CIRCULATORY EFFECTS OF S-(+)-KETAMINE

The S-(+) isomer of ketamine has about twice the analgesic potency of the clinically used racemic mixture. Therefore, the known side effects may be reduced when one-half of the usual dose is administered. Sever al prospective, randomised, and double-blinded studies have been perfo rmed to assess wh ether the S-(+) isomer of ketamine is superior to th e racemic mixture with respect to circulatory side effects. Studies in young, healthy volunteers showed that heart rate (HR) and arterial bl ood pressure (ABP) rise significantly after injection of 2 mg/kg ketam ine racemate and 1 mg/kg S-(+) isomer without any significant differen ce between groups. In the study of Doenicke et al. plasma levels of ad renaline (A) were higher in the racemate group, whereas no difference was found in elevated plasma levels of noradrenaline (NA). Premedicati on with midazolam blunted major haemodynamic changes. The investigatio n of Adams et al. confirmed that HR and ABP rise significantly after i njection of 2 mg/kg ketamine racemate and 1 mg/kg S-(+) isomer without any significant difference between groups. In this study, no differen ces were found between groups concerning elevated plasma levels of A a nd NA. A further study in healthy volunteers also showed comparable ha emodynamic changes following i.m. injection of 1.0 mg/kg ketamine race mate or 0.5 mg/kg S-(+) isomer without any significant difference betw een groups. In a previous clinical study including 40 elderly patients undergoing elective orthopaedic surgery, total intravenous anaesthesi a (TIVA) was performed with S-(+)-ketamine or ketamine racemate as an analgesic compound. For induction of TIVA, patients received 0.1 mg/kg midazolam and 1 mg/kg S-(+)-ketamine or 2 mg/kg racemic ketamine, res pectively. Throughout surgery, a continuous infusion of 2 mg/kg per ho ur S-(+)-ketamine or 4 mg/kg racemic ketamine was administered. Three patients in the racemate group showed severe arterial hypertension aft er induction of anaesthesia and were withdrawn from the study. In both groups plasma A and NA levels as well as HR and ABP increased signifi cantly. In our own randomised, double-blinded study, haemodynamic effe cts of 2 mg/kg S-(+)-ketamine and 4 mg/kg ketamine racemate, respectiv ely, were investigated in 14 patients undergoing elective aorto-corona ry bypass surgery. In both groups HR and ABP significantly increased i n 3 patients, each although all patients were deeply sedated with mida zolam. One patient in the S-(+)-ketamine group showed severe arterial hypertension and tachycardia after induction of anaesthesia and was wi thdrawn from the study. With respect to haemodynamic changes, the phar macodynamic effects of ketamine racemate and S-(+)-ketamine are compar able. Therefore, it can be concluded that neither ketamine nor S-(+)-k etamine should be used in patients who suffer, e.g., from arterial hyp ertension and coronary artery disease.