Medicine

Why Patients Need to Come Clean About Cannabis to Their Anesthesiologist

This post originally appeared on MedPage Today: Pain Management.

Anesthesiology resident Max Feinstein, MD, explores how marijuana use can complicate medical procedures and the perioperative period.

Following is a transcript:

Feinstein: If there is one person who you should definitely not lie to about any drug use, it’s your anesthesiologist. My name is Max Feinstein and I’m an anesthesiologist filming here at Mount Sinai Hospital in New York City. In this video, I describe the anesthesiologists’ considerations for patients who consume marijuana. If you find this video interesting or helpful, I’d really appreciate it if you liked it and subscribe to the channel. Let’s dive in.

This video does not contain medical advice. It’s just a YouTube video. But if you need medical advice, you should talk to your doctor. It’s estimated that about 15% of the population in the United States uses marijuana. That’s 25 million people.

News Anchor: It is about that time, 4:20 here on 4/20. We’re going to head back to Hippie Hill in San Francisco’s Golden Gate Park for the main event as we call it. Christien Kafton there right now and folks getting things fired up.

Feinstein: And so that means that an anesthesiologist is virtually guaranteed to encounter patients who use marijuana. Worldwide it’s estimated that about 200 million people use marijuana, so the same concept applies for anesthesiologists across the globe. For marijuana, as with any other drug, anesthesiologists are concerned about the effect that the drug has on the patient’s mind and also on their body in the perioperative period, meaning before, during, and after surgery. Many of the effects of marijuana are well-studied and the extent of those effects is really dependent on whether the marijuana use is acute or chronic. No pun intended, sorry.

As far as the brain or central nervous system is concerned, marijuana is known to have cross-tolerance with opioid receptors, meaning that patients may have an increased opioid requirement. It’s also been shown that patients who are regular marijuana users have a higher requirement for midazolam, which is a short-acting benzodiazepine in cases with sedation. Midazolam is also frequently given to help patients feel relaxed before surgery. This is the medication that makes up the anesthesia cocktail that people sometimes reference.

There are also documented effects that marijuana has on the heart, namely both acute and chronic use can lead to a higher baseline heart rate. There are also a number of arrhythmias that have been associated with marijuana use that include atrial fibrillation, ventricular tachycardia, ventricular fibrillation, and AV block to name a few.

The presence of an arrhythmia might be a reason that an anesthesiologist would delay a surgery for further workup and treatment or proceed to surgery with special precautions like electrodes to deliver a shock if needed. It’s also been documented the risk of a myocardial infarction is approximately eight times higher in patients who have used marijuana within the last 60 minutes. When marijuana is inhaled, it can also have effects on a patient’s airway. Namely whether it’s smoked or vaped, marijuana can lead to increased irritation throughout the airway. This can be associated with a number of complications, including airway edema, obstruction, bronchospasm, bronchitis, and emphysema.

There are also hematologic considerations or blood considerations for patients who use marijuana and also take the medication warfarin. Warfarin is a powerful blood thinner that is sometimes prescribed for people who have heart valve replacements, clotting disorders, or a heart rhythm called atrial fibrillation. It’s also the main ingredient used in rat poison, but that’s neither here nor there. Warfarin is a blood thinner that is metabolized through an enzyme made in the liver. That enzyme is called CYP3A4. Marijuana has the effect of inhibiting CYP3A4’s activity, meaning that there is less metabolism of warfarin, meaning that more warfarin is present in a patient’s blood, which means that a patient could be more prone to bleeding during surgery.

As I already alluded to, marijuana does alter some of the enzymes in a patient’s liver that are responsible for metabolism of medications. There is actually a very long list of medications whose metabolism is altered by marijuana. That list includes warfarin, clopidogrel, NSAIDs (or non-steroidal anti-inflammatory drugs), immunosuppressants, fentanyl, oxycodone, codeine, and steroids.

In a kind of funny-titled study about the effect that marijuana has on patients and their post-operative pain, it was found that patients who regularly use marijuana have significantly higher post-operative pain scores as compared to the patients who don’t use marijuana. This probably has to do with the fact that many of the medications that are given for pain control are actually metabolized by enzymes that are interfered with by marijuana. I can say from experience as an anesthesiologist that patients who I have taken care of who are regular users of marijuana do indeed tend to have higher requirements for pain control in the post-operative period.

In order to best take care of patients who do use marijuana regularly, there are some recommendations that have been published in the literature in anesthesiology. As for the amount of time to stop marijuana use prior to surgery, there is a recommendation for at least 72 hours to have elapsed. For patients who are acutely intoxicated with marijuana, there is also a recommendation to consider postponing surgery if it’s an elective surgery and not something that’s urgent or emergent.

Anesthesiologist: Hi, Surgery.

Surgeon: Yes, Anesthesia. What is it?

Anesthesiologist: We’re going to have to cancel the case.

Feinstein: There is also a recommendation to consider increasing the dose of medication that is provided for patients who are regular users of marijuana for the reasons that we’ve already talked about. Given the propensity for marijuana that’s smoked or vaped to irritate a patient’s airway, anesthesiologists should have everything ready to take care of a hyperreactive airway.

Everything that I mentioned in this video is evidence-based and all of the studies that I have cited are included in the description below. If you found this video interesting, you might want to check out this video where I go through all of the medications that are commonly used as part of a general anesthetic. Thanks very much for watching. I’ll see you next time.

Max Feinstein, MD, is a PGY-4 anesthesiology resident at the Mount Sinai Hospital in New York City, where he is also chief resident of teaching. His YouTube channel focuses on perioperative medicine, especially the role of the anesthesiologist.

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This post originally appeared on MedPage Today: Pain Management.

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