Association between the time-varying arterial carbon dioxide pressure and 28-day mortality in mechanically ventilated patients with acute respiratory distress syndrome

BACKGROUND: Recent studies have shown an association between baseline arterial carbon dioxide pressure (PaCO(2)) and outcomes in patients with acute respiratory distress syndrome (ARDS). However, PaCO(2) probably varies throughout the disease, and few studies have assessed the effect of longitudinal PaCO(2) on prognosis. We thus aimed to investigate the association between time-varying PaCO(2) and 28-day mortality in mechanically ventilated ARDS patients. METHODS: In this retrospective study, we included all adult (≥ 18 years) patients diagnosed with ARDS who received mechanical ventilation for at least 24 h at a tertiary teaching hospital between January 2014 and March 2021. Patients were excluded if they received extracorporeal membrane oxygenation (ECMO). Demographic data, respiratory variables, and daily PaCO(2) were extracted. The primary outcome was 28-day mortality. Time-varying Cox models were used to estimate the association between longitudinal PaCO(2) measurements and 28-day mortality. RESULTS: A total of 709 patients were eligible for inclusion in the final cohort, with an average age of 65 years, of whom 70.7% were male, and the overall 28-day mortality was 35.5%. After adjustment for baseline confounders, including age and severity of disease, a significant increase in the hazard of death was found to be associated with both time-varying PaCO(2) (HR 1.07, 95% CI 1.03–1.11, p<0.001) and the time-varying coefficient of variation for PaCO(2) (HR 1.24 per 10% increase, 95% CI 1.10–1.40, p<0.001) during the first five days of invasive mechanical ventilation. The cumulative proportion of exposure to normal PaCO(2) (HR 0.72 per 10% increase, 95% CI 0.58–0.89, p = 0.002) was associated with 28-day mortality. CONCLUSION: PaCO(2) should be closely monitored in mechanically ventilated ARDS patients. The association between PaCO(2) and 28-day mortality persisted over time. Increased cumulative exposure to normal PaCO(2) was associated with a decreased risk of death. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12890-023-02431-6.