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.