Gastric ultrasound and mitigating risk of glucagon‐like peptide‐1 receptor agonists

We read with great interest the review by Milder et al. on the implications of glucagon-like peptide-1 (GLP-1) receptor agonists on peri-operative care and welcome recommendations on this topic [1]. Increasing reports of gastric regurgitation with pulmonary aspiration in patients taking these drugs have prompted multiple international peri-operative recommendations. The role of peri-operative gastric ultrasound has been raised as an important tool to assess the risk of gastric regurgitation. We agree that this tool is likely to become incorporated increasingly into routine peri-operative care but must caution its introduction without due consideration. Milder et al. propose a multi-pronged approach to assess and mitigate the risk of gastric regurgitation [1]. A key recommendation made was that for patients taking GLP-1 agonists for management of obesity, the drug should be withheld for a minimum of three half-lives to minimise retained gastric contents. They report a decision aid to assess the risk of gastric regurgitation in patients on GLP-1 agonists which suggests that a gastric ultrasound should be performed on any high-risk patient. A high-risk patient includes one living with obesity, gastro-oesophageal reflux and high or escalating GLP-1 agonist dosing. When you consider the cohort taking this medication it might be difficult to find a patient that falls into the low-risk category. Will all patients on GLP-1 agonists in fact undergo a peri-operative gastric ultrasound for elective or emergency surgery irrespective of pre-operative planning and risk assessment? Gastric ultrasound has been described as a tool to augment decision making but we must be cognisant of how it can bias an airway plan. The use of routine gastric ultrasound has been cautioned, particularly for elective surgery [2]. A patient who exceeds the gastric volume cut-off of 1.5 ml.kg-1 of actual body weight suggests a volume of gastric secretions greater than the 95th percentile of fasted elective surgical patients. It does not however, indicate a threshold for an increased risk of regurgitation. Ultrasound findings vary depending on position and should be performed in both the supine and right lateral position. A positive finding will likely result in a change to the peri-operative plan such as a re-scan after the administration of a pro-kinetic, rapid sequence intubation (RSI), stomach decompression with a nasogastric tube or delay of surgery. Even with these measures it is likely that risk averse anaesthetists will err on the side of caution and perform RSI. Balancing risk is an integral part of anaesthesia practice, and RSI is not without peril. A heightened alertness should be maintained as case reports have already highlighted regurgitant events in patients on GLP-1 agonists despite RSI. Gastric ultrasound in trained hands has a high sensitivity and specificity to identify if the gastric volume is in keeping with an expected baseline gastric secretion burden. The fundamental principle of point of care ultrasound is that it is a 'rule in' test. If solids are visualised in the antrum, gastric paresis is a reasonable conclusion. A crucial question that must be addressed, however, is whether a negative study in this cohort of patients provides enough reassurance against the risk of gastric regurgitation. Studies have yet to support the safe use of supraglottic airways based on gastric volumes within the expected limits for a fasted patient. Many patients on GLP-1 agonists have additional risk factors for impaired gastric emptying which also limits the interpretation of gastric ultrasound. The accuracy of ultrasound is significantly reduced in those with previous gastric surgery or a known or unknown large hiatus hernia. A key mechanism of action of GLP-1 agonists is increased pyloric tone and impaired gastric paresis. The clinical effect of small bowel peristalsis remains less clear. Retrograde flow of small bowel contents upon the initiation of general anaesthesia may occur in these patients even with an apparent empty stomach on ultrasound. This not only has implications for induction but also emergence of anaesthesia and tracheal extubation. In high-risk patients, perhaps a form of a gastric fluid challenge may help identify those with impaired gastric paresis and at risk of gastric regurgitation. This technique has been described previously to help discern the antrum from small solid contents on gastric ultrasound [3]. A small volume of water (e.g. 50 ml) rapidly transits through the stomach with a half-life of 15 min [4]. A protocol that involves the administration of clear fluid followed by a gastric ultrasound at set time intervals may identify those with gastroparesis despite withholding GLP-1 agonists.