Use of airway pressure-based indices to detect high and low inspiratory effort during pressure support ventilation: a diagnostic accuracy study.

Background: Assessment of the patient's respiratory effort is essential during assisted ventilation. We aimed to evaluate the accuracy of airway pressure (P)-based indices to detect potential injurious inspiratory effort during pressure support (PS) ventilation.

Methods: In this prospective diagnostic accuracy study conducted in four ICUs in two academic hospitals, 28 adult acute respiratory failure patients undergoing PS ventilation were enrolled. A downward PS titration was conducted from 20 cmHO to 2 cmHO at a 2 cmHO interval. By performing an end-expiratory airway occlusion maneuver, the negative P generated during the first 100 ms (P) and the maximal negative swing of P (∆P) were measured. After an end-inspiratory airway occlusion, P reached a plateau, and the magnitude of change in plateau from peak P was measured as pressure muscle index (PMI). Esophageal pressure was monitored and inspiratory muscle pressure (P) and P-time product per minute (PTP/min) were used as the reference standard for the patient's effort. High and low effort was defined as P > 10 and < 5 cmHO, or PTP/min > 200 and < 50 cmHO s min, respectively.

Results: A total of 246 levels of PS were tested. The low inspiratory effort was diagnosed in 145 (59.0%) and 136 (55.3%) PS levels using respective P and PTP/min criterion. The receiver operating characteristic area of the three P-based indices by the respective two criteria ranged from 0.87 to 0.95, and balanced sensitivity (0.83-0.96), specificity (0.74-0.88), and positive (0.80-0.91) and negative predictive values (0.78-0.94) were obtained. The high effort was diagnosed in 34 (13.8%) and 17 (6.9%) support levels using P and PTP/min criterion, respectively. High receiver operating characteristic areas of the three P-based indices by the two criteria were found (0.93-0.95). A high sensitivity (0.80-1.00) and negative predictive value (0.97-1.00) were found with a low positive predictive value (0.23-0.64).

Conclusions: By performing simple airway occlusion maneuvers, the P-based indices could be reliably used to detect low inspiratory efforts. Non-invasive and easily accessible characteristics support their potential bedside use for avoiding over-assistance. More evaluation of their performance is required in cohorts with high effort.