Effects of pre-operative recreational smoked cannabis use on opioid consumption following inflammatory bowel disease surgery

This Short Report is accompanied by the following Invited Commentary: Touil N, Lavand’homme P. Cannabis hyperalgesia. A phenomenon underestimated in the peri-operative period? Eur J Anaesthesiol 2019; 36:623–624. Editor, Cannabis use has become prevalent in our society and is a factor that healthcare professionals should take into consideration when managing their patients. Anecdotally, members of the Acute Pain Service at our institution have observed that general patients who required unexpected increases in opioid postoperatively are often cannabis users. A previous study also found that reported cannabis use may be associated with an increase in postsurgical opioid requirements.1 We investigated whether elective inflammatory bowel disease (IBD) surgery patients who used cannabis pre-operatively required higher amounts of opioid in the first 24 h after surgery as compared to cannabis nonusers. It was hypothesised that patients who used cannabis pre-operatively required higher amounts of opioids postoperatively. Using a historical cohort study design, we conducted a retrospective chart review among patients undergoing elective IBD surgery with the primary objective of comparing opioid consumption in the first 24 h postoperatively between individuals who reported pre-operative cannabis use (group C) and those who reported no use (cannabis nonusers). The study (ID 15-0328-C) was reviewed and approved by the Sinai Health System Research Ethics Board. As this was a retrospective chart review deemed to expose patients to minimal risk, the requirement to obtain written patient consent was waived. The study population included patients from a tertiary care, university affiliated hospital that is a high-volume IBD surgical centre. Patients who underwent elective IBD surgery between 1 January 2014 and 31 December 2015 were identified to produce a sample size of convenience for this exploratory, hypothesis-generating study. Only patients who received intravenous patient-controlled analgesia (PCA) with morphine or hydromorphone were included. Patients were excluded if they received neuraxial analgesia, if they used methadone pre-operatively, if they used cannabis extracts pre-operatively or if they used synthetic forms of Tetrahydrocannabinol (THC) (e.g. nabilone, dronabinol). Included patients who reported cannabis use were assigned to the C group. All other patients were classified into the cannabis nonusers group. Cannabis use was classified as yes/no according to patient response during the pre-operative medication/social history with a nurse or pharmacist, and the amount of cannabis use reported was documented when provided. One cannabis ‘joint’ was estimated to be 0.75 g, which contains approximately 0.075 g THC, with daily use based on reported frequency and dose.2 The primary endpoint of the study was the amount of opioid used in the first 24 h postoperatively. Of the 592 charts reviewed, 354 individuals were included in the analysis and 238 were excluded. Of the patients included in the analysis, 312 (88.1%) were in the cannabis nonusers group while 42 (11.9%) were in the C group. All the patients in the C group had an approximate amount of cannabis consumed noted in their chart. The median estimated amount of cannabis used by patients in the C group was 0.24 g (IQR 0.05 to 0.75) per day. Referring to Table 1, the median postoperative morphine equivalent use in the cannabis nonusers group was lower (53.4; IQR 30.7 to 88.0) than for the C group (68.1; IQR 41.9 to 114.8) P = 0.043. Although the C group required a 14.7 (IQR 11 to 26) morphine equivalent higher dose of postoperative opioid than the cannabis nonusers group (P = 0.043), the difference was no longer significant once age, pre-operative opioid use and other variables (see Table 2) were included in the model (P = 0.06). The model estimates a 23% (95% CI −3 to 46) increase (about 12 morphine equivalent) in the amount of postoperative opioid use for the C group compared with the cannabis nonusers group, after adjusting for other model variables.Table 1: Summary of cohort groupsTable 2: Regression analysis results to determine the impact of variables on the amount of postoperative opioid use within 24 h postclosureIn conclusion, this study found that individuals consuming cannabis pre-operatively may have higher opioid requirements in the postoperative stage. These results suggest that individuals who report smoking cannabis may have more difficulty with pain management postoperatively and that their cannabis use could be considered when determining postoperative pain regimens. Future directions of research should include prospective studies that are appropriately powered, document cannabis dose, frequency and last use in a systematic manner, which expand beyond the IBD population and extend the opioid monitoring period beyond the first 24 h postoperatively. Acknowledgements relating to this article Assistance with the study: we would like to thank Peter Ramnath for his assistance with this project. Financial support and sponsorship: none Conflicts of interest: none

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