Obese ICU patients have lower mortality but longer ICU stays

Obese intensive care patients do not have a higher ICU death rate than non-obese ICU patients, but they remain in the ICU significantly longer and are intubated significantly longer than non-obese patients, a new study has found.

The data emerged from a meta-analysis of 14 studies of obese and non-obese ICU patients carried out by University at Buffalo researchers.

The analysis included studies that were conducted in the U.S., Europe, Australia and the Middle East between 2000 and 2007.

"This meta-analysis suggests that although mild and moderate obesity may be protective during critical illness, morbid obesity did not have an adverse effect on outcome in the ICU," said Morohunfolu E. Akinnusi, M.D., first author on the study.

"However, obese patients do have increased morbidity as measured by duration of mechanical ventilation and length of stay. As the waistline of the U.S. population continues to expand, longer lengths of stay might have significant implications for health care costs," he said.

Results of the study appeared in the January 2008 issue of Critical Care Medicine. Akinnusi is a pulmonary and critical care fellow and a clinical assistant instructor of internal medicine in the UB School of Medicine and Biomedical Sciences.

The analysis included descriptive and outcome data for 62,045 patients, 15,347 of whom were considered obese, with a body mass index (BMI) equal to or greater than 30. BMI is a measure of body fat based on height and weight. A BMI of 18.5-24.9 is considered normal, 25-29.9 overweight, and 30 or greater is considered obese.

While not all studies included all of the study endpoints, all 14 contained data on survival. Those results showed no difference in survival rates between obese and non-obese patients while they were in the ICU, but the obese had a slightly higher survival rate at hospital discharge.

Six studies included data on duration of mechanical ventilation. The number of days obese patients were on a ventilator ranged from 5.2-16 days, while the range for non-obese patients was 4.6-9.4 days, which resulted in a mean difference of 1.48 days.

Thirteen studies were included in the ICU length-of-stay analysis. Days in the ICU ranged from 2.1-19.4 in the obese and 2.6-12 days in the non-obese, for a mean difference of 1.08 days.

Akinnusi ventured two possible explanations for the better survival rates among the obese ICU patients. "Access to abundant body fat when tissue is breaking down during illness may help to prevent the long-term complications associated with critical illness, such as muscle fiber atrophy," he said.

"There is no clinical data to support this," Akinnusi continued, "but there is increasing evidence that hormones secreted by fat cells, such as leptin and interleukin-10, might curb the inflammatory response and improve patient survival in response to severe illness. This is well demonstrated in animal studies."

He noted also that because of earlier reports that obese patients had worse survival rates than non-obese patients, care givers may be paying closer attention to these patients. In addition, better management of glucose levels and blood-stream infections may contribute to a significant decline in ICU complications in obese versus non-obese patients, he said.

"While indiscriminate excessive weight gain is by no means encouraged," Akinnusi commented, "the findings of the study should help facilitate reversal of nihilism toward critically ill obese patients. Potentially beneficial biological characteristics that may be peculiar to the obesity genotype should be explored for future clinical applications.

"This analysis shows that outcomes of critically ill, morbidly obese patients are not as bleak as originally thought," noted Ali A. El Solh, M.D., M.P.H., senior author on the study. "Further studies are needed to improve morbidity in this population."

El Solh is an associate professor of medicine in the UB medical school and also is affiliated with the Department of Social and Preventive Medicine, UB School of Public Health and Health Professions. Lilibeth A. Pineda, M.D., UB assistant professor of medicine, also contributed to the study.

The University at Buffalo is a premier research-intensive public university, a flagship institution in the State University of New York system and its largest and most comprehensive campus. UB's more than 28,000 students pursue their academic interests through more than 300 undergraduate, graduate and professional degree programs. The School of Medicine and Biomedical Sciences, School of Dental Medicine, School of Nursing, School of Pharmacy and Pharmaceutical Sciences and School of Public Health and Health Professions are the five schools that constitute UB's Academic Health Center. Founded in 1846, the University at Buffalo is a member of the Association of American Universities.