patient – ventilator asynchrony

8/11/2019 Patient Ventilator Asynchrony

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Patient Ventilator Asynchrony

Dr Vincent IoosMedical ICU PIMS APICON 2008

Workshop on Mechanical Ventilation


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Goal of mechanical ventilation

Do you mechanically ventilate your patient toreverse diaphragmatic fatigue ?

or Do you encourage greater diaphragm use to

avoid ventilator-induced diaphragmaticdysfunction?


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Patient triggered ventilation

Assisted mechanical ventilation Avoid ventilator induced diaphragmatic

dysfunction Providing sufficient level of ventilatory supportto reduce patients work of breathing


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Volume or pressure oriented?


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Volume oriented modes

Inspiratory flow is preset

Inspiratory time determines the Vt

The variable parameter is the airway peak andplateau pressure


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Equation of insuflated gases

in flow assist control ventilation Describes interactions between the patient

and the ventilator Pressure required to deliver a volume of gas

in the lungs is determined by elastic andresistive properties of the lung

Paw = Vt/C +VR + PEP


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Airway Pressure

C = Vt / P and P = P Plat - PEEP

Paw= Po + Vt/C + RV


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Flow shapes


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Pressure oriented modes

Pressure in airway is the preset parameter

Flow is adjusted at every moment to reach thepreset pressure

The variable parameter is Vt


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Equation of motionin pressure support ventilation

Pressure = pressure applied by the ventilatoron the airway + pressure generated byrespiratory muscles

Pmus is determined by respiratory drive andrespiratory muscle strenght

Paw + Pmus = Vt/C + VxR + PEP


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Determinant factorsof inspiratory flow in PSV

Pressure support setting Pmus (inspiratory effort) Airway resistance Respiratory system compliance Vt directly depends on inspiratory flow, but

also on auto-PEEP (decreases the drivingpressure gradient)


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Look at the curves !


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A challenge for the intensivist

Discomfort anxiety Increased work of breathing Increased requirement of sedation Increased length of mechanical ventilation Increased incidence of VAP


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Patient-ventilator asynchrony

Mechanical ventilation: 2 pumps Ventilator controlled by the physician

Patients own respiratory muscle pump

Mismatch between the patient and the ventilatorinspiratory and expiratory time time

Patient fighting with the ventilator


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Ventilation phases


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Trigger asynchrony

Ineffective triggerring: muscular effort without ventilator trigger

Double triggerring

Auto-triggering Insensitive trigger: triggering that requires

excessive patient effort


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Ineffective triggering


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Double triggering

Cough

Sighs

Inedaquate flow delivery


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Auto-triggering

Circuit leak Water in the circuit

Cardiac oscillations Nebulizer treatments

Negative suction applied trough chest tube


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Flow asynchrony

Fixed flow pattern (volume oriented) Variable flow pattern (pressure oriented)


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Volume oriented ventilation(fixed flow pattern)

Inspiratory flow varies according to theunderlying condition

If patients flow demand increases, peak flowshould be adjusted accordingly Usually, peak flow is too low Dished-out appearance of the presure-wave-

form Importance of flow-pattern


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-Ineffictive triggering at

30 l/mn- Increase in flow rate

- Subsequent increase ofexpiratory time

- Decreased dynamichyperinflation

- Subsequent decreasein ineffictive trigerring


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Importance of flow pattern

Increase in peak-flow setting fron 60 to 120l/mn eliminated scooped appearance of the

airway pressure waveform


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Pressure oriented ventilation(variable flow)

Peak flow is depending on : Set target pressure

Patient effort Respiratory system compliance

Adjustement : rate of valve opening = rise time =presure slope = flow acceleration


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Termination asynchrony

Ventilator should cycle at the end of the neuralinspiration time

Delayed termination: Dynamic hyperinflation Trigger delay

Ineffective triggering

Premature termination


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Set inspiratory time < 1 sec

PSV = 10 cmH2O


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PSV = 10 cmH2O

Inspiratoy flow terminate despitecontinued Pes defelection

Double Trigerring

Patient 1 Patient 2


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Expiratory asynchrony

Shortened expiratory time: Auto-PEEP trigger asynchrony

Delay in the relaxation of the expiratorymuscle activity prior to the next mechanicalinspiration

Overlap between expiratory and insiratoryuscle activity Prolonged expiratory time


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Auto-PEEP created by flow patternsthat increases inspiratory time

Lower peak flow during control ventilation Switch from constant flow to descending ramp

flow Inadequate pressure slope during presure

controlled ventilation Termination criteria that prolong expiratory

time during PSV


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Conclusion

Look at your patient ! Look at the curves ! Have a good knowledge of the ventilation

modalities of the ventilator you are using Excessive ventilatory support leads to ineffective

triggering

Do not forget to set trigger sensitivity, to avoidexcessive effort and auto-triggering

patient – ventilator asynchrony

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