Beware Aspiration Risk in Chronic Pot Users

A 24-year-old man presented for a scheduled elective open reduction and internal fixation of his fractured right fibula. His BMI was 22. During the pre-operative assessment, the patient noted that he has used about 2 g of marijuana daily for the past 6 years. He said he does not use opioids or other medications that could delay gastric emptying. There was nothing in his medical history to suggest aspiration risk.

He had his last full meal at 10 p.m. the night prior to the procedure, which is within the standard nil per os (NPO) guidelines. Based on this, clinicians determined that use of a laryngeal mask airway (LMA) was appropriate. The patient was taken to the operating room, which was fully equipped with the standard monitors recommended by the American Society of Anesthesiologists.

The patient was placed in the supine position, and clinicians induced general anesthesia using standard induction medications; he continued to breathe on his own after placement of a laryngeal mask airway.

Shortly after the LMA was placed, clinicians observed it filling with 150 cc of gastric contents. They removed the mask immediately and suctioned 25 to 50 cc of gastric contents from the patient’s oropharynx. Then they performed rapid sequence induction and used an endotracheal tube to secure the airway and place an orogastric tube. They suctioned 500 cc of clear gastric contents from his stomach.

They followed up with a bronchoscopy, which showed that the tracheobronchial tree was clear of gastric contents. The patient continued to have adequate oxygen saturation and ventilation during the procedure. When the procedure was completed, clinicians safely extubated the patient. He was taken to the post-anesthesia care unit to recover and did not experience any further events.

Discussion

Clinicians presenting this case of gastroparesis-related aspiration in a long-term chronic user of marijuana noted that the legalization and subsequent increase in routine use of this drug “create a dangerous aspiration risk for the unsuspecting anesthesiologist, particularly in patients who endorse no other risk factors for aspiration.”

They pointed out that 14% of 9,000 adults in a nationally representative sample in 2017 reported using marijuana (whether smoked, vaporized, or consumed as edibles, concentrates, or topicals) over the prior year, and 8.7% of the same sample reported using marijuana in the prior 30 days.

Gastroparesis — delayed emptying of food from the stomach with no evidence of mechanical obstruction — typically causes upper gastrointestinal symptoms such as early satiety, feelings of fullness after eating, abdominal pain, or nausea and vomiting, case authors explained.

Although gastroparesis may be related to effects of viral infection, or have an unknown cause, people with type 1 diabetes are most commonly affected, they noted, citing a community-based study from Olmsted County, Minnesota. That study reported a 10-year cumulative incidence of symptoms and delayed gastric emptying of 5% in type 1 diabetes (age and gender adjusted HR 33.0, 95% CI 4.0-274), 1% in type 2 diabetes (adjusted HR 7.5, 95% CI 0.8-68), and 1% in controls.

Tetrahydrocannabinol (THC) – the primary active ingredient in marijuana – has been reported to roughly quadruple the time of gastric emptying, from an average of 30 minutes to 120 minutes, an effect thought to be related to “inhibition of gastrointestinal smooth muscle and anticholinergic effects,” case authors noted.

Still, gastroparesis associated with exposure to THC has been reported only rarely, authors wrote – making it difficult to determine whether patients who use THC will experience the typical symptoms, or whether THC’s “anti-emetic and analgesic effects…could blunt the abdominal pain associated with delayed gastric emptying.” Furthermore, up to 40% of all cases of gastroparesis may be asymptomatic, they said.

Authors pointed out that the extent of cannabinoids’ effect on “gastric motility and colonic propulsion, how much this impacts aspiration risk in the perioperative period, and the incidence of aspiration among marijuana users have yet to be studied,” adding that “the incidence of aspiration [associated with] general anesthesia in adults ranges between 1 and 5 per 10,000 patients, depending on risk factors.”

“While the connection between THC use and delayed gastric emptying is clear, the impact of THC on aspiration risk has yet to be defined and leaves unanswered questions for the anesthesiologist,” authors concluded.

Paradoxically, regular users of cannabis may also present with hyperemesis, despite its noted antiemetic effects, the team wrote. They observed that “the anesthetic implications of THC use have been identified in regards to the respiratory and cardiac systems.” However, their case report appears to be the first report of near-aspiration due to THC-related gastroparesis in an anesthetized patient.

In one other marijuana-related case report of confirmed gastroparesis, the patient arrived at the emergency department with severe nausea and vomiting, authors said; as in the present case, that individual had been previously in good health and had no other risk factors for gastroparesis.

“Our case raises important considerations for management of THC-dependent patients,” they wrote, noting that limitations of the case report call for further study and discussion.

Questions to be answered include the potential effect of various marijuana products, such as those containing only cannabidiol (CBD), on risk of gastroparesis and aspiration, they noted. Patients with preexisting gastroparesis-induced symptoms have reported reduced pain with use of dronabinol (synthetic) and marijuana, but this does not elucidate the impact of the drug on the disorder itself, leaving the need for precautions in patients using CBD-containing products unclear.

Furthermore, the effect of dosage, frequency, and duration of THC use on gastroparesis is unknown, they stated: “A dose of 10 mg/m² per body surface area has been found to significantly inhibit gastric emptying, but plasma THC levels did not correlate with the degree of gastric emptying inhibition,” making it difficult to predict how long these effects will last. In the case report, the patient reported use of 2 g/day for 6 years; but in the absence of any associated symptoms, it cannot be determined whether the gastroparesis was dose- or time-dependent, making future use of symptom-based risk-stratification unreliable, authors noted.

They questioned whether the American Society of Anesthesia Fasting Guidelines should be modified to account for use of THC – perhaps to allow cancellation of cases at potential risk of aspiration to allow further preoperative workup.

“Our case report puts forth the idea that cannabinoid use should be deemed an important risk factor for pulmonary aspiration [requiring appropriate precautions] until further studies can define its impact and incidence on aspiration in patients undergoing general anesthesia,” authors concluded.