Canadian Journal of Anesthesia, Vol 8, 477-487, Copyright © 1961 by Canadian Anesthesiologists' Society

Methoxyflurane (Penthrane): A Laboratory and Clinical Study

¹ Department of Anaesthesia, University of Saskatchewan and Department of Anaesthesia University Hospital, Saskatoon, Saskatchewan

Methoxyflurane is a new fluorinated and chlorinated saturated asymmetrical ether whose outstanding physical properties are an unusually high boiling point and the fact that it is non-flammable in anaesthetic concentrations.

Its greatest usefulness seems to lie in its role as an adjuvant to nitrous oxide anaesthesia. Methoxyflurane is a potent respiratory depressant but has relatively little effect on the cardiovascular system. Profound hypotension will occur with undue depth of anaesthesia but changes in the electrocardiogram have not been observed.

Methoxyflurane lacks a certain degree of flexibility as far as ready changes in depth of anaesthesia are concerned and on occasion recovery from anaesthesia is quite markedly delayed. There is some evidence that the drug concentration increases in the adipose tissue after administration has been discontinued, thus accelerating the lowering of plasma levels in the obese patient and decreasing wakening time. Since it is a rather long-acting agent, administration should be discontinued well before the end of operation and concentrations should be tapered off even earlier.

Methoxyflurane is capable of producing a degree of abdominal muscle relaxation but it is recommended that small doses of muscle relaxants be used in order to reduce the amount of methoxyflurane required. The agent enhances the effect of the non-depolarizing muscle relaxants. Although induction of anaesthesia with nitrous oxide-oxygen-methoxyflurane is possible and is not unpleasant, it is slow, implies the use of more methoxyflurane, and is undesirable from the point of view of awakening. It is therefore recommended that anaesthesia be induced with intravenous barbiturates and adequate premedication is desirable.

Administration of a nitrous oxide-oxygen-methoxyflurane sequence was accompanied by few operative and postoperative complications and in that regard the drug compared favourably with other anaesthetic techniques.

Note:

Generous supplies of methoxyflurane (Penthrane®) were made available through the courtesy of Dr. P. Nash of Abbott Laboratories, Montreal, P.Q. who also assisted with a Grant-in-aid.