basics of ventilatory support

8/9/2019 Basics of Ventilatory Support

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Basics of ventilatory support

Dr. Fiona


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Mechanical ventilation

Use of sophisticated life support technology aimed

at maintaining tissue oxygenation and removal of

carbon dioxide


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Indications for mechanical ventilation

Most common: respiratory failure Postoperative respiratory failure

Sepsis

Pneumonia

Trauma

ARDS

Aspiration Others: COPD exacerbation, coma,

neuromuscular disease etc.


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Signs of respiratory failure


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Goals of mechanical ventilatory support

Adequate alveolar ventilation

Oxygen delivery

Restore acid base balance

Reduce work of breathing

Minimize side effects


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Ventilator initiation

Choose a ventilator

Negative pressure ventilation? Positive pressure ventilation?

Invasive?Noninvasive?

Initial settings?

Choose a mode


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Ventilator initiation

Establishing an interface

Volume controlled versus pressure

controlled?


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PARTIAL

SUPPORTFULL

SUPPORT

CPAP PSV SIMV CMV

Partial ventilatory support versus full?


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Assist Control Ventilation Every breath supported by machine

Patient or time triggered

Volume or pressure limited

Provides full support

Advantages: minimum, safe level of ventilation

assured

Disadvantages: poorly tolerated by awake;

hyperventilation, high airway pressure are risks

Modes of ventilation


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Continuous Mandatory Ventilation Every breath delivered by machine

Time triggered


Provides full support

Advantage: eliminates work of breathing

Disadvantages: poorly tolerated by awake; danger

of disconnection, ventilator muscle atrophy



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Intermittent or Synchronized Intermittent MandatoryVentilation (IMV or SIMV)

Patients breathe spontaneously between mandatory

machine breaths

Machine breath time cycled (IMV) or patient triggered

(SIMV)


Provides full or partial support

Can be combined with pressure support ventilation

(PSV)



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IMV and SIMV

Advantages: lower mean airway pressures, can

vary amount of support, maintain ventilator

muscle strength, better synchrony, physiologic

spontaneous breathing incorporated

Disadvantages: hypoventilation, ventilatory

muscle fatigue, breath stacking, weaning may beprolonged


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Pressure Support Ventilation (PSV)

Patients spontaneous inspiration assisted

with selected level of positive pressure

Patient triggered

Pressure limited, flow cycled

Advantages: reduces work of breathing, may

improve synchrony



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Pressure-Control Ventilation Time or patient triggered

Pressure limited, time cycled

Advantages: useful when limiting Pplat is a concern,

prolonged I:E ratio can be administered, improved

gas distribution

Disadvantage: high mean airway pressure can

decrease venous return



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Commonly used modes

Assist-control

SIMV with PSV


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Key ventilatory settings

TriggerMethod

Pressure trigger Flow trigger

Sensitivity:

-0.5 to -1.5 cm H2O

Sensitivity:Specific to ventilator

Varies: 0.1 to 20 L min-1


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Tidal Volume (VT)

Volume control ventilation 8 10 ml kg-1

Pressure control ventilation Pressure limit

of 12 to 30 cm H2O to achieve VT : 8 10 ml kg-1

Rate

12 to 16 breaths min-1


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Tidal volume and rate settings

Patient typeVT

(ml kg-1)

Frequency

(breaths min-1)

Normal lungs 8-10 12-16

Neuromuscular disease,

postoperative period

10-12 8-12

Acute restrictive disease, ALI,

ARDS (Open lung strategy)

6-8 15-35

Obstructive lung disease(COPD)

8-10 10-12

Acute severe asthma

exacerbation

4-6 10-12


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FIO2

1.0 if little known about patient/ grave condition

Reduce to 0.4 to 0.5 or less as soon as possible

to avoid oxygen toxicity and absorption

atelectasis



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Inspiratory flow: 40 to 80 L min-1, adjusted to

meet patients spontaneous inspiratory flow

Inspiratory time: 0.8 to 1.2 s

I:E ratio: 1: 2 or lower

Inspiratory flow waveform: e.g.: constant,

decreasing, sine

Inspiratory pause: up to 10% of inspiratory time



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Positive end-expiratory pressure (PEEP) or

continuous positive airway pressure (CPAP)

Maintain lung volume, improve oxygenation

Indication to start: PaO2 e 50 - 60 mm Hg and

FIO2u 0.4 - 0.5

Start with 5 cm H2O and make small increments

of 2 - 3 cm H2O



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Limits and alarms

Low pressure, low PEEP alarms High pressure limit and alarm

Volume alarms (low VT, high/low minute

ventilation) High rate alarm

Apnea alarm

High/low O2 alarm

I:E ratio and alarm

High/low temperature alarm


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Humidification: inspired gas temperature 33

2

C

Periodic sighs

Open lung strategy: Pressure limited

ventilation with low VT of 4 - 8 ml kg-1, PEEP

2 cm H2O above lower inflection point

Lung recruitment strategy: sustained CPAP of

40 cm H2O for 30 40 s


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Care of a patient on a ventilator

Physical assessment

General appearance

Level of consciousness

Signs of anxiety

Colour

Examination of respiratory system:

inspection, palpation, percussion,

auscultation


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Care of the artificial airway:

placement, size, cuff pressure, depth

extra intubation equipment available by bedside

suction catheters, gloves, sterile water and

suction equipment

Bedside availability of manual resuscitator

with oxygen supply



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Ventilator setting assessment and

adjustment

Peak, plateau and airway pressuresRate and tidal volumes

Trigger effort, I:E ratio, humidification and

temperature

Patient ventilator interaction



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Monitoring:

continuous pulse oximetry

as needed ABGs

chest radiographs

Cardiovascular assessment: heart rate,

blood pressure, ECG

Other systems: CNS, hepatic, renal

Nutrition



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PEEP

Lung recruitment maneouvers

Bronchial hygiene: postural drainage, bronchodilators,

chest physiotherapy, humidification

Pressure controlled ventilation with prolonged

inspiratory time

Prone positioning

Open lung techniques

Techniques to improve oxygenation and

ventilation


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Monitoring oxygenation

Arterial Pulse Oximetry

Oxygen consumption:

Ficks method

Analysis of inspired and expired gases

Alveolar-Arterial Oxygen Tension difference:

[P(A-a)O2] Normal: 5 - 15 mmHg

PaO2/FIO2 ratio

Quantification of shunt


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Measurement of patients VT, rate, minute

volume

Dead space/tidal volume : VD/VT ratio.Normal: 0.2 to 0.4

Monitoring of inspired and exhaled gases, and

tidal volumes Capnography: PEtCO2 1 - 5 mmHg less than

PaCO2

Monitoring ventilation


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Other parameters to be noted

Respiratory system compliance: C= V/P

Normal 60 to 100 ml cm H2O-1

Airway resistance: Raw = (Ppeak- Pplat)/ Flow

Peak and plateau pressures, mean

airway pressure

Auto PEEP


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Weaning

Gradual reduction of mechanical

ventilatory support that allows the patient

to resume spontaneous breathing in an

incremental manner


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Assess patient type

1. Those for whom removal from ventilator

is quick and routine

2. Those who need a systematic approach

to discontinuing ventilatory support

3. Ventilator- dependable or unweanableDuration on ventilator: ife 72 hours, can be

removed quickly


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Criteria to consider before weaning

Subjective clinical assessments

Resolution of acute phase of disease

Adequate coughPhysician believes discontinuation

possible

Patient motivated and psychologically

prepared


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Objective measurements

Patient can breathe spontaneously

Adequate oxygenation

Stable CVS

PaO2 u 60 mm Hg with FIO2 e 0.4 0.5

PEEP e 5 8 cm H2O

PaO2/ FIO2 u150 - 300

HR < 140 min-1

stable BP

no or minimal pressors


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Objective measurements

Afebrile

No significant respiratory acidosis

Adequate Hb (u 8-10 g dl-1)

Adequate mentation

Stable metabolic state:

adequate nutritionelectrolytes and minerals


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Preparing the patient for weaning

Decrease disease imposed ventilatory load:

treat respiratory infection, bronchospasm, airway

edema

Patient should be allowed to sleep at night on a

level of ventilatory support that ensures

ventilatory muscle strength

Communication and encouragement


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Methods of weaning

Spontaneous breathingtrials(SBTs)

Synchronized intermittent

mandatory ventilation

(SIMV)

Pressure support

Ventilation

(PSV)

1

2

3


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Spontaneous Breathing T-tube Trials

Trials several times a day interspersed with periodsof mechanical ventilation

Start with 5 min off ventilator (or if patient can

tolerate 30 to 120 min) Work up to 20 to 30 min reassess condition

Unsuccessful give 24 hr period rest

Tolerates 30 to 120 min trial: disconnect ventilator During day, rest of 2 - 4 hours between trials

Trials stopped at night


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SIMV

Gradual reduction of machine rate based

on ABG analysis and patient assessment

Patient challenged to provide portion ofventilation

SIMV can be combined with PSV to

overcome work of breathing


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PSV

Supports patients spontaneous inspiration

with selected level of positive airway pressure

Initially set to achieve VT of8 to 10 ml kg-1

Then gradually reduced to 5 to 10 cm H2O to

overcome work of breathing

T-tube trial may then be attempted for 30 to

120 min


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Monitoring the patient during weaning

Ventilatory status: rate, pattern, dyspnea, fatigue,

sweating, use of accessory muscles, abdominal

paradox. Measurement of PaCO2

Rapid shallow breathing index: f/VT < 105

Oxygenation: Pulse oximetry, PaO2 and SaO2

CVS status: HR, BP, cardiac rhythm


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Thank you!

basics of ventilatory support

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