Expiratory Efforts During Insufflation are Associated with Increased Mortality in Ventilated Patients

Abstract

Abstract Background Breathing efforts during mechanical ventilation are associated with patient self-induced lung injury (P-SILI). We examined whether a noninvasive measure of Pmus, the portion of airway pressure attributed to breathing effort during insufflation, relates to patient mortality. Methods We analyzed recorded airway signals from 267 patients on invasive mechanical ventilation monitored between six hours and five days. Patients were divided into survivor and decedent groups according to all-cause 28-day mortality. Individual Pmus(t) functions, describing changes in Pmus during insufflation, were generated for 13.4 million insufflations by numerical analysis of the respiratory system’s one-compartment model. Pmus(t) was used to determine the magnitude and direction, expiratory or inspiratory, of peak Pmus(t) (PmusPeak) and its pressure-time product (PmusPTP). Mean and cumulative PmusPeak and PmusPTP were determined for each patient and compared between the groups. Results There were 67 decedents and 200 survivors. Decedents had greater mean and cumulative expiratory PmusPTP (p < 0.05 for each) than survivors. Neither inspiratory PmusPTP nor PmusPeak differentiated between the groups. Independent predictors of mortality were age, SAPS II score, and expiratory time. Discussion We report an association between expiratory efforts during insufflation and 28-day mortality. By opposing ventilator-delivered breaths, expiratory efforts might increase alveolar pressure (Palv), promoting P-SILI and subsequent worse outcomes. The apparent lack of association between mortality and inspiratory effort might be explained by its capacity to increase trans-pulmonary pressure without affecting Palv. Inspiratory efforts, however, could indicate air hunger. Conclusions Our findings highlight the need for further research into respiratory efforts during mechanical ventilation.