ANESTHETIC DOSAGE OF KETAMINE IMPROVES THE CONTROL OF NEUROPATHIC PAIN IN HUMANS

Abstract

S279 Introduction: Wind-up and N-methyl-D-aspartate (NMDA) receptor-mediated phenomena have been proposed as key mechanisms underlying persistent pain states. Intravenous subanesthetic dosage of ketamine, a weak NMDA antagonist, reduced the continuous, spontaneous, and evoked pain in patients with postherpetic neuralgia(PHN) [1]. On the contrary, ketamine relieved some neuropathic pains only during the infusion period [2]. The aim of this study was to explore, in patients with neuropathic pain, whether and to what extent subjective symptomatic relief develops by 1-h continuous infusion of an anesthetic dosage of ketamine. Methods: With informed consent and institutional approval, 12 patients with PHN (Group 1, 5 men, 7 women; 23-85 yr, mean age 66 yr) and 9 patients with reflex sympathetic dystrophy due to nerve damage (Group 2, 5 men, 4 women; 17-62 yr, mean age 43 yr) were studied. All patients received an anesthetic dosage of ketamine (1-2mg/kg bolus followed by 1-2mg/kg 1-h continuous infusion) in the operating room. The magnitude of spontaneous pain on the first posttherapeutic day was rated by 4 words verbal pain relief descriptors scale (WORSE, SAME, BETTER, MUCH BETTER). BETTER and MUCH BETTER were considered to be effective relief from pain, and WORSE and SAME were regarded as no pain relief. Results: Changes in verbal descriptor pain relief scale were shown in Table 1. Nine of twelve patients (group 1) and six of nine patients (group 2) had successful pain relief. After ketamine administration, one patient complained headache, one patient had aspiration pneumonia and successfully treated with antibiotics, and one patient had change of taste.Table 1: Changes in verbal descriptor pain relief scale after ketamineDiscussion: The present study demonstrates that intravenous ketamine administration in an anesthetic dosage relieved spontaneous pain in patients with neuropathic pain. We conclude that an anesthetic dose of intravenous ketamine may improve the control of neuropathic pain in patients with peripheral injury. But the role for a single treatment of anesthetic dose of intravenous ketamine to obtain sustained relief has not yet been established.