Does obesity matter in patients receiving venoarterial extracorporeal membrane oxygenation? The U-shaped relationship between body mass index and mortality after extracorporeal cardiopulmonary resuscitation

Abstract

Background

The impact of obesity on the prognosis of patients receiving venoarterial extracorporeal membrane oxygenation remains unclear. This study examines the association between body mass index and in-hospital mortality among patients on venoarterial extracorporeal membrane oxygenation support.

Methods

This retrospective study enrolled adult patients who received venoarterial extracorporeal membrane oxygenation support, which included extracorporeal cardiopulmonary resuscitation, at National Taiwan University Hospital between 2010 and 2021. Patients were classified as follows: underweight (body mass index <18.5), normal weight (18.5≤ body mass index <24), overweight (24≤ body mass index <27), class I obesity (27≤ body mass index <30), class II obesity (30≤ body mass index <35), and class III obesity (body mass index ≥35). Multivariable Cox regression with spline models was employed.

Results

The study included 1,329 patients; of these, 670 underwent extracorporeal cardiopulmonary resuscitation, and the overall mortality rate was 61.6%. Multivariable Cox regression revealed that class III obesity was significantly associated with higher mortality (hazard ratio 2.11, 95% confidence interval 1.48–3.02, P = .001), particularly in the extracorporeal cardiopulmonary resuscitation subgroup (hazard ratio 2.71, 95% confidence interval 1.71–4.29, P < .001). No significant association was observed in the non–extracorporeal cardiopulmonary resuscitation subgroup (hazard ratio 1.29, 95% confidence interval 0.70–2.36, P = .415). Although underweight patients initially exhibited higher mortality (hazard ratio 1.77, 95% confidence interval 1.12–2.80, P = .015), this effect was attenuated after adjusting the confounders (hazard ratio 1.46, 95% confidence interval 0.91–2.35, P = .119). Kaplan-Meier analysis indicated that class III obesity was associated with the highest in-hospital mortality, followed by the underweight group (log-rank P = .009).

Conclusion

Obesity increased mortality in patients who underwent venoarterial extracorporeal membrane oxygenation, but this was primarily due to a nonlinear U-shaped distribution between body mass index and in-hospital mortality observed in patients receiving extracorporeal cardiopulmonary resuscitation. Further studies are needed to clarify the causal factors underlying these associations.