Impact of BMI on outcomes in respiratory ECMO: an ELSO registry study

Purpose The impact of body mass index (BMI) on outcomes in respiratory failure necessitating extracorporeal membrane oxygenation (ECMO) has been poorly described. We aimed to assess: (i) whether adults with class II obesity or more (BMI ≥ 35 kg/m 2 ) have worse outcomes than lean counterparts, (ii) the form of the relationship between BMI and outcomes, (iii) whether a cutoff marking futility can be identified. Methods A retrospective analysis of the Extracorporeal Life Support Organization (ELSO) Registry from 1/1/2010 to 31/12/2020 was conducted. Impact of BMI ≥ 35 kg/m 2 was assessed with propensity-score (PS) matching, inverse propensity-score weighted (IPSW) and multivariable models (MV), adjusting for a priori identified confounders. Primary outcome was in-hospital mortality. The form of the relationship between BMI and outcomes was studied with generalized additive models. Outcomes across World Health Organisation (WHO)-defined BMI categories were compared. Results Among 18,529 patients, BMI ≥ 35 kg/m 2 was consistently associated with reduced in-hospital mortality [PS-matched: OR: 0.878(95%CI 0.798–0.966), p = 0.008; IPSW: OR: 0.899(95%CI 0.827–0.979), p = 0.014; MV: OR: 0.900(95%CI 0.834–0.971), p = 0.007] and shorter hospital length of stays. In patients with BMI ≥ 35 kg/m 2 , cardiovascular (17.3% versus 15.3%), renal (37% versus 30%) and device-related complications (25.7% versus 20.6%) increased, whereas pulmonary complications decreased (7.6% versus 9.3%). These findings were independent of confounders throughout PS-matched, IPSW and MV models. The relationship between BMI and outcomes was non-linear and no cutoff for futility was identified. Conclusion Patients with obesity class II or more treated with ECMO for respiratory failure have lower mortality risk and shorter stays, despite increased cardiovascular, device-related, and renal complications. No upper limit of BMI indicating futility of ECMO treatment could be identified. BMI as single parameter should not be a contra-indication for respiratory ECMO.