Chronic and occasional cannabis users are at no greater risk of complications from anesthesia, according to a new study published in the journal of the American Association of Nurse Anesthetists. The study was limited, however, and more research is needed before any broad conclusions can be drawn. Previous studies have had different results.
The retrospective review looked at nearly 50 self-reported cannabis users who underwent the same procedure under anesthesia at the same medical center. When it came to the administration of propofol, fentanyl, or ketamine, the researchers found no significant differences between cannabis users and the control group. Additionally, there were no adverse cardiac or respiratory events for either group within 30 days of the procedures.
The study set out “to examine the impact of cannabis use on anesthetic agent requirements, associated cardiac and respiratory morbidity, and overall satisfaction levels in patients undergoing esophagogastroduodenoscopy (EGD).”
Of the 23 cannabis users surveyed in the study, nine (39%) reported their use as daily or most days of the week, seven (30%) reported occasional use, and no frequency was recorded for the remaining seven patients. Over half of the cannabis users were 40 or younger.
In addition to the small sample size, another limitation of the study is that it did not differentiate between dose, method of administration, or frequency of cannabis use. The results of the study were also specific to a single procedure of short duration. Larger studies would be needed to confirm that there are no consequences for cannabis users who undergo anesthesia, but this study suggested no difference between groups.
The researchers listed a number of potential reasons for concern for cannabis users undergoing anesthesia, including that they may have airway inflammation and mucosal injury, increased incidence of coughing, wheezing, and phlegm production, and a greater propensity for heart and airway problems during surgery.
These reasons and more are most likely why the researchers stated that before beginning the study they hypothesized that cannabis users would require higher doses of the anesthetic agent propofol.
The observed interaction between cannabis use and higher propofol requirements prior to surgery is not yet understood or verified, but it may have to do with enzymes involved with cannabinoid metabolism and propofol metabolism.
‘No different than accommodating other medications’
According to Dr. Janice Knox, a board certified anesthesiologist, cannabinoid medicines specialist and clinical endocannabinologist, anesthesiologists should just treat cannabis like they would any other form of medication before, during, and after anesthesia.
“There are lists and lists of drugs that we deal with all the time and why cannabis is different is a puzzle to me,” Knox said, adding that anesthesiologists take other medications the patient is using into account when performing a detailed medical history and physical assessment.
“We juggle all those things in addition to their medical problems, that’s what we do.”
When asked if anesthesia could potentially be more dangerous if the patient was under the influence of cannabis, she said “that’s our job, to manipulate physiology. Everyone is at risk. Going to sleep under anesthesia isn’t normal, there’s nothing normal about it. But if someone is getting chronically high all the time and they need a surgical procedure they still need a surgical procedure, and it shouldn’t be any different than someone who comes to us drunk on alcohol or anything else.”
Knox said that just like in any other anesthetic procedure, with a cannabis patient they would do “exactly the same things we’d do for any medication, we’re watching their heart rate, everything and we adjust that anesthetic delivery to accommodate all those things. It’s no different.”
Lauren Vrabel, a cannabis pharmacist and pharmacy manager in Pittsburg, Pennsylvania, said that the study “has a few limitations such as population size, which makes it difficult to draw any conclusions that would make an impact on how medical professionals practice,” adding that there are other studies that present conflicting results.
Regardless, she advised that “because there is the potential for drug interactions between propofol or other anesthetics and cannabis, it’s a good idea to halt cannabis consumption prior to procedures requiring anesthesia. Being honest about cannabis consumption with your medical provider will give them the information they need to make the best decisions surrounding your medical care.”
Could cannabis help with anesthesia?
Could cannabis use actually help a patient going under anesthesia? According to a July 2021 report published in “Cannabis and Cannabinoid Research,” there is evidence that prior cannabis use “results in a decreased need for blood pressure support during general anesthesia.”
The researchers examined a total of 221 adult patients who underwent urgent orthopedic trauma surgery at University of California, Irvine Medical Center. All and were put under more than one hour of general anesthesia and intubation. Cannabis use was assessed by urine test obtained prior to surgery.
The findings showed that patients who tested positive for THC required less blood pressure support. This translates to the need for less medications, fluids, and potentially reduced risk of complications associated with blood pressure support. Interestingly, the study did not find differences in sedation medication requirements as other studies had.
The researchers stated that they don’t know the physiological basis for the finding, but it may be related to how exposure to cannabis can down-regulate cannabinoid receptor 1 and otherwise alter endocannabinoid levels.
While the results are intriguing, the study has its faults. This relatively small study utilized a urine drug screen, which can detect cannabis use for up to 30 days or more, as the only data point relating to use. Therefore it’s impossible to discern what level of THC use infers these changes in response to anesthesia. Despite this, and the fact that sample size for the study was relatively small, it does present an interesting contrast to some of the more well-known acute side effects of THC — decreased blood pressure and an increased heart rate.
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