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Canadian Journal of Anesthesia, Vol 8, 28-42, Copyright © 1961 by Canadian Anesthesiologists' Society

Observations on Pulmonary Circulation during Light Ether Anaesthesia in Man

GORDON M. WYANT F.F.A.R.C.S.1, HARRY V. DONALDSON M.D.1, and JOHN E. MERRIMAN F.R.C.P.(C)1

1 Departments of Anaesthesia and Medicine (Cardio-pulmonary Service), University of Saskatchewan and University Hospital, Saskatoon, Saskatchewan

Changes in the peripheral circulation under light ether anaesthesia were much less dramatic then in the pulmonary circulation. The only changes observed were in a reduction of the mean systemic blood pressure and of the stroke volume. Central blood volume was decreased only during spoataneous respiration. Changes in the pulmonary circulation, on the other hand, were quite remarkable in that both mean pulmonary artery blood pressure and total pulmonary resistance rose as ether anaesthesia became established before intubation, but a further rise occurred after the tube had been inserted. Thereafter a further rise was noted when respiration was manually controlled. This occurred despite the fact that there remained no positive airway pressure during the expiratory pause. Following extubation the pulmonary artery pressure and total resistance did not return to normal until the subjects were practically awake. Results were not influenced by resistance in the anaesthetic circuit.

From wedge pressure studies it would appear that the increase in total pulmonary resistance on spontaneous respiration is in a larger measure due to the vascular component, whereas during controlled respiration left atrial resistance plays the predominant role.

At this stage of the investigation one is somewhat reluctant to draw practical conclusions from these findings. Further studies must be carried out to determine what effects other anaesthetic agents have on pulmonary circulation. From previous studies it would appear that both halothane and azeotropic halothane-ether behave in a similar fashion but other agents and the role of depth of anaesthesia and of the relaxant drugs must be evaluated. Further studies are also needed with different patterns of ventilation before final conclusions can be drawn. However, the thought must naturally occur that, although the increased total pulmonary resistance observed in these studies may not be of great practical significance in healthy individuals, the strain imposed on the right heart by this increased resistance may become a significant factor indeed in patients with poor cardiac reserve.

Note:

Presented before the Second World Congress of Anaesthesiologists, September 4–10, 1960, Toronto, Ontario.






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Copyright © 1961 by the Canadian Anesthesiologists' Society.