Real-World Data Back ECMO Use in Critically Ill Patients With Obesity

Patients with obesity receiving extracorporeal membrane oxygenation (ECMO) for acute respiratory distress syndrome (ARDS) had lower mortality in the intensive care unit (ICU) compared with patients without obesity, according to the retrospective ECMObesity study.

Among nearly 800 patients receiving ECMO for ARDS, 24.1% of patients with obesity died compared with 35.3% of patients without obesity (P<0.001), reported Darya Rudym, MD, of New York University Langone Health in New York City, and co-authors.

In adjusted models, obesity was associated with a lower ICU mortality (OR 0.63, 95% CI 0.43-0.93, P=0.018), and higher body mass index (BMI) was associated with decreased ICU mortality in multivariable regression (OR 0.97, 95% CI 0.95-1.00, P=0.023), the authors noted in the American Journal of Respiratory and Critical Care Medicine.

In addition, when matching 199 patients with obesity to 199 patients without, patients with obesity had a lower probability of ICU death than those without (22.6% vs 35.2%, P=0.007).

Rudym and team explained that obesity has often been treated as a contraindication to the use of ECMO, and patients with obesity are often excluded from ECMO trials for ARDS, "further highlighting lack of familiarity with ECMO in this patient population and widening the data gap in supporting evidence-based care for such patients."

However, obesity has been proposed to act as a protective factor in some illnesses, sometimes described as the "obesity paradox."

"In particular, increased chest wall elastance in patients with obesity has been proposed to offer a protective benefit of partially absorbing transpulmonary pressure thereby decreasing ventilator-induced lung injury," they wrote. "In addition, higher plateau airway pressures generated by similar ventilator settings in patients with obesity may prompt lowering of ventilator volumes and pressures by clinicians, even though such pressures may reflect the combination of increased transpulmonary pressure and the increased chest wall elastance."

In an accompanying commentary, Peter Pickkers, MD, of Radboud University Medical Center in Nijmegen, the Netherlands, noted that despite the "obesity paradox," further research is needed to strengthen the current study's findings.

"It appears plausible that less sick obese patients may be in need for ECMO because of the unfavorable effects of obesity on pulmonary mechanics," he wrote. "An observed better survival may be the consequence of this collider bias. Also, it appears plausible that obese patients were more likely denied to receive ECMO and only those with a higher chance of surviving (young, less organ failure) may have received it, leading to selection bias."

Despite reservations, Pickkers stressed that obesity shouldn't stand in the way of necessary care. "The important lesson from the study is that overall the outcome following ECMO is definitely not worse in obese patients. Consequently, obesity should not be used in the decision making of whether or not a patient should receive ECMO," he said.

Rudym agreed that further research is warranted, but these findings may help guide treatment in patients with obesity and ARDS.

"We hope that, in practice, bedside clinicians will lean on the findings from this study to support their decisions when managing their patients with obesity who have severe ARDS and not preemptively withhold ECMO from those who may very well benefit from it," she told MedPage Today. "We believe our study provides some guidance for those who lack familiarity with ECMO in this patient population and, more importantly, advocate for inclusion of patients with obesity in future clinical trials, so that we can continue to improve care for these patients."

For this international study, Rudym and colleagues used data from over 20 medical centers from July 2012 through June 2017.

A total of 790 ARDS patients were included, of whom 320 had obesity, defined as a BMI ≥30. Average patient age was 44.2, and 58.8% were women.

The etiology of respiratory failure was available for 534 patients, with bacterial, viral, and aspiration pneumonias comprising 33.3%, 26.4%, and 14.6% of the cases, respectively, with no significant differences between the groups.

Limitations to the study included the possibility of selection bias, since ECMO was offered only to those who were deemed likely to benefit. In addition, data were lacking on the patients -- both with and without obesity -- who were ultimately deemed not fit to receive ECMO, and the researchers were unable to assess differences in sedation and mobilization practices across the participating centers.

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