Objective: We evaluated whether outpatient intravenous ketamine infusions were satisfactory for pain relief in patients suffering from various chronic intractable pain syndromes.
Design: Retrospective chart review.
Setting and patients: Following Institutional Review Board approval, we retrospectively analyzed our database for all ketamine infusions administered over 5 years from 2004 to 2009.
Outcome measures: Data reviewed included doses of intravenous ketamine, infusion duration, pain scores on visual analog scale (VAS) pre- and post-procedure, long-term pain relief, previous interventions, and side effects. All patients were pretreated with midazolam and ondansetron.
Results: We identified 49 patients undergoing 369 outpatient ketamine infusions through retrospective analysis. We excluded 36 infusions because of missing data. Among our patients, 18 (37%) had a diagnosis of complex regional pain syndrome (CRPS). Of the remaining 31 (63%) patients, eight had refractory headaches and seven had severe back pain. All patients reported significant reduction in VAS score of 5.9 (standard error [SE] 0.35). For patients with CRPS, reduction in VAS score was 7.2 (SE 0.51, P < 0.001); for the others, the reduction was 5.1 (SE 0.40, P < 0.001). The difference of 2.1 between groups was statistically significant (SE 0.64, P = 0.002). In 29 patients, we recorded the duration of pain relief. Using the Bernoulli model, we found (90% confidence interval) that the probability of lasting pain relief in patients with refractory pain states was 59-85% (23-51% relief over 3 weeks).
Conclusions: We conclude that in patients with severe refractory pain of multiple etiologies, subanesthetic ketamine infusions may improve VAS scores. In half of our patients, relief lasted for up to 3 weeks with minimal side effects.
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