Nancy A. Melville

January 21, 2015

PHOENIX — The phenomenon in which mortality rates are higher in normal-weight critically ill patients than in those who are overweight or obese — the so-called obesity paradox — can be offset when tube feeding is provided in the intensive care unit, according to the results of a new study.

"Our findings suggest that the mortality disadvantage observed in normal-weight patients is not observed in the subgroup of patients receiving an early enteral nutrition strategy," study investigator Omar Badawi, PharmD, MPH, from Philips Healthcare in Baltimore, told Medscape Medical News here at the Society of Critical Care Medicine 44th Critical Care Congress.

The obesity paradox has been described as "an inverse association between obesity and hospital mortality in critically ill patients" (Crit Care Med. 2013;41:1878-1883).

It is possible that the paradox is related to the presence of excess lipids in obese patients that bind circulating endotoxins and increase the circulation of macrophages, lymphocytes, and anti-inflammatory cytokines, explained Kimberley Harris, PharmD, from the University of Maryland Medical Center in Baltimore.

It is also possible "that obese patients have increased nutritional reserves that counteract the catabolic state of critical illness," she added.

Dr. Harris, along with Dr. Badawi and colleagues, evaluated data on 1,123,779 stays at 292 ICUs in the Philips eICU Research Institute database.

Mean age in the study cohort was 63.3 years, mean APACHE IV score was 54.5, and the mortality rate was 9.1%. Approximately 35% of patients were obese, which is consistent with current obesity rates in the United States.

The relative risk for mortality was higher in underweight patients than in normal-weight patients (BMI, 18.5 - 24.9 kg/m²), but lower in overweight and obese patients.

Table. Relative Risk for Mortality

Weight Classification BMI (kg/m²) Relative Risk 95% Confidence Interval
Underweight <18.5 1.22 1.19–1.25
Overweight 25.0–29.9 0.89 0.88–0.91
Obese class I 30.0–34.9 0.88 0.86–0.89
Obese class II 35.0–39.9 0.88 0.85–0.90
Obese class III 40.0–49.9 0.91 0.88–0.93

 

However, in a subset of 79,098 patients who received early enteral nutrition, initiated within 48 hours of ICU admission, mortality rates were similar in normal-weight patients and those who were overweight and obese.

This reduction in mortality differences is likely because "normal and underweight patients benefited from the enteral nutrition, therefore modifying the relationship between BMI and hospital mortality," Dr. Harris explained.

Table. Risk for Mortality After Early Enteral Nutrition

Weight Classification Relative Risk 95% Confidence Interval
Overweight 0.99 0.95–1.02
Obese class I 0.96 0.92–1.00
Obese class II 0.96 0.91–1.02
Obese class III 1.01 0.95–1.07

 

Dr. Badawi acknowledged that this study doesn't prove a causal relation, but noted that the findings offer insights into the role of nutrition in the ICU.

"We believe these data are provocative and support the notion that the disadvantage observed in patients who are not overweight could be due, in part, to inadequate nutritional reserves," he said.

"More importantly, this disadvantage can potentially be modified by providing early enteral nutrition," he added.

This study does offer useful information on the obesity paradox, said Jill Cherry-Bukowiec, MD, from the University of Michigan at Ann Arbor.

"The findings introduce a new angle on how enteral nutrition affects critically ill obese patients, and demonstrate that the normal-weight group may experience the greatest benefit, negating the negative effect a lower BMI has on mortality in critically ill patients," she told Medscape Medical News.

The fact that this is a multicenter trial "with a very large number of patients accrued from a robust electronic dataset, with contribution from just under 300 ICUs, makes the findings powerful and thought provoking," she said.

"Most previous studies have found the administration of early enteral nutrition beneficial to critically ill patients, secondary to trophic effects on the intestinal mucosa and immunologic benefits extending beyond the gut," Dr. Cherry-Bukowiec said.

"Further studies are needed to determine how enteral nutrition specifically affects septic patient physiology, with greater attention to BMI and gradations of obesity," she concluded.

Dr. Badawi is an employee of Philips Healthcare. Dr. Harris and Dr. Cherry-Bukowiec have disclosed no relevant financial relationships.

Society of Critical Care Medicine (SCCM) 44th Critical Care Congress: Abstract 23. Presented January 18, 2015.

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