Cannabis users appear to need more anaesthesia than non-users during surgery, and also more opioids to relieve pain after surgery, according to a University of Colorado preliminary study, writes Dennis Thompson for HealthDay. Patients should let doctors know about their cannabis consumption, to ensure an accurate anaesthetic dose.
Users of cannabis products who had surgery for a broken leg required higher doses of sevoflurane, an inhaled anaesthetic that keeps you asleep during a procedure. These patients also required nearly 60% more opioid painkillers per day while recuperating in the hospital, the researchers found.
The results jibe with earlier studies indicating that marijuana users might need more anaesthesia initially to put them under, said lead author Dr Ian Holmen, a resident anaesthesiologist at the University of Colorado Anschutz Medical Campus in Aurora.
"It's similar to flying a plane. You have a take-off section, and then you have your cruising section and then your landing. These in anaesthesia are induction, maintenance and emergence," Holmen said.
"We found that it's not just in the induction phase of anaesthesia that you need more anaesthesia, but even during that cruising phase you need more inhaled anaesthetic."
The findings were reported on 5 October 2020 at an online meeting of the American Society of Anesthesiologists (ASA), HealthDay reports. Research presented at meetings is typically considered preliminary.
The implications for most marijuana users are not dire, according to Holmen and Dr David Dickerson, vice-chair of the ASA's Committee on Pain Medicine.
Pot users should simply be honest with their doctors about their marijuana consumption, so they can dial in their anaesthetic dose more accurately, said Dickerson.
"We want to know there might be a need for more anaesthesia," he said. "The last thing we want to do is to be under-dosing if someone is going to have an increased requirement. The more information we have, the more we can react and monitor to keep a patient safe during a procedure."
But marijuana users who have heart or lung health issues might face some danger in the operating room, depending on how much additional anaesthetic they need during surgery, Holmen added.
"Sevoflurane has a very clear dose-dependent effect on blood pressure," he said. "The more sevoflurane you receive in the OR, the more a patient's blood pressure drops. If you have heart problems or lung problems coming into the OR, it could be dangerous."
The study
For this study, Holmen and his colleagues reviewed the records of 118 patients who had surgery at the University of Colorado hospital for a broken shin bone.
Of those, 30 patients reported using cannabis. Holmen said that the amount and frequency of use were not recorded, nor was the type of cannabis product used – CBD, THC, edibles or smoked pot.
During surgery, marijuana users not only needed more inhaled sevoflurane anaesthetic, but also higher doses of hydromorphone painkillers, the researchers found.
They also reported higher post-surgery levels of pain that needed larger doses of opioid painkillers to quell.
There are a few potential explanations. It could be that marijuana use alters the way that anaesthetic and pain medications are processed by the body, Dickerson said.
"Cannabis is metabolised in the liver. Medications like anaesthetics and our pain medicines are also metabolised in the liver," he said. "Is there a change in the way the liver's metabolic function is occurring after being exposed to cannabis?"
It's also possible that marijuana changes the way a person's nervous system responds to pain and to painkillers, Dickerson said.
"Is there a change in our neurophysiology or our nervous system that causes us to be in a more excited state, that then causes worsened pain after an injury or during surgical healing, or that actually increases the amount of anaesthesia that takes us to sleep or deeper than sleep?" Dickerson said.
Holmen noted that alcohol use has been shown to alter the amount of anaesthetic a person needs.
"Chronic alcohol users, oftentimes if they have not used prior to coming to the operating room, also require higher anaesthetic," Holmen pointed out. "However, if they use it in short-term period right before anaesthesia, they oftentimes require less."
Dickerson said there might be some other unknown variable regarding people who choose to use cannabis that requires them to need more anaesthesia, and what's been found is simply a link with no direct cause-and-effect relationship.
In any case, Holmen and Dickerson agree more research needs to be done on how marijuana affects anaesthesia.
"The first step is asking: Is there a pattern worth studying? And it's looking more and more like that is the case," Dickerson said.
Cannabis use prompts need for more anaesthesia during surgery, increases pain and postoperative opioid use, study shows
American Society of Anesthesiologists. Published on 5 October 2020
Not only might cannabis users require more anaesthesia during surgery than non-users, they may have increased pain afterwards and use higher doses of opioids while in the hospital, suggests first-of-its kind research presented at the Anesthesiology 2020 annual meeting.
According to the American Society of Anesthesiologists, the report adds to a growing body of research that shows patients who use cannabis have higher anaesthesia needs and more surgery-related pain, the study was the first to compare the effects of cannabis among users and non-users during and after surgery.
All patients in the study had surgery for a broken leg (shin bone).
“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 Dr Ian Holmen, lead author of the study and an anesthesiology resident at the University of Colorado Hospital in 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.”
The researchers looked at the charts of 118 patients who had surgery at the University of Colorado Hospital to repair a fractured tibia and found 30 (25.4%) had reported using cannabis prior to surgery. The timing, frequency and type of cannabis use was not indicated.
They then compared the two groups (users versus non-users), assessing the amount of anaesthesia provided during surgery, patient reported pain scores, and dosage of opioids consumed in the hospital after surgery. They found those who had used cannabis:
- Required more sevoflurane (anaesthetic):an average of37.4 ml
- Required more sevoflurane (anaesthetic): an average of 37.4 ml versus 25 ml
- Reported higher pain scores while in recovery: an average of 6 versus 4.8, a statistically significant difference (based on the patient’s response to their level of pain, with 0-3 being little to no pain, 4-7 being moderate but tolerable pain and 8-10 being severe pain)
- Received 58% more opioids per day while in the hospital (a typical stay was 2-3 days): an average of 155.9 morphine milligram equivalents (MME) per day vs. 98.6 MME per day
A physician anaesthesiologist increases the level of sevoflurane during surgery based on observations of the patient, such as involuntary body movements, increased heart rate, high blood pressure or increased rate of breathing, which are signs the patient may be experiencing more pain.
Researchers did not include patients who suffered from chronic pain or those whose University of Colorado health system records indicated they had been previously prescribed opioids.
“This study shows that it is important for patients to tell their physician anaesthesiologist if they have used cannabis products prior to surgery to ensure they receive the best anaesthesia 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.”
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[link url="https://www.asahq.org/about-asa/newsroom/news-releases/2020/10/cannabis-and-postoperative-pain"]Cannabis use prompts need for more anesthesia during surgery, increases pain and postoperative opioid use, study shows[/link]
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