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Canadian Journal of Anesthesia, Vol 5, 384-402, Copyright © 1958 by Canadian Anesthesiologists' Society

The Cardiovascular Effects of Halothane

GORDON M. WYANT F.F.A.R.C.S.1, J. E. MERRIMAN F.R.C.P.(C)1, C. J. KILDUFF F.A.C.A.1, and E. T. THOMAS F.F.A.R.C.S.2

1 Departments of Anaesthesia and Medicine (Card 10-pulmonary Service), University of Saskatchewan and University Hospital, Saskatoon, Saskatchewan
2 Departments of Anaesthesia and Medicine (Cardio-pulmonary Service), University of Saskatchewan and University Hospital, Saskatoon, Saskatchewan

The administration of controlled concentrations of halothane lowers the systemic blood pressure. This hypotension tends to reach a plateau and does not seriously affect cardio-vascular efficiency. There is good evidence that this hypotension is due to peripheral vasodilatation; it is associated with increased total pulmonary resistance.

Overdoses of halothane can easily be administered if either a closed system or a poorly calibrated vaporizer is used. The hypotension thus produced may reach profound levels in a very short period of time and seriously impairs circulatory efficiency. It is associated with some peripheral vasoconstriction. The increased total pulmonary resistance indicates that the hypotension is most likely due to myocardial impairment.

Bradycardia invariably occurs and becomes pronounced when excessive doses of halothane are administered. It can be reversed by atropine sulphate, which may also raise the blood pressure from its early plateau.

The profound hypotension produced by overdoses of halothane reverts spontaneously when the administration of the drug is stopped. It is imperative that the hypotension be recognized early because of the severe effect it has on myocardial efficiency. The hypotension can also be reversed by vasopressors, but these must be used cautiously since they may produce ventricular extrasystoles. The most frequent electrocardiographic abnormalities produced by halothane are inversion of the P wave and nodal rhythm. Ventricular extrasystoles may occur early or when hypotension becomes extreme.

Halothane does not seriously affect the circulation provided its concentration it rigorously controlled by means of a suitable vaporizer. Its administration in a closed system or from unsuitable vaporizers is fraught with grave potential hazard. The potentially adverse effects of halothane upon the cardiovascular system are such that the use of this drug must be restricted to those familiar with its properties.

Note:

Presented at the Annual Meeting of the Canadian Anaesthetists' Society, Seigniory Club Montebello, P.Q., June 23–25, 1958.

This study was supported by a grant-in-aid from Messrs. Ayerst, McKenna and Harrison, Ltd., Montreal, P.Q.






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Copyright © 1958 by the Canadian Anesthesiologists' Society.