Performance and applications of bedside visual inspection of airway pressure–time curve profiles for estimating stress index in patients with acute respiratory distress syndrome

Phunsup Wongsurakiat, Nadwipa Yuangtrakul

To determine the performance of bedside visual inspection of airway pressure-time (Paw-t) curve profiles (VI) for estimating stress index (SI) in patients with acute respiratory distress syndrome (ARDS). A prospective study in 30 subjects with ARDS receiving mechanical ventilation at two peak inspiratory flow (PIF) settings: 60 or 40 L/min. For each study session, two physicians inspected real-time Paw-t waveforms from mechanical ventilator's monitoring screens at bedside for 30 s and interpreted which of the three patterns (tidal recruitment, noninjurious ventilation or tidal overdistension) the Paw-t curve profile was compatible with. Subsequently, the study was repeated again at the second PIF setting. SI was derived from a standardized dedicated software program and categorized into three groups: SI < 0.9, or tidal recruitment; SI = 0.9-1.05, or noninjurious ventilation; and SI > 1.05, or tidal overdistension. The lower PIF setting increased the sensitivity of VI to correctly estimate SI (75% vs. 50%; p = 0.005). At PIF 40 L/min, the likelihood ratio of a positive test was 3.6, 5.4 or 7 if the Paw-t curve profile was interpreted as noninjurious ventilation, tidal recruitment or tidal overdistension, respectively. The likelihood ratio of a negative test ranged from 0.55 for tidal recruitment to 0.32 and 0.19 for noninjurious ventilation and tidal overdistension, respectively. Experience in mechanical ventilation did not influence the accuracy. Bedside VI is moderately accurate for estimating SI and may be used to monitor injurious ventilation in patients with ARDS, in addition to plateau airway pressure.