Endokrine Reaktionen, Kreislauf- und Aufwach- verhalten bei Ketamin-/Midazolam-Narkosen : Eine Vergleichsstudie Ketamin-Razemat vs. (S)-Ketamin bei Eingriffen am Knie

Clinically used ketamine is a racemic mixture of two isomers, (S)-and (R)-ketamine,in equal amounts. Previous investigations showed the anaesthetic potency of (S)-ketamine to be three times higher than that of (R)-ketamine.The aim of this study was to compare the effects of (5)-ketamine/midazolam and racemic ketamine/midazolam on endocrine and cardiovascular parameters, recovery, and side effects in unpremedicated patients during knee surgery. Methods: 41 patients scheduled for elective knee surgery were investigated in a prospective,double-blind,and randomised design. For induction of intravenous anesthesia, patients received 0.1 mg/kg midazolam, 0.003 mg/kg atropine, mg/kg (S)-ketamine or 2 mg/kg racemic ketamine, respectively. For tracheal intubation, 1 mg vecuronium and 1.5 mg/kg suxamethonium were injected. After intubation and relaxation with a total dose of 0.1 mg/kg vecuronium,a continuous infusion of 0.5 mg/kg/h (S)-or 1 mg/kg/h racemic ketamine was administered throughout the surgery. In addition, 0.05 mg/kg/h midazolam was infused continously in both groups throughout surgery. Ventilation was performed with N 2 0/0 2 (Fi0 2 0.3). Blood samples were taken using a central venous line fivetimes before induction as well as during and after surgery for analysis of adrenaline, noradrenaline (by high-pressure liquid chromatography with electrochemical detection),anti-diuretic hormone (ADH), adrenocorticotropic hormone (ACTH),and cortisol (by radioimmunoassay). In addition, systolic and diastolic arterial pressure (SAP, DAP), heart rate (HR), and arterial oxygen saturation were measured.The time intervals between the end of ketamine and midazolam infusion and the return of consciousness and orientation were recorded.The incidence and quality of dreams and other side effects were reported by the patients. Results: Biometric data of the groups were comparable. Plasma adrenaline and noradrenaline did not change significantly during anaesthesia.ADH increased significantly (p<0.05) after skin incision in both groups. ACTH and cortisol increased in both groups significantly during the course of anaesthesia. SAD, DAD and HR increased significantly after induction of anaesthesia. Recovery was not improved after administration of (S)-ketamine compared to the racemate. No intraoperative awareness and no negative dreams were reported. Conclusions: Increases in SAP, DAP and HR and insufficient reduction of the stress response with respect to ACTH and cortisol seem to require a premedication, which reduces ACTH secretion. Because of the significant reduction in quantitative drug load, (S)-ketamine offers a clinical advantage compared with currently used racemic ketamine.