Canadian Journal of Anesthesia, Vol 6, 40-50, Copyright © 1959 by Canadian Anesthesiologists' Society

Sodium Methohexital: A Clinical Study

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

Methohexital is the only intravenous anaesthetic agent tested by us so far which combines shorter action with a higher potency than thiopental. If dose per minute of anaesthesia for a standard procedure is taken as an indication, the relative potency of thiopental to methohexital is 1:1.54. Nevertheless, the ratio of total sleep time per minute of anaesthesia for thiopental and methohexital is 1:0.7.

Whereas apnoea following induction with sodium thiopental is a fairly constant phenomenon, it is less consistently seen after methohexital but tends to be a good deal more prolonged when it does occur. Induction with methohexital is slow. Not infrequently the patient remains conscious for as long as 10–15 sec. following injection of the drug. Therefore, one may be tempted to make a further injection on the assumption that the first dose had been inadequate. The second injection, however, may well have been unnecessary, and results in prolonged apnoea. As experience is gained in the use of this agent, such prolonged apnoea can usually be prevented. Unfortunately, this makes the agent a potentially more dangerous drug in the hands of the inexperienced. Persistent hiccough is a rather frequent feature of methohexital anaesthesia but is on the whole not too disturbing and terminates spontaneously at the end of anaesthesia. Jactitations were seen once in our series. They have also been observed by others (1).

The intermittent administration of methohexital has been found unsuitable. The high potency combined with very short duration of the drug makes it almost impossible to maintain smooth anaesthesia without causing either prolonged apnoea or awakening. Administration by a continuous intravenous drip is almost mandatory for any procedure lasting more than a very few minutes. This renders the administration of methohexital somewhat cumbersome for the short procedures for which it is most useful. It must, of course, be realized that an intravenous anaesthetic as the sole agent is not ideal, and that this type of anaesthesia was only used in this study to obtain valid comparisons. Some of the objections to methohexital may well not apply if it is used as an induction agent and thereafter only as a supplement to nitrous oxide maintenance. Patients were more awake and less disoriented after methohexital anaesthesia. The incidence of untoward emergence and recovery phenomena was no higher. Muscle relaxation for such procedures as bimanual pelvic examination was not always satisfactory and had then to be provided by succinylcholine. In this respect, methohexital is similar to sodium thiopental. The period elapsing between premedication and induction of anaesthesia was significantly different in the two groups; it is difficult to evaluate the importance of this factor upon the final statistical results.

Note:

Supplies of Methohexital were made available in generous quantities through the courtesy of Dr. C. M. Gruber, Jr., Eli Lilly & Company, Indianapolis, Ind., U.S.A.