As a growing number of U.S. states legalize marijuana for medical and recreational use, more patients who use the drug are showing up in operating rooms across the country.

The Four Types Of Anesthesia

During a research study of our own, we learned that there are four types of anesthesia.

General anesthesia is what people most often think of when they think of surgery. During general anesthesia, you are unconscious and have no awareness or sensations. Many different medications may be used to achieve this.

Regional anesthesia makes an area of the body numb to prevent the patient from feeling pain. It can completely block all sensation to the area of the body that requires surgery. This type is often used at the dentist.

Monitored anesthesia care refers to being kept under mild sedation. Medications are given, usually through an IV, to make the patient feel drowsy and relaxed.

Local anesthesia uses a needle to inject medications (most often lidocaine) into a smaller area, such as the thumb. Numbing cream may also be applied.

How To Calculate Anesthesia Dosage

Thankfully, as the patient, it’s never your job to determine how much anesthesia you need. “Hello, doctor, I would like 10mg of anesthesia, please!” Could you imagine a nightmare like that? Surgeons and doctors are professionally trained to calculate how much anesthesia patients need based on a variety of factors. Age comes into play, as well as weight and the duration of the surgery itself.

“One unit of time is recorded for each 15-minute increment of anesthesia time,” according to Medical Business Management. “For example, for a 63-minute procedure, one would receive 4.2-time units (four-time units x 15 minutes plus 1/5th of a time unit, or 0.2).”

Based On A Study In Colorado

In 2015, at a 60-bed hospital in Grand Junction, Colorado, the nurses began to notice something odd.

When patients came in for routine medical procedures, like endoscopies or colonoscopies, some of them needed a lot more of the drugs that kept them sedated, like propofol, fentanyl, and midazolam. Those same people also seemed to be the ones who reported that they used cannabis frequently.

Doctors always ask before invasive procedures and surgeries about illicit drug use. But when cannabis became legal in Colorado in 2012, the nurses realized that it was no longer “illicit” and they started to inquire if, and how often, patients used weed.

After reviewing the medical records of 250 Colorado patients who got colonoscopies and other endoscopic procedures, researchers determined that regular marijuana users needed more anesthesia than those who didn’t use cannabis, according to the study published in the Journal of the American Osteopathic Association. In fact, marijuana users needed more than twice the amount of propofol, a powerful anesthetic, compared to others, the researchers found.

Twenty-five patients, or 10 percent, said they regularly used cannabis. Compared to other patients, cannabis users needed more than twice as much of the anesthetic propofol, the study found.

When the researchers compared the records of the 25 to those from non-users they found increased levels of all three sedatives had been needed to achieve the right level of anesthesia. Compared to non-users, regular marijuana users required:

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14 percent more fentanyl

19.6 percent more midazolam

220.5 percent more propofol

Twardowski said his findings underscore the importance of patients telling their surgeons about marijuana use.

“Cannabis users cannot assume that their use will have no effects on their medical care,” said lead study author Dr. Mark Twardowski of Western Medical Associates in Grand Junction, Colorado.

“Clearly the fact that use affects the effectiveness of these three medicines certainly raises myriad questions about potential effects on other medications (pain medicines, anxiety medicines etc.),” Twardowski said by email.

“Because cannabis has such a long life in the body, it may take months to ameliorate the effect,” Twardowski said. “Patients absolutely need to inform their providers about cannabis use prior to any procedure.”

Dr. Jonathan H. Waters, chief of anesthesiology at UPMC Magee-Women’s Hospital in Pittsburgh, said many drugs increase the need for higher doses of anesthesia.

“For instance, regular alcohol use increases need,” he told Healthline. “So, it’s not really that surprising that cannabis has a similar effect.”

Twardowski said the study is an initial look into this topic, and the findings certainly seem to reflect a need for increased dosage of sedation in cannabis users.

“This is strong evidence, but we encourage and invite further research on this topic,” Twardowski said.

Twardowski hopes his study will bring more awareness about the effects that cannabis has on the efficacy of some medications. He also hopes it sheds more light on whether or not cannabis has effects on medications used for anxiety and psychiatric issues, as well as opiates and pain control. He hopes to find out if the effects may be related to tetrahydrocannabinol (THC) or CBD.

Medication levels matter

The concern about giving patients more sedation is that some of the medications pose a greater likelihood for problems the higher the dose gets.

“The dangers of progressively higher doses of sedatives and opiates is that of respiratory suppression. The other potential risk of some of the medications is low blood pressure,” Dr. Mark Twardowski, an osteopathic internal medicine physician and lead author of the study, told Healthline.

Twardowski said it’s unclear what the mechanism is that seems to make cannabis users require more sedation.

“We and others suspect that the effect lies at the receptor level — possibly through some sort of down regulation, but the specifics are not known,” Twardowski said.

Physicians who regularly work with sedation have a rough idea how much is used for the average person dependent on different procedures. They recognize when a patient is responding more slowly and less vigorously to usual sedation doses, he said.

Using more sedation poses health risks to the patient, and can create an increased cost burden when more medication must be used.

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