Objective: Cigarette smoking is not only has detrimental effects on the respiratory system but also contributes to development of atherosclerosis and inflammatory vascular reactions. We hypothesized whether smoking is associated with increased risk of acute respiratory distress syndrome (ARDS), systemic inflammatory response syndrome (SIRS), sepsis, distant organ dysfunctions, and the increase of total cost of surgical intensive care unit (SICU) in critically ill surgical patients.
Material and Method: We performed analysis using the THAI-SICU data, a prospective, observational, multicenter study in patients who admitted to SICU in nine university-based hospitals in Thailand. The patients were categorized into 3 groups based on their smoking histories, which were 1) never smoked, 2) former smoker, and 3) current smoker. The primary outcome was probability of ARDS and the secondary outcomes included incidences of SIRS, sepsis, distant organ dysfunction (included acute kidney injury (AKI) and acute myocardial infarction (AMI)), total SICU cost, and 28-day mortality.
Results: A total of 4,652 patients had complete data of smoking and were analyzed. The smoking status was never smoked (2,947 patients), former smokers (1,148 patients), and current smokers (557 patients). Compared to current smokers and former smokers, patients who had never smoked had significantly lower proportion of patients with chronic obstructive pulmonary disease (p<0.01) and had significantly higher PaO2/FiO2 ratio on SICU admission (p = 0.02). Compared to patients who had never smoked and former smokers, current smokers had significantly higher probability of ARDS (p = 0.003), higher incidence of SIRS (p = 0.006), and AKI (p<0.001), after adjustment for age, gender, APACHE II score, and patients’ pre-existing diseases. We found that every 1-pack year of cigarette smoking increased risk of ARDS with a hazard ratio of 1.02 (95% CI 1.01-1.03, p = 0.001). There was no difference in incidence of sepsis, AMI, and 28-day mortality among
three groups of patients. Current smokers had significantly higher SICU cost, followed by former smokers, and patients who had never smoked (p = 0.02).
Conclusion: In critically ill surgical patients, we found dose-response association between smoking pack year and risk of ARDS. Compared to patients who had never smoked and former smokers, current smokers had significantly higher probability of ARDS, higher incidence of SIRS, AKI, and higher total SICU cost. Our findings demonstrated harm of cigarette smoking in critically ill surgical patients who admitted to SICU.

Keywords: Smoking, Acute respiratory distress syndrome, Intensive care unit outcome, Surgical intensive care unit