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Adults with cannabis use disorder had a moderately increased risk of morbidity and in-hospital mortality after major elective surgery compared with those without cannabis use disorder, a large retrospective study found.

Among 12,422 hospitalized patients, a composite outcome of perioperative complications and mortality occurred in 7.73% of the cannabis use disorder group and 6.57% of a matched control group (adjusted OR 1.19, 95% CI 1.04-1.37, P=0.01), reported Paul Potnuru, MD, of the University of Texas Health Science Center in Houston, and co-authors in .

"Probably the biggest takeaway is to consider cannabis as a not harmless substance," Potnuru told 麻豆传媒. "It does have real impacts on health. We don't fully know what they are yet, but now there's enough evidence that it can be harmful."

A number of smaller studies have suggested cannabis use may affect anesthesia in surgery, , or use of pain medicine. One study found minimal differences in postoperative complications between cannabis users and non-cannabis users among patients from . "Between increased use and maybe increased potency, our guess was we would probably start to notice some differences" now, Potnuru said.

It's difficult to design a randomized trial of cannabis because of federal regulatory restrictions but it's important to interpret population-level studies like this one with caution, said Samer Narouze, MD, PhD, of Northeast Ohio Medical University in Rootstown, who wasn't involved with the study.

"We cannot build up a good patient story just from an Excel sheet," because details about a patient could be lost, Narouze told 麻豆传媒. How cannabis was administered and the amount of time since a patient last used it may have clinical implications, he noted. "Even smoking within 2 hours of surgery leads to a higher risk of heart attack from surgery," he said.

Postoperative pain may be more severe for regular cannabis users due to "rebound pain" or "paradoxical pain" (cannabinoid hyperemesis) and withdrawal from cannabis during surgery, he added.

New guidelines from the American Society of Regional Anesthesia and Pain Medicine call for screening all surgery patients for cannabis use, which may capture details about how and when cannabis was used and help patients and physicians better manage risk factors, Narouze pointed out.

The study from Potnuru and colleagues used National Inpatient Sample data from 2016 to 2019 to identify adults ages 18 to 65 who were hospitalized for major, noncardiac, non-obstetric elective surgeries: cholecystectomy, colectomy, inguinal hernia repair, femoral hernia repair, mastectomy, lumpectomy, hip arthroplasty, knee arthroplasty, hysterectomy, spinal fusion, and vertebral discectomy.

Overall, 44% of participants were female, 70% were white, and the median age was 53 years. A cohort of 6,211 patients with cannabis use disorder defined by ICD-10 codes was matched with 6,211 patients without cannabis use disorder.

The primary outcome was a composite of perioperative morbidity and in-hospital mortality. Secondary outcomes included individual components of the primary outcome. Some occurred more frequently in the cannabis use disorder group, including in-hospital mortality, myocardial ischemia, acute kidney injury, stroke, respiratory complications, venous thromboembolism, hospital-acquired infection, and surgical procedure-related complications. After adjustment, however, no statistically significant differences between groups on the individual components remained.

Hospital length of stay was a median of 2 days for both groups. Total hospital costs were 6% higher in the cannabis use disorder group (adjusted cost ratio 1.06, 95% CI 1.03-1.09, P<0.001).

The study had several limitations, the researchers acknowledged. It relied on an administrative database that did not capture certain aspects of cannabis use like dose or route, or whether cannabis was used recreationally or medicinally. "It's just a big black box of things you don't know," Potnuru said.

Administrative records may be more likely to identify moderate-to-severe cannabis use disorder cases and miss mild cases, the researchers added. Unmeasured confounders may have influenced results, and findings cannot be generalized to other kinds of surgical procedures that were not studied.

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