Cigarette smoking as a risk factor for acute respiratory distress syndrome: a systematic review and meta-analysis

Background and objectives: Numerous experimental studies have linked cigarette smoking to lung injury. However, it is still debated on whether cigarette smoking is a risk factor for the development of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). The study aimed to solve the controversy by performing systematic review and meta-analysis. Methods: Electronic databases including Pubmed, Google scholar, Embase and Scopus were searched from inception to April 2014. Studies investigated the association of cigarette smoking and ALI/ARDS were included. Non-randomized studies were assessment for their methodological quality by using Newcastle-Ottawa scale. Meta-analysis was performed by using random effects model and subgroup analyses were performed to address the clinical heterogeneity. Publication bias was assessed by using Egger’s test. Main result: Of the 17 studies included in our analysis, 15 provided data on effect size and were meta-analyzable. Component studies involved heterogeneous populations including major surgery, trauma, septic shock, general population, influenza A infection and transfusion. The combined results showed that cigarette smoking was not a risk factor for the development of ALI/ARDS (OR: 1.00, 95% CI: 0.99-1.01). In subgroup analysis, the same result was obtained in general population (OR: 2.03, 95% CI: 0.06-4.01), patients with major surgery or trauma (OR: 1.20, 95% CI: 0.48-1.93) and patients with other risks of ALI/ARDS (OR: 1.00, 95% CI: 0.99-1.01). Conclusion: Our study demonstrates that cigarette smoking is not associated with increased risk of ALI/ARDS in critically ill patients. However, the relationship in general population is still controversial and requires further confirmation.