Postoperative Ketamine Use For Postoperative Pain Control in
Opioid Tolerant Patients Undergoing Back Surgery
Dustin Goetz, Tejinder Swaran Singh, Jay Diaz-Parlet
Opioids are the principal medications used for postoperative pain control. Unfortunately, their use is often limited by adverse side effects, including hyperalgesia and tolerance. It has been shown that individuals with a history of prior opioid consumption require larger in hospital opioid doses than opioid naïve individuals (1,2). Benefits of decreasing inpatient opioid usage are seen in reductions of opioid induced side effects. Perhaps more importantly, when viewed within the context of a society in which opioid use, dependence, and abuse has become a pressing health concern, limiting opioid utilization has become increasingly emphasized (3). Numerous studies have demonstrated that Ketamine can significantly decrease postoperative opioid requirements (4,5). The goal of this study was to evaluate the effect of a low dose Ketamine infusion on postoperative opioid requirements in opioid tolerant patients undergoing back surgery.
Materials and Methods
IRB approval was obtained for a retrospective cohort study performed on opioid tolerant patients undergoing back surgery utilizing the University of Iowa Hospitals and Clinics database from 2012-2014. 1,633 patients underwent back surgery during this time period. Of these patients, 13 met inclusion requirements for the postoperative Ketamine infusion group and 8 for the control group. For inclusion into either group; patients needed to be greater than 18 years of age and must have been taking greater than 60mg of oral Morphine equivalent daily for at least one month prior to surgery. For inclusion into the Ketamine group; patients needed to be on a Ketamine infusion (5-10mg) for a minimum of 24 hours postoperatively.The total amount of oral Morphine equivalent consumed during inpatient stay, average hour oral Morphine equivalent consumption at 24 hours and discharge compared to preoperative consumption, and pain scores were compared.
Average total Morphine equivalent consumed during inpatient stay was higher in the Ketamine group compared to the control group (1,186mg vs 700mg). Average hourly oral Morphine equivalent consumed at 24 hours and discharge compared to hourly preoperative consumption increased by a significantly smaller percentage in the Ketamine group compared to the control (14.8% vs. 18.6%; 15.7% vs. 29.7%). When compared to preoperative pain scores, pain at 24 hours and discharge were slightly lower in the Ketamine group (2.05 vs. 2.63; 2.12 vs. 2.25)
Average total Morphine equivalent consumption was higher in the Ketamine group at 24 hours and discharge when compared to the control group. This is not an unexpected result, as the Ketamine group was taking a 44% greater preoperative Morphine equivalent dose in comparison to the control (180.54mg vs. 125.25mg). Numerous studies have demonstrated that higher preoperative Morphine consumption will lead to higher postoperative consumption (1,2). However, when the hourly Morphine equivalent consumption was compared, it demonstrated a significantly smaller increase in percent consumed per hour in the Ketamine group. Given higher preoperative opioid use in the Ketamine group, one can assume that without the Ketamine infusion, the increase in hourly percent usage would have increased by a larger amount. This study demonstrates that a low dose postoperative Ketamine infusion can lead to reductions in opioid consumption in opioid tolerant patients.