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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