On chloroform and other anæsthetics: their action and administration

by John Snow

In the human being and all other creatures of warm blood, any vapour which is inhaled and absorbed in the lungs passes at once to the left side of the heart, and as the coronary arteries are the first branches given off from the aorta, the heart must, during the process of inhalation, be always a very little in advance of the rest of the body, as regards the amount of vapour to which it is subjected. This, however, is no source of danger, as regards chloroform, if the inhalation takes place in a gradual and uniform manner; for the heart being able, as shown by the above experiments on frogs, to bear a greater amount of this narcotic than the brain, its action continues even after respiration has ceased, if the vapour is added only by a little at once to the blood, as it passes through the lungs. But if the air which the patient breathes be too highly charged with vapour, it is easy to understand how the sensibility of the nerves of the heart may be paralysed, notwithstanding their power to bear somewhat more of this agent than the brain and nerves of respiration. I calculated (p. 74) the quantity of chloroform which would suffice to arrest respiration in the adult of average size to be thirty-six minims, provided it were equally diffused through the circulation; but supposing a patient breathes, at any time, air containing ten per cent. of vapour of chloroform, a considerable part of this might enter the lungs at a very few inspirations, for thirty-six minims of chloroform occupy only 37·5 cubic inches, and would be contained in 375 cubic inches of air, and might be breathed in less than a minute; but for the whole of the blood to pass through the lungs occupies a considerable time—I believe about four minutes in the adult—and therefore the portion of blood which is passing through the lungs, at the time when vapour of the above strength is inhaled, must become much overcharged with chloroform, making every allowance for the portion of vapour which is expired again, without being absorbed.

I have observed the manner in which the breathing and circulation ceased in a great number of instances, with the stethoscope applied to the chest of the animal, when the quantity of chloroform contained in the air it breathed was known, and have notes of the result. The animals were chiefly cats, which would otherwise have been killed by prussic acid, or in some other way. In every instance in which the quantity of vapour in the air breathed by the animals was from three to six per cent., the respiration ceased whilst the sounds of the heart were still very distinct, as in Experiment 23, related above; in many instances the heart continued to beat from two to three minutes after the breathing had ceased, and, in a great number of instances, there were one or more gasping inspirations just at the moment when the sounds of the heart ceased. In many cases these gasping inspirations caused the action of the heart to return, as in Experiment 23, if the animal had been withdrawn from the chloroform; but this was not always the case; and if the chloroform was still breathed during these gasping efforts, all signs of life immediately ceased in every instance.

When, on the other hand, the air breathed by the animals contained eight or ten per cent., or upwards, of vapour of chloroform, the action of the heart was always seriously affected and rendered extremely feeble, if it did not actually cease, at the time the breathing was arrested. In several instances, indeed, the sounds of the heart entirely ceased before the breathing, as in Experiment 25; and although the chloroform was withdrawn, in this and many other experiments, the moment the heart ceased to beat, and fresh air was drawn in by inspiratory efforts, it very rarely had the effect of restoring the heart’s action, although this happened so frequently when that organ had gradually ceased to act on account of suspension of the breathing, by the effect of more diluted vapour.

In order to see more precisely the action of the vapour of chloroform on the heart, when not sufficiently diluted, the chest and pericardium were opened on four occasions, in cats and a rabbit, and chloroform was exhibited by artificial respiration. I was assisted by Mr. Peter Marshall in these experiments, and the following is the account of one of them.[^[60]]

Experiment 28. A young rabbit, rather more than half-grown, was made insensible by breathing air charged with four per cent. of vapour of chloroform in a large jar. The trachea was then opened, and a tube was introduced and tied. The lungs and heart were then exposed, by making an incision and removing the lower half of the sternum, with the adjoining part of the cartilages of the ribs on each side. The front of the pericardium was also cut away, to expose the heart. Whilst these operations were performed, artificial respiration was kept up by means of a bladder of air attached to the tube in the trachea. The heart contracted vigorously and quickly, and the lungs were of a light red colour. The rabbit was beginning to show signs of returning sensibility, when the bladder of air was changed for one containing ten per cent. of vapour of chloroform. The bladder contained 125 cubic inches, and twelve minims of chloroform were put in before it was filled with the bellows. Three or four inflations of the lungs only were made, when I perceived that the heart was beginning to be affected, and I changed the chloroform for a bladder containing only air. These three or four inflations of the lungs with chloroform, had the effect of causing the right cavities of the heart to become distended with blood, and its pulsations to become much slower. In two or three minutes, however, the action of the heart was quite reestablished by the artificial respiration, the pulsations being vigorous and frequent, and the ventricles being apparently emptied at each contraction. The bladder charged with ten per cent. of chloroform was again attached, and artificial respiration was made with it. The right ventricle began almost immediately to become distended; and, by the time that eight or ten inflations of the lungs had been made, the contractions of the heart were very slow and feeble. Artificial respiration with air was resumed, but without the effect of restoring the action of the heart. The lungs were observed at the time when the right ventricle was becoming distended, and it was noticed that their colour was unchanged. They afterwards became paler, as the artificial respiration was continued after the ventricle had ceased to empty itself. No contractions of the diaphragm were observed after the first inflation of the lungs with chloroform, and the rabbit did not gasp at any time; whilst the cats were observed to make a few gasping efforts at the time when the heart’s action was ceasing.

The circumstance of the lungs not changing in colour at the moment when the right ventricle was becoming distended, which was observed in the cats as well as in the rabbit, shows that the distension arose from the failure of the contractile power of the heart, and not from impediment to the pulmonary circulation; for, in the latter case, the lungs would have become congested, and of a deeper colour. In one of the cats, it appeared to me that the left, as well as the right ventricle, was distended with blood; but this distension of the left ventricle did not continue.

In the Experiments 24 and 25, related above, the animals were first made insensible by vapour of moderate strength, in order to keep them quiet for the application of the stethoscope whilst the stronger vapour was inhaled, but when animals are made to breathe air containing ten per cent. or so of vapour of chloroform from the first, death takes place in the same manner, i. e. by the direct action of the chloroform on the heart. Under these circumstances the creatures die suddenly, after a brief interval of agitation and excitement, without previous insensibility. This is what has happened in some of the accidents from chloroform, to be related further on; whilst in many cases death has happened after a longer or shorter period of insensibility.

In many of the fatal cases of inhalation of chloroform the alarming symptoms commenced whilst the patient was still inhaling, but in a considerable number there was no sign of danger until after the inhalation had been left off; and this is a result which may be imitated on animals. The two following experiments, which were made at Dr. Sibson’s on December 27th, 1849, illustrate this point.

Experiment 29. The subject of this experiment was a young guineapig, about half-grown. Ten or twelve drops of chloroform were put into a short bent metal tube, lined with bibulous paper, which formed part of an inhaler, and one end of the tube was applied to the animal’s nose, which closed it. The guineapig consequently breathed backwards and forwards through the tube, which was, moreover, warm from being held in the hand. It struggled at first, endeavouring to get away from Dr. Sibson, who held it; but in twenty or thirty seconds it became quiet; and observing that the conjunctiva was insensible, I withdrew the chloroform, and the guineapig was laid on the table. We remarked that the breathing was very slow; and scarcely had this remark been made, when it ceased altogether, three or four inspirations only having been made since the inhalation was left off. Dr. Sibson proceeded immediately to open the body; but as soon as he had divided the integuments of the chest the animal began to make some convulsive gasping inspirations, during which the mouth was widely opened, and we observed that the diaphragm acted alone, the ribs being pressed inwards by the atmosphere. The heart was not contracting at all when the pericardium was first opened; but in a few moments the auricles began to contract rhythmically. The lungs were of a light red colour.

Experiment 30. Another guineapig of the same age was treated in the same manner, except that I removed the tube from the nose for a short time between every two or three inspirations, in order to see if I could not make it insensible in this way without a fatal result. In half a minute or so the animal no longer required to be held, but lay on the table without making any resistance, the conjunctiva being still sensible, and some motion of the limbs, apparently voluntary, remaining. It only inhaled once after Dr. Sibson ceased to hold it, and whilst in the state just described, and then only for two or three inspirations. After this it appeared quite insensible, and no more chloroform was given. It breathed at first naturally, except more slowly and gently than before the inhalation; but the breathing became slower, and ceased altogether about a quarter of a minute after the inhalation had been left off. The body was opened immediately. When the pericardium was opened, the auricles were observed to contract slightly, and the contractions increased after their exposure to the air.