Episode #108 Keeping Patients Who Use Cannabis Safe During Anesthesia Care

July 26, 2022

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Welcome to the next installment of the Anesthesia Patient Safety podcast hosted by Alli Bechtel.  This podcast will be an exciting journey towards improved anesthesia patient safety.

We are returning to the June 2022 APSF Newsletter. Our featured article is “Perioperative Considerations of Cannabis Use on Anesthesia Administration” by Dylan Irvine, Tricia Meyer, John Williams, and Jeffrey Huang. Thank you so much to Tricia Meyer for contributing to the show today.

Here are some important considerations for cannabis and THC:

Pharmacokinetic Drug Interactions with THC and Their Consequences:

  • Increased effects of clobazam, warfarin, hexobarbital
  • Decreased effects of theophylline.
  • Additive pharmacodynamic effects with other agents having similar physiological properties, such as sedation with CNS depressant drugs, including benzodiazepines, opioids, and volatile agents.

Cannabis Withdrawal Symptoms:

  • Anger
  • Decreased appetite
  • Malaise
  • Irritability
  • Feelings of depression
  • Abdominal pain
  • Nervousness/anxiety
  • Chills
  • Sweating
  • Insomnia
  • Nightmares
  • Tremors

Symptoms of acute cannabis intoxication:

  • Increased anxiety
  • Paranoia
  • Psychosis

The APSF 2022 Stoelting Conference is right around the corner. It is on September 7-8th in Nashville, TN and will focus on crucial patient safety issues in office-based and non-operating room anesthesia or NORA. We hope to see you there. Check out this link for more information and to register.

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© 2022, The Anesthesia Patient Safety Foundation

Hello and welcome back to the Anesthesia Patient Safety Podcast.  My name is Alli Bechtel, and I am your host. Thank you for joining us for another show. We are jumping back into the June 2022 APSF Newsletter. There are still so many great articles to cover in this newsletter. Today, we are going to be talking about how to keep patients who use cannabis safe during anesthesia care.

Before we dive into the episode today, we’d like to recognize Edwards Lifesciences, a major corporate supporter of APSF. Edwards Lifesciences has generously provided unrestricted support to further our vision that “no one shall be harmed by anesthesia care”. Thank you, Edwards Lifesciences – we wouldn’t be able to do all that we do without you!”

Our featured article is “Perioperative Considerations of Cannabis Use on Anesthesia Administration” by Dylan Irvine, Tricia Meyer, John Williams, and Jeffrey Huang. To follow along with us, head over to APSF.org and click on the Newsletter heading. First one down is the current issue. Then, scroll down until you get to our featured article today. I will include a link in the show notes as well. You can also get to the June 2022 APSF Newsletter by clicking on the Newsletter heading and 5th one down is the Newsletter archives and then scroll down until you get to the June 2022 APSF Newsletter. This is also where you can find all the APSF Newsletters all the way back to 1986.

Before we get into the article, we are going to here from one of the authors. Let’s take a listen.

[Meyer] “Hi, my name is Tricia Meyer. I’m a PharmD and an adjunct professor of anesthesiology for Texas A&M College of Medicine. I am on the APSF Newsletter Editorial Board and Committee on Education and Training. I want to thank you and the Anesthesia Patient Safety Foundation for having me on the podcast and discussing this topic with the listeners.

[Bechtel] To kick off the show, I asked Meyer, why she decided to write this article with her co-authors. Here is what Meyer had to say.

[Meyer] “My idea for the topic of patient cannabis use on anesthesia administration began after a conversation with an oncology patient who had a diagnosis of a glioblastoma. The patient was using a cannabis product daily and felt that it enhanced her quality of life. But she was also an oncology surgery patient undergoing multiple surgeries. As probably are a subset of the 49.6 million Americans who have used marijuana at some point during a year.”

[Bechtel] And now it’s time to get into the article. The article opens with information about the scope of cannabis use in the United States since in 2018, about 9.5% of the US adult population used cannabis regularly and this percentage has likely increased since then with increased recreational and medicinal cannabis availability. While cannabis use is illegal on the federal level in the US, medicinal cannabis is legal in 37 states and recreational cannabis is legal in 18 states. This is a patient safety issue since regular cannabis use can have cardiopulmonary, gastrointestinal, and central nervous system effects which may impact patients undergoing surgery and anesthesia.

We’ll start the discussion by reviewing the pharmacological considerations of cannabis. The cannabis plant has over 500 compounds which includes cannabinoids, terpenoid, and flavonoids. The main cannabinoids include delta-9-tetrahydrocannabinol which you may know by the initials THC and cannabidiol which you may know as CBD. THC is a psychoactive compound that may cause sedation, analgesia, and euphoria. The term cannabis refers to all of the compounds derived from the plant while the term marijuana refers to the parts of the plant which includes dried leaves, flowers, stems, and seeds. Keep in mind that marijuana may contain significant amounts of THC. The concentration of THC is what determines the strength of this drug. The strength has been increasing from about 3% in 1980 to 12% in 2012 which was measured in marijuana samples from the Drug Enforcement Agency. Over that same time period, there has been an increase in emergency department visits related to cannabis use as well. The more potent form of cannabis is called sinsemilla which is the female cannabis plant that has not been pollinated and is the major component found in the stronger confiscated samples. Another contributing factor is the production of marijuana extracts and resins with 3-5 times the amount of THC than can be found in the plant alone.

So, how do cannabinoids work? The mechanism of action includes partial agonist activity on two types of G-coupled cannabinoid receptors, called cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 or CB2. The CB1 receptors can be found mostly in the brain and nervous system tissue with lower concentrations in the liver, adipose tissue, and vascular endothelium. Activation of CB1 receptors prevents the release of the following neurotransmitters: acetylcholine, L-glutamate, GABA, norepinephrine, dopamine, and serotonin. CB2 receptors are found in immune cells including macrophages and mast cells.

Now, let’s get into the pharmacokinetics. Marijuana intake may be through smoking or vaporization inhalation or oral intake of an edible product. Following inhalation, THC is transferred from the lungs to the bloodstream rather quickly with psychoactive effects that occur within seconds to minutes. Maximum effect is at about 15-30 minutes which tapers by 2-3 hours with a total duration of action of up to 4 hours. These effects reflect the plasma concentration of THC. Keep in mind that even a small dose of inhaled TCH, about 2-3 mg may lead to psychoactive effects in a naïve user. Other considerations include the pulmonary bioavailability which is variable at about 10-35 percent of an inhaled dose depending on the depth of inhalation and breath-holding. While smoking is the most common intake route, vaporization is increasing. With vaporization, there may be similar psychoactive effects with less exposure to by-products of combustion. However, flavored cannabis vaping products may contain harmful and carcinogenic aerosols. Edible cannabis products have a slower onset of action at 60-120 minutes with a low bioavailability due to degradation in gastric acid and first pass metabolism in the liver and a duration of action of 4-6 hours. With oral intake, cannabis naïve users may experience psychoactive effects with only about 5-20mg of THC. The elimination half-life of THC is slow at approximately 25-36 hours. Cannabis acts as a slow-release drug due to lipid storage areas and enterohepatic circulation and increased elimination half-life occurs in regular cannabis users. Characteristics of THC include the following: It is

  • Highly lipophilic
  • Highly protein bound to lipoproteins (about 95-99%)
  • Distributed to highly perfused tissues
  • Has a volume of distribution of 2.5-3 L/kg
  • Metabolized in the liver through the P450 pathway

So, what are the consideration for drug interactions with regular cannabis use? The information is still limited due to the complexity of the plant, variability of THC concentrations, and lack of studies (it is difficult to study a Schedule 1 drug after all.) Some of the information that we have comes from cannabinoid-derived pharmaceutical medications. Since metabolism of cannabis is in the liver by the P450 pathway and this is similar to many anesthetic drugs so there may be  a potential pharmacokinetic interaction of inhibition or induction of these enzymes. Check out table 1 in the article which we will review now. Reported drug interactions may include increased effects of clobazam, warfarin, and hexobarbital with decreased effects of theophylline. In addition, increased sedation may occur with cannabis in combination with other central nervous system depressant drugs such as benzodiazepines, opioids, and volatile anesthetics.

There’s no time for a commercial break. We are moving right into the Pre-operative holding area to review the pre-operative considerations for cannabis users. Do you screen your patients for cannabis use every time, sometimes, or never? The first step is to take a good medical history which includes enquiring about a history of cannabis use. For patients who use cannabis, it is important to obtain the following information:

  • the composition of the products used
  • history of adverse effects
  • dose consumed
  • the effects caused by missed doses
  • and the time since last exposure.

The preoperative history is vital and will help to identify patients at increased risk for cardiovascular and respiratory complications, withdrawal symptoms, delayed gastric emptying due to THC, and those who are at increased risk for proceeding with anesthesia and surgery while acutely intoxicated with cannabis. You want to make sure that you identify patients who may be acutely intoxicated. There is a significant risk to proceeding with anesthesia care for patients with acute cannabis intoxication. Signs of acute intoxication are listed in Table 3b and include the following: increased anxiety, paranoia, and psychosis. Signs of withdrawal from cannabis use are listed in Table 3a and include the following:

  • Anger
  • Decreased appetite
  • Malaise
  • Irritability
  • Feelings of depression
  • Abdominal pain
  • Nervousness/anxiety
  • Chills
  • Sweating
  • Insomnia
  • Nightmares
  • Tremors

I will include this information in the show notes as well.

Considerations for patients with acute intoxication include the following:

  • Patients are more likely to be violent during emergency from anesthesia which puts the patient and members of the healthcare team at risk.
  • Patients at risk for coronary artery disease who use cannabis have an increased risk of myocardial infarction in the first hour following cannabis use. Anesthesia professionals will need to discuss this risk with the surgeon and consider delaying non-emergent surgery by at least one hour following the use of cannabis.

Preoperative testing for cannabis users may need to include cardiac function tests and a cardiology consultation. Patients who are on anticoagulation and antiplatelet medications may need an evaluation for coagulation function since cannabis may inhibit P450 enzymes. Checking PTT, INR, and platelet function tests may be necessary.

Now, it’s time to move into the operating room. There is not a lot of research or literature on intraoperative anesthetic management for patients who use cannabis. Here is what we know now.

Regular cannabis users may need larger anesthetic doses for induction and maintenance.

In addition, cannabis users may require increased doses of propofol for sedation during endoscopy procedures, but there is still a need to well-designed studies to investigate this claim.

A 2020 retrospective study by Holman and colleagues evaluating preoperative cannabis use in patients undergoing open reduction and internal fixation of tibia fractures reported that in the cohort of 118 patients with 25% reporting cannabis use prior to surgery found that there was no significant difference in doses of propofol, dexmedetomidine, etomidate, ketamine, desflurane, midazolam, and fentanyl for patients with self-reported cannabis use of any cannabis product in the month prior to surgery compared with non-cannabis users who did not report any cannabis use during the month before surgery.  Interestingly, there was a significantly higher average total volume of Sevoflurane administered to patients in the cannabis user group compared to the non-users of 37.4 mls compared to 25 mls, respectively. Perhaps, preoperative cannabis user leads to increased increased tolerance to Sevoflurane, but more studies are needed in this area especially given the retrospective study with a small sample size. So, we will need to stay tuned for future research in this area. Another important consideration in the operating room is the administration of sympathomimetics and beta-blockers for cannabis users since cannabis may inhibit CYP-450. In addition, stay vigilant for hemodynamic instability,  airway hyperactivity from potential airway irritation as well as any signs of myocardial infarction or stroke.

Phew, we made it out of the operating room, but there are still some important postoperative considerations in order to keep patients who use cannabis safe following anesthesia care, but you will have to tune in next week for the exciting conclusion. Plus, we are going to hear from Tricia Meyer again so mark your calendars and tune in next week.

If you have any questions or comments from today’s show, please email us at [email protected]. Please keep in mind that the information in this show is provided for informational purposes only and does not constitute medical or legal advice. We hope that you will visit APSF.org for detailed information and check out the show notes for links to all the topics we discussed today.

Do you have any plans for September? The APSF 2022 Stoelting Conference is on September 7-8th in Nashville, TN and will focus on crucial patient safety issues in office-based and non-operating room anesthesia or NORA. For more information, head over to APSF.org and click on the Conferences and Events tab. Second one down is the 2022 APSF Stoelting Conference.  This will be a hybrid meeting with virtual and in-person options. We hope to see you there!!

Until next time, stay vigilant so that no one shall be harmed by anesthesia care.

© 2022, The Anesthesia Patient Safety Foundation