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Regular Cannabis Consumers Require More Anesthetic, Study Finds

By Alexander Beadle

Published: Oct 02, 2020   
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Those who regularly consume cannabis tend to require more anesthesia during surgery, say researchers from the University of Colorado.

In a first-of-its-kind study presented this week at the Anesthesiology 2020 annual meeting, the researchers observed a group of patients within the University of Colorado Hospital who all had surgery for a broken shin bone.

They found that cannabis consumers not only required more anesthesia during the procedure, but that they reported higher levels of pain following the procedure and received higher doses of opioid pain medications while in hospital.

Cannabis and acute pain

There is already a modest body of research on the topic of cannabis consumers having greater anesthesia needs and more post-operative pain. But this new study is the first to directly compare the experiences of cannabis users and non-users during and after surgery.

“There is some evidence that cannabis may be beneficial for chronic and nerve pain. However, early research suggests that this is not the case for acute pain such as for surgery of a broken leg,” said Ian Holmen, lead author of the study and an anesthesiology resident at the University of Colorado Hospital, Aurora.

“We now understand patients who chronically use opioids prior to surgery often have exaggerated pain responses and need increased pain medication after surgery because they have an increased tolerance. We speculate that cannabis use may cause a similar effect, but we need more research to determine if this is the case.”

To allow for better comparisons, all the data reviewed by the researchers came from patients undergoing the same operation, to repair a fractured tibia. Patients suffering from chronic pain and those whose medical records indicated that they had previously received a prescription for opioid medications were excluded from the study.

The effects of cannabis use on anesthesia and pain

In total, the charts of 118 patients were studied. Approximately one-quarter of participants reported some cannabis use prior to the surgery, though the timing, frequency, and type of cannabis use was not indicated in the available patient data.

Cannabis users on average required 37.4 milliliters (ml) of sevoflurane (an inhalable general anesthetic) during the operation, versus 25 ml for non-users. During surgery, sevoflurane dosage was controlled by an attending anesthesiologist who monitored for any signs that a patient was in pain (involuntary body movements, increased heart rate, etc.).

Following the procedure, patients were asked to rate their pain during recovery on a scale of zero to ten; 0-to-3 was equivalent to “little to no pain,” 4-to-7 represented “moderate but tolerable,” and 8-to-10 stood for “severe.” On average the cannabis users rated their pain at around six. On average, non-users rated their pain significantly lower, 4.8 out of 10.

Additionally, the cannabis users received 58 percent more opioids per day while recovering in the hospital. Across the 2-to-3 days the patients were in the hospital, the researchers calculated that the regular cannabis consumers were given an average of 155.9 morphine milligram equivalents (MME) per day, compared to 98.6 MME given to those who didn’t consume cannabis.

“This study shows that it is important for patients to tell their physician anesthesiologist if they have used cannabis products prior to surgery to ensure they receive the best anesthesia and pain control possible, including the use of non-opioid alternatives,” said Dr Holmen. “It also confirms that more research is needed to understand how cannabis impacts pain.”

Cannabis as a post-operative painkiller

While pre-operative cannabis use appears to result in an increase in post-surgical pain, there are suggestions that using cannabis post-operatively could actually reduce the pain felt in recovery and reduce the need for subsequent opioid use.

One prominent study from 2006, published in Anesthesiology, found that patients given a single dose of 2:1 THC:CBD cannabis plant extract reported a reduction in pain “equivalent to the best available postoperative analgesia” and displayed “significant dose-related improvements” in the number of patients requesting additional painkillers following surgery.

More recently, studies have suggested that using a combination of cannabinoids and morphine can actually reduce the risk of developing opioid dependence in patients prescribed opioids for pain management. Additionally, orthopedic surgeons based in areas with legal medical cannabis have reported issuing fewer opioid prescriptions following surgery than their peers in states with restricted cannabis access, again hinting that post-operative cannabis use might be effective at suppressing post-surgical pain.

The United States is currently in the grips of an opioid epidemic, one serious enough to have been declared a public health emergency in 2017. With this in mind, it is clear that more research on cannabis and pain is sorely needed if scientists are to be able to understand the complex effects of pre- and post-operative cannabis use on pain and painkiller use.


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