Recovery and psychic emergence reactions after S-(+)-ketamine

Ketamine is a racemic mixture containing equal parts of S-(+)-ketamine and R-(-)-ketamine. Their potency relation is approximately 4:1. In early human studies S-(+)-ketamine was presumed to produce the desired anaesthetic effects and R-(-)-ketamine the undesired psychic emergence reactions. Therefore, ketamine was compared in a number of randomised studies in volunteers and patients with racemic ketamine. This review adresses the impact of S-(+)-ketamine on recovery from anaesthesia, incidence and content of vivid dreams,and other side effects. The dose relation applied in the studies was 1:2. With only one exception, the recovery phase was clearly shorter after S-(+)-ketamine compared to racemic ketamine irrespective of its application as a single bolus, a bolus followed by continuous infusion, or an intramuscular injection. However,the incidence of psychic emergence reactions was lower after S-(+)-ketamine in only a single study. In conclusion, S-(+)-ketamine should be always combined with a hypnotic or sedative drug in clinical anaesthesia.