Abstract
BackgroundProportional assist ventilation+ (PAV+) delivers airway pressure (Paw) in proportion to patient effort (Pmus) by using the equation of motion of the respiratory system. PAV+ calculates automatically respiratory mechanics (elastance and resistance); the work of breathing (WOB) is estimated by the ventilator. The accuracy of Pmus estimation and hence accuracy of the delivered Paw and WOB calculation have not been assessed. This study aimed at assessing the accuracy of delivered Paw and calculated WOB by PAV+ and examining the factors influencing this accuracy.MethodsUsing an active lung model with different respiratory mechanics, we compared (1) the actual delivered Paw by the ventilator to the theoretical Paw as defined by the equation of motion and (2) the WOB value displayed by the ventilator to the WOB measured from a Campbell diagram.ResultsIrrespective of respiratory mechanics and gain, the ventilator provided a Paw approximately 25 % lower than expected. This underassistance was greatest at the beginning of the inspiration. Intrinsic PEEP (PEEPi), associated with an increase in trigger delay, was a major factor affecting PAV+ accuracy. The absolute value of total WOB displayed by the ventilator was underestimated, but the changes in WOB were accurately detected by the ventilator.ConclusionThe assistance provided by PAV+ well follows Pmus but with a constant underassistance. This is associated with an underestimation by the ventilator of the WOB. PEEPi can be a major factor contributing to PAV+ inaccuracy. Clinical recommendations should include using a high trigger sensitivity and a careful PEEP titration.Electronic supplementary materialThe online version of this article (doi:10.1186/s13613-016-0131-y) contains supplementary material, which is available to authorized users.
Highlights
Proportional assist ventilation+ (PAV+) delivers airway pressure (Paw) in proportion to patient effort (Pmus) by using the equation of motion of the respiratory system
Accuracy of Paw delivered during PAV+ Effect of different respiratory mechanics and gains Irrespective of respiratory mechanics and gain, imeas was always lower than iTh (Δi and %Δi were −2.9 ± 0.9 cmH2O and −25.4 ± 4.6 %, respectively), indicating a lower assistance provided by the ventilator than expected from the equation of motion (Table 1)
Pmus and positive end-expiratory pressure (PEEP) The underassistance of PAV+ was highlighted under different trigger, Pmus or PEEP settings in normal respiratory mechanics
Summary
Proportional assist ventilation+ (PAV+) delivers airway pressure (Paw) in proportion to patient effort (Pmus) by using the equation of motion of the respiratory system. Proportional assist ventilation (PAV), described by Younes [1], was the first ventilator mode that introduced the concept of ‘patient-driven’ ventilation: a patient’s effort could influence the timing and the magnitude of the ventilator assistance This two-way interaction aimed to bypass numerous disadvantages linked to conventional assisted ventilation: patient–ventilator asynchrony, lack of adaptability to changing ventilator demands and loss of normal breathing variability. In critically ill mechanically ventilated patients, PAV has Through automatic calculation of the respiratory system elastance and resistance and using the respiratory system equation of motion, PAV with load adjustable gain factors (PAV+) is able to partition the ventilator (Paw) and the patient (Pmus) contribution to total pressure of the respiratory system (Ptot) [7,8,9]. This information would be extremely useful to evaluate the efficacy of assistance, to adjust ventilator settings
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