General Anaesthetics

These are drugs which lead to a total loss of consciousness, so that pain is no longer felt; at the same time reflex action is abolished. They illustrate admirably the law of dissolution, and also the fact that, after excitement, paralysis often succeeds; and the stages consequent upon these laws can be readily observed in any one who is taking an anaesthetic. Firstly, in obedience to the law of dissolution the highest faculty, the imagination, becomes excited, the patient sees visions and hears noises. He next begins to chatter wildly and incoherently, for in the excitement of any function by a drug the exaltation is usually irregular, and confusion results. Next, the other motor centres of the cortex are stimulated irregularly, so that he gesticulates, throws his arms about wildly, and tosses his body. By this time the brief stimulation of the higher intellectual faculties has probably ceased, and, in obedience to the second law, vision, hearing, and touch are dulled, and he has lost control over his reason, so that he feels light-headed, as he expresses it, crying and laughing easily; now he is totally irresponsible for his actions and careless as to their results. It will be noticed that the functions are paralyzed in the order stated in the law of dissolution. Next there follows upon the stimulation of the motor areas, stimulation of the heart and respiration. The pulse and respiration both increase in number, the blood-pressure rises, the face flushes. Then comes depression of all the functions previously excited; first the higher parts of the cerebrum give way, and the patient loses consciousness - neither bright lights, sounds, nor painful impressions arouse him; he becomes quiet, and ceases to throw his arms and legs about; the reflexes disappear, and consequently touching the conjunctiva does not produce closing of the eyelids; the feet do not move when they are tickled, the pupil is contracted, and the previous quickening of the pulse and respiration are succeeded by a slowing of their rate. It is at this period that the patient cannot feel pain, and that therefore operations are performed. The depression of the motor centres is followed by the depression of the muscular tone, and the muscles become quite flaccid and cease to respond to mechanical stimulation. This is the degree of narcosis that is required for the easy reduction of dislocations and for the easy manual examination of the abdominal viscera. Anaesthetics should not be pushed beyond this stage. If they are, even the involuntary muscles lose their tone and reflex excitability, so that the sphincters of the rectum and the bladder relax. The depression of the pulse and respiration continues, the movements of the chest become weaker and weaker, and slower and slower, the pulse becomes very feeble, slow, and irregular, and the heart finally stops in diastole. Death occurs partly by the heart and partly by the respiration. At any period of the administration during which recovery is possible, the functions of the body will return in just the reverse order to that in which they were lost, thus again illustrating the law of dissolution. It is often many hours before the mental faculties have recovered their equilibrium, and long after the patient can move his muscles, he cannot co -ordinate them. There are individual differences in the different anaesthetics and in different persons.

The general anaesthetics are -

(1) Chloroform.

(2) Ether.

(3) Nitrous oxide.

(4) Pental.

(5) Ethyl bromide.

(6) Many other substitution products derived from alcohols and ethers.

Therapeutics

esthetics are given to cause unconsciousness, so that pain may not be experienced during operations, to relax muscles in cases of dislocations, abdominal examinations, phantom tumors, etc., to relieve severe pain, such as that of parturition, biliary and renal colic, to quiet the body during convulsions, as in tetanus and hydrophobia.

The chief dangers of anaesthetics are - 1. Death from shock. This usually takes place before the patient is fully under the influence of the anaesthetic; reflex action is not yet quite abolished, and the heart is stopped reflexly from the peripheral stimulus of the operation. This is one of the greatest and most common dangers of anaesthetics, especially of chloroform. It is, to a large extent, avoidable if care be taken that the patient is fully under the influence of the anaesthetic before the operation is begun; often, when it is trivial, the operator is in too great a hurry to begin, and the patient suddenly dies from failure of the heart.

2. Death from paralysis of respiration. This is usually due to a combination of circumstances. Too much of the anaesthetic may have been given, respiration may be difficult because the patient suffers from some disease of the lungs, or the operation may demand that he should lie on his side or in some other position which hampers respiration. It is not a very great danger, for it is heralded by lividity; and if then the posture is changed, the administration of the anaesthetic is stopped, and artificial respiration is performed, the patient usually quickly recovers; even if he does not, artificial respiration, with the head thrown back and the tongue pulled out, should be carried on as long as there is any evidence that the heart is beating, or if the patient draws a breath when artificial respiration is stopped for half a minute. Patients have recovered, although it has been necessary to keep up artificial respiration for hours.

3. Cardiac failure may occur if the vapor is too concentrated. The patient almost suddenly becomes pale, and the pulse stops. In such a case no more of the anaesthetic should be given, artificial respiration must be kept up in the manner just mentioned, after the patient has been inverted so that the head is lowest. The heart may be stimulated by large rectal injections of hot normal saline solution or of coffee, if at hand, by the inhalation of amyl nitrite, by the plunging of electric needles into the heart, or if the reflexes are not abolished, by flicking the chest over the heart with hot towels and placing hot compresses over it. The use of brandy subcutaneously is to add the effect of one poison to that of another. The application of the faradic cur - rent over the cardiac region is also objectionable.

4. Vomited matter and, if the operation is about the mouth, blood may suffocate the patient. To avoid the first contingency no food should be taken for some time before the operation, and if the patient is sick, he should be turned on his side; to avoid the latter special precautions must be taken, which are described in books on operative surgery.

For the relative advantages of the different anaesthetics and the mode of giving each, the account of the different individual drugs must be consulted.

G. Drugs acting on the Eye.

1. Drugs acting on the Pupil. - The first thing to determine is whether any drug which dilates or contracts the pupil acts locally or centrally. It is dropped into one eye: if it only acts feebly and after some time on both eyes, it follows that it has acted centrally after absorption from the conjunctiva into the general circulation; but if it acts quickly, powerfully, and only on the eye into which it was dropped, its action is local. If it acts on an excised eye its action must be local. If, when all the vessels going to the eye are ligatured, the drug will act when dropped into the eye, but will not when thrown into the general circulation, this again shows that its action is local, and that when it acts after being thrown into the circulation when no vessels are ligatured, it does so because it is circulating locally through the eye. If all the arteries and veins of the eye are ligatured, and the drug will not act when locally applied, although it would before and will now, when thrown into general circulation, it shows that its action is central, and that it acts when dropped into the eye because some of it is absorbed. If it has been proved by these means to act centrally, the further investigation is difficult, for the central mechanism is complex.

If it has been proved to act locally, it may act either on the muscular fibres of the iris, on the terminations of the third nerve in them, or on the terminations of the cervical sympathetic in them. Stimulation of the third nerve causes the pupil to contract; section of it causes the pupil to dilate. Stimulation of the sympathetic causes the pupil to dilate; section of it causes the pupil to contract. If the pupil is dilated by the local action of a drug, and stimulation of the third nerve will not cause it to contract, but yet the muscle is responsive to mechanical stimulation, it shows that the endings of the third nerve are paralyzed. If the pupil is contracted by the drug, and, although responsive to mechanical stimulation, will not dilate when the third nerve is cut, it shows that the ends of the third nerve are stimulated. If a drug locally dilates the pupil, but not as powerfully as stimulation of the sympathetic, it is clear that its whole effect is not due to a stimulation of the sympathetic; and if the muscle remains locally irritable, the third nerve ending must be paralyzed. A series of similar experiments may be made with regard to the sympathetic. By these means the mode of action of many drugs has been made out, but often they act both on the sympathetic and the third nerve. In the following list they will be classified under their main actions:

Mydriatics {dilate the pupil} -

A. Paralyze the termination of the third nerve.

(1) Atropine.

(2) Homatropine.

(3) Daturine.

(4) Hyoscyamine.

(5) Coniine.

(6) Gelsemine.

(7) Muscarine.

(8) Hydrocyanic Acid.

(9) Aconite. (10) Amyl nitrite.

probably.

B. Stimulate the terminations of the sympathetic. - Cocaine.

C. Act centrally. - Anaesthetics (late in their action).

Myotics (contract the pupil).

A. Stimulate the terminations of the third nerve. - Pilocarpine, and nicotine (probably).

B. Stimulate the muscle. - Physostigmine.

C. Act centrally. - Anaesthetics (early in their action), Opium.

Therapeutics

Dilators of the pupils, especially atropine and homatropine, are used to dilate the pupil for ophthalmoscopic examination, and to prevent or break down adhesions of the iris. Contractors of the pupil, especially physostigmine, are used to overcome the effects of atropine, to prevent or break down adhesions of the iris, and to prevent too much light entering the eye in painful diseases of it.

2. Drugs acting on the Ciliary Muscle.- The following drugs impair or paralyze accommodation:

(1) Atropine.

(2) Daturine.

(3) Hyoscyamine.

(4) Homatropine.

(5) Cocaine.

(6) Physostigmine.

(7) Pilocarpine.

(8) Gelsemine.

(9) Coniine.

Intra-ocular tension is increased by atropine (large doses), hyoscyamine, and daturine. It is decreased by cocaine, hyos-cine, and physostigmine.

Gelsemine paralyzes the external ocular muscles, especially the elevator palpebrae and the external rectus, by its action on the terminal nerve filaments.

Cocaine, by stimulating the unstriped fibres in the orbital membrane and the eyelids, causes the eye to protrude. Coniine produces ptosis when given in large doses.

The capacity for seeing blue is increased by strychnine. Santonin causes first violet, then yellow vision.

H. Drugs acting on the Ears. - We know very little about the action of drugs on them. Quinine and salicylic acid cause noise and buzzing.

I. Drugs acting on the Sympathetic System. - Much of this subject has already been discussed when speaking of the action of drugs on vessels. The curious fact has been made out that if an animal be treated with a large dose of nicotine, or if this be applied locally to the superior cervical ganglion, stimulation of the nerve below the ganglion no longer produces its characteristic effects, although stimulation above the ganglion does.