Presentation on theme: "Patient – Ventilator Asynchrony Dr Vincent Ioos Medical ICU – PIMS APICON 2008 Workshop on Mechanical Ventilation."— Presentation transcript:
Patient – Ventilator Asynchrony Dr Vincent Ioos Medical ICU – PIMS APICON 2008 Workshop on Mechanical Ventilation
Goal of mechanical ventilation Do you mechanically ventilate your patient to reverse diaphragmatic fatigue ? or Do you encourage greater diaphragm use to avoid ventilator-induced diaphragmatic dysfunction?
Patient triggered ventilation Assisted mechanical ventilation Avoid ventilator induced diaphragmatic dysfunction Providing sufficient level of ventilatory support to reduce patients work of breathing
Volume or pressure oriented?
Volume oriented modes Inspiratory flow is preset Inspiratory time determines the Vt The variable parameter is the airway peak and plateau pressure
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 and resistive properties of the lung Paw = Vt/C +VR + PEP
Airway Pressure C = Vt / P and P = P Plat - PEEP Paw= Po + Vt/C + RV
Pressure oriented modes Pressure in airway is the preset parameter Flow is adjusted at every moment to reach the preset pressure The variable parameter is Vt
Equation of motion in pressure support ventilation Pressure = pressure applied by the ventilator on the airway + pressure generated by respiratory muscles Pmus is determined by respiratory drive and respiratory muscle strenght Paw + Pmus = Vt/C + VxR + PEP
Determinant factors of 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 driving pressure gradient)
Look at the curves !
A challenge for the intensivist Discomfort anxiety Increased work of breathing Increased requirement of sedation Increased length of mechanical ventilation Increased incidence of VAP
Patient-ventilator asynchrony Mechanical ventilation: 2 pumps –Ventilator controlled by the physician –Patients own respiratory muscle pump Mismatch between the patient and the ventilator inspiratory and expiratory time time Patient « fighting » with the ventilator
Volume oriented ventilation (fixed flow pattern) Inspiratory flow varies according to the underlying condition If patients flow demand increases, peak flow should be adjusted accordingly Usually, peak flow is too low Dished-out appearance of the presure-wave- form Importance of flow-pattern
-Ineffictive triggering at 30 l/mn - Increase in flow rate - Subsequent increase of expiratory time - Decreased dynamic hyperinflation - Subsequent decrease in ineffictive trigerring
Importance of flow pattern Increase in peak-flow setting fron 60 to 120 l/mn eliminated scooped appearance of the airway pressure waveform
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
Termination asynchrony Ventilator should cycle at the end of the neural inspiration time Delayed termination: –Dynamic hyperinflation –Trigger delay –Ineffective triggering Premature termination
Set inspiratory time < 1 sec
PSV = 10 cmH2O Inspiratoy flow terminate despite continued Pes defelection Double Trigerring Patient 1Patient 2
Expiratory asynchrony Shortened expiratory time: Auto-PEEP trigger asynchrony –Delay in the relaxation of the expiratory muscle activity prior to the next mechanical inspiration –Overlap between expiratory and insiratory uscle activity Prolonged expiratory time
Auto-PEEP created by flow patterns that 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
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 avoid excessive effort and auto-triggering