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A study by anesthesiology researchers suggests that diabetic patients do not experience a larger stomach volume than non-diabetic people after following standard preoperative fasting instructions.
But endocrinologists criticized the study because participants appeared healthier than the general population with type 1 and type 2 diabetes. The issue is further complicated by the widespread use of glucagon-like peptide 1 (GLP-1) receptor agonists to treat both type 2 diabetes and weight loss. These drugs, introduced after the study's enrollment period, work in part by slowing gastric emptying.
The new data comes from a prospective study of 84 diabetic patients (85% type 2) and 96 non-diabetic patients (all with a BMI less than 40) undergoing elective surgery. After following standard preoperative fasting guidelines of ceasing solid foods eight hours before surgery and draining liquids two hours before, gastric ultrasound was used to assess stomach contents.
There were no significant differences between the two groups in gastric volume (0.81 mL/kg with diabetes and 0.87 mL/kg without diabetes) or in the percentage of patients with a “full stomach” (solids or clear liquids >1.5 mL/kg) as defined by the American Society of Anesthesiologists (ASA) guidelines (13 patients (15.5%) with diabetes and 11 patients (11.5%) without diabetes).
Published in AnesthesiologyThe findings reassure patients with diabetes that different fasting instructions are not usually necessary to minimize the risk of pulmonary aspiration during surgery, said lead author Anahi Perlas, MD, professor of anesthesiology and pain medicine at the University of Toronto. Medscape Medical News.
“We don't completely change our practice based on one study, but based on our findings, it appears that, in general, most diabetics are no different from non-diabetics in terms of stomach contents after fasting, and our standard fasting instructions are similarly effective in terms of stomach emptying.”
But, she adds, “If you have symptoms of gastroparesis or suspect it, we can do a bedside stomach ultrasound to see if your stomach is full or empty. This is very quick and not difficult.”
Experts point out notable limitations of study
in Accompanying editorialMark A. Warner, MD, professor of anesthesiology at Mayo Clinic in Rochester, Minnesota, said the study's findings “will be very helpful to anesthesiologists,” but noted that excluding people with a BMI over 40 is a limitation.
However, Michael Horowitz, MBBS, PhD, FRACP, director of the Endocrinology and Metabolism Unit at the Royal Adelaide Hospital in Adelaide, Australia, and professor of medicine at the Adelaide Medical School, disagreed with the study's conclusions. Dr. Horowitz noted that the sample size was small, and participants had an average A1c of 7.2%. Fewer than half had microvascular or neuropathy complications. Thus, they were healthier than the general population with diabetes.
“They picked the wrong group of diabetics,” said Horowitz, who specializes in the digestive complications of diabetes. “You wouldn't expect to see a very high incidence of delayed bowel movements in this group.”
Gastric emptying of solids and liquids to differ greatly This is true among healthy people and even more so among people with type 2 diabetes: About one-third of people who are above their target A1c level have gastroparesis, while those within the target range tend to have faster eliminations, he explained.
And with regard to the use of gastric ultrasound in symptomatic patients, Horowitz said, “The relationship between symptoms such as nausea, vomiting and bloating and gastric emptying rate is weak at best. The association is not simply causal.”
Are fasting guidelines flawed, regardless of diabetes status?
Horowitz, of the ASA 2017 Guidance Update We do not distinguish between caloric and non-caloric fluids and allow clear liquids up to 2 hours before anesthesia.
“If people with or without diabetes are allowed to have sugary drinks up to two hours before surgery, most people become hungry at about 4 calories per minute, so some of the drink will still be in their stomach,” he said. “If you want to empty your stomach, the ASA guidelines are wrong.”
This, he said, is why the study found that the proportion of people who felt “full” was relatively high in both groups — 15.5% in diabetics and 11.5% in non-diabetics.
GLP-1 agonist factors
The study did not mention the use of GLP-1 receptor agonists, but Warner wrote in an accompanying editorial that the rapid adoption of the drugs “will likely change how intraoperative fasting guidelines are used. These drugs delay gastric emptying, adding another risk factor for pulmonary aspiration that must be considered when applying fasting guidelines. The effects of GLP-1 agonists on gastric emptying are inconsistent, ranging from slight to significant, making it difficult for anesthesiologists to determine whether a patient taking a GLP-1 agonist may have gastric fluids or solids preoperatively that could regurgitate and cause subsequent damage.”
Warner wrote that a gastric ultrasound could be helpful in these situations. 2023 ASA Guidancewhich calls for discontinuing daily GLP-1 agonists on the day of surgery and suspending weekly doses for 1 week, and postponing elective procedures if gastrointestinal symptoms are present.
But Horowitz said those recommendations probably also fall short. Pointing to Data Studies suggest that daily liraglutide administration may slow gastric emptying for up to approximately 16 weeks. One third of patientsThe manufacturer has not conducted such studies, particularly for the once-weekly formulation, and the risk of aspiration is unknown.
“The hypoglycemic effect occurs at doses much smaller than those of hypoglycemic agents,” Horowitz says. “It's very likely that extremely low plasma concentrations would be required to avoid hypoglycemic effects in the stomach. Current guidelines don't take this into account, so stopping a short-acting medication for a day is probably a mistake, and stopping a long-acting medication for a week is almost certainly a mistake.”
But as to what should be done, “the fact is, I don't know what to do. And nobody knows, because we don't have the data to answer that question,” he said.
This study was funded by the Physicians' Services Incorporated Foundation and the Canadian Society of Anesthesiologists. Perlas has received preclinical support from the Department of Anesthesiology and Pain Medicine at the University of Toronto, the Department of Anesthesiology and Pain Management at Toronto Western Hospital, and the University Health Network through a distinguished service award. He is Editor-in-Chief of Regional Anesthesia and Pain Medicine and serves as a consultant for FujiFilm SonoSite. Horowitz has no relevant disclosures.
Miriam E. Tucker is a freelance journalist based in the Washington, DC area. She is a regular contributor to Medscape Medical News and has also written for The Washington Post, NPR's Shots blog, and Diatribe. You can find her at X @MiriamETucker.
