Surgical patients with a body mass index at the lower end of the normal range were more likely to die within 30 days of the procedure than those in the moderately overweight range, researchers found. Compared with patients with a BMI of 26.3 to 29.6, those with a value below 23.1 had a significantly higher risk of death (adjusted OR 1.40, 95% CI 1.25 to 1.58), according to an analysis of 189,533 surgeries performed in 2005 and 2006 and recorded in the National Surgical Quality Improvement Program (NSQIP) database.
Patients with higher BMI values above 23.1 -- including the morbidly obese -- had about the same risk of 30-day mortality as the moderately overweight, George J. Stukenborg, PhD, of the University of Virginia in Charlottesville, and colleagues, reported online in Archives of Surgery. But for some individual types of surgeries, obesity was associated with increased mortality, the researchers found.
"These individual types of procedures include procedures with which the general surgeon should have definite experience: colorectal resection, colostomy formation, cholecystectomy, hernia repair, mastectomy, and wound debridement," Stukenborg and colleagues wrote.
NSQIP data in the study were extracted from medical records at 183 participating hospitals. Those with low volumes reported all cases performed each year whereas high-volume hospitals reported the first 40 consecutive cases for 42 eight-day cycles each year.
Patients in the study were categorized into BMI quintiles, with values of less than 23.1 being the lowest and those above 35.2 being the highest. For the overall 30-day mortality risk calculation, the middle quintile -- 26.3 to 29.6 -- served as the reference. BMI values of 20 to 25 are considered normal. A value of 30 is the standard threshold separating overweight from frank obesity.