Source: Snow, John. London Med. Gazette, vol. 43,  June 8, 1849, pp. 983-85 (part 11).

On narcotism by the inhalation of vapours

By John Snow, M.D.

Vice-President of the Westminster Medical Society.

PART XI.

The combination of chloroform and ether--of chloroform and alcohol--Chloric ether--Strong chloric ether--New mode of inhaling vapours.

It has been shown in former parts of this essay, that the action of chloroform can be rendered perfectly mild and safe by diluting it sufficiently with air. If the properties of this body were such, or if another body could be met with having such properties, that the relation between its intrinsic power and its volatility would prevent the air from taking up so much vapour, under the usual circumstances of temperature and pressure, as could enable a patient to get an overdose without ample warning, this would be an advantage; as there would then be no fear of accidents in the hands of medical men, even when not armed with a suitable inhaler, and special experience on the subject. This, however, is not the nature of chloroform, and although there are substances of this character, of which I intend to give a further account, they do not possess, at the same time, all the other convenient and agreeable qualities which would enable them to supersede chloroform in the majority of surgical operations. As the most desirable strength of a volatile narcotic liquid, not requiring great care in its use, is between that of chloroform and that of sulphuric ether, it might be supposed that by mixing the two medicines the desired end would be attained: but such is not the case; they have been so mixed by some practitioners, and I have tried them together, but the result is a combination of the undesirable qualities of both, without any compensating advantage. Ether is about six times as volatile as chloroform--that is to say, if equal measures of each be placed in two evaporating dishes kept side by side, at the same temperature, the ether evaporates in about one-sixth the time of the chloroform; and when the two liquids are mixed, although they then evaporate together, the ether is converted into vapour much more rapidly; and, in whatever proportions they are combined, before the whole is evaporated the last portion of the liquid is nearly all chloroform: the consequence is that at the commencement of the inhalation the vapour inspired is chiefly ether, and towards the end nearly all chloroform: the patient experiencing the stronger pungency of ether when it is most objectionable, and inhaling the more powerful vapour at the conclusion, when there is the most need to proceed cautiously.

Chloroform was first employed for inhalation in the form of solution in alcohol, in which state it was called chloric ether. Mr. Jacob Bell was, I believe, the first person who exhibited it,* and it was afterwards employed occasionally in St. Bartholomew's Hospital, and in the private practice of Mr. Lawrence. (*See Pharm. Journ. Feb.). This so-called chloric ether contained from twelve to eighteen per cent of chloroform. When inhaled it yielded a little vapour of chloroform at the beginning of the process. Each hundred cubic inches of air passing over it, would take up, if saturated at 60?, from one and a half to two cubic inches, mixed with some vapour of spirit, and this was enough to produce insensibility if continued of the same strength, but by the time a third part of the liquid was inhaled, the quantity of vapour given off was reduced to less than half a cubic inch, which is insufficient either to induce or keep up insensibility; and when about half the chloric ether had evaporated, the remainder was reduced to spirit and water, with scarcely a trace of chloroform. Consequently, unless the inhaler were frequently emptied and replenished with fresh ether, insensibility failed to be induced; and under any circumstances the use of this preparation was troublesome and expensive.

In some able and interesting articles recently published in the Medical Gazette, Dr. John C. Warren, of Boston, U.S., has recommended a strong chloric ether, containing one part chloroform to two parts alcohol; this would be undoubtedly much more efficient than the ordinary chloric ether; but there is the same kind of irregularity in its effects, as in the case of the weaker preparation. The chloroform [983/984] evaporates chiefly with the first portion of spirit, and when a little more than half the liquid has been used, the remainder contains very little chloroform, and is, therefore, of no use for inhalation, since vapour of alcohol has very little effect.

I had often considered the subject of diluting chloroform with spirit, and since Dr. Warren's papers appeared have given the matter additional attention. I have mixed chloroform in various proportions with alcohol of 92.5 per cent and ascertained the quantity of vapour the compounds would give off. I have also placed these compounds in a current of air, in imitation of what takes place during inhalation, and by measuring the liquid from time to time, and weighing it in the specific gravity bottle, have been able to calculate the changes of composition which take place as evaporation proceeds. In so doing, a correction was made for the small quantity of water in the spirit, the proportion of which increases as the alcohol evaporates. The following table, which is as accurate as can be made without introducing fractions, shows how the proportion of chloroform decreases when it is mixed with an equal volume of alcohol, or with any other quantity marked in the table. For instance, when the hundred parts are diminished to sixty, they constitute the strong chloric ether of Dr. Warren, and the alterations in that compound are subsequently shown. The fourth column exhibits the quantity of chloroform in the mixed vapour that 100 cubic inches of air would take up, if saturated at 60?. The quantity that 100 cubic inches of air will thus take up from pure chloroform, is fourteen cubic inches.

Chloroform and Alcohol.

Alcohol.

Chloroform.

Cubic Inches of Vapour.

100

50

50

8.1

90

48

42

7.8

80

46

34

7.4

70

43

27

6.8

60

40

20

5.9

50

37

13

4.5

40

33

7

2.1

30

27

3

0.9

20

19½

½

0.0

10

10

0

0.0


Dr. Warren recommends the strong chloric ether, in order to prevent the accidents that have resulted from the too rapid action of chloroform. The quantity of vapour of chloroform that air would take up from this compound would, under the usual circumstances of inhalation, not exceed six per cent--a proportion which, I believe, would not cause any sudden accident; but unless the person using it have such skill as would enable him to avoid the risk of accident in using chloroform, he would be liable to fail in producing insensibility with its solution in spirit, owing to its rapidly decreasing strength, and the diminishing quantity of vapour that it gives off: indeed, Dr. Warren has himself experienced the irregularity of the action of strong chloric ether, having failed to induce insensibility with it in two or three cases; but he attributes the failure to a defect of susceptibility in the patients, and he advises the resort to chloroform in such cases. This is virtually yielding the point, and incurring in some cases the very risk which the proposed practice is intended to obviate. A case which occurred recently in Westminster, the account of which had not reached America when Dr. Warren's papers were written, shows that an apparent want of susceptibility does not protect the patient from accident. In that case,* a gentleman, who, as I am informed, had many times used chloroform in the same way before, employed half an ounce on a handkerchief without making the man insensible; but, a fresh supply being obtained an hour or two afterwards, the patient got an overdose, and lost his life, although the quantity used was not greater than on the previous occasion. (* See Lancet, Feb. 24.) When chloroform is given in such a way that the strength of the vapour can be regulated, it is found that there is no appreciable difference in the susceptibility to its action, whatever variety there may be in the symptoms induced previous to insensibility, and in the extent to which it is requisite to carry the narcotism in order to obtain relaxation or immunity from pain; and since it has been shown in the first three parts of these papers, that there is a definite rule for the proportion of chloroform [984/985] and other narcotic vapours in the blood, which applies alike to animals of different classes, it cannot be supposed that any human being could form an exception, since he would have to differ, not only from his own species, but from the animal kingdom in general.

When it is necessary to give chloroform on a sponge, during a surgical operation, it is not a bad plan to use it diluted with spirit, as recommended by Dr. Warren. In two or three recent cases of operation on the face, insensibility having been induced before the operation, by means of the apparatus as usual, it was requisite to employ the sponge to keep the patient insensible during its performance; and I employed a solution of chloroform in spirit, sometimes in equal parts, at other times in the proportion constituting the strong chloric ether. Both preparations answer the purpose very well, and can be employed more freely than undiluted chloroform. I poured, for instance, half a drachm on the sponge at once, in these cases, instead of a few minims.

If the strong chloric ether were used exactly as recommended by Dr. Warren, there would, I fear, be danger of accident from a cause independent of the action of the vapour inhaled. An ounce of the medicine is directed to be poured on a sponge only twice the size of an egg, which must thereby be rendered dripping wet, and should the patient be on his back, there would be risk of some drops of the ether being drawn into the glottis, in a liquid form. I have been informed by the operator of a case in which a patient was threatened with suffocation from a drop of chloroform falling into the throat from a sponge, and the solution of it in alcohol is scarcely less irritating, and would undoubtedly cause spasm of the glottis.

It follows from the above considerations, that, as a general rule, there can be no advantage in using a mixture of two or more substances of different volatility, by any ordinary method of inhalation, since the mixture cannot be uniformly introduced into the circulation. If, however, it should hereafter be found that there is any physiological advantage in combining any vapours, they could easily be given together in any uniform proportion, by a method which I have been employing lately for the exhibition of chloroform in cases in which I wished to be more than usually precise, or to gain a more exact experience. This method consists in putting a definite quantity of liquid to be inhaled into a balloon made of thin membrane, the capacity of which is known, and is not less than two thousand cubic inches, then filling the balloon with air by means of the bellows, and allowing the patient to inhale from it: the expired air being prevented from returning into the balloon, by one of the valves in the face-piece to which it is attached.

(To be continued)

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