August 23, 2019

Editor's note: This popular story from the Daily Briefing's archives was republished on Sept. 17, 2020.

It's long been medical advice for patients to avoid food and drink in the hours before they receive anesthesia, but with the rising popularity of cannabis, doctors have a new pre-surgical precaution: Avoid marijuana beforehand—and tell your doctor if you use it, Naomi Martin reports for the Boston Globe.

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What could happen if you use marijuana before surgery

There are a number of reasons doctors are asking patients not to smoke marijuana before surgery, doctors say.

For one, the physical effects of marijuana can increase the risk of complications. It's especially risky for patients to go under surgery within an hour or two of consuming marijuana, according to David Hepner, an anesthesiologist at Brigham and Women's Hospital. That's because marijuana raises a person's heart rate and lowers their blood pressure. Patients who get high before being sedated could see an increased risk of cardiac problems, including heart attack, Hepner said. Patients could also experience breathing problems from heightened airway sensitivity.

"Most of those conditions, in the worst case scenario, may lead to death," Hepner said. "I'm not saying that it's very common, but the potential is there."

For patients who consume cannabis days or weeks before a surgery but not the day of, the risks seem to be less severe, Hepner said.

Further, recent studies show that consumers of cannabis often need higher dosages of anesthesia to become sedated and stay unconscious, and higher dosages of anesthesia could lead to an increased risk of complications, Martin writes.

For example, one small study in Colorado published in the Journal of the American Osteopathic Association, found that marijuana users needed more of a variety of anesthetics during endoscopic procedures than nonusers. Specifically, marijuana users needed an average of 14% more fentanyl, 20% more midazolam, and 220% more propofol.

Research also suggests that marijuana users could have increased sensitivity to pain after surgery, Martin writes. To address that issue, John Alexander, an associate professor of anesthesiology at the University of Texas Southwestern, said doctors can use multiple pain medications and inject local anesthetic to numb the surgery site. Still, marijuana users may need more opioids or other painkillers than those who don't use marijuana, Alexander said.

Hepner cautioned that these new guidelines do not mean patients shouldn't be honest with their doctors about their marijuana use.

"We're not going to have any judgment—there's no stigma," Hepner said. "It's just important for us to know, because the cannabis could interact with the anesthetic and we need to know how to adjust."

A lack of research

Making matters more challenging for doctors is the lack of research on marijuana. According to Alexander, research on how cannabis affects patients is lacking, in part because federal prohibitions against marijuana make it nearly impossible to conduct a clinical study on it.

As a result, doctors aren't entirely sure what happens in the bodies of marijuana users to make these problems occur, Alexander said.

According to Hepner, it could be that marijuana use affects the central nervous system in a way that changes how the body reacts to anesthetics, but research hasn't looked into that theory yet.

The lack of research also means there aren't any clear guidelines on how to treat patients who use marijuana, Alexander said.

"We've got slivers of information," Alexander said. "It's a growing population and we want to know how best to take care of these patients" (Martin, Boston Globe, 8/21).

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