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22-11-2011 | Surgery | Article

Normal or low BMI linked to greater risk for death after surgery


Free abstract

MedWire News: Body mass index (BMI) significantly predicts a person's 30-day post-surgery mortality risk, report researchers in the Archives of Surgery.

George Stuckenborg and colleagues, at the University of Virginia in Charlottesville, USA, analyzed an American College of Surgeons database of 189,533 cases of general and vascular surgery for the relationship between mortality and BMI.

"General and vascular surgeons are treating an increasing population of obese patients for non-weight loss procedures. A better understanding of the relationship between perioperative mortality risk and BMI is needed," they write.

Of the patients studied, 3245 died within 30 days of surgery.

The researchers note that the distribution of BMI values in the study population did not correspond to those of the general population. Only 2.6% of the patients were classed as underweight using the standard cutoff of BMI below 18.5 kg/m2, 30.4% were classed as overweight (BMI 25-29 kg/m2), and 38.2% were obese (BMI ≥30 kg/m2).

The population was therefore divided into quintiles according to BMI, with the following thresholds: 23.1, 26.3, 29.7, and 35.3 kg/m2.

Stuckenborg and team found that the percentage of deaths 30 days after surgery in the group with a BMI less than 23.1 kg/m2 was over twice that of those with a BMI over 35.3 kg/m2 (2.8 vs 1.0%). In addition, patients with a BMI below 23.1 kg/m2 were a significant 40% more likely to die within 30 days of surgery than patients whose BMI was between 26.3 and 29.7 kg/m2 (2.8 vs 1.5%).

Patients who were classed as obese, with BMI values above 29.7 kg/m2, had lower odds of death than patients placed in the quintile below (26.3-29.7 kg/m2), but this difference was not significant.

The dataset also allowed the researchers to adjust their findings according to type of surgical procedure. This analysis revealed that the effect of BMI on mortality differed significantly for patients who underwent procedures such as colostomy, wound debridement, ileostomy, and colorectal resection, compared with those who underwent laparoscopy.

Of note, patients who underwent exploratory laparotomy had the highest percentage of deaths, at 13.9%.

"Our data are unique in that the analysis of such a large number of patients allowed us to analyze individual procedures done by general surgeons to a level of specificity not previously available," say Stuckenborg and team. "Interestingly, but in agreement with other studies, the combined group of patients with the highest BMI values do not show an increased mortality compared with the reference group."

They conclude: "BMI is a significant predictor of mortality within 30 days of surgery, even after adjusting for the contribution to mortality risk made by type of surgery."

By Chloe McIvor

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