“Obesity Paradox” in Acute Respiratory Distress Syndrome: Asystematic Review and Meta-Analysis

Background: It is unclear whether an “obesity paradox” exists in the respiratory system, especially in acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Previous studies have postulated a causal relation between obesity and ARDS/ALI but have lacked power to form a definitive conclusion. Objective: To investigate the relationships between obesity, ARDS/ALIrisk, and mortality. Methods: A systematic search current to April 2016 was performed in Pubmed, EMBASE, Medline, Cochrane databases to find relevant studies. All studies that estimate the effect of obesity in the morbidity and mortality of ARDS/ALI were included. Results: A total of 24 studies including 9,187,248 subjects were analyzed. The combined results from 16 studies that examined the effect of obesity in morbidity of ARDS/ALI showed an89% increase in odds ratio(pooled odds ratios (OR) 1.89, 95% confidence intervals (CI) 1.45 to 2.47). In subgroup analysis, compared to normal weight, obesity was associated with an increased risk of ARDS/ALI (OR1.57, 95% CI 1.30–1.90 for obese (BMI30-39.9kg/m2); OR1.75, 95% CI 1.42–2.15 for obese(BMI≥30kg/m2); OR1.67, 95% CI 1.04–2.68 for morbid obese(BMI≥40kg/m2)). The combined results from 9 studies that examined the effect of obesity in mortality of ARDS/ALI had a pooled odds ratio(pooled OR 0.63, 95% CI 0.41 to 0.98). Inversely, obesity was significantly associated with reduced risk of ARDS/ALI mortality(OR0.88, 95% CI 0.78–1.00 for overweight(BMI≤18.5m2); OR0.74, 95% CI 0.64–0.84 for obese (BMI30-39.9kg/m2);OR0.84, 95% CI 0.75–0.94 for 60days mortality; OR0.38, 95% CI 0.22–0.66 for 90days mortality). Conclusions: Our data identify obesity as an important risk factor for the development of ARDS/ALI; however, ARDS/ALI outcomes are improved in this population when compared to individuals with a normal body mass index. This meta-analysis results supported ‘‘obesity paradox” in ARDS/ALI.