On nitrous oxide gas and its use as an anæsthetic / by Roderick MacLaren.

  • MacLaren, Roderick.
Date:
1871
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Licence: Public Domain Mark

Credit: On nitrous oxide gas and its use as an anæsthetic / by Roderick MacLaren. Source: Wellcome Collection.

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    tends to render it more concave, to empty it, if it exert any obvious effect, renders it red.” The mode in which the gaseous narcotics influence the blood is to be explained by the physical effects of their endosmosis, and also probably by the preventive action on oxygena¬ tion which their presence within and around the blood-corpuscle induces. Mr Clover observes, u Nitrous oxide acts by preventing the oxida¬ tion of the nervous centres, principally by depriving the blood of its proper supply of free oxygen in the lungs. Although there is oxygen in the nitrous oxide, it is in a state of chemical combination with nitrogen, not free, and merely mixed with nitrogen as in the air. It is probable that the presence in the blood of nitrous oxide is exciting, so long as some oxygen remains, but as soon as the oxygenating property of the blood is lost, the functions of the ner¬ vous centres fail; and if fresh air were not soon admitted, their functions would cease altogether. The functions of the brain proper cease before those of the medulla oblongata; hence we have loss of consciousness before failure of breathing, and the functions of the medulla are abolished before those of the ganglia presiding over the action of the heart, and hence the heart continues to beat after the breathing has ceased.” To the practical importance of this last paragraph I would direct your attention, for it shows that after the breathing has ceased, the patient may be safe so long as the heart pulsates. Dr Richardson belifeves that this agent acts simply by producing asphyxia, and is therefore a most dangerous anaesthetic. I do not propose to indicate my adherence to any of these theories, nor do I intend to propound a new one of my own, believ¬ ing as I do, that we have up to the present time been indulged with rather too many theories, and too few accurate observations or facts. And in leaving this part of the subject, I would simply quote to you the words of a wise man—Sir Humphry Davy: “It would be easy,” he says, “ to form theories referring the action of blood impregnated with nitrous oxide to its power of supplying the nervous and muscular fibre with such proportions of condensed nitrogen, oxygen, light or ethereal fluid, as enabled them more rapidly to pass through those changes which constitute their life; but such theories would be only collections of terms derived from known phenomena, and applied by loose analogies of language to unknown things.” With some slight change of terms, would the remarks not as well suit our day as they did the beginning of the century ? Nitrous oxide has been chiefly used as an ansesthetic in dentistry, and seems eminently suited in every respect for this work. In general surgery, cases are recorded in which, by alternating it with air, insensibility has been kept up for eight minutes, twenty minutes (Dr Marion Sims), sixteen minutes (Dr Colton) ; and in this country, eight minutes thirty seconds (Dr Regg), twenty minutes (Mr Fox).