Is postoperative ARDS different from medical ARDS?

BACKGROUND: Postoperative patients have been underrepresented in randomized controlled trials of acute respiratory distress syndrome (ARDS). Whether postoperative ARDS differs from medical ARDS in its clinical trajectory, outcomes, and prognostic determinants remains unclear. We aimed to compare postoperative and medical ARDS with respect to early trajectory, mortality, and risk factors for mortality.

METHODS: We conducted a retrospective analysis of prospectively collected data in a tertiary ICU from 2003 to 2023. All consecutive intubated adults fulfilling the ARDS New Global Definition were included. ARDS cases were labeled as postoperative when onset occurred within 15 days after surgery. The primary outcome was 90-day mortality, assessed with multivariable Cox analysis. Early ARDS trajectories were assessed at day 3. Multivariable Cox analyses were used to identify factors independently associated with mortality.

RESULTS: Among 1,077 intubated ARDS patients, 455(42%) had postoperative ARDS. Compared with medical ARDS, postoperative ARDS showed more favorable early trajectories (p = 0.03) and lower 90-day mortality (36% vs. 49%, p < 0.001). Postoperative ARDS remained independently associated with lower 90-day mortality after adjustment (adjusted hazard ratio[aHR] = 0.68, 95%CI:0.56-0.83, p < 0.001). Prognostic determinants differed markedly. In postoperative ARDS, mortality was independently associated with extrapulmonary organ dysfunction (non-respiratory SOFA score: aHR = 1.10, 95%CI:1.05-1.15; bicarbonate: aHR = 0.81 per 5mmol/L, 95%CI:0.69-0.96) and surgical context, (esophageal surgery: aHR = 0.41, 95%CI:0.24-0.70; upper abdominal surgery: aHR = 0.64, 95%CI:0.46-0.91 versus lower abdominal surgery), while no marker of respiratory failure was independently associated with mortality. In medical ARDS, mortality was independently associated with respiratory failure, including PaO2/FiO2 ratio (aHR = 0.88 per 50mmHg, 95%CI:0.81-0.96) and driving pressure (aHR = 1.13 per 5cmH2O, 95%CI = 1.01-1.27), and extrapulmonary organ dysfunction.

CONCLUSION: Postoperative ARDS differs from medical ARDS in its early clinical trajectory, outcomes, and prognostic determinants. These findings support postoperative ARDS as a distinct clinical subtype, mainly driven by extrapulmonary and surgery-related factors rather than by the lung injury itself, supporting a management approach focused on perioperative prevention and early identification of surgery-related complications.