Outcome Measurements in Chronic Neuropathic Pain Patients Receiving Multiple Rounds of Ketamine Infusions.

Background: Chronic neuropathic pain is known to impact many aspects of quality of life (QOL). Ketamine, a phenycyclidine derivative with both anesthetic and analgesic properties, has been previously shown to provide relief in patients receiving outpatient infusions of the drug. Objective: To assess the effect of outpatient ketamine infusions on QOL outcome measurements in patients with chronic neuropathic pain who have received several rounds of ketamine infusions. Methods: Patients with chronic neuropathic pain were asked to complete the brief pain inventory (BPI) concerning the impact of their chronic pain on aspects of their QOL (overall daily pain score, general activity, walking, work, relationship with others, sleep, and enjoyment of life) before receiving ketamine infusion and two to four weeks after the ketamine infusions at the follow up clinic visit. The patients ranked the impact of pain on QOL, from a scale of zero (no impact) to ten (severely impacts). Overall change in QOL both prior to treatment with ketamine infusion and after administration were evaluated. Four predictors (age, sex, race, and BMI) were also used in order to evaluate any change on QOL due to demographics. Only patients who received more than one infusion were included in the study. Results: There were 34 patients in the sample, with mean age 43.0 (SD 12.8), mean BMI 26.0 (SD 8.2), 68% female, 74% white, 18% black, and 9% other or unknown race. 11 patients had 2 episodes of ketamine infusion, 6 had 3 episodes, and the remaining 17 patients had between 4 and 19 episodes (median number of episodes = 3.5). The model predicting mean BPI score pre-infusion (using each subject’s first episode of ketamine infusion only), was significant (p=.036), indicating a significant effect with moderate effect size. The only predictor with a significant independent association with mean BPI pre-infusion was pain (p=.0042). The model predicting post-infusion mean BPI score was not significant (p=.59). In the model predicting change from pre to post-infusion in mean BPI score at episode 1, the only significant predictor was BMI (p=.041). In the mixed model predicting pre-infusion mean BPI across repeated episodes of ketamine infusion, there was a significant episode effect (p=.029). After adjusting for covariates, the mean pre-infusion BPI scores at episodes 2 through 15 are not significantly different from episode 1, but starting with episode 16, all later episodes have significantly lower pre-infusion BPI scores than episode 1. In the model predicting the pattern of pre-infusion BPI scores across episodes, there was a significant interaction by age (p=.016), with older patients have reduced pre-infusion BPI scores at episodes 5 & 12, compared with younger patients. Conclusion: Expanding upon our previous study, we examined QOL outcomes for returning ketamine infusion patients with chronic neuropathic pain based on their BPI scores. Ketamine infusions were found to continuously improve patient’s pain scores over multiple rounds of infusion. Ketamine infusions were also found to have greater affect in older patients as well as patients with a greater BMI. However, other predictors or QOL were not found to be significantly different