INTUBATION AND MECHANICAL VENTILATION

Dr Virbhan Balai

TRACHEAL INTUBATION IN ADULTS

• INTRODUCTION — Laryngoscopy and tracheal intubation are essential skills for the emergency clinician.

• This topic will discuss the- – Indications – Contraindications – Preparation, Equipment – Techniques needed to perform tracheal intubation

in adults.

INDICATIONS 

• The most common indications for tracheal intubation are- – Acute respiratory failure. – Inadequate oxygenation or ventilation. – Airway protection in a patient with altered mental

status. – In the perioperative setting- General anesthesia.– Short-term hyperventilation to manage ↑ed ICP.

CONTRAINDICATIONS 

• There are few absolute contraindications to tracheal intubation. • Supraglottic or glottic pathology that precludes placement of an

ETT.– Blunt trauma to the larynx may cause a laryngeal fracture or

disruption of the laryngotracheal junction– Penetrating trauma of the upper airway may also result in conditions

exacerbated by ETT placement. • Relative contraindications to tracheal intubation involve

– Potential difficulties performing the procedure- Anatomic features, injuries, or illness.

ANATOMY

ORAL CAVITY

• Modified Mallampati Scoring:[3]

• Class I: Soft palate, uvula, fauces, pillars visible.

• Class II: Soft palate, uvula, fauces visible.• Class III: Soft palate, base of uvula visible.• Class IV: Only hard palate visible

LARYNGEAL INLET

• PREPARATION — have a mental or written checklist for the necessary tools and steps.

• Essential preparations include the following:– Assess the patient's airway.– Preoxygenate the patient whenever possible.– Place a functioning suction device and bag-valve mask at the bedside.– Attach monitors, including BP, pulse oximetry, and cardiac .– Establish intravenous access. – Whenever possible, two peripheral intravenous catheters should be

placed.– Prepare all necessary medications for RSI- induction agent and a

neuromuscular blocking agent.

• Array the tools needed to perform intubation beside the clinician. These include:– Laryngoscope handle and assorted blades. – Check for adequate lighting and the integrity of all parts.– Endotracheal tubes and a stylet. – Include ETTs one size larger and one size smaller than the ETT to be used initially.– Adjunct airway management devices (eg, ETT introducer or "bougie").– Oral and nasal airways. – Rescue airway (eg, laryngeal mask airway (LMA), Combitube). – End-tidal CO2 monitor (eg, capnography) and esophageal detector to confirm proper

ETT placement.– Equipment to hold the tube in position (eg, tape, prefabricated ETT holder).– Check the cuff of the ETT for leaks by inflating it and removing the syringe (the cuff

should remain inflated) and then deflating it. – Avoid contaminating the ETT.

• Perform all emergent intubations with a stylet in the ETT. • It is essential to have a clear back-up approach prepared

in advance in case of an unsuccessful intubation attempt.• This may consist of a rescue airway (eg, LMA), or in the

case of a failed airway, cricothyroidotomy. • Proper patient positioning is crucial to successful

laryngoscopy. • An assistant strong enough to lift the patient's head

should stand at the bedside to help with positioning.

• The "STOP MAID" mnemonic is described here:• S: Suction• T: Tools for intubation (laryngoscope blades, handle)• O: Oxygen• P: Positioning

• M: Monitors, including ECG, pulse oximetry, blood pressure, end-tidal CO2, and esophageal detectors

• A: Assistant; Ambu bag with face mask; Airway devices (different sized ETTs, 10 mL syringe, stylets); Assessment of airway difficulty

• I: Intravenous access• D: Drugs for pretreatment, induction, neuromuscular blockade (and any

adjuncts)

LARYNGOSCOPE DESIGN

• The Macintosh – curved.• Miller – straight. • The curved blade is designed to minimize stimulation of the

posterior epiglottis.

• The straight blade may offer advantages in particular circumstances, such as – When the glottis is deep. – Prominent upper incisors complicate insertion of a curved blade, or – A long, floppy epiglottis obscures the glottis and must be lifted out of

the line of sight.

Macintosh laryngoscope blade

MILLER AND PHILLIPS LARYNGOSCOPE BLADES

LARYNGOSCOPY TECHNIQUE

• Key points • The critical step in DL is to locate the epiglottis.• Limit the depth of insertion of the laryngoscope blade so

it does not bypass the epiglottis.• The best ways to improve a limited laryngeal view are to:– Increase elevation of the patient's head and flexion of their

cervical spine AND– Perform bimanual laryngoscopy by manipulating the epiglottis

with the laryngoscope and the glottis with the right hand.

Overview 

• The basic steps for performing DL and tracheal intubation include the following:– Obtain assistance.– Prepare equipment, monitors, and medications. – Assess, preoxygenate, and position the patient.– Open the patient's mouth and carefully position the laryngoscope.– Deflect the tongue and soft tissue out of the line of sight.– Locate the epiglottis.– Identify and optimize the view of the glottis using bimanual laryngoscopy, head

elevation, and neck flexion (head elevation and neck flexion are NOT performed when cervical spine precautions are necessary).

– Insert the tracheal tube.– Confirm positioning of the tube within the trachea using CO2 detection, physical

examination, and a chest radiograph.– Secure the tracheal tube.– Set parameters for mechanical ventilation.– Provide sedation and analgesia as needed

Positioning the patient • Elevation of the patient's head by approximately 5 to 7 cm.• Flexing their cervical spine, and performing external laryngeal manipulation. • Bag-mask ventilation can be performed between attempts as needed.• A useful guide for determining adequate head elevation is to ensure that

the patient's ear (external auditory meatus) and sternal notch are aligned when examined from the side.

• This alignment also allows for flexion of the cervical spine.• In some patients, cervical flexion makes it difficult to insert the laryngoscope

blade. • To offset this & provide easier access to the mouth, place towels or blankets

behind the thoracic spine.• Tilting the head back by extending the cervical spine (primarily the

atlanto-occipital joint) can compromise the glottic view.

Opening the mouth and inserting the blade

• The scissor technique is an effective and time-honored method for opening the mouth.

• To perform the technique, hold the tips of the thumb and middle finger of the right hand together, insert them between the upper and lower incisors, and "scissor" them past one another by flexing each digit.

• An alternative method of opening the mouth involves pushing the occiput with the right hand, thereby extending the neck and changing the angle of insertion.

• Regardless of the method chosen, the blade is inserted in a controlled fashion to avoid injuring teeth or soft tissue.

• Difficulty inserting the blade may occur when the mouth is small, the chest wall is large, or the cervical spine is held in extreme flexion.

• If the patient has a small mouth, a smaller blade (eg, Macintosh or Miller size 2) or having an assistant retract the lip may be helpful.

Optimizing the view

• General guidance — The following techniques can be used to improve an inadequate view of the glottis:

• Be certain the tip of the laryngoscope blade is correctly seated in the vallecula when performing curved blade laryngoscopy.

• Make certain the tongue is well controlled and completely contained within the left side of the mouth.

• Increase the degree of cervical flexion by lifting the head and flexing the neck. • Have an assistant perform these maneuvers. • Avoid the common tendency to extend the neck, which generally does not

improve the view.• Should the techniques above fail, use a laryngoscope blade of a different size

or shape, a tracheal tube introducer, or try a different approach (eg, paraglossal straight blade).

Glottic view scores• Two scoring systems are used to describe the view of the glottis obtained by

DL. • The Cormack-Lehane system provides a general description using four

categories: – Grade I is a full view of the entire glottis; – Grade II is a view of the posterior portion of the glottic opening;– Grade III is a view of the epiglottis only; and with – Grade IV neither the epiglottis nor the glottis can be seen.

• The POGO score attempts to quantify the percentage of glottic opening . – POGO score of 50 percent means that approximately half of the glottis can be seen. – POGO score greater than 50 percent should allow placement of a tracheal tube with

relative ease. – Extremely limited views (eg, POGO score of zero, Cormack-Lehane score of III or

IV) suggest that tube placement will be difficult

CORMACK-LEHANE GRADING SCHEME FOR LARYNGOSCOPY

CURVED BLADE LARYNGOSCOPY

• Step 1: Open the mouth sufficiently to allow blade insertion without traumatizing the teeth .

• Step 2: Insert the blade and control the tongue.• Step 3: Carefully advance the blade toward the

epiglottis in a controlled manner, gently lifting the blade tip every few centimeters.

• Step 4: Advance the tip of the blade into the vallecula, the recess between the base of the tongue and the epiglottis.

• Step 5: Identify the best spot for elevating the epiglottis.

• Each spooning movement involves advancing the blade a few millimeters and then lifting forward in the direction of the handle.

• The lift should be sufficient to allow pulling the handle back without levering on the teeth.

• Touching the teeth indicates excessive levering or insufficient lift.

• Alternatively, external manipulation of the larynx can be used to identify the best location for the blade tip.

• This is done by pressing on the thyroid cartilage with the fingers of the right hand.

• Step 6: Lift the laryngoscope in the direction of the handle, thereby exposing the glottis; do not lever back on the teeth with the laryngoscope handle.

• Keep your elbow in (ie, arm adducted) for maximal lifting strength. • When lifting a laryngoscope with a curved blade, the correct force 

vector points approximately 45 degrees from the plane of the floor. • Lift in the direction of the junction of the ceiling and the wall beyond 

the patient's feet. • This lifting motion elevates the epiglottis, keeps the tongue out of the 

line of sight, and maximizes exposure of the glottis.• The natural inclination for many novice intubators is to lever backwards 

on the laryngoscope handle. • This motion impairs the laryngoscopist's view and can damage teeth.

Laryngoscope lifting

INCORRECT LARYNGOSCOPE MOTION

• Step 7: Optimize the glottic view as needed with external laryngeal manipulation, head elevation, and neck flexion.

• Step 8: Place the tracheal tube.• Once the tip of the ETT has passed the vocal cords, the

laryngoscopist should pause and ask an assistant to remove the stylet. • Inserting the ETT further with the stylet in place may cause injury or

obstruct tube passage. • Advance the ETT until it rests at 21 cm at the front incisors for a

woman or 23 cm for a man. • Adjustment may be needed based upon the position noted on chest x-

ray.

• Stop laryngoscopy and perform bag-mask ventilation with high flow oxygen if the patient's SpO2 falls below 90 percent.

• Individual attempts at intubation should not exceed 30 seconds

STRAIGHT BLADE LARYNGOSCOPY

Uses and advantages — • It frequently allows a more complete view of the laryngeal inlet

since the epiglottis is lifted out of the way. • Also provides a superior view

– When the larynx is situated anterior to the line of sight or – In pt`s with a receding chin or pathology at the BOT .

• It is often easier to insert a straight blade if – The pt's mouth is small– Mouth-opening is limited, or – The front incisors are prominent.

• May be more effective during difficult intubations, particularly if a paraglossal approach is used.

Straight blade techniques • A straight blade may be inserted to the right of the

tongue (paraglossal technique) or in the midline.• The paraglossal approach involves inserting the

straight blade into the natural gutter between the tongue and the lower molars.

• When using a midline approach, the technique is much like that for a curved blade, with the exception of lifting the epiglottis.

• The "retromolar" or "molar" approach uses a more extreme insertion site lateral to the molars.

• Paraglossal technique — The paraglossal technique using a straight laryngoscope blade is performed as follows:

• Step 1: Introduce the blade into the mouth to the right of the tongue, between the tongue and the patient's right lower molars.

• Step 2: Advance the tip of the blade along the tongue into the groove between the tongue and tonsillar pillar.

• Step 3: In a controlled and deliberate manner, continue to advance the blade tip while looking for the epiglottis.

• Step 4: Use lateral and anterior pressure to keep the tongue displaced to the left.

• Step 5: Once the epiglottis is identified, advance the tip of the blade posterior to the epiglottis and into the laryngeal inlet. Use the blade tip to lift the epiglottis anteriorly (upwards in the supine patient), exposing the glottis.

• Avoid levering back with the laryngoscope.

• Step 6: Optimize the glottic view as needed with external laryngeal manipulation, head elevation, and neck flexion.

• If the view remains poor, turning the head slightly to the right may be helpful.

• Step 7: Insert the tracheal tube.• Insert the endotracheal tube (ETT) from the right side of the mouth.• insert it directly into the trachea while watching the tube pass between the vocal

cords.

ANATOMIC LANDMARKS DURING DIRECT LARYNGOSCPY

CONFIRMING PROPER TRACHEAL TUBE PLACEMENT

• End-tidal carbon dioxide — EtCO2 determination (either colorimetric or quantitative capnography) is the most accurate means of confirming proper ETT placement.– Esophagus may yield small but detectable amounts of CO2 during the first few

positive pressure ventilations.– Thus, at least five exhalations with a consistent CO2 level must be evident

before one can confidently assume that the ETT is in the trachea. – In pt`s without detectable pulses, gas exchange in the lungs is markedly reduced

and CO2 may not be detectable, despite proper positioning of the ETT. – Pt`s in cardiac arrest may not generate CO2, making the absence of CO2

detection meaningless. – However, when CO2 is detected in the cardiac arrest patient and persists for six

breaths, the ETT is in the airway. • Physical examination and plain chest radiography may provide useful information

but cannot be used as proof of proper placement.

CO2 detector for endotrachel tube confirmation.

• Clinical findings — • visualization of the ETT through the cords. • Listen for equal breath sounds in both axillae. • No breath sounds should be appreciable over

the epigastrium. • Rise of the chest wall with positive pressure

ventilation. • Mist in the ETT with each exhalation.

• Alternative methods — Alternative methods for determining proper ETT placement have been used successfully in pulseless patients.

• One example is the suction method. • This approach uses syringe or bulb suction devices to

distinguish between the trachea and the esophagus.• The likelihood of tracheal placement is high if over 30 mL of

gas can be withdrawn from the ETT into the bulb without resistance.

• Fiberoptic visualization of the tracheal rings and carina may also be used to confirm tracheal placement.

• Chest x-ray (usually AP) – – Helpful for determining the depth of the ETT in

the trachea.– But cannot reliably exclude esophageal intubation

• Ultrasound is the subject of ongoing study in both adult and pediatric populations as a method for confirming ETT placement.

• Mainstem bronchus intubation — • Endobronchial intubation can produce major complications over

time, such as hypoxia, hypercapnia, and pneumothorax. • Endobronchial placement occurs more often in women and during

emergency intubations.• EtCO2 detection does not distinguish between endotracheal,

endobronchial (too deep), and supraglottic (too shallow) ETT placement.

• Breath sounds that are significantly louder on one side suggest endobronchial intubation.

• Ultrasound can be used to confirm ventilation by observing the “lung sliding sign .

• Depth of tracheal tube insertion — In women the ETT should be inserted to a depth of 20 to 21 cm.

• In men the appropriate depth is 22 to 23 cm. • Use the teeth or gums as the benchmark for

insertion depth (rather than the lips) because they are fixed landmarks.

• The tip of a properly placed ETT should lie approximately 2 cm above the carina(CXR-AP).

• POSTINTUBATION MANAGEMENT • The ETT should be secured with tape or a

commercially available tube holder. • Tube holders are often easier to manage if the

position of the ETT must be changed and may be more comfortable for patients.

• Sedation and analgesia are provided using validated treatment algorithms.

COMPLICATIONS • Direct blunt or penetrating trauma to the oropharynx, larynx,

and trachea can occur from the laryngoscope or the stylet and tracheal tube.

• Lacerations of the lips, teeth, tongue, pharyngeal wall, laryngeal structures, including the glottis and the esophagus.

• Glottic trauma may involve vocal cord injury or dislocation of the arytenoid cartilages.

• Cervical spinal cord injury in susceptible individuals.• Dislocation of the temporomandibular joint-: may occur

if great force is used to open the mouth.

• Nontraumatic complications- – Aspiration of gastric contents.– Bronchospasm.– Hypoxic injury from prolonged attempts at intubation.– Unrecognized esophageal intubation. – Tachycardia, arrhythmias, hypertension, and

myocardial ischemia or infarction may result. – Long-term consequences of tracheal tube placement

include damage to the airway, including laryngomalacia, tracheomalacia, or laryngeal stenosis.

OVERVIEW OF MECHANICAL VENTILATION

INTRODUCTION • Mechanical ventilation is also called positive pressure

ventilation.• Following an inspiratory trigger, a predetermined mixture of

air is forced into the central airways and then flows into the alveoli.

• As the lungs inflate, the intraalveolar pressure increases. • A termination signal eventually causes the ventilator to stop

forcing air into the central airways and the central airway pressure decreases.

• Expiration follows passively, with air flowing from the higher pressure alveoli to the lower pressure central airways.

INDICATIONS

• It is indicated for acute or chronic respiratory failure, which is defined as – Insufficient oxygenation– Insufficient alveolar ventilation, or both.

• Mechanical ventilation should be considered early in the course of illness and should not be delayed until the need becomes emergent.

• Physiologic derangements and clinical findings can be helpful in assessing the severity of illness.

PHYSIOLOGIC OBJECTIVES

Support pulmonary gas exchange based on alveolar ventilation and arterial oxygenation

Reduce the metabolic cost of breathing by unloading the ventilatory muscles

Minimize ventilator-induced lung injury

CLINICAL OBJECTIVES

Reverse hypoxemia

Reverse acute respiratory acidosis

Relieve respiratory distress

Prevent or reverse atelectasis

Reverse ventilatory muscle fatigue

Permit sedation and/or neuromuscular blockade

Decrease systemic or myocardial oxygen consumption

Stabilize the chest wall

PARAMETER VALUE

CLINICAL ASSESSMENTApnea  

Stridor  

Severely depressed mental status  

Flail chest  

Inability to clear respiratory secretions (eg, excessive secretions, loss of protective reflexes, neuromuscular failure)

 

Trauma to mandible, larynx, trachea  

LOSS OF VENTILATORY RESERVERespiratory rate >35 breaths/min

Tidal volume <5 mL/kg

Vital capacity <10 mL/kg

Negative inspiratory force Weaker than –25 cm H2O (2.44 kPa)

Minute ventilation <10 L/min

Rise in PaCO2 >10 mmHg (1.33 kPa)

Refractory hypoxemiaAlveolar-arterial gradient (FiO2 = 1) >450

PaO2/PAO2 <0.15

PaO2 with supplemental O2 <55 mmHg (7.32 kPa)

\RESPIRATORY ABNORMALITIES SUGGESTIVE OF THE NEED FOR MECHANICAL VENTILATION

BENEFITS — The principal benefits of mechanical ventilation during respiratory failure are-

1. Improved gas exchange- by improving ventilation-perfusion (V/Q) matching.

2. Decreased work of breathing.

    

• TYPES OF BREATHS — Mechanical ventilation can deliver different types of breaths- – Volume control. – Volume assist.– Pressure control. – Pressure assist, and – Pressure support.

• They are defined by the combination of three features:1. Trigger – Breaths can be triggered by a timer (ventilator-

initiated breaths) or patient effort (patient-initiated breaths).

2. Target – The flow of air into the lung can target a predetermined flow rate (ie, the peak inspiratory flow rate) or pressure limit.

3. Termination – The signal for a ventilator to end inspiration may be volume-, time-, or flow-related.

     

• Volume control — VC breaths are ventilator-initiated breaths with a set inspiratory flow rate.

• Inspiration is terminated once the set tidal volume has been delivered.

• Airway pressure is determined by the airways resistance, lung compliance, and chest wall compliance.

• Modes of mechanical ventilation that can deliver VC breaths include volume-limited assist control and volume-limited synchronized intermittent mandatory ventilation.

• Volume assist — VA breaths are patient- initiated breaths with a set inspiratory flow rate.

• Inspiration is terminated once the set tidal volume has been delivered.

• Airway pressure is determined by the airways resistance, lung compliance, and chest wall compliance.

• Modes of mechanical ventilation that can deliver VA breaths include volume-limited assist control and volume-limited synchronized intermittent mandatory ventilation.

• Pressure control — PC breaths are ventilator-initiated breaths with a pressure limit.

• Inspiration is terminated once the set inspiratory time has elapsed.

• The tidal volume is variable and related to compliance, airway resistance, and tubing resistance.

• A consequence of the variable tidal volume is that a specific minute ventilation cannot be guaranteed.

• Modes of mechanical ventilation that deliver PC breaths include pressure-limited assist control and pressure-limited synchronized intermittent mandatory ventilation.

• Pressure assist — Pressure assist (PA) breaths are patient-initiated breaths with a pressure limit.

• Inspiration is terminated once the set inspiratory time has elapsed.

• The tidal volume is variable and related to compliance, airway resistance, and tubing resistance.

• A consequence of the variable tidal volume is that a specific minute ventilation cannot be guaranteed.

• Modes of mechanical ventilation that deliver PA breaths include pressure-limited assist control and pressure-limited synchronized intermittent mandatory ventilation.

• Pressure support — PS breaths are patient-initiated breaths with a pressure limit.

• The ventilator provides the driving pressure for each breath, which determines the maximal airflow rate.

• Inspiration is terminated once the inspiratory flow has decreased to a predetermined percentage of its maximal value.

• Pressure support is a mode of mechanical ventilation. 

MODES 

• The modes of mechanical ventilation are distinguished from another by the types of breaths that they deliver. 

• Common modes include- – Assist control.– Synchronized intermittent mandatory ventilation.– Pressure support, numerous other modes also exist (table 4). 

ModeBreath

strategy(target)

TriggerCycle

(breath termination)

Types of breaths

Ventilator Patient Mandatory Assisted Spontaneous

CMV

Volume-limited Yes No Volume Yes No No

Pressure-limited Yes No Time Yes No No

AC

Volume-limited Yes Yes Volume Yes Yes No

Pressure-limited Yes Yes Time Yes Yes No

IMV

Volume-limited Yes Yes Volume Yes Yes* Yes*

Pressure-limited (also called APRV)

Yes Yes Time Yes Yes* Yes*

PSV Pressure-limited No Yes

Flow, pressure, or time

No Yes No

CPAP No Yes Flow No Yes No

Tube compensation

No Yes Flow No No Yes

Modes of mechanical ventilation

INITIATION• Invasive versus noninvasive — Mechanical ventilation

can be delivered invasively or noninvasively. • The decision about whether to initiate invasive or

noninvasive mechanical ventilation requires that the entire clinical situation be considered.

• A trial of NPPV is worthwhile in pt`s with acute cardiogenic pulmonary edema or hypercapnic respiratory failure due to COPD.

• Invasive mechanical ventilation is appropriate for most other patients.

• Choosing a mode — The selection of the mode is generally based on clinician familiarity and institutional preferences.

• Level of support — The level of ventilatory support refers to the proportion of the patient's ventilatory needs that are met by the ventilator.

• The level of ventilatory support is determined by the mode and other settings. 1. Assist control provides the most support. 2. Synchronized intermittent mandatory ventilation provides the

widest range of support, and 3. Pressure support tends to provide less support.

• Settings — There are numerous settings that need to be considered when mechanical ventilation is initiated.

• These include the trigger mode and sensitivity, respiratory rate, tidal volume, positive end-expiratory pressure, flow rate, flow pattern, and fraction of inspired oxygen.

• Trigger — There are two ways to initiate a ventilator-delivered breath-:1. Pressure triggering or 2. Flow-by triggering.

• When pressure triggering is used, a ventilator-delivered breath is initiated

• A trigger sensitivity of -1 to -3 cm H2O is typically set.

• Auto-PEEP (intrinsic positive end-expiratory pressure) interferes with pressure triggering. 

• Auto-PEEP refers to end-expiratory pressure that is created when inspiration begins before expiration is complete.

• When flow-by triggering is used, a continuous flow of gas through the ventilator circuit is monitored. 

• A ventilator-delivered breath is initiated when the return flow is less than the delivered flow, a consequence of the pt's effort to initiate a breath. 

FLOW-BY TRIGGERING IN MECHANICAL VENTILATION

• The trigger sensitivity should allow the patient to trigger the ventilator easily.

• A trigger sensitivity that is too sensitive may cause a breath to be delivered in response to patient movement or subtle pressure deflections caused by water moving within the ventilator tubing.

• In contrast, a trigger sensitivity that is not sensitive enough increases patient effort.

• Pressure triggering can be used with the assist control or synchronized intermittent mandatory ventilation modes of mechanical ventilation.

• Tidal volume — The tidal volume is the amount of air delivered with each breath.

• During volume-limited ventilation, the tidal volume is set by the clinician and remains constant.

• During pressure-limited ventilation, the tidal volume is variable.;

• The appropriate initial tidal volume depends on numerous factors, most notably the disease.

• ARDS –tidal volumes of ≤6 mL per kg of predicted body weight improved mortality in patients with ARDS

• Respiratory rate — An optimal method for setting the respiratory rate has not been established. 

• For most patients, an initial respiratory rate b/w 12 and 16 breaths/minute is reasonable.– For pt`s receiving assist control, the RR is typically set 

four breaths per minute below the pt's native rate.– For pt`s receiving synchronized intermittent 

mandatory ventilation, the rate is set to ensure that at least 80 percent of the patient's total minute ventilation is delivered by the ventilator.

• Return to the previous respiratory rate is indicated if the patient develops auto-PEEP >5 cm H2O.

• For pt`s with ARDS, the required RR is higher (up to 35 breaths /minute), in order to facilitate low tidal volume ventilation.

• PEEP — Applied PEEP (extrinsic positive end-expiratory pressure) is generally added to mitigate end-expiratory alveolar collapse.

• A typical initial applied PEEP is 5 cm H2O. • However, up to 20 cm H2O may be used in patients undergoing

low tidal volume ventilation for ARDS. • Elevated levels of applied PEEP can have adverse

consequences, such as-:– Reduced preload (decreases cardiac output). – Elevated plateau airway pressure (increases risk of barotrauma), and – Impaired cerebral venous outflow (increases intracranial pressure).

• Flow rate — The peak flow rate is the maximum flow delivered by the ventilator during inspiration.

• Peak flow rates of 60 L per minute may be sufficient, although higher rates are frequently necessary.

• An insufficient peak flow rate is characterized by – Dyspnea – Spuriously low peak inspiratory pressures, and – Scalloping of the inspiratory pressure tracing

• The need for a high peak flow rate is particularly common among patients who have – Obstructive airways disease with – Acute respiratory acidosis.

• In such patients, a higher peak flow rate shortens inspiratory time and increases expiratory time (ie, decreases the inspiratory to expiratory [I:E] ratio).

• These alterations increase carbon dioxide elimination and improve respiratory acidosis, while also decreasing the likelihood of dynamic hyperinflation (auto-PEEP).

• Flow pattern — Microprocessor-controlled mechanical ventilators can deliver several inspiratory flow patterns, including a square wave (constant flow), a ramp wave (decelerating flow), and a sinusoidal wave. 

• The ramp wave may distribute ventilation more evenly than other patterns of flow, particularly when airway obstruction is present. 

VENTILATOR FLOW AND PRESSURE WAVEFORMS

• Fraction of inspired oxygen — The lowest possibleFiO2 necessary to meet oxygenation goals should be used.

• As an example, a patient with IHD requires greater oxygenation than a patient with chronic hypoxemia due to lung disease.

• Typical oxygenation goals include an PaO2 ≥ 60 mmHg and SpO2 ≥ 90 percent.

• In patients with ARDS, targeting a PaO2 of 55 to 80 mmHg and a SpO2 of 88 to 95 percent is acceptable.

• ASYNCHRONY — Patient-ventilatory asynchrony exists if the phases of breath delivered by the ventilator do not match that of the patient.

• It is common during mechanical ventilation: more than 10 percent of breaths are asynchronous in approximately 24 percent of mechanically ventilated pt`s.

• Patient-ventilator asynchrony can cause dyspnea, increase the work of breathing, and prolong the duration of mechanical ventilation .

• It can be detected by careful observation of the patient and examination of the ventilator waveforms.

 There are several common causes of patient-ventilator asynchrony:1. Ineffective triggering of a ventilator-delivered breath –

Ineffective triggering may occur in as many as one-third of inspiratory effort.

2. Double triggering ventilator-delivered breaths – When this occurs, the ventilator delivers two breaths in rapid sequence.

3. This can be lessened or eliminated by decreasing the trigger sensitivity (eg, from -1 to -3 cm H2O).

3. Prolonged inspiratory time – Inspiratory time is the tidal volume divided by the inspiratory flow rate.

4. Attempts to increase the minute ventilation by raising only the tidal volume result in an increased inspiratory time, causing patient discomfort and asynchrony .

• Breath stacking is a manifestation of asynchrony that occurs when a patient triggers a new breath before the completion of the prior ventilator-delivered breath. 

Modes of mechanical ventilation

• The mode refers to the method of inspiratory support. 

• Common modes of mechanical ventilation are described in this topic. 

• VOLUME-LIMITED VENTILATION — Volume-limited ventilation (also called volume-controlled or volume-cycled ventilation) requires the clinician to set the peak flow rate, flow pattern, tidal volume, RR, applied PEEP, and FiO2.

• Inspiration ends after delivery of the set tidal volume.• The I:E ratio are determined by the peak inspiratory flow rate. • Airway pressures (peak, plateau, and mean) depend on both the ventilator

settings and patient-related variables (eg, compliance, airway resistance). • High airway pressures may be a consequence of

– Large tidal volumes, – A high peak flow, – Poor compliance (eg, acute respiratory distress syndrome, minimal sedation), or – Increased airway resistance.

Waveforms for volume-cycle ventilator

Airway pressures during various modes of ventilation

• Modes — Volume-limited ventilation can be delivered via several modes, including CMV, assist control AC, IMV, and SIMV.

• CMV — During CMV, the minute ventilation is determined entirely by the set respiratory rate and tidal volume. 

• The patient does not initiate additional minute ventilation above that set on the ventilator. 

• CMV does not require any patient work.

• AC — During AC, the clinician determines the minimal minute ventilation by setting the respiratory rate and tidal volume.

• The patient can increase the minute ventilation by triggering additional breaths.

• Each patient-initiated breath receives the set tidal volume from the ventilator.

• Pressure regulated volume control (PRVC) is similar to AC. • The main difference is that the ventilator is able to auto regulate

the inspiratory time and flow so that the tidal volume generates a smaller rise in the plateau airway pressure.

• IMV — IMV is similar to AC in two ways: – The clinician determines the minimal minute ventilation (by

setting the RR and tidal volume) and – The patient is able to ↑the minute ventilation.

• IMV differs from AC in the way that the minute ventilation is increased.

• Pt`s increase the minute ventilation by spontaneous breathing, rather than patient-initiated ventilator breaths.

• The precise minute ventilation depends on the size of the tidal volume for each spontaneous breath.

• SIMV — SIMV is a variation of IMV, in which the ventilator breaths are synchronized with patient inspiratory effort.

• SIMV (or IMV) can be used to titrate the level of ventilatory support over a wide range.

• This is an advantage unique to these modes. • Ventilatory support can range from full support (set respiratory

rate is high enough that the patient does not overbreathe) to no ventilatory support (set respiratory rate is zero).

• The level of support may need to be modified if hemodynamic consequences of positive pressure ventilation develop.

• Comparisons — SIMV and AC are the most frequently used forms of volume-limited mechanical ventilation.

• Possible advantages of SIMV compared to AC include – Better patient-ventilator synchrony. – Better preservation of respiratory muscle function.– Lower mean airway pressures, and – Greater control over the level of support. – Auto-peep may be less likely with simv.

• In contrast, AC may be better suited for critically ill pt`s who require a constant tidal volume or full or near-maximal ventilatory support

Methods of weaning from mechanical ventilation

• Weaning is the process of decreasing the amount of support that the patient receives from the mechanical ventilator.

• The purpose is to assess the probability that mechanical ventilation can be successfully discontinued.

• Traditional methods of weaning include spontaneous breathing trials (SBTs), progressive decreases in the level of pressure support during PSV, and progressive decreases in the number of ventilator-assisted breaths during IMV.

•  An SBT refers to a patient breathing through the endotracheal tube either without any ventilator support (eg, through a T-piece) or with minimal ventilator support (eg, a low level of pressure support, automatic tube compensation (ATC), or continuous positive airway pressure (CPAP)). 

• Once it has been determined that a patient is ready to be weaned, we suggest weaning via once-daily SBTs, rather than PSV or IMV (Grade 2B). 

• For most p`ts, the SBT may be performed using a T-piece, low level of pressure support (eg, ≤8 cm H2O), ATC, or CPAP (eg, ≤5 cm H2O). 

• However, for pt`s with a small, high resistance endotracheal tube (size ≤7.0 mm), we suggest using low level pressure support or ATC, rather than a T-piece or CPAP (Grade 2C). 

• An initial SBT of 30 minutes duration is generally sufficient to determine whether mechanical ventilation can be discontinued.

• For pt`s who fail their initial SBT, or required prolonged mechanical ventilation prior to the initial SBT (eg, more than ten days), we suggest that subsequent trials be 120 minutes, rather than 30 minutes (Grade 2C).

• Weaning by progressive decreases in the level of pressure support (2 to 4 cm H2O per day) during PSV is a reasonable alternative for pt`s who do not tolerate SBTs. We suggest that IMV alone NOT be used for weaning (Grade 1B).

• Clinical impression determines whether a patient fails or tolerates weaning.

• Patients who tolerate the SBT should be considered for extubation.

• In contrast, patients who fail the SBT should be returned to mechanical ventilation.

• When a patient fails weaning, the reason for failure should be sought and corrected.

• Meanwhile, the patient should be assessed daily for readiness to wean. We suggest weaning such patients via once-daily SBTs, rather than SBTs multiple times daily, PSV, or IMV (Grade 2B).

• A SBT refers to a patient spontaneously breathing through the endotracheal tube (ETT) for a set period of time (usually 30 minutes to two hours) either without any ventilator support (eg, through a T-piece) or with minimal ventilator support.

• Methods of minimal ventilator support for a SBT include a low level of PSV (eg, 5 to 7 cm H2O), automatic tube compensation (ATC), or CPAP.

• A successful SBT is one where a patient passes a number of pre-set physiologic criteria (eg, heart rate, respiratory rate, blood pressure, gas exchange) at completion of the SBT that potentially indicate candidacy for extubation.

• When a patient successfully passes a SBT and no contraindication to extubation is present, the ETT is typically removed.

• When a patient fails a SBT, then the patient is typically not extubated and a work up for weaning failure is performed.

• Our preference for SBTs as the initial weaning strategy for most patients with acute respiratory failure, is based upon clinical experience and empirical studies, which indicate that compared to other weaning methods, SBTs are simple, efficient, safe, and effective.

• Patients undergoing daily SBTs were more likely to wean successfully than those who were weaned by IMV or PSV.

DISEASE-SPECIFIC VENTILATORY MANAGEMENT

• Asthma and COPD — • The major reason for instituting mechanical ventilation in these patients is 

clinical manifestation of respiratory distress, related to deteriorating gas exchange. 

• For patients with severe asthma or COPD requiring mechanical ventilation, following approach is recommend :1. Use larger-sized endotracheal tube (eg, ≥8 mm). 2. Keep minute ventilation (MV) below 115 mL/kg.3. Keep tidal volume (VT) below 8 mL/kg.4. Maintain respiratory rate at 10 to 14 breaths per minute.5. Maintain inspiratory flow rate at 80 to 100 liters/minute.6. Allow increased expiratory time with decreased I:E ratio (1:3 or 1:4 up to 1:5).7. Maintain plateau pressures below 30 cmH2O if possible.8. Allow hypercapnea for patients with high peak pressures.

Acute cardiogenic pulmonary edema 

• Extrinsic positive end-expiratory pressure (PEEPe) can be increased as tolerated to improve oxygenation and further reduce preload.

• Excessive PEEPe can result in hypotension in patients dependent upon preload to maintain cardiac output (eg, patients with right ventricular dysfunction).

• Many patients with acute CPE benefit from NPPV treatment. NPPV improves cardiac performance and decreases pulmonary edema.

• However, some patients are not amenable to treatment with NPPV .

• Acute respiratory distress syndrome — Acute respiratory distress syndrome (ARDS) is defined as a syndrome of acute and persistent lung inflammation with increased vascular permeability.

• ARDS is characterized by four features:– Timing – Develops within one week of a known clinical insult or new or

worsening respiratory symptoms.– Radiographic appearance – Bilateral opacities not fully explained by

effusions, lobar/lung collapse, or nodules.– Pulmonary edema – Respiratory failure not fully explained by cardiac failure or

fluid overload; Need objective assessment (eg, echocardiography) to exclude hydrostatic edema if no risk factor present.

– Compromised oxygenation – Mild: 200 mmHg <PaO2/FiO2 ≤300 mmHg with PEEP or CPAP ≥5 cmH2O; Moderate: 100 mmHg <PaO2/FiO2 ≤300 mmHg with PEEP ≥5 cmH2O; Severe: PaO2/FiO2≤100 mmHg with PEEP ≥5 cmH2O.

Rapid sequence intubation in adults

• DEFINITION — Rapid sequence intubation (RSI) is the virtually simultaneous administration of a sedative and a neuromuscular blocking (paralytic) agent to render a patient rapidly unconscious and flaccid in order to facilitate emergent endotracheal intubation and to minimize the risk of aspiration.

• Preoxygenation is required to permit a longer period of apnea without clinically significant oxygen desaturation.

• Bag-mask ventilation is avoided during the interval between drug administration and endotracheal tube placement, thereby minimizing gastric insufflation and reducing the risk of aspiration

• Indications — RSI is the standard of care in emergency airway management for intubations not anticipated to be difficult.

• Contraindications — Contraindications to RSI are relative.

• Circumstances exist where neuromuscular blockade is undesirable due to the high likelihood of intubation or mechanical ventilation failure.

• Depending on clinical circumstances, particular sedative or neuromuscular blocking agents may be relatively contraindicated, due to the risk of potential side effects.

THANKYOU