Use and efficacy of low-dose ketamine in the management of acute postoperative pain: a review of current techniques and outcomes

Ketamine hydrochloride is a well known general anesthetic and short acting analgesic in use for almost 3 decades. The role of the NMDA receptor in the processing of nociceptive input has led naturally to renewed clinical inte rest in N-methyl-D-aspartate (NMDA) receptor antagonists such as ketamine. This paper reviews the use and efficacy of low-dose ketamine in the managem ent of acute postoperative pain. The literature was obtained from a compute r search of the MEDLINE(R) database from 1966 through December 1998, Studie s were included for review if they were randomized, prospective, controlled , double-blind and reported pain scores. We evaluate the clinical literatur e and discuss the efficacy of low-dose ketamine in the management of acute postoperative pain when administered alone or:in conjunction with other age nts via the oral, intramuscular, subcutaneous, intravenous and intraspinal routes. Low-dose ketamine is defined as a bolus dose of less than 2 mg/g wh en given intramuscularly or less than 1 mg/kg when administered via the int ravenous or epidural route. For continuous i.v. administration low-dose ket amine is defined as a rate of less than or equal to 20 mu g/kg per min. We conclude that ketamine may provide clinicians with a tool to improve postop erative pain management and to reduce opioid related adverse effects. The e vidence suggests that low-dose ketamine may play an important role in posto perative pain management when used as an adjunct to local anesthetics, opio ids, or other analgesic agents. Further research is required in the followi ng areas: (a) dose-finding studies for ketamine as an adjunct to opioids an d local anesthetics (b) efficacy and optimal route of administration (c) th e role of S(+)-ketamine; (d) the influence of ketamine on long-term outcome such as chronic pain (e) long-term physical and chemical stability of mixt ures containing ketamine (f) spinal toxicity of ketamine and (g) effects of low-dose ketamine on cognitive and memory functioning after surgery. (C) 1 999 International Association for the Study of Pain. Published by Elsevier Science B.V.