Effects of low-dose ketamine and thiopentone on cardiac performance and myocardial oxygen balance in high-risk patients.

Induction of anaesthesia may pose a significant hazard to patients with critical cardiovascular status. Ketamine has been advocated as the drug of choice for maintaining cardiovascular performance during induction of anaesthesia in severely ill surgical patients. The purpose of this study was to compare the relative changes in the haemodynamic effects of ketamine and thiopentone during the first 30 min of anaesthesia induction measured by thoracic impedance cardiography. Twelve adult high-risk surgical patients, ASA class III-V, were induced with thiopentone and fentanyl or with infusion of ketamine. Cardiac output decreased to 69% in the thiopentone group (P less than 0.05), but was hardly affected in the ketamine group. The pre-ejection period to left ventricular time (PEPI) and the pre-ejection period index ratio increased significantly after thiopentone (P less than 0.05), while ketamine caused only minimal changes in left ventricular performance. The diastolic pressure time index to systolic pressure time index ration decreased significantly in both groups.