Abstract
BACKGROUND: Assessment of the patient's respiratory effort is essential during assisted ventilation. We aimed to evaluate the accuracy of airway pressure (P(aw))-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 cmH(2)O to 2 cmH(2)O at a 2 cmH(2)O interval. By performing an end-expiratory airway occlusion maneuver, the negative P(aw) generated during the first 100 ms (P(0.1)) and the maximal negative swing of P(aw) (∆P(occ)) were measured. After an end-inspiratory airway occlusion, P(aw) reached a plateau, and the magnitude of change in plateau from peak P(aw) was measured as pressure muscle index (PMI). Esophageal pressure was monitored and inspiratory muscle pressure (P(mus)) and P(mus)-time product per minute (PTP(mus)/min) were used as the reference standard for the patient's effort. High and low effort was defined as P(mus) > 10 and < 5 cmH(2)O, or PTP(mus)/min > 200 and < 50 cmH(2)O s min(-1), 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(mus) and PTP(mus)/min criterion. The receiver operating characteristic area of the three P(aw)-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(mus) and PTP(mus)/min criterion, respectively. High receiver operating characteristic areas of the three P(aw)-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(aw)-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.