Summary
Metliohexital 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 seconc 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 1the 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.
Résumé
Nous avons étudié, chez 50 malades qui devaient subir des opérations gynécologiques mineures tes effets cliniques du methohexital, un barbiturique non sulfuré à action très courte. Nous avons comparé ces malades à une série de malades semblables à qui on a donné du thiopental. Pour l induction, le methohexital a été injecté en solution à 1% et, pour le maintien de ľanesthésie, en goutte-à-goutte intraveineux en soluion à 0.2%. Nous avons fait inhaler de ľoxygène en circuit semi-fermé à un débit de 6 litres/min.
Nous avons constaté que le methohexital est un médicament très puissant et à action courte. Quand on emploie le methohexital, ľinduction de ľanesthésie est lente et il faut faire attention de ne pas injecter une dose additionnelle de médicament avant ďavoir ľeffet total de la première dose, car il pourfait s’ensuivre une apnée prolongée. Dans la plupart des cas, ľinduction de ľanesthésie est douce à part ľapparition fréquente ďun hoquet tenace. Nous avons été témoins ďun seul cas ďagitation. Nous n’avons pas toujours obtenu un relâhement musculaire suffisant pour permettre un examen bimanuel du bassin ce qui peut être comparé au thiopental à ce point de vue. Après le methohexital, les malades sont plus complètement réveillés et moins désorientés.- Il est difficile ďadministrer le methohexital de façon intermittente car il est presqu’impossible de maintenir un niveau égal ďanesthésie à cause de ľaction brève et du grand pouvoir du médicament.
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Supplies of Methohexital were made available in geneious quantities through the courtesy of Dr. C. M. Gruber, Jr, Eli Lilly & Company, Indianapolis, Ind., U.S.A.
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Wyant, G.M., Chang, C.A. Sodium methohexital: a clinical study. Canad. Anaesth. Soc. J. 6, 40–50 (1959). https://doi.org/10.1007/BF03014194
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DOI: https://doi.org/10.1007/BF03014194