Mary Jane. Weed. Pot. Marijuana is known by many different names. While it's been used recreationally for years, more states are legalizing its use. The variety and availability of marijuana-derived products seem to be endless, from hemp facial cleansers and shampoo to CBD gummies, THC-based pain relief creams, CBD vapes and tinctures.
As marijuana consumption ramps up across the country, anesthesia providers can expect to care for an increasing number of patients using the drug and its derived products. Current research describes the use of marijuana as an analgesic, antiemetic, anti-inflammatory agent, anti-depressant, immunosuppressant and muscle relaxant. The inhibitory and excitatory physiologic effects of marijuana are attributed to the dose-dependent effects of THC, which in turn are attributed to the route of administration. For example, when marijuana is smoked, THC's effects peak in about 15 minutes and last approximately four hours, depending on the dose inhaled. If eaten, the effects of THC peak around 90 minutes and last approximately six hours, with some case reports stating the effects can last up to 24 hours depending on the amount consumed.
Marijuana primarily affects the same organ systems impacted by anesthetic agents: respiratory, cardiovascular and the central nervous system.
- Respiratory effects. Current literature hints at an association between smoking marijuana and developing chronic obstructive pulmonary disease (COPD), emphysema and lung cancer. Some case reports suggest a higher incidence of uvular edema, excess oral and pulmonary secretions, and an increased risk of bronchoconstriction.
Patients who use marijuana and who need to be intubated for their surgical procedures, as well as those undergoing general anesthesia with a laryngeal mask airways, may require a deeper level of anesthesia during the time of airway instrumentation. These patients are more likely to have "reactive" airways and may be prone to coughing on wake-up. Additionally, the increased oral and pulmonary secretions can predispose a patient to both aspiration and laryngospasm.
Consider giving patients a nonparticulate antacid or proton pump inhibitor preoperatively and employ a rapid sequence induction when performing endotracheal intubation. Ventilator settings during the surgical procedure will need to be adjusted to the individual patient, depending on the frequency of marijuana use, as a longer expiratory time may be needed.
- Cardiovascular effects. Research has shown an increased risk of cardiovascular and cerebrovascular events attributed to chronic marijuana use. Patients using smaller doses of marijuana can experience tachycardia and display symptoms of hypertension. In extreme circumstances, the increase in heart rate can lead to increased myocardial oxygen demand, which can cause ischemic events such as a heart attack. Myocardial depression has also been reported with cannabis use. Patients using higher doses of THC can experience hypotension and bradycardia, while patients who take sildenafil-related medications and use marijuana are at a higher risk of myocardial ischemia and infarction.
Anesthesia should be administered with the goal of avoiding tachycardia and keeping the patient's blood pressure as close as possible to their normal range. During the preoperative assessment, the anesthesia provider will look for signs and symptoms of cardiac ischemia, such as new onset shortness of breath or chest pain.
A full cardiac work-up, including an EKG, echocardiogram and stress test may be indicated prior to administering anesthesia. Anesthetic drugs that cause cardiac depression, such as inhalational agents, should be used cautiously. Inhalational agents work synergistically with marijuana to sensitize the heart to catecholamines, resulting in an exaggerated and potentially harmful response.
- Central nervous system (CNS) effects. Most marijuana users report feelings of euphoria, enhanced perception of sensory stimuli, calmness and clarity. Others report dysphoric sensations, paranoia, psychosis or panic-like attacks. Although the response to marijuana is subjective, literature has shown a slowing in cognitive functions, such as learning and memory. Like alcohol, the THC found in marijuana acts like a CNS depressant.
Any anesthetic drug that can cause CNS depression — such as narcotics, benzodiazepines and propofol — should be used with caution as they may exacerbate the depressant effects of marijuana. Delayed wakening from anesthesia has been reported. Chronic marijuana users can develop a cross tolerance to certain anesthetic medications and may need higher doses of anesthesia than what would normally be expected. Multiple studies have described the need for higher induction doses of propofol and higher doses of inhalational agents in habitual marijuana users.
If a patient is using marijuana for medical reasons, providers need to know the symptoms being treated (glaucoma versus nausea, for example). They also need to know when the patient last used marijuana, as long-term users can experience symptoms of withdrawal such as anxiety and irritability.
Anesthesia providers must therefore have frank conversations with patients about their marijuana use. The negative stigma associated with the drug remains, however, and most people do not want to share this information. Anesthesia providers must assure patients that they will be safe in their care, and keeping them safe requires having a complete picture of their health histories and the medications they take, including marijuana. OSM