The Relationship between Body Mass Index and Mortality is Not Linear in Patients requiring Venovenous Extracorporeal Support.

Publication date: Nov 30, 2023

Morbid obesity may influence candidacy for venovenous extracorporeal membrane oxygenation (VVECMO) support. Indeed, body mass index (BMI) > 40 is a considered to be a relative contraindication due to increased mortality observed in patients with BMI above this value. There is, however, scant evidence to characterize this relationship beyond speculating about the technical challenges of cannulation and difficulty in optimizing flows. We examined a national cohort to evaluate the influence of BMI on mortality in patients requiring VVECMO for severe acute respiratory virus -2 (SARS-CoV-2) infection. We performed a retrospective cohort analysis on National COVID Cohort Collaborative data evaluating 1,033,229 patients with BMI ≤ 60 from 31 US hospital systems diagnosed with SARS-CoV-2 infection from September 2019 to August 2022. We performed univariate and multivariable mixed-effects logistic regression analysis on data pertaining to those who required VVECMO support during their hospitalization. A subgroup risk-adjusted analysis comparing ECMO mortality in patients with BMI 40 to 60 with the 25, 50, and 75 BMI percentile was performed. Outcomes of interest included BMI, age, comorbidity score, body surface area and ventilation days. A total of 774 adult patients required VVECMO. Of these, 542 were male, median age was 47 years, mean adjusted Charlson Comorbidity Index (CCI) was 1, and median BMI was 33. Overall mortality was 47. 8%. There was a non-significant overall difference in mortality across hospitals (standard deviation: 0. 31, 95% CI: 0, 0. 57). After mixed multivariable logistic regression analysis, advanced age (p < 0. 0001) and CCI (p = 0. 009) were each associated with increased mortality. Neither gender (p=0. 14) nor duration on mechanical ventilation (p=0. 39) was associated with increased mortality. An increase in BMI from 25th to 75th percentile was not associated with a difference in mortality (p=0. 28). In our multivariable mixed-effects logistic regression analysis, there exists a nonlinear relationship between BMI and mortality. Between BMI of 25 to 32, patients experienced an increase in mortality. However, between BMI of 32 to 37, the adjusted mortality in these patients subsequently decreased (Figure). Our subgroup analysis comparing BMIs 40 to 60 with the 25, 50, and 75 percentile of BMI (Table 3) found no significant difference in ECMO mortality between BMI values of 40 to 60 with the 25, 50, 75 percentile. Advancing age and higher CCI are each associated with increased risk for mortality in patients requiring VVECMO. A non-linear relationship exists between mortality and BMI and those between 32 and 37 have lower odds of mortality than those between BMI 25 to 32. This nonlinear pattern suggests a need for further adjudication of the contraindications associated with VVECMO, particularly those based solely on BMI.

Concepts Keywords
August ARDS
Hospitalization COVID19
Obesity ECMO
Virus Obesity


Type Source Name
disease MESH Morbid obesity
disease MESH contraindication
disease MESH infection
disease MESH SARS-CoV-2 infection
pathway REACTOME SARS-CoV-2 Infection
disease MESH comorbidity
disease MESH Obesity

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