Ketamine is an N-methyl-D-aspartate receptor antagonist with analgesic properties as well as common side effects including psychomimetic effects. Mayo Clinic Arizona recently approved the use of low dose ketamine for post-operative pain control as part of a multimodal pain treatment program. Multiple prospective studies and systematic reviews have shown that ketamine infusions can decrease opiate consumption during hospitalization with an incidence of psychomimetic effects of 7-8%. A recent retrospective study reported sedation in 9.4% of patients receiving ketamine infusions, though co-administration of other central nervous system depressants such as gabapentinoids was not reported.
As part of a quality improvement effort, we performed a retrospective chart review of the first 45 Mayo Clinic Arizona patients who received low dose ketamine infusions after the therapy was approved in June of 2016. We determined the type of surgery and the team ordering the ketamine infusion. Opioid consumption prior to surgery, during surgery, and post-operative opioid consumption were calculated as well as the duration of the ketamine infusion. The reason for discontinuation of the infusion as well as adverse events such as hallucinations, dysphoria, diplopia, and nausea were documented. Medication adjuvants were noted such as nonsteroidal antiinflammatory, SSRI’s, muscle relaxants and gabapentinoids.
There were a total of 13 neurosurgery surgeries included laminectomy and lumbar fusions. There were a total of 25 colorectal and general surgeries including gastric bypass, Ileostomy creation, laparoscopic colostomy, and laparoscopic sigmoid resection. There were 2 orthopedic surgeries including left above knee amputation, and right femur ORIF. There were 5 patients that were admitted for pain syndromes such as CRPS. The ketamine infusion was started by anesthesia in 27 out of the 45 patients and the remaining 18 were started by pain medicine is the post op period. The patient’s opioid consumption ranged from 0 to 720 daily morphine equivalents with 19 out of 45 patients not taking any opioid prior to surgery. The average duration of the ketamine infusion during the Post-Operative period was 37 hours. Other ketamine related adverse events such as hallucination, dysphoria, and sedation occurred 1/3 of the study population. Out of the 15 patients who experienced ketamine related adverse events 10 of the patients were taking, gabapentinoids, and SSRI’s.
The rate of adverse events in our data was higher at 33% compared to 16.2%-22% in other observational ketamine infusion studies with higher infusion rate used in these studies. Also of note that 66% of the patients that experienced adverse events were also taking opioids, gabapentinoids, and SSRI’s as part of their pain regimen. There could be a correlation between adverse events and polypharmacy.
