On the safe abolition of pain in labour and surgical operations, by anaesthesia with mixed vapours

Front matter

YALE MEDICAL LIBRARY

HISTORICAL LIBRARY

ON THE SAFE ABOLITION OF PAIN

Contents

Chap. page.

I. On some Defects of existing Anaesthetic Processes .. .. 1

II. On the Vaporization of Anaesthetic Fluids 12

Chapter II. On The Vaporization Of Anaesthetic Fluids

It need scarcely be remarked that but for the swift vaporization of fluids possessing an anesthetic property, their influence and usefulness would be greatly impaired, if not destroyed. If, for example, it were necessary to repeat the ancient practice of inhaling the fumes arising from burning substances in order to produce tho narcosis which is necessary for the abolition of pain, it can be little doubted but that anesthetics would be employed only in a very limited degree. The value of alcohol, ether, and chloroform, and of any other fluids used in this capacity, is greatly influenced by their respective volatility. The properties which these fluids possess in affecting the sensibility are, it is true, very different from each other, and boar only a modified relation to their rate of evaporation. But unless that were adequate at the ordinary atmospheric pressure and temperature to enable the air of an inhaler to take up a sufficient dose at each inhalation, however powerful the anassthetic, its utility would diminish in proportion to its low property of vaporization. Thus, the fumes of the plant called Lyeoperdum Girjanteum produce a very safe anaesthesia, but in actual practice the difficulties of easily applying the agent have wholly interfered with its adoption. In like manner opium and Indian hemp might be employed, though not with equal safety, but their fixity of character forbids their convenient use.

The vaporization of anaesthetic fluids at ordinary temperatures becomes consequently of very great importance, and requires careful study. Especially does this become true when we consider the requirements necessary for anaesthesia by the vapours of several fluids blended together. In the Eeport of the Chloroform Committee it would appear that but a few experiments were made upon this important subject, and although that report so strongly urges the adoption of anaesthetic mixtures, it is evident that sufficient care was not exercised in determining the proper rates and order of evaporation of the constituents of these mixtures.

Thus, instead of using absolute alcohol, the alcohol really employed was of the specific gravity of 838 ; in other words, it contained not more than eighty-four per cent, of pure alcohol, the rest being water. The ether* also evidently contained a considerable percentage of alcohol, its specific gravity being as high as 735, that of pure ether not exceeding 720 or 725. The chloroform alone appears to have been good and pure. These facts would go far to vitiate any of the results obtained by the experiments of this committee, and it may here be said that such alcohol, and such ether, are not adapted for any experimental anaesthetic process, even if used separately, simply from the circumstance that they do not furnish a true standard of purity.

It is also very remarkable that in this report only a very indistinct allusion is made to a subject of vital consequence to the success of an anaesthetic mixture — namely, the equalisation of the rate of vaporization of its fluid elements. This is thus conveyed — " Ether is a more volatile fluid than chloroform, and in a mixture of the two the ether evaporates

* In the published Eeport occurs a curious error ; the specific gravity of the ether, 735, having been given to the chloroform, and that of the latter, 141)7, to the ether.

li ON THE VAPORIZATION OF ANAESTHETICS.

more quickly than the chloroform. The relative rate of evaporation of the two was observed by placing a known quantity on a cloth and exposing it to the air; it was then found that the percentage lost was, after exposure for—

3 minutes, ether 89 parts ; chloroform 75 parts ; 15 minutes, ether 93 parts; chloroform 85 parts.

The fact that the constituents of a mixture escape in somewhat unequal proportions, is proved by observing the specific gravity of the mixture before and after exposure, and it was found in all cases that after exposure the specific gravity was to a certain extent increased, proving ether had escaped before chloroform."*

The result, therefore, of this experiment goes to prove that if such a mixture were i nhaled in any quantity, the percentage of chloroform would continue steadily to increase from the first, until, after protracted use, the inhaler would contain very much more chloroform than ether. This will more clearly appear from the experiments narrated further on. It can easily be understood how far such a result interferes with the protective powers exerted by the mixture — the proportion of the heart-stimulant steadily decreasing, and that of the heart-depressant constantly becoming more and more potent. In the writer's judgment this fact is to a great extent fatal to the use of anassthetic mixtures in the fluid form, at any rate for obstetric purposes, or for hospital practice — cases in both which a considerable amount of the mixture passes through the inhaling apparatus.

In this same report no notice whatever is taken of the low vaporizing properties of the alcohol — and especially

* The experiments detailed further on throw very considerable donbt over the accuracy of these results, and 'appear to prove that the ether really escapes in a much larger proportion than that here given.

of such alcohol as was employed in the mixture, containing, as it did, not less than sixteen per cent, of water. A single drachm of the mixture recommended cannot be evaporated from a cloth without exhaling for nearly ten minutes after the chloroform and ether have vanished the characteristic odour of alcohol ; and when this is dissipated the water still remains, sensibly damping the fabric : thus clearly showing the vast inequality in the vaporization of the different ingredients of this fluid. And, necessarily, as the quantity employed increases, so does this inequality become more and more obvious, until at length the absorbent material is quite wet with the heavier parts of the fluid — the more volatile parts of which have escaped before.

The consideration of these facts will furnish one very obvious reason for the small amount of favour with which these anaesthetic mixtures have been received by our profession. They also appear to justify a fresh inquiry into the subject. And although I cannot pretend to minute scientific accuracy in the investigations I have made in the spare moments of busy daily practice, it is hoped that for all practical purposes the results I have obtained are correct and will bear examination ; at any rate they are comparable with each other, and some pains have been taken to give them a useful tendency. What is perhajjs of the most consequence is, that they have led to aa entirely new system of inducing anaesthesia, and that in public and private practice that method has been found to be most safe and effectual.

First, of the Alcohol. It was found almost impossible to procure really pure absolute alcohol, there being no commercial demand for such an article. The strongest commercial spirit was therefore taken, care being had that it contained no compound of methyl. This was first treated with carbonate of potash, and then drawn off and distilled from fused chloride of calcium, and only three-fourths of the distillate was kept for use, the rest being thrown away. In this manner was obtained a very pure and delicate spirit, of a fresh agreeable odour,, of a specific gravity of about 800 to 805, and possessing very volatile properties as compared with such alcohol as is described above. It contained, at specific gravity 800 to 801, little more than two per cent, of water.

Then, as to the Ether. Commercial ether is fairly represented by the specimen employed by the Chloroform Committee, which had a specific gravity of 735. But the purest ether has a specific gravity of about 720. In order to obtain it in this condition, the best procurable commercial etherwas well washed in distilled water, by which its alcohol was removed, and it was then drawn off and distilled from chloride of calcium, at a very moderate temperature, in a water bath. The fluid thus obtained had a specific gravity a little over 720, and was very pleasant to the smell, presenting in this respect a striking contrast to the commercial ether, the smell of which was acrid and pungent.

The Chloroform was that prepared by Messrs. Duncan and Flockhart, from pure alcohol, and possessing a specific gravity of about 1495. It was fresh and agreeable to the smell, and may be taken as a good standard specimen of the best description of chloroform.

The specific gravities were ascertained with as much care as I had power to bestow, and were taken, and the experiments performed, at a general temperature of 60° Fahr., the barometric pressure being 30.

Thus the three most valued anaesthetic fluids were obtained in a state of definite purity. My object was not so much to obtain a standard of ideal excellence — for which purpose absolute ether and absolute alcohol in a chemical sense, and chloroform of still higher specific

ON THE VAPORIZATION OF ANiESTHETICS. 17

gravity would have been requisite — as to deal with fluids which can easily be obtained with a little care for practical use, and of sufficient volatility and purity to answer the purpose of anaesthetic induction. Any operative chemist could without the least difficulty supply fluids of the quality described, by the gallon, for professional use.

It will be manifest, on consideration of the nature of the fluids thus obtained, that a series of good standard specimens was obtained of almost the highest volatilizing power, and therefore the best fitted for the composition of anassthetic mixtures. If, therefore, the idea of combining these fluids into one mixture were a good working thought, we had here the best means of carrying it into operation.

In the first place, their comparative volatility at a temperature of 60° was ascertained in the following manner — a few drops of each fluid were passed up into the Torricellian vacuum of different barometer tubes, and the depression of the mercurial column carefully observed. The amount of vapour capable of being given off by the respective fluids at the temperature given, was thus read off at a glance — it being well understood that* " when a liquid evaporates into a vacuum the point of greatest density (of its vapour) is attained at once, while with a space filled with air some time elapses before this happens ; the particles of air appear to oppose a sort of mechanical resistance to the rise of the vapour." In this way a ready estimate of the differing volatility of these three liquids were obtainable. The vapour of Alcohol was given off in such a quantity as to depress the column of mercury one inch and five-eighths. The vapour of Chloroform depressed the column in the adjoining tube to 6 inches. The vapour of Ether depressed it in a third tube 17-^ inches.

It was thus rendered evident to the eye that at the same * Fownes.

c temperature these three fluids gave off vastly different measures of vapour — that afforded by the ether, for instance, being more than eight times as much as that given off by alcohol, and nearly three times that given off by chloroform ; and, though it be certainly true that each of these liquids gives off vapour of varying tension at varying temperatures, the above may be taken as sufficiently accurate for the purpose of our comparison.

The effect of mixing these three fluids was tried, and the experiments yielded several very curious and interesting results. Into the barometer tube containing the alcohol, a few drops of chloroform were carefulty introduced, and the fluids were mixed by agitation. The result was singular — the mercurial column only descended to 5 inches, instead of 6, which may be taken to represent the tension of the pure chloroform atmosphere. It was thus evident that the alcohol exercised a sort of restraint upon the volatilization of the chloroform to the extent of about an inch of the mercurial column.

Into the tube containing pure chloroform vapour, the depression being about 6 inches, a few drops of ether were introduced, and the fluids agitated together. Again, a singular result was observed — the depression of the column sank from 6 inches to 12 inches, or about only two-thirds of the full amount producible by ether alone. Thus proving that the mixed fluid resulting had a twice greater volatility than chloroform, and one-third less than that of ether.

Into the tube containing ether vapour, and standing at 17* inches of depression, a little alcohol was introduced. The effect was equally remarkable — the mercurial column actually rose from 17i inches to about 10. From which it was evident that over this fluid also the alcohol exercised an influence of restraint, reducing its volatility and the consequent tension of its vapour. That this influence was

ON THE VAPORIZATION OF AN/ESTHETICS. 19

really exerted by the alcohol was proved by another very striking experiment. A few drops of distilled water were passed into the combined alcohol and ether space, and the fluids well shaken. The effect was instantly to liberate the ether vapour so that it depressed the mercurial column once more to \1\ inches, showing that the water exercised over the alcohol in this combination the same property of solution and absorption which is noticeable in washing ether in the ordinary way.

I then found that some differences could be obtained by altering the proportion of the fluids mixed together. Thus, if the proportion of the ether were increased to two or three times that of the alcohol, an additional depression of about an inch or so was obtained ; and this doubtless would occur in an increasing ratio if the experiment had been carried farther. As far as possible the experiments detailed were conducted with equal portions of the respective fluids employed.

It appeared desirable to test the tension in vacuo of the vapour of mixture A of the Chloroform Committee, and this was done as in the former experiments — the fluids being first mixed together in the proportions given, and then injected in a small quantity into the barometer tube. It is necessary, however, to remember that the ether and alcohol employed in this mixture were of a much higher standard of purity than that used by the Committee. The result was extremely curious — the mercurial column was depressed to the extent of 8i inches, or, as nearly as possible, the half of that which would have arisen from ether alone. The mixture, therefore, in vacuo, possessed a volatility intermediate between that of alcohol and that of ether alone ; and theoretically it would seem well adapted for its purpose. On injecting a little more ether the depression sunk to 12 inches. It is doubtless the alcohol, in great measure, which affects the volatilization of this mixture, holding it in check to a considerable degree, but only so long, as will shortly appear, as the experiment is conducted in a confined and vacuous space.

The general conclusions which may fairly he drawn from these investigations is, that so far as evaporation in vacuo is concerned, a mixture of these volatile liquids possesses a different volatility from that of either of them separately, and might, therefore, seem to favour the theory of an anaesthetic mixture of uniform evaporation. But since the rate at which evaporation takes place in vacuo is not the same as that which occurs in the open air, it remained to examine the behaviour of the same substances under this condition — the condition in which, in fact, and in which alone, they are available for our practical employ.

The inquiry was thus prosecuted.* The anaesthetic mixture A of the Chloroform Committee, consisting of, by measure, alcohol one part, chloroform two parts, and ether three parts, was used, and ten drachms were put into a small retort. This was placed in a water-bath, kept at a temperature of 130° Fah. The specific gravity of the mixture was about 1000. After a lapse of twenty minutes a sample of the distillate was taken and carefully weighed, it was found to have a specific gravity of 900. In half an hour more another sample was taken, and the specific gravity of this specimen was found to be 1000. When all but about one fluid drachm was distilled, the specific gravity of the last sample had risen to 1100. On examining the

* The writer has a fear that he may be thought, from the text, to have conducted these simple experiments with all the rigid accuracy of philosophical investigation. Such was not the case. Though they are believed to be true representations of certain leading facts, they are not pretended to be more than this.

residue in the retort, it was found to be chiefly unevaporated alcohol, with a small quantity of water.

The examination of these products showed that the first sample consisted chiefly of ether and chloroform, with a mere trace of alcohol — the ether being greatly in preponderance. The specific gravity of pure ether being 720, and of chloroform 1495, and that of this sample 900, and the specimen being found to consist chiefly of ether and chloroform, it may be fairly concluded that the proportion of its ingredients was, of ether, little less than seven-eighths, and of chloroform one-eighth, with a trace of alcohol. In the second sample the proportions were reversed, and it consisted chiefly of chloroform and alcohol, with a little ether. From the third sample the very odour of ether was gone entirely, and it consisted of chloroform and alcohol in pretty equal proportions. In order to completely volatilize the two latter specimens, it was found necessary to increase the heat of the bath from 130° to nearly 200°.

Poured on a cloth, in order to test their powers of evaporation, the first of these samples at first exhaled chiefly ether, the vapour of which came off with some of the chloroform. Then, when this had evaporated, a strong odour of chloroform remained for a short time, and Bnally vanished, leaving only a faint soupcon of alcohol behind. The second sample lost its ether still more quickly ; the odour of chloroform remained longer, and was more decided, and after its dissipation it left a very strong and characteristic smell of alcohol behind. The third sample had no odour of ether at all, smelt strongly of chloroform, and when that had vanished, a long-remaining smell of alcohol was left, which extended over several minutes.

When agitated in a test tube with distilled water, the first sample, which consisted chiefly of ether, with a small portion of chloroform, separated itself from the water, and

22 ON THE VAPORIZATION OF ANESTHETICS.

remained in a semi-transparent stratum, the water appearing to hinder the union of the ether and chloroform. The second and third samples became quite milky, showing, as in Mialhe's test, the blending of the alcohol and chloroform together.

To a fair extent, this gentle distillation of the anassthetic mixture represents the order and sequence of volatilization of its different ingredients, and it proves that these ingredients escape from the mixture in that order which is indicated to us in another way — namely, by their differing boiling points. Thus ether, which is converted into vapour at below 96°, came off first ; then chloroform, which boils at 141°, and lastly, alcohol, which boils at 172°. In all probability had the distillation been conducted at a lower temperature than that of the water-bath, 130°, the proportion of ether would have been found to be still higher than that given above.

Since, however, these fluids give off vapour at all temperatures, though in a very different ratio as to quantity and velocity, it was to be expected that in the distillates a portion of the three ingredients was discoverable. Even in the first a trace of alcohol, for example, was found present ; but this does not affect the conclusion' which must be arrived at — namely, that this anaesthetic mixture does not equally part with all its constituents, and that these must be arranged in very different proportions to perfectly effect this object.

It would no doubt be possible so to adjust the proportions of alcohol, chloroform, and ether as to obtain a mixture which would volatilize equally. But in order to effect this, it would be necessary to reduce greatly the proportions of the alcohol and chloroform, in order to render their alliance with their fugacious companion permanent. And the result of this would be that the properties of such

OS THE VAPORIZATION' OF ANAESTHETICS. 23

a mixture would so nearly resemble those of ether alone as to defeat the very purpose of these combinations.

The whole subject of the vaporization of these fluids in union, and of the behaviour of different combinations of them, is interesting, and deserves a far more careful study than could be given by the writer of this little book. The restraining influence of the alcoholic element over both ether and chloroform, so manifest in the barometric vacuum, appears to be almost — it is certainly not wholly lost when evaporation into air takes place. A precisely analogous influence is indeed exerted over the alcohol by water.

The vaporization of these anaesthetics into a vacuum, and on distillation at a very moderate temperature, having thus been glanced at, a few investigations were made into their evaporation at ordinary temperatures— as, in fact, it occurs for the practical purpose of inducing insensibility. At a temperature of 65°, half a drachm of ether alone was poured on a cloth about 4 inches long by 2 in width. It was completely dissipated at the expiration of ninety seconds. The same quantity of chloroform was poured upon a similar fabric, and it was found that nearly five minutes elapsed before it was all evaporated. A similar quantity of alcohol was then poured on the cloth, and nearly twelve minutes were consumed in its evaporation, and the lint was damp with a little unvaporized water. It was found that if equal parts of alcohol and ether were mixed together, the restraining influence of the alcohol over the volatility of the ether was very obvious. Fifteen minims of each being mixed together, and poured on the same cloth, it was found that the ether took longer in evaporating than when that fluid was used by itself. Thus it was nearly two minutes before all the ether was dissipated — the same quantity (15 minims) vanishing in seventy-five seconds wheu used alone. The residual alcohol occupied nine minutes in its evaporation.

The evaporation of the anaesthetic mixtures, A* and C, was now investigated. The temperature being 65° and the barometer at 30, a piece of lint of the same dimensions as before was used. Half a drachm of mixture A, weighing about 21 grains, was poured upon it. At the expiration of about seventy-five seconds all the ether had evaporated, with a little chloroform. At the end of four minutes all the chloroform was dissipated, with some of the alcohol ; and there then remained on the fabric, alcohol (with a trace of water) to the amount of 2 J grains. At the expiration of six minutes this was reduced to 1£ grain. A second quantity, and a third, and a fourth of the same mixture were poured on the same cloth at intervals of about ten minutes, and it was found that after each sucessive dose the residual unevaporated fluid accumulated in the cloth to tho amount of 1 A grains, or one-fourteenth of the total quantity each time.

The result of several experiments proved that — 1, All the ether of the mixture, with a small portion of chloroform, and still less of alcohol, was exhaled in a little more than from sixty to seventy-five seconds ; 2, That chloroform and alcohol, the former preponderating, continued to evaporate for three or four minutes more ; 3, That the residual alcohol was dissipated in about one and a half or two minutes more ; and 4, That a trace of water, with some alcohol, weighing in all about li grains, was left in the cloth, making it sensibly damp to the touch.

Thus, out of the six or seven minutes occupied by the evaporation of the half drachm of fluid, the first was occupied chiefly by the ether, the next three by the chloroform, with a little alcohol, and the last by the alcohol alone. In

* It will be remembered that the anaesthetic mixture prepared with the fluids used in these experiments was of a nature much more favourable to its volatilization than that used by the Committee on Chloroform.

ON THE VAPORIZATION OF AN2ESTHLT1CS. 25

an inhaler, the patient would have breathed, for one-fifth of the time, chiefly the vapour of ether ; for the next threefifths, that of chloroform, with a little alcohol ; and at last only the vapour of a minute quantity of alcohol. In all probability, as the doses were repeated, less and less alcohol would be inhaled, because of the constantly increasing accumulation of water (from both alcohol and ether), which would exert its attractive influence over that fluid, and so hinder its vaporization. It would be difficult to obtain a more clear expression of the uncertainty of anaesthetic mixtures in the fluid form than is found from a consideration of these experiments.

The mixture C, consisting of ether two parts and chloroform one part, was then tried. Half a drachm of this was employed over the same evaporating surface. At the expiration of from ninety to one hundred seconds, nearly all the ether had evaporated. From this to the end of three minutes, the evaporation of chloroform proceeded, and at the close of four minutes all had evaporated, a faint smell of alcohol being left behind for a few seconds — a result of some slight impurities in either ether or chloroform, or in both. Sixty minims were then used, and it was found that before the expiration of from two and a half to three minutes, all the ether had disappeared, and that from six to seven minutes elapsed before all the chloroform had evaporated.

This same mixture (C) of ether and chloroform was subjected to a gentle distillation at a temperature not exceeding 120°. The specific gravity of the mixture before distillation was 990. The distillate taken at the end of half an hour yielded a sample of specific gravity 910. The specific gravity of the liquid left in the retort was then taken, and it amounted to 1120. Thus in the clearest way showing the rapid volatilization of the ether and the slower evaporation of the chloroform. The first sample, mixed with water, immediately separated into a clear supernatant layer, evidently consisting chiefly of ether, with some chloroform. The residual fluid, treated in the same way, exhibited the very opposite phenomenon — the water now being in a clear layer at the surface ; thus proving that much of the heavy fluid at the bottom was unevaporated chloroform, mixed with some ether, thus affording a most decisive testimony to the fact I have been contending for — namely, the inequality of the vaporous exhalations of these anaesthetic mixtures.

It is true that the temperature of the inhaling apparatus sinks much below that of the surrounding air, and this must be remembered in considering the results here obtained. But in all probability the lower the temperature of evaporation, the more unequal would its effects become on these fluids, and a still larger difference in their relative proportions of escape would be manifested.

Before closing the present chapter, it may be fairly de j duced, from the inquiry here detailed, that —

First. The ingredients of the anassthetic mixtures evaporate in a great degree, independently of each other, and in extremely differing quantities.

Second. That though alcohol exerts, in vacuo, a powerful influence in restraining and equalizing their vaporization, this influence is in a great measure annulled on evaporation into free air, as in an inhaler.

Third. That the only method of obtaining a true anaesthetic mixture of fluids is by consideration of the respective volatility of its ingredients, and so adjusting their proportions as to provide that all should evaporate simultaneously.

Fourth. But as this can only be done by a very great reduction of the quantities employed, both of alcohol and chloroform, then the object of the mixture is entirely frustrated, and it is reduced in its properties to one similar to

ON THE VAPORIZATION' OF ANESTHETICS. 27

ether only — the most volatile of the ingredients always taking precedence of the rest.

Fifth. That if impure alcohol and ether are used, these defects of unequal volatilization become still more exaggerated, and the result vitiated by the water left behind after evaporation.

Only a conviction of the real value of a mixture of anaesthetics would have induced me to discuss this subject at the length of the present chapter, or to have given the requisite time to its investigation in the numerous experiments fiom which these conclusions have been derived. But acting on a sincere belief that there lay a real power for good under the recommendation of the Chloroform Committee on this head, and that anaesthesia might be more safely induced \>y a definite mixture of the vapours of these three substances than by any other known means, I shall have obtained my object in demonstrating the fallacy of the method advised and hitherto practised, if it leads others to adopt a plan at once easy to put in practice, of a reasonable quickness in operation, and of as perfect safety in operation as can be conceived possible.