MONDAY, May 8, 2023 (HealthDay News) -- Here's one more reason to watch your weight: Obesity can increase your odds for serious complications after surgery.

Compared with patients of normal weight, those who are obese are at greater risk for developing blood clots, infections and kidney failure after surgery, a new study reports. Patients with obesity were also more likely to be hospitalized for these complications.

"This is indicative of the obesity epidemic in this country," said senior researcher Dr. Robert Meguid, a professor of cardiothoracic surgery at the University of Colorado in Aurora.

The increase in complications owes to a variety of factors. These include body inflammation, which is more common with obesity. It can also be more difficult for patients who are overweight or obese to get up and move around after surgery, increasing their risk for blood clots in the legs.

"With infection, there's an issue of fatty tissue in the body which doesn't heal as well and doesn't have as good blood flow as muscular tissue," Meguid said. "With the blood clots it's a combination of inability for walking easily and readily, and also the body's inflammatory state in obesity."

Changes in blood flow in patients who are obese probably contribute to the risk for kidney failure, he added.

It's also more difficult doing surgery on someone who is obese, Meguid said, which may boost complication rates.

"In general, operations of patients who are obese are a little bit longer on average," he said. "I'm a thoracic surgeon, so I operate on lung cancer, esophageal cancer in the chest, and in patients who are obese, the operations are more technically challenging."

As a result, patients are exposed to more issues due to being in the operating room longer, Meguid explained.

"Patients get colder during surgery," he said. "We know that hypothermia or cold during the operating room is associated with more infections."

Patients with excess weight need to be in their best physical shape before having an operation, he noted. That includes not smoking or drinking alcohol in the weeks before surgery.

If the procedure is elective, Meguid said it may be better to delay while the patient tries to lose weight.

"Physicians caring for the patient after surgery need to be cognizant of these things and look out for infections, blood clots and kidney failure," he advised.

At the same time, doctors need to be willing to confront obesity and discuss what patients can do to minimize their risks, he added.

For the study, Meguid and his colleagues collected nationwide data on nearly 6 million surgery patients. Among them, 45% were obese.

The patients had procedures in nine surgical specialties including gynecology, neurosurgery, orthopedics, ear/nose/throat, thoracic, urology, vascular and plastic surgery.

For patients with obesity, operations took a little longer than for patients whose weight was normal — a median of 89 minutes versus 83 minutes. (Median means half took more time, half took less.)

All of those with obesity had greater odds of developing infection, blood clots and kidney complications.

Except for patients who were severely obese (body mass index over 40, compared to 18.5-24.9 for normal weight), the odds for other post-surgical complications — including bleeding, stroke and lung problems — were no higher for obese people than for other patients, the study found.

Patients who are obese have bodies that are older than their age, said Dr. Mitchell Roslin, director of bariatric surgery at Northern Westchester Hospital in Mount Kisco, N.Y. He was not involved with the new study but reviewed the findings.

"The best way I can explain it is your biological and physiological age is older than your chronological age — more miles on the speedometer," Roslin said.

Patients with obesity are more likely to have metabolic syndrome and high blood pressure, which contribute to kidney problems, Roslin noted. High blood pressure and underlying blood vessel disease, as well as higher inflammation, explain the blood clots, he added.

Roslin agreed that patients need to be in the best physical shape possible before having surgery.

"Obviously, have surgery that you require," he said. "The most important thing is to have a healthy lifestyle, which means eating the right amount of food and the right foods and being physically active. Surgery is like anything else — the healthier you are coming in, the healthier you are going to be coming out."

The findings were published in the May issue of the journal Surgery.

More information

For more on obesity and surgery, head to the University of Pittsburgh Medical Center.

SOURCES: Robert Meguid, MD, MPH, professor, cardiothoracic surgery, University of Colorado, Aurora; Mitchell Roslin, MD, director, bariatric surgery, Northern Westchester Hospital, Mount Kisco, N.Y.; Surgery, May 2023