Imprecision in lower 'inflection point' estimation from static pressure- volume curves in patients at risk for acute respiratory distress syndrome

Background: Static pressure-volume (PV) curves have been promoted as a tool for selecting positive end-expiratory pressure (PEEP) by identifying a lower 'inflection point' (P(flex)) from these curves. Their visual interpretation is subjective and difficult, however, particularly with subtle changes in the slope of the curves. This study was designed to examine the physician-to-physician variability in estimating the lower P(flex) from these curves. Methods: Static PV curves for eight patients were obtained within 24 hours of admission. Five intensivists and one respiratory therapist independently estimated the lower P(flex) from these curves. Results: P(flex) estimates for individual patients were highly variable, ranging from 5 to 9 cm H₂O. This variability was not attributable to a single discordant estimate, nor was a single physician responsible for consistently high or low estimates. Conclusion: Static PV curve interpretation with current methods imprecisely estimates the lower inflection point and is of limited usefulness in PEEP selection.