Some physiological effects of ketamine in sheep.

The effects of intravenous injections of ketamine in sheep on the cardiovascular and respiratory systems are compared with the effects of intracerebroventricular injections of the same drug and also with the effects of intravenous barbiturate and steriod anaesthetics. Intravenously administered ketamine caused an initial fall in arterial blood pressure the extent of which was dose dependent. This depression was short lived and was occasionally followed by a mild pressor phase. Intracerebroventricular injection of the drug provoked only a mild transient rise in mean arterial blood pressure. The intravenous injection of ketamine gave a brief period of respiratory depression which was mirrored in the PaO2 and PaCO2 levels followed by a period of respiratory stimulation with elevated PaO2 levels. The comparison of the three injection anaesthetics showed that the blood gas tensions with ketamine showed there was a brief period of respiratory depression similar to that seen with the steroid anaesthetic but that the barbiturate caused a much longer depression similar to that seen with the steroid anaesthetic but that the barbiturate caused a much longer depression. The blood gas tensions following the steroid anaesthetic soon returned to normal while the tensions following ketamine indicated an elevated PaO2 after the initial depression. The blood gas tensions following intracerebroventricular injection of ketamine were difficult to evaluate due to the variable period of apnoea which followed the injection.