Ketamine is a phencyclidine-like dissociative agent. At doses commonly used for procedural sedation (1.0-1.5 mg/kg), it produces a trancelike cataleptic state, whereas at subdissociative doses (0.1 to 0.6 mg/kg; most commonly 0.3 mg/kg) it maintains potent analgesic and amnestic effects that are accompanied by preservation of protective airway reflexes, spontaneous respiration, and cardiopulmonary stability. Emerging data on subdissociative-dose ketamine as a single agent in out-of-hospital settings has suggested that it compares favourably to morphine.