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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 tocompare the relative changes in (he haemodynamic effects of ketamine and thiopentone during the first 30 min of anaesthesia induction measu red 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<0.05), but was hardly affected in the ketamine group. The pre‐ejection period to left ventricular time (PEPI) and thr pre‐ejection period index ratio increased significantly after thiopentone (P<0.05), while ketamine caused only minimal changes in left ventricular performance. The diastolic pressure time index to systolic pressure time index ratio decreased significantly in both groups.