This section is from the book "Materia Medica: Pharmacology: Therapeutics Prescription Writing For Students and Practitioners", by Walter A. Bastedo. Also available from Amazon: Materia Medica: Pharmacology: Therapeutics: Prescription Writing for Students and Practitioners.
When one of these drugs is administered in sufficient amount to put the patient into a state of coma, with muscular relaxation and the abolition of nearly all reflexes, the patient is in a condition of "complete general anesthesia." The study of general anesthesia is, then, a study in toxicology; and the production of ether or chloroform anesthesia is the production of acute ether or chloroform poisoning, the patient being drugged into a state of narcosis bordering on collapse.
The objects of general anesthesia are: to abolish pain, consciousness, and muscular resistance. To be useful as a general anesthetic a drug must be very rapidly absorbable, must act quickly to produce narcosis, and must be very rapidly eliminated; and it must be capable of producing muscular relaxation as well as complete unconsciousness, i. e., abolishing cerebral and spinal activity, without dangerous depression of the vital medullary centers or any permanent effect upon the central nervous system.
As these drugs are highly volatile and their vapor is rapidly absorbed by the lungs, their administration by inhalation is preferred as being more controllable and more easily continued for a long time; but a sufficient dose by mouth or rectum or vein will also produce anesthesia.
We shall take up ether anesthesia first, then compare chloroform anesthesia with it.
For general anesthesia, ether is regularly administered by inhalation, the vapor being diluted with air or oxygen and absorbed by the lungs. To avoid dangerous irritation of the respiratory passages and to prevent asphyxia, the ether vapor must be diluted with air for administration by the lungs, just as Hoffmann's anodyne must be diluted with water for administration by the stomach. "To establish and maintain full surgical anesthesia the blood flowing past the neuron must contain constantly about ¼ per cent. of ether, or, in terms of tension, 50 mm. of ether - and it is only by high percentages of vapor in the pulmonary air that the arterial blood can be recharged constantly to proper anesthetic tension and the central nervous system reduced to a state of quiet anesthesia within reasonable time" (Connell). Therefore to induce anesthesia quickly it is necessary that the air-ether mixture, which is begun at about 4 per cent. to avoid primary irritation, shall rapidly reach 16 to 24 or even 28 per cent. To maintain anesthesia it must be kept at about 6 to 7 per cent. With a proper adjustment of the amount of air and the amount of ether a patient may generally be kept anesthetized for a long period, even for three or four hours, without any serious symptoms manifesting themselves.
Fig. 39. - Vapor pressure of ether in tidal air for induction and maintenance of full anesthesia. Partial pressure of vapor in millimeters of mercury (Karl Connell in "Operative Therapeusis," edited by A. B. Johnson, D. Appleton& Co. 1915)
For convenience of study the production of ether anesthesia may be divided into four stages:
1. Local action and blunted perceptions.
3. Stupor, or partial surgical anesthesia.
4. Coma and muscular relaxation, or complete surgical anesthesia.
Beyond this stage we get collapse, and finally death, a highly regrettable outcome of our voluntary poisoning.
It must be borne in mind that there is no sharp line of demarcation between these several stages, and that some of the symptoms of one stage may occur with some of the symptoms of another stage. The division into stages is arbitrary, and is purely for convenience of study.
Fig. 40. - Zones of ether anesthesia (Karl Connell in "Operative Therapeusis," edited by A. B. Johnson, D. Appleton & Co., 1915).
This is characterized by local irritation, followed by local numbness and blunted senses.
The ether vapor causes irritation of nose, throat, and bronchi, producing a sensation of choking or lack of air and a tendency to cough. Soon the lips, throat, and nose become numb, there is ringing in the ears, and the perceptions become dulled, so that voices sound rather distant and only things close by are noticed; but the patient can answer questions and may talk. As he loses consciousness he feels as if, no matter what happens, he is powerless to lift even a finger to help himself; but he is in a dreamy, resigned state, and doesn't really care what does happen.
The skin soon becomes warm and flushed, the pupils are dilated from excitement or from irritation of the nose and throat, the heart is rapid, and arterial pressure is raised from the reflex stimulation of the vasoconstrictor center. Respiration is also reflexly stimulated, but, because of the cough and the irritation of the respiratory tract, there is resistance to breathing, hence it is irregular.
The second stage is characterized by intoxication, or drunkenness, similar to that from alcohol. The highest centers of the cerebrum - those which exert judgment, self-restraint, etc. - the intellectual centers, are depressed, and the emotional and the lower animal tendencies are more or less freed from the normal intellectual control. So the patient is childish, or may sing, or shout, or rave, or swear. He may push away the inhaler, or try to get up. He may repeat over and over something that the doctor has said, and may make ugly comments on the characters of his attendants - in fact, he is drunk. Though his perceptions are dulled, he is still sensitive to pain. On recovery from the anesthesia he has no memory of this stage.
The skin is flushed and may show an ether rash; and because of the resistance to respiration and the necessity at this stage of giving rather concentrated vapor, it may become somewhat cyanotic. If the stomach contains food, there may be vomiting. The pupils are dilated and react to light, and there may be rolling of the eyeballs or strabismus, with the eyelids wide open. The heart continues somewhat rapid and there may be raised blood-pressure. If the patient is an alcoholic, very fat, or robust and athletic, this stage is rather prolonged; and a very large amount of ether, or a vapor concentrated even up to 30 per cent., or the addition of chloroform, may be required to complete the anesthesia.