Preoperative Fasting – One Size Does Not Fit All

Young May Cha, MD

Preoperative fasting guidelines have not changed much since the introduction of the 2-hour rule for clear liquids. There is growing literature to support liberalizing clear liquid fasting times but there are other considerations, such as individual patient risk factors, surgery type, and use of SGLT inhibitors or GLP-1 agonists that can influence aspiration risk and morbidity. These were addressed in the session, “Preoperative Fasting – Does One Size Fit All?,” co-sponsored by the Early-Stage Anesthesiology Scholars (eSAS), on Friday, May 17, at the 2024 Annual Meeting, presented by IARS and SOCCA.

Dr. Alexander Nagrebetsky, MD, MSc, assistant professor of anaesthesia at Harvard Medical School, opened the session highlighting the missing quantitative data linking fasting duration, stomach contents/volume, and the negative sequelae of aspiration. It has been a long-held belief that an inappropriately fasted patient will aspirate and suffer severe consequences, but most aspiration events are asymptomatic. On the other hand, prolonged fasting can cause increased thirst, increased postoperative pain, and increased postoperative nausea and vomiting. Other international societies have liberalized clear liquid fasting intervals and Germany has allowed unrestricted drinking prior to anesthesia since 2018. These changes have spurred the creation of relaxed clear liquid fasting guidelines from non-anesthesiology societies.

Decreasing the fasting interval from 2 hours does not seem like a big change, but most patients end up fasting for a much longer time. Tara Ramaswamy, MD, clinical assistant professor at Stanford University, continued this discussion by highlighting other risk factors that seem to be common among aspiration events. She noted surgical risk factors, such as thoracic esophageal surgery, anesthetic risk factors, such as use of MAC, and other patient risk factors, such as emergency surgery and gastrointestinal obstruction, that commonly contributed to aspiration events. NPO status may be a contributor to aspiration events, but it is not the only risk factor. In 2023, ASA updated its guidelines to allow for more permissive language, allowing patients to drink up to 2 hours before surgery in an attempt to limit prolonged fasting times.

Ying Hui Low, MD, assistant professor at Dartmouth Health, then expanded on this topic explaining the perils associated with preoperative fasting in patients taking SGLT2 inhibitors and GLP1R agonists. SGLT2 inhibitors (the “gliflozin” drugs) increase the risk of euglycemic diabetic ketoacidosis with decreased PO intake. This complication can occur even in nondiabetic patients who are taking these medications for heart disease indications. Reducing NPO times can be very beneficial for these patients who are at risk for developing an anion gap acidosis from prolonged fasting.

GLP-1 agonists (the “natide” or “glutide” drugs) are a second line option for glycemic control in diabetes. Their use has exploded in popularity since being approved in June 2022 for weight loss with a weight-related condition. The current ASA consensus is to hold these medications for one dose and to consult endocrinology if a bridge is needed for antidiabetic therapy. A flow chart published in Anesthesia & Analgesia provides some guidance on how to proceed based on gastrointestinal symptoms and gastric ultrasound (with the caveat that there is disagreement on the accuracy of gastric ultrasound to assess gastric contents). Promotility drugs can also be considered for high-risk patients taking GLP-1 agonists but, in truth, the optimal fasting duration is unclear. Some institutions are suggesting these patients limit PO intake to clear liquids for 48 hours.

The Canadian Journal of Anesthesia recently published an editorial suggesting GLP-1 agonists be held for 3 half-lives if the indication for its use is weight loss, and to consult endocrinology for a risk/benefit discussion if used for diabetes. Due to their benefits on renal and cardiac disease, we will probably see even more patients on these medications in the future (and they can be on both an SGLT2 inhibitor and a GLP-1 agonist). Many questions remain about how to safely manage these patients. It is currently still unclear if a clear liquid fasting interval of 2 hours is still safe for procedures typically done without a secure airway, such as ERCP.