Source: Snow, John. London Med. Gazette, vol. 42, Sept. 8, 1848, pp. 412-16
On narcotism by the inhalation of vapours
By John Snow, M.D.
Vice-President of the Westminster Medical Society.
Description of the physiological effects of chloroform, continued--when inhaled it acts on the nerves as well as on the nervous centres. Phenomena attending death from chloroform--its action on the heart of the frog.
The advent of the third degree of narcotism is marked by cessation of all voluntary motion. Usually the eyes become inclined upwards at the same time; and there is often a contracted state of the voluntary muscles, giving rise to more or less rigidity of the limbs. This contraction is greater and more frequent from chloroform than from ether, and, by affecting the muscles of the jaw, it sometimes causes a considerable obstacle to operations on the mouth. As there are no signs of ideas in this degree, I believe that there are none, and that the mental faculties are completely suspended: consequently the patient is perfectly secured against mental suffering from any thing that may be done. It does not follow, however, that an operation may always be commenced immediately the narcotism reaches this degree, for anæsthesia is not a necessary part of it; and unless the sensibility of the part to be operated on be suspended, or very much obscured, there may be involuntary movements sufficient to interfere with a delicate operation--not merely reflex movements, but also coordinate actions, such as animals may perform after the cerebral hemispheres are removed, the medulla oblongata being left. Under these circumstances an operation usually causes a contraction of the features expressive of pain, and sometimes moaning or cries, but not of an articulate kind. Whether or not these signs are to be considered proofs of pain, will depend on the definition given to the word; and if they do not interfere with the operator, or influence the recovery, they can be of no consequence as there is no pain which has an existence for the patient. To obtain anæsthesia when it does not exist in this degree, and thus to prevent these symptoms if we desire, it is not necessary to carry the narcotism further, but only to wait at this point a few moments, giving a little chloroform occasionally to prevent recovery, and allow time for it to permeate the coats of the small vessels, and act more effectually on the nerves. The sensibility of the conjunctiva is a correct index of the general sensibility of the body; and until it is either removed or very much diminished, an operation of delicacy cannot be comfortably performed. Accordingly, in administering chloroform, as soon as the patient has inhaled sufficient to suspend voluntary motion, I raise the eyelid gently, touching its free border. If no winking is occasioned the operation may begin in any case, but if it is I wait a little time, till the eyelids either become quite passive or move less briskly. The state of the eye itself is observed, by this means, at the same time. It is usually turned up, and the pupil contracted, as Mr. Sibson has stated,* in the condition which I term the third degree of narcotism. (*Med. Gaz., Feb. 18. I think that the turning up of the eyes is not so constant as Mr. Sibson believes, as I have been unable to observe it in some patients at any stage.) The vessels of the conjunctiva, also, are sometimes injected, but more frequently they are not.
Dr. Hughes Bennet, in his able report on the properties of chloroform,† argues that the sensibility of the nerves is not suspended under its influence, because respiration, circulation, and uterine contractions continue, which could not be the case if the sensibility of the nerves connected with these functions were destroyed. (†Monthly Journal, Jan. 1848.) This argument would have some weight if the nerves of common sensibility did not differ from those of the organic system, or those which arise from the respiratory tract of the medulla oblongata; but as the case stands, it has none: and there is no more difficulty in conceiving a variable degree of susceptibility and of resistance to the effects of chloroform in different sets of nerves, than in different nervous centres. A careful observation of cases shows that the amount of local insensibility by no means keeps pace with the degree of sopor or coma, but [412/413] is later in coming on and going off, and varies in amount in different patients; and as we know that chloroform, like other narcotics, produces some effect on parts to which it is locally applied, the conclusion seems irresistible, that it acts on the nerves as well as on the nervous centres. This view of the subject explains some circumstances which before seemed inexplicable; such as that of the patient recovering his consciousness, and telling the bystanders that he does no feel what is being done. For, whilst the vapour is escaping from the blood by way of the lungs, there is no difficulty in understanding how the brain may recover its influence sooner than the branches and peripheral expansion of the nerves; since, in the brain, not only is the circulation more rapid, but there is little, if any, lymph external to the vessels; whilst, in the body at large, the chloroform, having transuded through the coats of the capillaries into the extra-vascular liquor sanguinis, remains there for a little time, acting on the nervous fibrillæ, before it can pass again by endosmose into the vessels. It is in young subjects, in whom, connected with the more active process of nutrition, the quantity of lymph external to the vessels is greatest, that the general insensibility most frequently remains, whilst the cerebral hemispheres are resuming their functions.
In the fourth degree of narcotism there is relaxation of the voluntary muscles, together with general insensibility. I am better acquainted with this degree as induced by ether than by chloroform, for with the latter agent the third degree appears to encroach somewhat on this; chloroform seeming to differ from ether, and approaching somewhat in its effects to benzin and bisulphuret of carbon, which, we have seen, are not attended with muscular relaxation at any stage of their effects. Accordingly, I am inclined to prefer the use of ether, to assist the reduction of dislocations and strangulated herniæ. There is, however, often sufficient relaxation of the muscles to effect these objects even in the second degree of narcotism, especially if the effect have been kept up a little time. I was at one time inclined to believe that the functions of the spinal cord were more or less suspended in this degree, since reflex movements cannot be excited by any impressions made on the eyelids, or general surface of the body; but these reflex movements are absent in every degree of narcotism, when the common sensibility is abolished, and, thereby the circumstance is best explained attributing it to the narcotism of the nerves. Other functions of the spinal cord certainly remain; for the sphincters of the bladder and rectum continue contracted, and respiration goes on. The sensibility of the glottis continues, apparently unimpaired, in this degree of narcotism, but that of the pharynx is probably suspended; for, in operations on the mouth and nose, the blood sometimes finds its way into the stomach, without any visible act of swallowing. This takes place frequently, when the narcotism does not exceed the third degree. In these cases, it probably runs along the channel there is at each side of the epiglottis. The breathing is not unfrequently attended with some degree of stertor in the fourth degree; and the reason why one does not often meet with stertor in exhibiting chloroform, is, that one seldom carries the narcotism so far. There is a little stertor occasionally, even in the third degree of narcotism; and this symptom, and rigidity of the muscles, are met with altogether. There may be simple snoring in any degree of narcotism, and even in the natural sleep which often follows the state of insensibility; but it never comes on during the first minutes of the inhalation of chloroform, unless the narcotism reaches to the third or fourth degree. The iris is less sensible to light in this degree than under ordinary circumstances, and the pupil is about the usual size. I have never observed it widely dilated, or totally insensible to light.
I have not mentioned the pulse in the above outline of the action of chloroform on the human subject, as it is not indicative of the amount of narcotism. It is usually somewhat increased in force and frequency, as it is by a moderate amount of fermented liquor. This effect subsides with the effect of the vapour; but I have not remarked the pulse become slower after chloroform than it might be expected to be, in the same patient, in a state of perfect repose. 52 is the slowest pulse I have met with, and that was in a healthy [413/414] man. This moderate acceleration is, I believe, the only direct effect of chloroform on the pulse. Indirectly, it may affect it in other ways. If, for instance, the breathing is interrupted by the pungency of the vapour, or from any other cause, the pulse becomes small and frequent, and when sickness is induced, it is diminished in force. If it is very frequent at the beginning of the inhalation, from mental perturbation, as is often the case, when the patient is about to undergo an operation, the frequency diminishes, as all anxiety departs with the loss of consciousness.
When animals are killed with chloroform, and not too abruptly, there is a stage between the fourth degree and the cessation of respiration in which the breathing is difficult, and sometimes slow and irregular. This I have named the fifth degree of narcotism. It is not every irregularity of breathing which is to be considered indicative of this degree,--for patients occasionally hold their breath for a short time, on account of the pungency of the vapour, and sometimes also, without any evident cause, in the second or third degree; but that need be no source of alarm. The fifth degree of narcotism, on the contrary, is the commencement of dying. I have only met with it in animals. It is sometimes accompanied with convulsive movements of the limbs--a result I never witnessed from ether.
Phenomena attending death from chloroform.
When the animal is made to breathe vapour of chloroform of such a strength that the respiration is stopped in the course of a few minutes, the heart continues to beat for a short time, and the circulation ceases only, as in asphyxia, for want of the respiration, without the heart having been brought under the influence of chloroform. The reason of this, as I explained, with respect to ether, on another occasion,* (*On the Inhalation of Ether, p.81.) is not that the vapour is incapable of affecting the heart, but because a smaller quantity suffices to arrest the respiration, and the process of inhalation ceases, without the heart and blood vessels being narcotized. The two following experiments illustrate and prove these points:--
Exp. 41.--A nearly full-grown rabbit was placed in a jar containing 1600 cubic inches, with 64 grs. of chloroform, being four grains to each 100 cubic inches. At first it tried to get out, afterwards it struggled involuntarily, and then sank slowly down, and lay, when four minutes had elapsed, in a flaccid condition, breathing naturally. It did not stir afterwards, except from a slight convulsive twitch of its paw once or twice. In three or four minutes more, the breathing became slower, and ten minutes after it was put in, it breathed its last. It was immediately taken out, and the stethoscope applied to the chest. The heart was heard to beat for between two and three minutes, at first nearly as rapidly as before the experiment, but more slowly and less audibly towards the end. The chest was opened a few minutes afterwards, and feeble rhythmic contractions of both auricles and ventricles were observed, not strong enough to expel the blood with which the heart was filled, but not to distension. These contractions continued unabated during the half hour the inspection continued. The lungs were perfectly healthy, and not congested. Next morning the body was rigid, and the blood in the heart and adjoining vessels coagulated. The sinuses in the cranium were filled with blood, and the vessels on the surface of the brain were somewhat injected, but not those in its substance.
Exp. 42.--Four and a half grains of chloroform were introduced into a jar containing 600 cubic inches, being three quarters of a grain to each 100 cubic inches, and, the vapour having been equally diffused, two frogs were put in. They tried to climb up the side of the jar, as if wishing to make their escape, and one or the other occasionally ceased to breathe for a minute or two, probably from disliking the vapour, but commenced to breathe again. In about five minutes the efforts to escape ceased, and they only moved to adjust their equilibrium when the jar was disturbed. They were now breathing regularly, and continued to do so till about ten minutes after their introduction, when all voluntary power ceased, and the breathing began to be performed only at intervals. They were allowed to remain till half an hour had [414/415] elapsed, during the last ten minutes of which time no respiratory movement was observed in either of them. On taking them out, and laying them on their backs, the pulsation of the heart were observed on each side of the sternum. These pulsations were more distinct from the lungs being apparently empty. Now an experiment with chloroform on the frog does not necessarily cease with its pulmonary respiration, for it is capable of both absorbing and giving off vapour by the skin. Accordingly I continued the experiment on these frogs, placing one of them back again, in the course of two or three minutes, in the same jar, with three grains of chloroform, and the other in a jar of 400 cubic inches capacity, with five grains. They were laid on their backs, and the heart of the former one, in air containing half a grain of chloroform for each 100 cubic inches, continued to beat distinctly and regularly, 45 times in the minute, for four hours that it remained in the jar, and it was not observed to breathe during the whole time, although it was watched almost constantly. The respiration commenced again within half an hour after its removal. In about an hour it recovered its power of voluntary motion, and it was not injured by the [l]ong narcotism.
The pulsation of the heart of the other frog, in air containing a grain and a quarter of chloroform to each 100 cubic inches of air, became slower and more feeble, and in a quarter of an hour could not be observed. The frog was left in the jar a quarter of an hour longer, and removed when it had been in half an hour. The under part of the thorax was immediately opened sufficiently to expose the heart. It was moderately full of blood, but not contracting at all, and it did not evince the least irritability on being pricked, either now or after exposure to the air for some time. It is evident that the heart of this last frog became paralysed by the absorption into the blood of more vapour, in addition to the quantity that was sufficient to arrest the respiration. The temperature of the room during this experiment was 65.
The effect of chloroform on the heart of the frog is further shewn by the next experiment.
Exp.43.--A frog was placed in the jar containing 600 cubic inches, with six grains of chloroform. In twenty minutes the respiration had ceased, but the heart continued to pulsate strongly. At the end of three-quarters of an hour the pulsations were more feeble, and had diminished from 40 to 30 in the minute. An hour and five minutes from the commencement of the experiment, no movement of the heart could be observed. The frog was taken out of the vapour, and a portion of the sternum and integuments removed, so as partly to expose the heart, when it was found to be still contracting, with a very feeble undulatory motion. This motion increased in force, and, in a quarter of an hour after its removal, the heart was pulsating regularly and strongly, the ventricle apparently emptying itself perfectly. When the frog had been out twenty minutes, it was placed again in the same jar, with the same quantity of chloroform. In about ten minutes the heart’s action began to fail again, and in about twenty minutes the slightest movement could no longer be perceived in it. The frog was immediately taken out, and the ventricle of the heart was pricked with a needle. In a few seconds a slight quivering was observed,--whether the result of the prick is not certain, and the action of the heart became gradually reestablished as before. It was arrested a third time by exposure to the vapour; and although, in its third removal, the anterior extremities of the frog had become rigid, the heart resumed its action partially, and continued to contract feebly for three or four hours after the rigidity of death had invaded the body and limbs of the animal.* The temperature of the room was 62° during this experiment. (*The setting in of rigidity in the frog is accompanied by a partial change of posture, and the contraction is sometimes strong enough to move the whole body.)
We learned from some of the experiments detailed in the early part of this paper, that the presence in the blood of one twenty-second part as much chloroform as it would dissolve, had the effect of arresting the respiration. From the last experiment we can determine how much it takes to stop the action of the heart. One grain of chloroform, as was stated before, produces 0.767 of a cubic inch of vapour; [415/416] and at 62°--the temperature during this experiment--air, when saturated, contains 13.8 cubic inches. Therefore 0.767 ÷ 13.8 gives 0.0555, or one-eighteenth of what the blood would dissolve as the quantity which has the effect of arresting the heart’s action.
(To be continued)
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