Originally published by our sister publication, Anesthesiology News
As more North Americans are partaking of legal cannabis, exposure to the substance does not seem to affect major surgical outcomes, according to the results of a large cohort study.
Canadian researchers have concluded that routine cannabis use does not affect a composite outcome of respiratory/cardiac arrest, ICU admission, stroke, myocardial infarction and mortality during hospital stays.
“Cannabis contains cannabinoids, which can interact with neurotransmitters, thereby creating potential drug interactions in the perioperative period,” said Betty Huiyu Zhang, MD, a resident at the University of Ottawa, in Ontario. “Preclinical studies indicate the potential for such cardiovascular complications as arrhythmias and blood pressure changes.
“Smoking cannabis can also cause airway hypersensitivity, and smaller retrospective studies have suggested that cannabis may be associated with increased propofol requirements for induction and sedation,” Dr. Zhang added.
Other research has found a potential link between cannabis use and perioperative analgesic difficulties, and mixed results with respect to postoperative pain control.
Therefore, Dr. Zhang and her colleagues evaluated the effect of routine cannabis use on perioperative outcomes in a large patient cohort. The researchers captured data from 1,818 surgical patients presenting to the institution between January 2018 and March 2019. Cannabis users were identified by self-disclosure at their preoperative visit.
Multiple logistic regression with propensity score matching was used to adjust for a number of potentially confounding baseline variables, including age, sex, body mass index, smoking status, other recreational drug use, surgical setting (inpatient vs. ambulatory), type of surgery and type of anesthesia.
No Difference Across Several End Points
In a presentation during the 2021 Annual Regional Anesthesiology and Acute Pain Medicine Meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 1875), Dr. Zhang noted that 606 patients preoperatively reported cannabis use, while the remaining 1,212 served as controls. The total prevalence of reported cannabis use was 4% (606/15,048).
For the propensity score–matched analyses, there was a final cohort of 524 cannabis users with complete information and 1,152 controls. No difference was found between groups with respect to the study’s primary end point: Seven cannabis users (1.2%) experienced the composite outcome of respiratory/cardiac arrest, ICU admission, stroke, myocardial infarction or mortality during their hospital stay, compared with 11 controls (0.9%), yielding an odds ratio of 1.06 (95% CI, 0.23-3.98).
Although cannabis users experienced a greater incidence of arrhythmias than controls (2.7% vs. 1.6%; P=0.15), along with a decreased incidence of postoperative nausea and vomiting requiring treatment (9.6% vs. 12.6%; P=0.08), these differences were not statistically significant. The incidence of severe pain during recovery was also comparable between groups, affecting 30.9% of cannabis users and 33.5% of their counterparts who did not use cannabis (P=0.31).
Cannabis Use Hard to Pinpoint
“More rigorous study should be designed to examine these outcomes,” Dr. Zhang said.
As the researchers discussed, the study represents the largest single-center effort examining regular cannabis use in average doses. Nevertheless, the analysis was not without its shortcomings, which included self-reporting of cannabis use (which may create underreporting); the researchers’ inability to quantify the amount, duration or type of cannabis use; and a lack of categorization of other recreational drug use.
Marco Echeverria-Villalobos, MD, an assistant professor of anesthesiology at The Ohio State University Wexner Medical Center, in Columbus, said the primary challenge in studies such as this is accurately estimating the percentage of cannabis users in a population of surgical patients.
“Despite the wide use that cannabis or cannabinoids have as recreational or medical drugs, the percentage of patients that can be identified preoperatively as recreational or medical cannabis users by self-disclosure is still very low (4.0%-4.2%), as we can observe in other studies that have included larger sample sizes [Int Orthop 2019;43:283-292]. This continues to be an important limiting factor of studies that seek to accurately estimate the real impact of cannabis use on perioperative outcomes.
This article is from the December 2021 print issue.