Especially for those with morbid obesity, slight preoperative weight loss prior to bariatric surgery reduced post-operative mortality, researchers reported.

Among 480,000 adults with obesity, those with a preoperative BMI of 40 or higher had higher odds of 30-day mortality after bariatric surgery compared with those with preoperative BMI between 35 and 39.9 (P<0.001 for trend), Yangbo Sun, MD, PhD, of the University of Iowa College of Public Health in Iowa City, and colleagues reported in JAMA Network Open:

• BMI of 40.0 to 44.9: adjusted odds ratio 1.37 (95% CI 1.02-1.83)
• BMI 45.0 to 49.9: aOR 2.19 (95% CI 1.64-2.92)
• BMI 50.0 to 54.9: aOR 2.61 (95% CI 1.90-3.58)
• BMI 55.0+: aOR 5.03 (95% CI 3.78-6.68)

Interestingly, those who lost a small percentage of weight prior to undergoing surgery significantly cut the odds of postoperative mortality.

Compared with those who didn’t lose any weight before surgery, those who lost less than 5% of their body weight cut their risk of 30-day mortality by 24% (aOR 0.76, 95% CI 0.60-0.96), while those who lost between 5% to 9.9% reduced their chance of death by 31% (aOR 0.69, 95% CI 0.53-0.90). And those who lost 10% or more of their body weight prior to bariatric surgery slashed their 30-day mortality risk by 42% (aOR 0.58, 95% CI 0.41-0.82).

“Each year, hundreds of patients in the U.S. die after undergoing bariatric surgery,” Sun’s group highlighted. “Although current clinical guidelines do not require preoperative weight loss and a decision to perform bariatric surgery should not be based on whether and how much preoperative weight loss is achieved, it may be beneficial for patients with obesity to be referred to an established weight loss program before surgery to reduce the risk of mortality.”

Drawing on data from the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP), the cohort was comprised of nearly 80% women from the U.S. and Canada. Preoperative weight loss was determined as the difference between weight one year before surgery and 30 days prior to surgery. All patients underwent bariatric surgery between 2015 and 2017, with the majority of patients undergoing sleeve gastrectomy (64%), followed by laparoscopic or open Roux-en-Y gastric bypass (26%) and gastric band (5%).

Within 30 days of bariatric surgery, 511 (0.1%) deaths occurred.

In an invited commentary, Micaela Esquivel, MD, and Dan Azagury, MD, both of Stanford University School of Medicine in California, wrote that this “important topic continues to be debated after more than a decade of contradictory publications.” They noted that a 2019 study using the same MBSAQIP data set, but a smaller sampling, found no differences in 30-day mortality.

Esquivel and Azagury praised the current study for its large sample size, allowing “for assessment of rare occurrences.”

“Postoperative mortality within 30 days of bariatric surgery is rare but certainly worth understanding, although a causal or mechanistic relationship cannot be established with this retrospective cohort,” they pointed out, adding that prior research has implicated venous thromboembolism as one common cause of mortality following bariatric surgery.

However, the commentators noted important limitations of this study: lack of data on causes of death or method of preoperative weight loss, as well as inability to control for perioperative anticoagulation prophylaxis practices, which may be linked with postoperative mortality.

Nonetheless, Esquivel and Azagury said these findings shouldn’t be used to create “artificial insurance barriers,” such as imposing duration-based preoperative weight loss stipulations upon patients. Instead, “the answer is treating patients in the earliest possible stage of their disease to negate the increased morbidity and mortality that is associated with more advanced disease and higher BMI.”