of sedative drugs Tracheostomy tubes may be inserted early during treatment in patients with pre-existing severe respiratory disease or in any patient who is expected to be difficult to wean from mechanical ventilation ie patients who have little muscular reserve


35

Uuml Mouthpiece - Less common interface It does not provide protection against aspiration There are lip seal mouthpieces with flanges to help hold them in place if patient is unable

The other method of classifying mechanical ventilation is based on how to determine when to start giving a breath Similar to the termination classification noted above microprocessor control has resulted in a myriad of hybrid modes that combine features of the traditional classifications Note that most of the timing initiation classifications below can be combined with any of the termination classifications listed above

Uuml Assist Control (AC) In this mode the ventilator provides a mechanical breath with either a pre-set tidal volume or peak pressure every time the patient initiates a breath Traditional assist-control used only a pre-set tidal volume--when a preset peak pressure is used this is also sometimes termed Intermittent Positive Pressure Ventilation or IPPV However the initiation timing is the same--both provide a ventilator breath with every patient effort In most ventilators a back-up minimum breath rate can be set in the event that the patient becomes apnoeic Although a maximum rate is not usually set an alarm can be set if the ventilator cycles too frequently This can alert that the patient is tachypneic or that the ventilator may be auto-cycling (a problem that results when the ventilator interprets fluctuations in the circuit due to the last breath termination as a new breath initiation attempt)

Uuml Synchronized Intermittent Mandatory Ventilation (SIMV) In this mode the ventilator provides a pre-set mechanical breath (pressure or volume limited) every specified number of seconds (determined by dividing the respiratory rate into 60 - thus a respiratory rate of 12 results in a 5 second cycle time) Within that cycle time the ventilator waits for the patient to initiate a breath using either a pressure or flow sensor When the ventilator senses the first patient breathing attempt within the cycle it delivers the preset ventilator breath If the patient fails to initiate a breath the ventilator delivers a mechanical breath at the end of the breath cycle Additional spontaneous breaths after the first one within the breath cycle do not trigger another SIMV breath However SIMV may be combined with pressure support (see below) SIMV is frequently employed as a method of decreasing ventilatory support (weaning) by turning down the rate which requires the patient to take additional breaths beyond the SIMV triggered breath

Uuml Controlled Mechanical Ventilation (CMV) In this mode the ventilator provides a mechanical breath on a preset timing Patient respiratory efforts are ignored This is generally uncomfortable for children and adults who are conscious and is usually only used in an unconscious patient It may also be used in infants who often quickly adapt their breathing pattern to the ventilator timing

Uuml Pressure Support Ventilation (PSV) When a patient attempts to breath spontaneously through an endotracheal tube the narrowed diameter of the airway results in higher resistance to airflow and thus a higher work of breathing PSV was developed as a method to decrease the work of breathing in-between ventilator mandated breaths by providing an elevated pressure triggered by spontaneous breathing that supports ventilation during inspiration Thus for example SIMV might be combined with PSV so that additional breaths beyond the SIMV programmed breaths are supported However while the SIMV mandated breaths have a preset volume or peak pressure the PSV breaths are designed to cut short when the inspiratory flow reaches a percentage of the peak inspiratory flow (eg 10-25) Also the peak pressure set for the PSV breaths is usually a lower pressure than that set for the full ventilator mandated breath PSV can be also be used as an independent mode However since there is generally no back-up rate in PSV appropriate apnoea alarms must be set on the ventilator

Uuml Continuous Positive Airway Pressure (CPAP) A continuous level of elevated pressure is provided through the patient circuit to maintain adequate oxygenation decrease the work of breathing and decrease the work of the heart (such as in left-sided heart failure - CHF) Note that no cycling of ventilator pressures occurs and the patient must initiate all breaths In addition no


36

additional pressure above the CPAP pressure is provided during those breaths CPAP may be used invasively through an endotracheal tube or tracheostomy or non-invasively with a face mask or nasal prongs

Uuml Positive End Expiratory Pressure (PEEP) is functionally the same as CPAP but refers to the use of an elevated pressure during the expiratory phase of the ventilatory cycle After delivery of the set amount of breath by the ventilator the patient then exhales passively The volume of gas remaining in the lung after a normal expiration is termed the functional residual capacity (FRC) The FRC is primarily determined by the elastic qualities of the lung and the chest wall In many lung diseases the FRC is reduced due to collapse of the unstable alveoli leading to a decreased surface area for gas exchange and intrapulmonary shunting with wasted oxygen inspired Adding PEEP can reduce the work of breathing (at low levels) and help preserve FRC

Complications of Mechanical Ventilation Multiple direct complications of mechanical ventilation have been described

Other indirectly associated complications of mechanical ventilation include critical illness polyneuropathy acalculous cholecystitis and venous thromboembolism Three of these barotrauma ventilator-induced lung injury and altered hemodynamics will be discussed below as both direct and indirect complications have important practical implications

Pulmonary

Barotrauma (eg pneumothorax pneumomediastinum systemic gas embolism etc)

Ventilator-induced lung injury (ie volutrauma atelec-trauma biotrauma)

Oxygen toxicity

Ventilator-associated pneumoni

Tracheal stenosis

Cardiac

Reduced cardiac outputhypotension

Right ventricular ischemia

Propagation of right-to-left interatrial shunt

Gastrointestinal

Ileus

Gastrointestinal hemorrhage

Renal


37

Fluid retention

Hyponatremia

Cerebrovascular

Increased intracranial pressure

BAROTRAUMA Uuml Barotrauma is the term for the specific complications of extra-alveolar air such as

pneumothorax or pneumomediastinum thought to occur from alveolar rupture into the adjacent bronchovascular interstitium

Uuml It is less common than in earlier days of positive pressure ventilation likely because of attention to patient ventilator synchrony and high peak airway pressures

Uuml In rare instances the air extravasates into blood vessels with resultant air emboli in the brain heart or skin causing changes in mental status cardiac arrhythmias and livedo reticularis

VENTILATOR-INDUCED LU NG INJURY (VILI)

Uuml Intriguingly although VILI is synergistic with preexistent lung injury positive-pressure

ventilation of even the normal lung can produce pathological hyaline membrane changes

indistinguishable from ARDS Studies in the early 1970s introduced the concept of

barotrauma or pressure-induced lung injurydemonstrating that high inflation pressures injured

the lung Subsequent studies showed that the injurious variable was the transpulmonary pressure

distending the lung rather than peak alveolar pressure (ie alveolar pressure minus pleural

pressure) or more simply end-inspiratory volume This in turn led to the current VILI concept

of volume-induced lung injury or volutrauma with its implication that patients with decreased

chest wall compliance from abdominal distention or other restrictive causes may be relatively

protected from high airway pressures on the ventilator

Uuml A multicenter NIH-sponsored ARDS trial which demonstrated improved mortality using a low (6

mLkg ideal body weight) compared to a high tidal volume strategy (12 mLkg ideal body

weight) supports this volutrauma idea

Uuml The lung in patients with ARDS is heterogeneously affected with the dependent consolidated

lung not participating in gas exchange Only the relatively nondiseased compliant portion of the

lung is vulnerable to overdistention by the delivered tidal volume This has led practitioners to

theorize that pressure ventilation with a uniform pressure ceiling in all lung units is less injurious

to the relatively normal lung than volume ventilation which directs volume along the path of least

resistance primarily to the nondiseased lung


38

Uuml Despite these claims however no well-designed randomized controlled trial has shown a

difference in outcome between pressure- and volume-targeted ventilation in patients with ARDS

Uuml Finally perhaps the most interesting recent concept of VILI is that of biotrauma the idea that

VILI may lead to multiple organ dysfunction syndrome by leakage of both stretch-induced

injurious lung cytokines and bacteria into the systemic circulation Lower tidal volumes have been

shown to generate fewer cytokines and are associated with less extrapulmonary organ

dysfunction

Uuml This phenomenon may explain why most patients with ARDS die of extrapulmonary

complications rather than from respiratory failure itself

ALTERED HEMODYNAMICS Uuml Positive-pressure ventilation and PEEP both cause hypotension by reducing

cardiac output with a blood pressure drop that is most dramatic immediately following endotracheal intubation

Uuml PEEP decreases venous return and thus cardiac output primarily by compressing the inferior vena cava By increasing pulmonary vascular resistance and right ventricular afterload high levels of PEEP may also

not decrease right ventricular systolic function particularly for patients with underlying right ventricular dysfunction or right coronary artery disease

not aggravate right ventricular ischemia and

not propagate right-to-left interatrial shunting through a patent foramen ovale PEEP reduces left ventricular afterload and thereby may occasionally lead to improved left ventricular function and cardiac output in patients with dilated cardiomyopathy

Uuml Because of this therapeutic effect of the ventilator both occult left ventricular ischemia and left ventricular systolic dysfunction may occasionally complicate ventilator weaning

When to Withdraw Mechanical Ventilation

Uuml Withdrawal from mechanical ventilationmdashalso known as weaningmdashshould not be

delayed unnecessarily nor should it be done prematurely Patients should have their ventilation considered for withdrawal if they are able to support their own ventilation and oxygenation and this should be assessed continuously

Uuml There are several objective parameters to look for when considering withdrawal but there is no specific criteria that generalizes to all patients

Uuml The best measure of when a patient may be extubated is the Rapid Shallow Breathing Index (RSBI) (Tobin Index)


39

Uuml This is calculated by dividing the respiratory rate by the tidal volume in liters(RRTV) A rapid shallow breathing index of less than 100 is considered ideal for extubation Certainly other measures such as patients mental status should be considered

WEANING STRATEGY Uuml First most patients (75) do not need to be weaned from the ventilator a

graduated reduction of support is unnecessary particularly for postoperative patients

Uuml The majority can simply be extubated after their first successful attempt at spontaneous breathing For patients who fail their initial attempts at spontaneous breathing synchronized intermittent mandatory ventilation (SIMV) weaning appears to be inferior and may even prolong the duration of mechanical ventilation

Uuml Next most of the long list of classic weaning parameters (eg maximum inspiratory pressure respiratory rate vital capacity) are poorly predictive of successful liberation The clinical gestalt of even experienced practitioners is often poorly predictive of successful liberation

Uuml Lastly the duration of ventilation can be reduced by using validated clinical parameters such as the rapid-shallow breathing index (RSBI) in a protocol-directed approach

Uuml Most experts agree that the process of liberation should involve an initial achievement of clinical criteria of readiness (eg SaO2 90 with FIO2 05 and PEEP 5 cm H2O no or low-dose vasopressors mental status at least easily arousable some indication of improvement in the initial cause of respiratory failure minute ventilation ideally lt12ndash15 Lmin) followed by some form of initial spontaneous breathing trial (SBT)

Uuml The initial trial may be by a T-piece (breathing without any assistance through the endotracheal tube with a flowing gas source) PSV or CPAP (ie PEEP without inspiratory pressure assistance)

Uuml Initial SBT failure should be followed by reassessment and a more gradual weaning mode


40

Criteria for Assessing Tolerance of a Spontaneous Breathing Trial

Uuml Acceptable oxygenation SaO2 90 or PaO2 60 mm Hg on FIO2 05

Uuml Acceptable ventilation increase in PaCO2 10 mm Hg or pH decrease 010

Uuml Acceptable respiratory rate respiratory rate 35 breathsmin or lt 50 increase in rate

Uuml Acceptable hemodynamics heart rate 140 beatsmin or an increase 20 of baseline systolic blood pressure 80 mm Hg and 160 mm Hg or change of lt 20 from baseline

Uuml RSBI (ratetidal volume) lt 100 breathsminL

Uuml No signs of elevated work of breathing such as thoracoabdominal paradox or excessive use of accessory muscles

Uuml No signs of distress such as diaphoresis or agitation

Perhaps the best-validated and easiest index to assess readiness to wean is the RSBI which is the respiratory rate divided by tidal volume in liters When the RSBI is less than 100 as measured for 1 min on T-piece the patient is likely to achieve successful extubation

Uuml For those patients who fail the initial SBT three different methods for subsequent weaning are generally used SIMV PSV and T-piece The latter two have gained predominant support in the literature as effective weaning modes and the former should be abandoned as a primary weaning strategy

Uuml SIMV involves a stepwise reduction of the mandatory respiratory rate (eg a decrease by two breathsmin twice daily) until the patient can tolerate a minimal rate ( 4 breathsmin) with the remainder of breaths unassisted

Uuml PSV typically involves the stepwise reduction in PS level (eg by 2 cm H2O twice daily) until a minimal PS level is reached (eg 5 cm H2O) This low pressure is thought to approximate the work of breathing off the ventilator by overcoming the additional work of breathing imposed by the endotracheal tube PSV was the most effective mode when compared to SIMV and T-piece in a large randomized trial and is used in many centers

Uuml T-piece involves unassisted spontaneous breathing by disconnection of the endotracheal tube from the ventilator circuit and reconnection to a flowing oxygen-enriched source of gas It was the most effective weaning mode in a second large randomized controlled trial Although progressive increases in T-


41

piece trial duration and daily number (eg increasing from a few minutes twice a day to two or more hours several times daily) are commonly used and in fact may be necessary in chronically ventilator-dependent patients once-daily T-piece trials have been shown to be as effective as multiple daily trials for patients without complications

Uuml In sum for the patient who fails an initial attempt at spontaneous breathing several strategies all using SBTs are available for progressive withdrawal from the ventilator daily SBTs (T-piece CPAP or PS) T-piece CPAP or PS trials of increasing duration or gradual decreases in PS level In certain cases an argument can be made for the superiority of one of these methods For example patients with COPD may occasionally have difficulty tolerating PSV Second because patients with congestive heart failure (CHF) may derive enough assistance in cardiac performance from positive pressure ventilation it is arguably most predictive to perform their SBTs on T-piece

THE DIFFICULT-TO-WEAN PATIENT Uuml Failure to wean commonly reflects an imbalance of excessive respiratory

workload and insufficient respiratory muscle strength or endurance with a typical pattern of tachypnea and shallow tidal volumes

Uuml Depending on the clinical scenario occult coronary ischemia occult left ventricular dysfunctionpulmonary edema PEEPi concretions narrowing the endotracheal tube and critical illness myopathypolyneuropathy should be considered

Uuml Most patients particularly those with diaphragmatic dysfunction congestive heart failure emphysema morbid obesity or abdominal distention should be positioned upright during weaning

Uuml Electrolytes affecting muscle function including potassium magnesium and phosphate should be repleted and correction of metabolic acidosis should be considered particularly if excessive minute ventilation persists

Uuml Lastly in patients with COPD exacerbation who fail SBTs extubation straight to noninvasive positive pressure ventilation [ie bilevel positive airway pressure (BiPAP)] can be tried In such patients studies show improved weaning rates less nosocomial pneumonia and decreased mortality


42

Causes of Failure to Wean from Mechanical Ventilation

Respiratory muscle weakness

Electrolyte depletion (eg hypokalemia hypomagnesemia) malnutrition

Critical illness polyneuropathy

Inadequate rest

Prolonged paralysis or myopathy (eg neuromuscular agents corticosteroids aminoglycosides)

Decreased ventilatory drive

Hypothyroidism

Excessive administration of sedatives or opiates

Increased ventilatory load

Increased resistance bronchospasm secretions plugged endotracheal tube

Decreased lung compliance pulmonary edema ARDS

Decreased chest wall compliance pleural effusions abdominal distention and obesity

Increased minute ventilation elevated dead space ventilation fever and overfeeding

Intrinsic PEEP

Cardiac problems

Left ventricular dysfunction

Coronary ischemia


43

Daily evaluation (Do NOT wean if any one is present)

Uuml Dopamine infusion gt5mcgkgmin

Uuml Systolic BP lt90 mmHg

Uuml HR lt50 or gt 130 bpm

Uuml Temperature gt1004rsquoF

Uuml FiO2 gt50 or PEEP gt8 cm H20

Weaning assessment (Do NOT wean if any one is present)

Uuml RR gt35 breathsmin

Uuml Spontaneous tidal volume lt03 L

Uuml Rapid Shallow Breathing Index gt100

Uuml O2 saturation lt90

Uuml HR lt50 or gt130 bpm or increase from baseline gt20 bpm

Uuml Prominent accessory muscle use


44

A System for Analyzing Ventilator Waveforms

Step 1 -determine the CPAP level

This is the baseline position from which there is a downward deflection on at least beginning of inspiration and to which the airway pressure returns at the end of expiration

Step 2 Is the patient triggering

There will be a negative deflection into the CPAP line just before inspiration


45

Step 3 What is the shape of the pressure wave

If the curve has a flat top then the breath is pressure limited if it has a triangular or sharkrsquos fin top then it is not pressure limited and is a volume breath

Step 4 What is the flow pattern

If it is constant flow (square shaped) this must be volume controlled if decelerating it can be any mode

Step 5 Is the patient gas trapping

Expiratory flow does not return to baseline before inspiration commences (ie gas is trapped in the airways at end-expiration) This indicates auto-PEEP


46

Step 6 The patient is triggering ndash is this a pressure supported or SIMV or VAC breath

This is easy the pressure supported breath looks completely differently than the volume control or synchronized breath the PS breath has a decelerating flow pattern and has a flat topped airway pressure wave The synchronized breath has a triangular shaped pressure wave


47

Step 7 The patient is triggering ndash is this pressure support or pressure control

The fundamental difference between pressure support and pressure control is the length of the breath ndash in PC the ventilator determined this (the inspired time) and all breaths have an equal ldquoirdquo time In PS the patient determined the duration of inspiration and this varies from breath to breath


48

Step 8 Is the patient synchronizing with the ventilator

Each time the ventilator is triggered a breath should be delivered If the number of triggering episodes is greater than the number of breaths the patient is asynchronous with the ventilator Further if the peak flow rate of the ventilator is inadequate then the inspiratory flow will be scooped inwards and the patient appears to be fighting the ventilator


49

Patient-Ventilator Dysynchrony

Uuml Dysynchrony is a term which describes a patient fighting the ventilator If we

assume that this is not because the patient is undersedated and is rebelling against the endotracheal tube in the majority of cases failure to synchronize is due to inadequate flow delivery from the ventilator

Uuml If the flow of gas is inadequate the patient attempts to suck gas out of the ventilator ndash which is extremely unpleasant This only occurs in volume control modes

Uuml In pressure control flow is unlimited ndash the reason is that flow is related to the pressure gradient between the upper and lower airway ndash a deeper attempted inspiration makes the pressure in the alveoli more negative in relation to the upper airway (this is true also in normal individuals how else would you take a deep breath) and the pressure gradient is larger ndash and the flow greater

Uuml In volume limited ventilation this flexibility (which is physiological) does not exist Of course as with most problems in critical care a number of technological solutions have been developed the first was pressure augmentation


50

Mechanical Ventilation

Definition

It is a method to mechanically assist or replace spontaneous breathing when patients can not do so on their own

General Considerations Mechanical ventilation has resulted in profoundly improved survival from acute and chronic respiratory failure

Mechanical ventilation in the intensive care unit (ICU) is delivered under positive pressure in contrast to normal human breathing in which inspiration induces negative pressure in the thorax This makes the complications of barotrauma and hypotension predictable To achieve ventilation rate tidal volume (VT) fraction of inspired oxygen (FIO2) and positive end-expiratory pressure (PEEP) are selected It is useful to track the product of VT and rate the minute ventilation (E) to assess for complications and readiness to wean A normal E is less then 10 Lmin Pressures in ventilators There are two types of pressures used in ventilators

a Negative pressure ventilators The best example is ldquoiron lungrdquo that creates a negative pressure environment around the patientrsquos chest thus sucking air into the lungs This is a large elongated tank which encases the patient up to the neck The neck is sealed with a rubber gasket so that the petientrsquos face and airway are exposed to the room air This was largely used to treat patients with respiratory paralysis due to poliomyelitis


3








4

Bi-PAP setting


5

Nasalface mask


6


7


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50








4

Bi-PAP setting


5

Nasalface mask


6


7


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50

Bi-PAP setting


5

Nasalface mask


6


7


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50

Nasalface mask


6


7


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50


7


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50


8



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



9



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



10













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50













11












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50












12













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50













13










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50










hours


14











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50











gas results

Benefits of NPPV



15



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



















16













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50













Uuml trigger

Uuml limit

Uuml cycle


17















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50















18





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50





19






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50






20


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50


21





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50





22





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50





Ventilator Settings



not tidal volume



not PEEP level

Respiratory rate





23

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50

Tidal Volume












not sinusoidal


24









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50









25



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



















26




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50




Indications





27


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50


Positioning


Sedation


Prophylaxis







28








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50








moment depends on


airflow resistance)













29






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50






zero




airways)









30













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50













31






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50






32



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



33



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50



Sighs









34







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50







35









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50









36





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50





Pulmonary



Oxygen toxicity


Tracheal stenosis

Cardiac




Gastrointestinal

Ileus


Renal


37

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50

Fluid retention

Hyponatremia

Cerebrovascular



























38







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50







dysfunction
















39











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50











40















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50















41










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50










42





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50





Inadequate rest



Hypothyroidism







Intrinsic PEEP

Cardiac problems


Coronary ischemia


43















44







45








46




47




48




49








50















44







45








46




47




48




49








50







45








46




47




48




49








50








46




47




48




49








50




47




48




49








50




48




49








50




49








50








50

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