GLP-1 medicines and aspiration pneumonia after common surgery

Why this study matters

Before an operation under anaesthesia, people are asked to fast so the stomach is empty. If food or liquid comes back up during the procedure and enters the lungs, it can cause aspiration pneumonia, a serious lung infection. GLP-1 medicines such as semaglutide (Wegovy, Ozempic) and liraglutide (Saxenda, Victoza) slow stomach emptying, so anaesthesia teams have worried that people taking them could still have food in the stomach after fasting. This concern has led to guidelines about withholding these medicines before surgery. This study tested whether the worry showed up as more pneumonia in real surgical patients. Canadian readers who take a GLP-1 medicine and are planning an operation will find it relevant.

Who was in the study

The study included 366476 adults who had one of 14 common surgical procedures between April 1, 2020 and September 30, 2022, using MarketScan commercial insurance claims in the United States. People were excluded if they were under 18, had more than one procedure, or had pneumonia or acute respiratory failure in the 90 days before surgery.

The median age was 53 years (interquartile range 43 to 62), and 56.4% were women. Of the whole group, 5931 people (1.6%) had a prescription for a GLP-1 receptor agonist before surgery. Compared with non-users, GLP-1 users were more likely to be female (59.0% versus 56.4%) and much more likely to have both obesity and diabetes recorded (47.5% versus 6.8%). Outcomes were measured over the 30 days after surgery.

What the researchers did

This was a retrospective cohort study, meaning the researchers looked back at existing insurance records. No one was assigned to a treatment by chance. The researchers compared people who had a GLP-1 prescription before surgery with people who did not.

The main outcome was aspiration pneumonia in the 30-day period after the operation. The researchers used multivariable logistic regression, a statistical method that adjusts for differences between the groups such as age, sex, other health conditions and the type of surgery. Results are given as an odds ratio. An odds ratio compares the chance of an event in one group with the chance in another. A value of 1 means no difference.

What they found

After adjustment, the odds of aspiration pneumonia were not significantly different between GLP-1 users and non-users. The adjusted odds ratio was 0.78, with a 95% confidence interval of 0.57 to 1.06 (R32-C126). A confidence interval is the range in which the true value is likely to sit. Because the range crosses 1, the study did not find a clear increase or decrease. The P value was 0.12, meaning the difference could easily be due to chance.

The summary we reviewed does not report how many people in each group actually developed aspiration pneumonia.

The authors conclude that they found no significant association between GLP-1 use before surgery and short-term aspiration pneumonia, and suggest it may be worth reassessing guidelines that recommend pausing these medicines before surgery.

Side effects and people who stopped

This study measured aspiration pneumonia only. It does not report other complications or side effects, and it does not report whether people stopped or paused their medicine before surgery.

What this study does not tell you

• Having a prescription is not the same as taking the medicine. The claims data could not show whether people were still taking their GLP-1 medicine on the day of surgery, or whether they had paused it as their care team advised.
• The records do not show how severe any aspiration event was, and mild cases may not have been coded.
• GLP-1 users were a small share of the cohort (1.6%), which limits the precision of the estimate. The confidence interval does not rule out a small increase in risk.
• The 14 procedures were common operations. Finding no association here does not mean every type of procedure or anaesthesia is safe.
• This is an observational study, and differences between users and non-users that were not measured could affect the result.
• The summary we reviewed does not state who funded the study.

What it means in Canada

For Canadian readers, this study is one piece of evidence that GLP-1 use was not linked to more aspiration pneumonia after common surgery. It does not answer whether pausing the medicine before an operation is needed, because it could not tell who had paused. That decision sits with the surgical and anaesthesia team together with the prescriber. See the page on multisociety guidance for GLP-1 medicines before surgery. For how these medicines are used in Canada, see semaglutide in Canada and tirzepatide in Canada.

Related reading

Other studies in this library that bear on the same question.

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