Usefulness of the perfusion index for monitoring the response to intravenous ketamine infusion therapy in patients with complex regional pain syndrome

Abstract

AbstractBackgroundThis study was performed to compare the perfusion index (PI) between affected and unaffected limbs in patients with complex regional pain syndrome (CRPS); it also evaluated the usefulness of the PI for monitoring the response to intravenous ketamine infusion therapy in such patients.MethodsIn total, 46 patients with CRPS in one arm or leg were enrolled in this study. The PIs of the unaffected (PIControl) and affected (PICRPS) limbs were simultaneously evaluated before and after treatment.ResultsPICRPS was significantly lower than PIControl at all time points. The change in PI from immediately before to 30 min after intravenous ketamine infusion therapy (TBefore and T30 min, respectively) in the affected limb was significantly correlated with the change in visual analog pain scale (VAS) between the two time points (r = 0.646, p < 0.001). The area under the curve for the changes in VAS and PICRPS between TBefore and T30 min was 0.928. The optimal threshold value for the change in PICRPS between TBefore and T30 min, to distinguish responders with a ≥ 50‐point reduction in VAS score from nonresponders, was 22.60% with a sensitivity of 0.811 (95% CI: 0.774–0.848) and a specificity of 0.889 (95% CI: 0.848–0.930). Thirty‐one patients showed a ≥ 50‐point reduction in VAS score [67% (95% CI: 54%–80%)] and 15 patients showed a < 50‐point reduction in VAS score [33% (95% CI: 20%–46%)]. Thirty patients showed an increased PI ≥ 22.60% [65% (95% CI: 50%–78%)] and 16 patients showed an increased PI < 22.60% [35% (95% CI: 22%–50%)]. Twenty‐seven patients had a ≥ 50‐point reduction in VAS score and an increased PI ≥ 22.60% [59% (95% CI: 44%–74%)]. Eleven patients had shown a < 50‐point pain reduction in VAS score and increased PI < 22.60% [24% (95% CI: 13%–37%)].ConclusionThe PI significantly differed between affected and unaffected limbs in patients with CRPS. The PI may be useful for monitoring the response to intravenous ketamine therapy in patients with CRPS.