Should you fast before anaesthesia? If you’re taking slimming medicines, your stomach might not be empty
Anti-obesity and anti-diabetes medicines have transformed the lives of millions of people. However, anyone taking them must remember to always tell the anaesthetist before undergoing surgery
Key points
A British study involving over 47,000 patients has raised new concerns regarding GLP-1-based medicines: in cases where general anaesthesia is administered for surgery, the risk of regurgitation and pulmonary aspiration increases 11-fold. Although the absolute risk of aspiration pneumonia remains very low, this is therefore a new potential risk to bear in mind prior to anaesthesia.
Anti-obesity and anti-diabetes drugs from the GLP-1 family have transformed the lives of millions of people. However, anyone taking them must remember to always inform the anaesthetist before undergoing surgery or a procedure requiring general anaesthesia. A UK study, recently presented at the annual congress of the Association of Anaesthetists in Liverpool and published in the journal Anaesthesia, has in fact shown that people taking these medicines have an incidence of gastric regurgitation and/or pulmonary aspiration approximately 11 times higher than those who do not take them.
The paradox of a full stomach whilst ‘fasting’
The reason for this phenomenon is linked to one of the effects produced by GLP-1-based medicines. Semaglutide and tirzepatide slow down gastric emptying; food and liquids can remain in the stomach for longer. This is helpful in controlling blood glucose levels and contributes to the effect on satiety and weight, but it can become a problem when general anaesthesia is planned, as this requires patients to fast beforehand, precisely to avoid the risk of regurgitation and aspiration. Before an operation, patients are asked to fast for a specified period (usually from midnight for procedures scheduled for the following morning), precisely to ensure they go into anaesthesia on an empty stomach. However, if gastric emptying is slowed down, the usual hours of pre-anaesthesia fasting may not be sufficient to ensure that the stomach is completely empty. During anaesthesia, the contents of the stomach may therefore rise back up into the oesophagus and into the mouth: this is known as regurgitation. If the material from the stomach then enters the airways and reaches the lungs, this results in pulmonary aspiration, a potentially very serious complication as it can lead to what is known as aspiration pneumonia.
The absolute risk of regurgitation and aspiration is low, but not negligible
The British study, which was recently presented in Liverpool, involved 47,039 adults undergoing urgent or elective procedures requiring anaesthetic care at 119 centres across the UK. Of these, 1,348 participants (2.9 per cent) had been taking a GLP-1 medication for at least three months – approximately one in 36 patients due to undergo anaesthesia.
In the group not taking GLP-1, regurgitation and/or aspiration occurred in 57 out of 45,691 patients, i.e. 0.12 per cent. Among those taking these medicines, there were 19 such events out of 1,348, equivalent to 1.41 per cent. In other words, there was approximately 1 case of regurgitation for every 802 patients in the untreated group, compared with 1 case for every 71 among those taking GLP-1, representing an 11-fold higher incidence.
