Who uses Cannabinoids?: The Impact of Preoperative Cannabinoid Use on Pain in the Perioperative Period
The use of cannabinoids has been increasing due to recreational use of cannabis and medical access via special exemptions. While most studies have looked at whether cannabinoids have a role in the management of acute pain, there has been no study that has examined the postoperative outcomes of surgical candidates who use cannabinoids preoperatively. Therefore, we designed a propensity score matched (PSM) retrospective cohort study to examine the impact of preoperative cannabinoid use on postoperative pain scores and pain-related outcomes in patients undergoing major orthopedic surgery.
After REB approval was obtained from Toronto Western Hospital, we conducted a retrospective observational study of patients who had major orthopedic surgery at Toronto Western Hospital between April 1 2015 and June 30 2017. Data was obtained from a local database which contained data of patients followed-up by the Acute Pain Service. Propensity matching was used to balance baselines variables including age, gender, type of surgery, history of depression or anxiety and perioperative use of regional anesthesia. The primary outcomes were numerical rating scores (NRS) for pain at rest and on movement, and analgesic consumption in the first 24 hours following surgery. The secondary outcomes were the presence of pruritus, nausea and vomiting, sleep, sedation, delirium, constipation, physical activity impairment, satisfaction and required length of APS follow-up.
A total of 3793 patients were included in the study. Of these, 156 patients were on cannabinoids in the preoperative period. After propensity matching, we analysed 156 patients who were on cannabinoids and 156 patients who were not on cannabinoids. There was no difference in the baseline characteristics of these two groups of patients. We found that patients who were on preoperative cannabinoids had higher NRS(SD) at rest (4.38(2.57) vs 3.66(2.34), p=0.045) and NRS(SD) on movement (6.85(2.96) vs 5.96(3.13), p=0.045). (Figure 1) There was however, no differences in postoperative day 1 opioid consumption (185.8(232.1)mg vs 155.8(318.1)mg. p=0.448). There were also no differences in the incidence of pruritus, nausea, vomiting, patient satisfaction, sedation, delirium and constipation. Patients on cannabinoids reported a higher incidence of sleep impairment (72.1% vs 56.6%, p=0.027) and a lower incidence of physical activity impairment (82% vs 94%, p=0.010)
In our study, we found that chronic cannabinoid use preoperatively was associated with slightly higher pain scores at rest and movement in patients undergoing major orthopedic surgery. There were no differences in all other secondary outcomes except for physical activity impairment and sleep impairment. We propose that the possible causes for the findings in our study are cannabinoid withdrawal or chronic cannabinoid use inducing hyperalgesia. Future studies should evaluate the impact of perioperative cannabinoid supplementation as well as mechanisms behind poorer analgesia in patients with a history of cannabinoid use.