Clinical factors associated with success of proportional assist ventilation in the acute phase of critical illness: pilot study.

REASON Proportional assist ventilation plus (PAV+) applies pressure depending on the patient's inspiratory effort, automatically adjusting flow and volume assist to changes in respiratory mechanics. We aimed to assess the clinical factors associated with the success of PAV+ as first-line support in the acute phase of critical illness. METHODS A prospective cohort study was carried out. Mechanically ventilated patients>24h were switched from assist-control ventilation to PAV+ as soon as they regained spontaneous breathing activity. PAV+ was set to deliver the highest assistance. We compared patients in whom PAV+ succeeded versus those in whom it failed. RESULTS PAV+ succeeded in 12 (63%) patients, but failed in 7 (37%) due to tachypnea (n=4), hypercapnia (n=2), and metabolic acidosis (n=1), but without statistical significance. Both groups had similar clinical parameters. On the day of inclusion, total work of breathing per breath was lower in the successful PAV+ group (WOBTOT: 0.95 [0.8-1.35] vs. 1.6 [1.4-1.8] J/L; P<.007). The area under the ROC curve was 0.89 ± 0.08 for WOBTOT. The best cut-off for predicting PAV+ success was WOBTOT<1.4 J/L (sensitivity: 1 [0.7-1], specificity: 0.6 [0.4-0.6], PPV: 0.7 [0.5-0.7], and NPV: 1 [0.6-1]). CONCLUSION PAV+ proved feasible as first-line ventilatory support in 63% of the patients, mostly in individuals without extreme derangements in WOBTOT. Tachypnea and hypercapnia were the clinical factors associated with failure, though statistical significance was not reached.