Obese patients with high blood pressure and diabetes are at much higher risk for major complications following non-cardiac surgery compared to otherwise healthy obese patients and patients of normal weight.
The new finding diverges from previous research demonstrating that obesity is associated with a lower risk of death and complications after non-cardiac 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.
In the study, researchers separated obese patients into two groups - those who were metabolically healthy and those with additional risk factors related to the metabolic syndrome, specifically, diabetes and hypertension. They found that obese patients with the additional risk factors were at substantially greater risk for cardiac, pulmonary and neurologic complications, and, to the researchers' surprise, had a striking three to seven-fold increased risk of kidney problems.
"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," said Laurent G. Glance, M.D., lead study author and professor of Anesthesiology and Community and Preventive Medicine at the University of Rochester Medical Center. "The obesity paradox may be explained in part by the large number of metabolically healthy but obese patients included in previous studies."
Glance's study is one of very few that has looked at subgroups of metabolically healthy versus unhealthy obese patients and their outcomes following surgery.
"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," said Rabih Salloum, M.D., study author and associate professor in the Department of Surgery at the Medical Center.
The study, published in the journal Anesthesiology, is the first of its kind in non-cardiac surgery and presents a very 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," said Richard N. Wissler, M.D., Ph.D., study author and 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," added Glance.
Glance's team used data from a large database managed by the American College of Surgeons and 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.