By Dr Ananya Mandal, MD
A new study has found that thinner people are at a higher risk of dying within 30 days of an operation than heavier people. The cause behind this trend is not clear.
The researchers set out to see what effect obesity had on survival after surgery, but instead found that the thinner a patient was, the greater the risk of death. The measurement the investigators used was body mass index (BMI), which takes into account both height and weight.
BMI is calculated by dividing weight in kilograms by height in meters squared. According to the U.S. Centers for Disease Control and Prevention, people with a BMI of 18.5 to 24.9 are normal weight, those with a BMI of 25 to 29.9 are overweight, and those with a BMI of 30 and above are obese.
“Patients with low body mass index are at significantly higher risk of 30-day mortality following general and vascular surgical procedures,” said lead researcher George Stukenborg, an associate professor in the department of public health sciences at the University of Virginia. Body mass index is a significant predictor of death risk, independent of the differences in risk associated with the type of surgical procedure and other patient characteristics, he noted. “Low body mass index should be recognized as an important risk factor for 30-day mortality and should be taken into account in preoperative decision-making, discharge planning and patient education,” Stukenborg said. The study was published in the Nov. 21 online edition of the Archives of Surgery.
In the study the researchers looked at deaths in the month after operations in 189,533 people who underwent surgery in 2005 or 2006. The data came from the American College of Surgeons National Surgical Quality Improvement Program. Of these patients, more than 3,200 died within 30 days after their operation. Of those with a BMI of less than 23.1, which put them in the normal-to-thin range, the percentage who died was 2.8 percent, compared with 1 percent among people whose BMI was 35.3 or higher (considered obese). And those with a BMI of less than 23.1 had a 40 percent higher risk of dying than people with mid-range BMIs of 26.3 to 29.6 (overweight), the researchers found.
Further the patients who underwent exploratory abdominal surgery were at the greatest risk of death (nearly 14 percent), compared to other operations. The lowest risk was for breast lumpectomy, to remove small tumors (0.1 percent). Colostomy, wound cleaning, musculoskeletal system procedures, upper gastrointestinal procedures, colorectal surgery and hernia repair were other surgeries where BMI played a role, the study found.
“Unfortunately, our research does not shed any light on why BMI is a risk factor for mortality,” Stukenborg said. “This is an interesting question, though, and something we should think more about,” he added.
Dr. Nestor de la Cruz-Munoz, chief of bariatric surgery at the University of Miami Miller School of Medicine said that he was not surprised by the finding. “It's kind of something we suspected but no one has ever looked at it in a big series like this,” he said. Speaking on underweight patients he said, “A lot of these patients are malnourished -- maybe cancer patients, patients undergoing treatment for other medical problems. A lot of time these patients don't have the defenses to do well with a major surgery… These patients are not your skinny young girl, but more like a frail 80-year-old woman.”
Being overweight or obese carries many other risks like raising chances of heart disease, diabetes, some cancers, arthritis and other conditions. Obesity-related diseases account for nearly 10 percent of medical spending in the United States or an estimated $147 billion a year.