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CT1341 is a mixture of two steroids dissolved in cremophor EL (table 1). The results of studies in animals show that it is a rapidly acting intravenous induction agent with a high therapeutic index and is free from irritant effects when injected intravascularly 1. Initial studies in man2-5 have confirmed the animal findings, but its action on the cardiorespiratory system has not been previously fully investigated and therefore, in this study, measurements of the cardiorespiratory effects of CT1341 were undertaken in fit, unpremedicated patients prior to surgery. Electroencephalographic (EEG) changes and biochemical effects were also studied. METHODSThe purpose of the investigation was explained to the patients pre-operatively and written consent was obtained for the insertion of the arterial and venous cannulae, which were required for measurement of blood pressure, central venous pressure (CVP) and cardiac output. The patients were divided into three groups (table 2). Two standard dosages based on observations from animal studies1 were used and, in the case of the lower dosage, two rates of injection were employed.

The cardiorespiratory effects of the recently introduced steroid induction agent Althesin are similar to those of the intravenous barbiturates methohexitone and thiopentone.' These agents have a mainly depressant effect on the cardiorespiratory system in man. In contrast the phencyclidine derivative ketamine is a cardiovascular ~t i m u l a n t~-~ and has minimal action onIn this study the cardiorespiratory effects of Althesin and ketamine, in clinically accepted doses, were measured and compared when given under similar conditions to fit unpremedicated patients awaiting surgery. MethodThe purpose of the investigation was explained to the patients pre-operatively and written consent obtained for insertion of the arterial and venous cannulae which were used for measurement of blood pressure, central venous pressure (CVP) and cardiac output.The electrocardiogram (ECG) was displayed on an oscilloscope and the heart rate continuously recorded by a Devices instantaneous ratemeter. Respiratory rate and variations in depth were monitored by a chest stethograph. All these parameters were measured using appropriate transducers and were continuously recorded by a Devices M 19 recorder.The cardiac output was measured using the indocyanine green dye dilution technique with a Waters densitometer. Three measurements of cardiac output were made prior to induction and then subsequently at 3 , 6 and 9 minutes. The total peripheral resistance was calculated by dividing systemic pressure gradient by cardiac output and is reported in cgs units.

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