Four groups of 20 dogs were anaesthetised by means of target-controlled infusions of propofol designed to achieve 2·5 µg/ml, 3·0 µg/ml, 3·5 µg/ml or 4·0 µg/ml of propofol in blood. The dogs’ pulse rate and respiratory rate were recorded before premedication and induction, immediately after endotracheal intubation and three and five minutes later (times 0, 3 and 5, respectively), and their arterial blood pressure was recorded oscillometrically just before induction and at times 0, 3 and 5. The targets of 2·5, 3·0, 3·5 and 4·0 µg/ml resulted in the successful induction of anaesthesia in 13 (65 per cent), 16 (80 per cent), 20 (100 per cent) and 20 (100 per cent) of the dogs, respectively. The incidence of postinduction apnoea was 0 (0 per cent), one (5 per cent), two (10 per cent) and eight (40 per cent) at time 5 for groups 2·5, 3·0, 3·5 and 4·0 µg/ml, respectively, and its incidence at time 5 was significantly higher in the 4·0 µg/ml group (P<0·05) than in the other groups. In all the groups there was a significant (P<0·05) decrease in blood pressure between just before induction and the later measurements. Although there were no statistically significant differences between the groups in terms of inducing anaesthesia at a specific target, a target of 3·5 µg/ml appears to ensure a successful induction of anaesthesia without a significant increase in the incidence of apnoea.
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