July 31, 2018
3 min read

Obesity increases infection risks after colorectal surgery

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BMI serves as an independent risk factor for many adverse 30-day postoperative outcomes among patients with obesity who undergo colorectal surgery, according to results from a retrospective study.

“We performed the study because we know obesity is a growing problem in the United States with a third of our population being classified as overweight or obese,” Tyler S. Wahl, MD, MSPH, a general resident surgery physician at University of Alabama at Birmingham Health System, said in a video abstract. “Studies have shown that obesity is associated with morbidity and mortality and oftentimes colorectal patients are associated with having the highest rates of complications.”

The aim of the study, according to Wahl, was to understand how obesity was associated with colorectal outcomes.

“Specifically, our hypothesis was that an increase of BMI or an increase in obesity classification was associated with an increase in surgical site infection rates and outcomes,” he said.

The researchers reviewed the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) Participant User Data File to assess patients who underwent elective colorectal surgery from 2011 to 2013.

Thirty-day postoperative surgical site infection (SSI) served as the primary endpoint.

All ACS-NSQIP–assessed 30-day postoperative complications served as the secondary endpoint.

The researchers stratified 74,891 patients who underwent elective colorectal by using the six standardized WHO BMI classifications.

A patient was considered underweight if they had a BMI less than 18.5 kg/m2, normal weight if their BMI was between 18.5 and 24.9 kg/m2, or overweight if their BMI was between 25 and 29.9 kg/m2.

Under the WHO classifications, obesity is divided into three classifications. Individuals were in obesity class I if they had a BMI between 30 and 34.9 kg/m2, obesity class II if they had a BMI between 35 and 39.9 kg/m2 and obesity class III if their BMI was 40 kg/m2 or greater.

Less than 5% (4.4% of patients) were underweight, while 29% of patients were listed as normal weight and 33% were considered overweight.

Approximately 20% (19.8%) of patients were classified as obesity class I, while 8.4% were listed as class II and 5.5% were considered class III.

The most commonly performed procedures included partial colectomy (39.8%), low anterior resection (23.1%), and ileocecectomy (18.4%).

Underweight patients had the lowest odds of SSI (OR = 0.98; 95% CI, 0.87–1.11). The adjusted odds of developing an SSI significantly increasing as BMI class increased from overweight (OR = 1.28; 95% CI, 1.2-1.36) to obesity class III (OR = 2.06; 95% CI, 1.87-2.28).


“This is a proportional effect where patients were compared from normal weight physiology to more obese classifications,” he said. “What’s interesting is this is the largest colorectal surgery cohort looking at obesity and outcomes and we do see that there is an incremental association with postoperative outcomes.”

Wahl said that the hope is for providers to analyze the results and understand that more work is needed in the field.

“We think there are different mechanisms at play with immune system responses and nutritional deficits,” he said. “We’re hopeful that providers will not be biased against doing surgery on obese colorectal patients but understand the risks and find strategies that will move them toward more normal weight physiology.”

Additionally, Wahl noted that the hope is for future work to focus on prehabilitation in the obese colorectal population.

“Oftentimes, colorectal surgery patients are undergoing surgery for cancer or inflammatory bowel disease and often can’t wait more than 30 days to have an operation,” he said. “Our hope is that future work will focus on obesity as an actionable item for interventions that may improve patients to a more normal weight physiology and hopefully decrease their risk for having poor perioperative outcomes.” – by Ryan McDonald

Disclosures: The researchers report no relevant financial disclosures. The study was funded by a grant from the Agency for Healthcare Research and Quality.