Ventilator Driving Pressure and Mortality after Cardiac Surgery

Abstract

Background: ARDS affects nearly 10% of mechanically ventilated postoperative cardiac surgery patients. Driving pressure (∆P) is defined as the difference in static airway pressure at end inspiration (Pplat) and end expiration (intrinsic PEEP) during controlled mechanical ventilation with a passive patient expressed in cm H₂O. Is driving pressure significantly associated with mortality after cardiac surgery? We hypothesized that driving pressure is not significantly associated with mortality after cardiac surgery.

Methods: This was an IRB-approved, single center, retrospective analysis. Data from 960 subjects was extracted from electronic medical records and analyzed from January 1, 2017-October 1, 2019. Data collected included initial driving pressure upon admission to the ICU from the OR and all-cause mortality to hospital discharge. Inclusion criteria for our study included patients over 18 years of age who had cardiac surgery during the data collection period and were not actively breathing upon admission to the ICU. Chi square of independence was applied to compare group mortality association. Data are reported as mean (SD). Alpha was set at 0.05. Data was analyzed with SPSS v25 (IBM, Armonk, NY).

Results: Our sample included 960 subjects, of which 9% (n=94) died. Mortality was 29% (n=27) for subjects who had a ∆P > 13 cm H₂O whereas only 13% (n=116) of the surviving 900 subjects had a ∆P of > 13 cm H₂O (P < .001). The mean (SD) ∆P for subjects who died was 11 (3.8) cm H₂O whereas ∆P for those who survived was 9 (2.9) cm H₂O.

Conclusions: ∆P > 13 cm H₂O is significantly associated with increased all-cause mortality among adult mechanically ventilated postoperative cardiac surgery patients. All-cause mortality may overestimate the number of deaths related to increased driving pressure. Future studies should include respiratory-related mortalities.