Obesity may not protect post-surgery

U. ROCHESTER (US) — Obese patients with diabetes and hypertension have a three to seven-fold increased risk of kidney problems following non-cardiac surgery compared to patients of normal weight.

The new research, which also finds those patients are at greater risk for cardiac, pulmonary, and neurologic complications, goes against the grain of previous studies that associate obesity with a lower risk of death and complications after surgery and helps clarify the so-called obesity paradox, or notion that a high body mass index (BMI) confers a protective effect in certain circumstances.

“I think the general population has the sense that individuals with obesity are all alike and struggle with the exact same health problems, but that is not the case,” says Laurent Glance, professor of anesthesiology and community and preventive medicine at the University of Rochester.

“The obesity paradox may be explained in part by the large number of metabolically healthy but obese patients included in previous studies.”

“The results of our study suggest that whether or not a patient is obese shouldn’t be our main concern. It is really the presence of obesity plus other metabolic risk factors that should raise a red flag,” says Rabih Salloum, associate professor of surgery.

The study, published in the journal Anesthesiology, presents a simple, clinically useful way of identifying patients who may be at high risk. Obesity, high blood pressure, and diabetes are all straightforward, easily recognizable conditions, allowing physicians to quickly distinguish patients who may require special attention.

“For surgeons and anesthesiologists, knowing that there are higher risks for obese patients with metabolic disease will allow us to better counsel these patients ahead of time and make them aware of the complications they may face,” says Richard Wissler, associate professor of anesthesiology and obstetrics and gynecology.

“If you identify a patient with a high likelihood of complications you may use more extensive monitoring, get additional specialists involved and be more aggressive about intervening should any problems arise,” Glance says.

Using data from a large database managed by the American College of Surgeons, the researchers looked at more than 310,000 patients who underwent general, vascular, or orthopedic surgery between 2005 and 2007. Based on BMI, patients were classified as underweight, normal, overweight, obese, morbidly obese, and super obese.

The obese patients were further divided based on their metabolic health. One group included patients with high blood pressure and diabetes, a diagnosis dubbed the “modified metabolic syndrome,” because it aligns closely with the well-established metabolic syndrome.

Individuals diagnosed with the metabolic syndrome have three or more of the following risk factors: high blood pressure, glucose intolerance, or diabetes, abdominal obesity (being apple-shaped), increased triglycerides (fats in the blood), and low levels of good HDL cholesterol.

The remaining obese patients were deemed metabolically healthy. After taking age, sex, surgical complexity, and other factors into account, mathematical models were used to determine the rate of major complications in each group 30 days following surgery.

In addition to the substantially increased risk of kidney problems, obese patients with the modified metabolic syndrome experienced a nearly two to three-fold higher risk of cardiac complications; a one-and-a-half to two-and-a-half-fold higher risk of pulmonary complications; and a two-fold higher risk of neurologic complications, compared to normal weight and metabolically healthy obese patients.

With the exception of patients with the modified metabolic syndrome and super obesity, the modified metabolic syndrome was not associated with increased risk of death.

“In today’s healthcare system, we have to be very careful with how we use our resources. We want to concentrate our efforts on patients who are more likely to have trouble following surgery, and our findings give surgeons and other physicians a much better way to predict who those patients will be,” says Salloum.

Researchers from the University of California, Irvine and the University of Iowa contributed to the study, that was funded in part by the Agency for Healthcare Research and Quality.

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