Under this short and convenient title, the author proposes to discuss all the changes observable in the patient’s condition, the causation of which can be traced to the procedure of the surgeon. The use of the term shock was at one time, and by some teachers still is, restricted to a definite clinical condition. The patient was described as lying pallid and almost pulseless, with dilated pupils, cold sweating skin, and gasping, irregular respirations. In the view more generally taken to-day, that is but the extreme and final manifestation of a syndrome, which any patient who suffers trauma (whether inflicted accidentally or by the surgeon) exhibits in a greater or less degree, and from which general anæsthesia protects a patient to a very limited extent only.
Professor Crile, to whose work we owe so much of our knowledge on this subject, has said, “In general anæsthesia, part of the brain only is asleep.” Though consciousness is abolished, many parts of the brain are quite capable of responding to centripetal impulses passed to the brain through sensory nerves injured by the knife. A full account of the changes demonstrated by Crile in some of the cells of the grey matter of the brain as a result of such stimuli, and of the interpretation put upon these by their discoverer, is not suitable for a text-book of anæsthesia. It is sufficient to say that such changes have been discovered, and that their occurrence as a result of trauma is not prevented by inhalational anæsthesia. Such changes, though of the utmost interest scientifically, cannot be demonstrated clinically, and it is to alterations of blood pressure and of respiration that we must look for clinical evidence of the effects of shock stimuli.
Fig. 1.—Shock—Blood pressure of a dog undergoing laminectomy under general anæsthesia (Grey and Parsons.)
(Reproduced by kind permission of the Authors.)
With every incision by the surgeon, sensory nerve twigs are of necessity injured. The fibres found in sensory nerves are, it will be remembered, either pressor, or depressor—that is, stimulation of them, causes either an increase or decrease of the blood pressure, the depth and frequency of respiration being usually affected in the same direction as the B.P. That such changes do commonly occur is easily recognised by clinical observation. The veriest beginner in anæsthesia soon learns to expect a deeper, quicker respiration and a stronger pulse as soon as the operation has begun. These changes have been studied experimentally upon animals and upon the human subject by the use of the sphygmomanometer: Fig. 1, drawn from Grey & Parson’s Arris and Gale Lectures of 1912, shows a tracing from a dog undergoing laminectomy under general anæsthesia, and gives a good idea of the early evidences of shock.
We may condense the results of much work on this subject under the following headings:—
(a) Most stimuli from the field of operation cause a sharp rise of blood pressure, followed by a sharp fall.
(b) Successive stimuli delivered quickly one after another add their effects together, the total result being considerably greater than from one severe trauma.
(c) After a time, the pressor effect of stimuli begins to lessen: the animal or patient “wears out,” and finally no pressor result can be obtained by the most massive stimulation: the curve of B.P. steadily falls: the condition of full surgical shock is produced.
(d) The tearing or pulling of tissues produces more powerful stimuli than the use of a sharp knife, and, therefore, brings on the full condition of shock more rapidly.
(e) Stimuli from some tissues cause much more reflex effect upon the organism than from other less sensitive structures. This is well exemplified when an abdominal section is in progress. Incision of skin causes immediate response in deepened respiration and higher B.P.: division of the fascia very little effect. If the muscle is divided by the knife, again little reflex effect is noticeable, but if it be stretched and split by the fingers, the response is powerful. The parietal peritoneum, however delicately handled, is one of the most sensitive structures in the body, and, unless the patient is fully under at the stage either of opening or closing this layer, actual breath-holding or straining will occur. On the other hand, incision or suture of the hollow viscera will cause practically no response however light the anæsthesia, provided these structures, and their connections with the parietes, are not pulled upon.
(f) Stimulation of certain selected areas, of which the spermatic cord is a well-known but by no means the only example, results in an almost immediate fall of blood pressure with little or no preliminary rise. In the operating theatre, we sometimes see faintness or syncope arising quite suddenly during operations in such regions. This subject is explained more fully in Chapter XVI. under the term “Reflex Syncope.”
Fig. 2.—Combined blood pressure chart showing the average of a number of experiments.—A—Under nitrous oxide and oxygen. B—Under ether. At each spot marked x, a trauma (burning of the paw) was inflicted. (After Crile.)
(g) While no general anæsthetic protects absolutely from shock stimuli, some anæsthetics give more protection than others. Nitrous oxide is the most effective in this respect, its powers being two and a half times greater than that of ether: chloroform is even less effective than ether (see Fig. 2).
(h) The claim made by the older generation of surgeons that shock could be prevented by the use of a deep anæsthesia, and that the occurrence of any “Reflex syncope” was always a sign of too light an anæsthesia cannot be made good. At the same time, it must be admitted that too light an anæsthesia does increase the likelihood of shock. Prolonged deep anæsthesia, on the other hand, produces by itself a condition indistinguishable from shock, with the single exception of nitrous oxide gas.
(i) Operative shock is predisposed to by several factors of which the following are the most important:—
1. Hæmorrhage before or during operation.
2. Sepsis.
3. Fear.
4. Prolonged starvation.
5. Certain diseases, especially hyperthyroidism (exopthalmic goître).
So far as we have touched in the above upon theory, it has been theory which receives general acceptance and which accords with known clinical facts. When we come to discuss the reason why blood-pressure falls in shock, we are in more debatable country.
Crile’s original view was that the upstroke seen in such charts as shown in Fig. 1 are caused by reflex vaso-constriction, and that the final fall of B.P. was due to exhaustion of the vaso-motor centre. This view he does not seem to have modified as a result of his later discovery of degenerative changes in certain cells of the grey matter of the brain.
Other workers, J. D. Malcolm in this country, and Yandell Henderson, of Yale, U.S.A., maintain an opinion diametrically opposite. In their view, in fully developed shock, the vessels are in vaso-constriction, and the circulation is arrested from undue internal resistance to blood flow.
A third explanation of lowered B.P. has been offered, and while its significance is not understood, there is fairly general agreement as to its validity. This factor is a reduction in the total blood volume—an oligæmia. No one has as yet demonstrated to what region or organ the missing blood volume has retreated.
Acapnia is a condition in which the CO2 content of the blood and tissues has been brought to too low a level. Those who climb mountains suffer from it, and so do those who breathe rapidly and heavily for a prolonged period. Carbon dioxide is necessary for the vigour of the respiratory centre, of which it may be termed the natural regulator. Moreover, the heart and the great veins which empty into it require a certain proportion of CO2 in the blood.
Admittedly, patients inhaling anæsthetics do on occasion breathe too deeply. Sometimes they do so voluntarily before losing consciousness, sometimes reflexly as a result of such a manœuvre as stretching the sphincter ani. Do they thereby bring their CO2 down to a level which does serious harm and which can be considered a cause of collapse under anæsthesia? Henderson says they can and do: most other workers deny the possibility.
Fig 3.—Diagram (after Crile) to illustrate anoci-association. In “A” the trauma is inflicted on the leg, and the brain being wholly unprotected, considerable shock is suffered. In “B” the brain is protected by inhalational anæsthesia from the effects of fear, etc. In “C” the sensory nerves from the seat of trauma are blocked by novocaine, and the brain also protected by inhalational anæsthesia. Theoretically no shock is suffered.
There are many theories of shock but only one anti-shock technique which will bear examination. Founding upon his own theory, Crile about 1913 elaborated his ANOCI-ASSOCIATION method of which the following are the leading features (see Fig. 3):—
(a) Prevention of fear.—Every member of this team is taught the all-important art of so dealing with the patient that no unnecessary fear is allowed to remain in his mind. That art does not consist in endless repetition of the phrase, “Do not be frightened,” but rather in each so bearing himself or herself before the patient that he may gradually acquire the conviction that he is surrounded by careful, kindly, and skilful persons who are doing for him what they do for hundreds of others, and doing it with an expectation of his early and complete recovery so certain that they do not need to put it into words unless definitely questioned. Such an art is not acquired in a day, and some unhappy few are so constituted that they can never acquire it.
As a further preventative of fear, and also for other reasons explained in Chapter vi., the patient receives a dose of morphia (⅙th grain, with ¹⁄₁₂₀th grain atropine, hypodermically) three quarters of an hour before operation. Some surgeons go further, and give a sedative the night before operation. Veronal gr. viii. is the favourite prescription of Prof. Alexis Thomson of Edinburgh.
(b) The sensory nerves are “blocked” by infiltration with novocain. By the systematic use of local in conjunction with general anæsthesia, the harmful stimuli from the area of operation are prevented from reaching the brain. For the details of this measure, the reader is referred to Chapter xx.
(c) The anæsthetic of choice in Crile’s practice is nitrous oxide and oxygen (see Chapter vii.).
The whole of this technique has not been generally adopted as a routine, but nevertheless the teachings of Crile have greatly influenced the mind and practice of most surgeons and anæsthetists. Traces of that teaching are to be found everywhere in the organisation built up during the Great War to save as many as possible of the lives of badly smashed men. At no previous time in the history of surgery was the problem of shock so pressing, and a brief resumé of the methods adopted is here set down, as an example of how shock should be dealt with.
Fig. 4.—Lane’s apparatus for subcutaneous infusion of saline solution.
The first essentials demanded were the most careful organisation, the provision of equipment far in advance of most home civilian hospitals, and of surgical teams specially trained to a high level of excellence. Upon recovery from the field, the injured man received at the Advanced Dressing Station, such first aid dressing as was necessary, and a substantial dose of morphia. When the latter had had time to take effect, the case was passed back to the Field Ambulance (where he received his first dose of antitetanic serum), and from there to the Casualty Clearing Station. During every stage of the journey, he received as much warm fluid nourishment as possible. Arrived at the C.C.S., the severe case was passed first into the Resuscitation Ward. This department, under the charge of a specially trained M.O., concentrated largely upon two measures—the thorough warming of the patient, and the replacing as far as possible of the fluids lost to him by hæmorrhage and shock. The warming in many C.C.S.’s was effected by electric radiant heat baths. The fluids were replaced either by way of infusing blood from another patient, or by the use of gum saline solution. Introduced into a vein, the action of this solution persists for a much longer period than that of ordinary saline, being less easily lost by osmosis through the capillaries into the tissues. From the resuscitation ward, the patient passed to the Operating Theatre. Though the full technique of anoci-association was not always possible, the maxims which Crile had sought to inculcate into the practice of surgery influenced the work of surgeons and anæsthetists very profoundly. Nitrous oxide and oxygen was used for all the severely shocked cases, and infiltration with local anæsthetics where feasible and necessary.
For those who do not feel bound to adopt the Crile technique this is a simple measure which does much to minimise shock in prolonged abdominal operations. Saline infusion into a vein is so rapidly excreted that its influence is very fugacious, but if the fluid be introduced under the skin during the period of operation it is slowly absorbed as required by the blood. Sir Arbuthnot Lane is a strong advocate of this measure.
Fig. 4 shows a suitable apparatus. The needles are thrust into the loose areolar tissue under the breast, one on each side, and a pint or more of fluid is slowly run in from the reservoir.