Low dose intravenous infusion technique with ketamine

Abstract

Low dose ketamine is a relatively new technique. The recommended doses vary considerably. It was therefore decided to establish the minimum dose of ketamine required to produce satisfactory analgesia, sedation and amnesia in 50% of a population of adult volunteers. Twenty adult volunteers aged 20 to 42 years were the subjects of the study. Twenty minutes following intravenous (iv) pre-treatment with 0·3 mg of atropine and 0·2 mg/kg of diazepam each volunteer received a bolus of ketamine 1·0 mg/kg iv followed by ketamine iv infusion at the rate of either0·5 mg/kg/hour(10cases) or 1·0 mg/kg/hour (10 cases). The grade of sedation was determined on a scale of 1–5 and the frequency of amnesia was assessed using visual memory cards. Analgesia was determined by pin prick. Diazepam alone produced no analgesia and only moderate degree of sedation. Ketamine produced satisfactory analgesia to pin prick in both the groups. Ketamine bolus produced marked sedation for about 20 min followed by moderate sedation during iv infusion in both the groups. During the iv infusion of ketamine at arate of 0·5 mg/kg/hour the amnesic effects declined to 20% in 45 minutes, while during infusion of 10 mg/kg/hour the frequency reached a maximum at 50–60%. The minimum dose of ketamine required to produce amnesia in 50% of this population was therefore 1·0 mg/kg/hour after a bolus injection of 1·0 mg/kg given iv.