Background and aim: Studies suggest S-ketamine is an effective analgesic in Complex Regional Pain Syndrome (CRPS). We assessed the effects of our intravenous S-ketamine treatment on refractory pain of CRPS patients.

Methods: In this retrospective study, CRPS patients aged ≥18 years who received intravenous S-ketamine in the last 10 years were included. According to our inpatient clinical protocol, S-ketamine dose is increased until pain-reduction is achieved or side-effects are observed. Maximum dose is 14mg/hour. Average treatment duration is 7 days. Primary endpoints were pain scores (Numeric Rating Scale/Visual Analogue Scale) at baseline (T0), end of infusion (T1) and approximately 4 weeks post-infusion (T2). Patients were categorized as responder/non-responder at T1 and T2. Patients were considered a responder if there was a ≥2 points drop in pain score or if treatment was defined successful in electronic medical records.

Results: Fifty-seven patients were included. Mean disease duration was 6.2 (sd±0.8) years. Mean duration of s-ketamine infusion was 6.8 (sd±2.6) days. Median pain score significantly decreased from 8.0 (IQR=9.0-7.0) at T0 to 6.0 (IQR=7.0-3.3) at T1 (P< 0.001). At T1, 64.9% of patients were responders. At T2, 40.4% of patients remained a responder. A significant proportion of responders at T1 turned into non-responders at T2 (P=0.016).

Conclusions: In a group of CRPS patients with refractory pain, low-dose intravenous S-ketamine treatment resulted in significant and effective pain relief during infusion. However, a significant proportion of initial responders change to non-responders at follow-up. Further research is needed to ascertain possible predictors of response to S-ketamine.

EFFECT OF INTRAVENOUS S-KETAMINE ON PAIN IN PATIENTS WITH COMPLEX REGIONAL PAIN SYNDROME