Rise in plasma free-norepinephrine during anesthetic induction with ketamine.

Mean plasma free-norepinephrine concentration rose significantly (p less than 0.001) during induction of anesthesia with intravenous ketamine (2.0 mg/kg) in 12 patients. In contrast, no change occurred during induction with thiamylal (5.0 mg/kg) in a control group of 8 patients. No significant rise in plasma free-epinephrine concentration occurred in either ketamine or thiamylal groups. These data support the suggestion that increased venous return mediated by the sympathetic nervous system may be responsible for the increased cardiac output and hypertension known to occur during ketamine anesthesia.