The Association Between Body Mass Index and Mortality Mediated by Medical and Mechanical Complications in Venovenous Extracorporeal Membrane Oxygenation.

Abstract

Objectives: To estimate the associations between body mass index (BMI) and mortality and between BMI and complications in patients receiving venovenous extracorporeal membrane oxygenation (ECMO) and to estimate if any mortality association was mediated by complications.

Design: Retrospective analysis of an international, multicenter registry.

Setting: ICUs.

Patients: Adults in the Extracorporeal Life Support Organization database who received venovenous ECMO between January 1, 2015, and December 31, 2021.

Interventions: None.

Measurements and main results: Logistic regression with BMI transformed using fractional polynomials was used to estimate the association between BMI and hospital mortality and between BMI and complications. Mediation analysis was used to estimate if the association between BMI and mortality was a direct effect or was mediated by complications. Of the 24,796 patient runs, 10,361 patients died (48%). After adjusting for confounders, we found nonlinear associations between BMI and mortality. Compared with BMI = 25 kg/m2, a BMI = 20 had an 11% higher risk of dying, odds ratio (OR) =1.11 (95% CI, 1.08-1.15); a BMI = 30 had an 8% lower risk, OR = 0.92 (95% CI, 0.90-0.95); and a BMI = 40 kg/m2 had an 18% lower risk of death OR = 0.82 (95% CI, 0.78-0.87). BMI was also associated with mechanical, renal, pulmonary, and neurologic complications. The association between BMI and mortality was both a direct effect and mediated via pulmonary complications, while mechanical, renal replacement therapy, and neurologic complications were suppressors having a negative association with improved mortality in patients with higher BMI.

Conclusions: We confirmed that patients with higher BMI requiring venovenous ECMO were less likely to die. This finding was partially mediated by pulmonary complications and partially via a direct association between BMI and mortality. BMI was also associated with mechanical, renal replacement therapy, and neurologic complications that acted as suppressing mediators and were associated with increased mortality for increasing BMI despite the overall trend of improved survival.