Association between comorbid asthma and prognosis of critically ill patients with severe sepsis: a cohort study

Basic research suggests some contributing mechanisms underlying asthma might at the same time benefit patients with asthma against sepsis, while the potential protective effect of comorbid asthma on prognosis of sepsis has not been well studied in clinical research. The study aimed to assess the association between comorbid asthma and prognosis in a cohort of patients admitted to intensive care unit (ICU) with severe sepsis. Patients with severe sepsis admitted to ICUs were included from the MIMIC-III Critical Care Database, and categorized as patients without asthma, patients with stable asthma, and patients with acute exacerbation asthma. The primary study outcome was 28-day mortality since ICU admission. Difference in survival distributions among groups were evaluated by Kaplan–Meier estimator. Multivariable Cox regression was employed to examine the association between comorbid asthma and prognosis. A total of 2469 patients with severe sepsis were included, of which 2327 (94.25%) were without asthma, 125 (5.06%) with stable asthma, and 17 (0.69%) with acute exacerbation asthma. Compared with patients without asthma, patients with asthma (either stable or not) had a slightly younger age (66.73 ± 16.32 versus 64.77 ± 14.81 years), a lower proportion of male sex (56.81% versus 40.14%), and a lower median SAPS II score (46 versus 43). Patients with acute exacerbation asthma saw the highest 28-day mortality rate (35.29%), but patients with stable asthma had the lowest 28-day mortality rate (21.60%) when compared to that (34.42%) in patients without asthma. Consistent results were observed in Kaplan–Meier curves with a p-value for log-rank test of 0.016. After adjusting for potential confounding, compared to being without asthma, being with stable asthma was associated with a reduced risk of 28-day mortality (hazard ratio (HR) 0.65, 95% confidence interval (CI) 0.44–0.97, p = 0.0335), but being with acute exacerbation asthma was toward an increased risk of 28-day mortality (HR 1.82, 95% 0.80–4.10, p = 0.1513). E-value analysis suggested robustness to unmeasured confounding. These findings suggest comorbid stable asthma is associated with a better prognosis in critically ill patients with severe sepsis, while acute exacerbation asthma is associated with worse prognosis.