Ketamine—Its Use as an Intravenous Anaesthetic

Abstract

SUMMARY Ketamine is a safe, rapid-acting parenteral anaesthetic and analgesic agent, which has been in clinical use for more than 15 years. In early investigations, ketamine markedly elevated blood pressure and heart rate, produced profuse salivation, lacrimation, diaphoresis, skeletal muscle hypertonus, involuntary purposeless movements and agitation or even frank delirium during emergence. Subsequent studies have shown that benzodiazepines are highly effective in preventing the marked cardiovascular responses and unpleasant emergence reactions associated with ketamine anaesthesia. Furthermore, by using a continuous infusion technique the anaesthetist can titrate the drug more closely and thereby reduce the amount of drug administered (Albin, 1976; White, 1983). Never the less, Pedersen (1981) reported an unacceptably high incidence of side-effects following an anaesthetic technique consisting of diazepam (10 mg), ketamine (2 mg/kg bolus followed by an infusion at 2-6 mg/min) and nitrous oxide (66 per cent). Experience at Stanford University with a thiopental (4 mg/kg), ketamine (2-6 mg/min), nitrous oxide (70 per cent) combination in outpatients undergoing minor procedures indicates a more prolonged recovery, with a higher incidence of side-effects compared with a thiopental, fentanyl, nitrous oxide combination (White et al, 1983a). The availability of shorter-acting, less cumulative and thus potentially less toxic intravenous anaesthetics (e.g., alfentanil, midazolam), and a rising concern about operating room anaesthetic gas pollution has renewed interest in total intravenous anaesthetic techniques. Obviously, many of the desired objectives in an ideal intravenous anaesthetic have not been reached with any of the available drugs (Clarke, 1983). However, ketamine is the only available intravenous agent that can function as a sole anaesthetic (without requiring adjunctive agents) because of its unique sedative, amnesic, analgesic and anaesthetic properties. It is water-soluble, stable in solution and painless and non-irritating following parenteral injection. Ketamine produces a rapid onset of action, frequent excitatory activity and hypertonus, minimal (if any) cardiorespiratory depression, analgesia, amnesia, rare hypersensitivity reactions and a relatively rapid recovery with frequent emergence reactions. Intravenous anaesthetic techniques using combinations of short-acting compounds with mutually complementary pharmacological properties allow