Proportional Assist Ventilation (PAV)


Need for Spontaneous Mode of Mechanical Ventilation

  • Once Criteria are Met

Comparison Between Pressure Support Ventilation (PSV) and Proportional Assist Ventilation (PAV)

  • Definitions
    • Pressure Support (PSV) (see Pressure Support Ventilation, [[Pressure Support Ventilation]]): once triggered by patient effort, PS provides a pre-set fixed pressure until a cycling-off criterion is reached
      • As a result, the patient, by altering the pressure generated by respiratory muscles, may change the inspiratory flow and thus have partial control over the mechanical breath
      • This ability, however, is seriously compromised in the presence of abnormal respiratory system mechanics
      • Variability in tidal volume is generally low (assuming constant respiratory mechanics)
    • Proportional Assist Ventilation (PAV): ventilator pressure is proportional to instantaneous flow and volume and hence to pressure generated by the respiratory muscles
  • PAV Improves Patient-Ventilator Synchrony, as Compared to PSV [MEDLINE] (see Pressure Support Ventilation, [[Pressure Support Ventilation]])
    • PAV May Decrease Sleep Disruption, as Compared to PSV [MEDLINE]
  • PAV is Superior in Terms of Respiratory Muscle Unloading, as Compared to PSV (see Pressure Support Ventilation, [[Pressure Support Ventilation]])
    • PAV Increases the Probability of Remaining on Assisted/Unassisted Spontaneous Breathing Mode, as Compared to PSV [MEDLINE]
  • PAV Produces Higher Tidal Volume Variability, as Compared to PSV (see Pressure Support Ventilation, [[Pressure Support Ventilation]])
    • Decreased Tidal Volume Variability Has Been Associated with Impaired Lung Function and Higher Degree of Lung Damage in Experimental Acute Lung Injury Models [MEDLINE] [MEDLINE]
  • PAV Redistributes Ventilation from the Central to the Dorsal Lung Regions, as Compared to PSV (see Pressure Support Ventilation, [[Pressure Support Ventilation]])


  • Flow/Volume/Airway Pressure are Not Pre-Set
  • Requires Regular Assessment of Respiratory System Mechanics: represents an obstacle to widespread adoption
    • PAV+: modified mode of PAV where software automatically adjusts the flow assist and volume assist so that they always represent constant fractions of the measured values of resistance and elastance of the respiratory system


  • Respiratory function during pressure support ventilation. Chest 1986: 89:677–683 [MEDLINE]
  • Patient–ventilator interaction during acute hypercapnia: pressure-support vs. proportional-assist ventilation. J Appl Physiol 1996: 81:426–436 [MEDLINE]
  • Effects of chemical feedback on respiratory motor and ventilatory output during different modes of assisted mechanical ventilation. Eur Respir J 1999: 13:873–882 [MEDLINE]
  • Response of ventilator-dependent patients to different levels of pressure support and proportional assist. Am J Respir Crit Care Med 1999: 159:1716–1725 [MEDLINE]
  • Compensation for increase in respiratory workload during mechanical ventilation. Pressure-support versus proportional-assist ventilation. Am J Respir Crit Care Med 2000: 161:819–826 [MEDLINE]
  • Patient–ventilator interaction and sleep in mechanically ventilated patients: pressure support versus proportional assist ventilation. Crit Care Med 2007: 35:1048–1054 [MEDLINE]
  • Proportional assist ventilation with load-adjustable gain factors in critically ill patients: Comparison with pressure support.  Intensive Care Med  2008; 34:2026-2034 [MEDLINE]
  • Variable tidal volumes improve lung protective ventilation strategies in experimental lung injury.  Am J Respir Crit Care Med  2009; 179:684-693 [MEDLINE]
  • Distribution of regional lung aeration and perfusion during conventional and noisy pressure support ventilation in experimental lung injury.  J Appl Physiol  2011; 110:1083-1092 [MEDLINE]