CIRCULATORY EFFECTS OF ATROPINE IN PATIENTS ANAESTHETIZED WITH NITROUS OXIDE AND TUBOCURARINE

Atropine was given intravenously in a dose of 0.012 mg/kg toten artificially ventilated patients anaesthetized with nitrousoxide and tubocurarine. The heart rate increased from a meanof 68 to a mean of 96 beats/min. This was accompanied by a 31per cent increase in cardiac output and a 12 per cent rise inmean arterial pressure. There was no significant change in strokevolume or left ventricular stroke work. Total peripheral resistancefell by 14 per cent and circulation time by 22 per cent. Useof 0.5 per cent halothane in the inspired mixture in five casesresulted in smaller increases in heart rate and cardiac outputthan were seen in the other five. The results were comparedwith those in an earlier report in which the patients breathedspontaneously during halothane-nitrous oxide anaesthesia (Farman,1967). The response to atropine depends not only on the effectof the drug on the heart, but also on the control state of thecirculation, both of which are heavily influenced by other anaestheticdrugs, by the arterial Pco₂ and by the mechanical effect ofartificial ventilation.