Page:EB1922 - Volume 32.djvu/486

Rh A new Shipping Board, appointed in June 1921, by President Harding, headed by Albert D. Lasker of Chicago and including Admiral William S. Benson in its membership, quickly effected an important reorganization of the executives of the Board, installing a group of practical shipping men as officials of the Emergency Fleet Corporation, and committing to these men the active management of the government-owned merchant fleet. Following this reorganization, the new Shipping Board addressed itself to the working put of a comprehensive subsidy system for postal liners and cargo ships, intended to facilitate the sale of the government-owned fleet to private owners, as directed by the Merchant Marine Act of 1920.
 * (W. L. M.)

 SHOCK, in surgery (see ). Experience during the World War has thrown new light on the nature of “shock” in pathology. The first effect of an injury is usually to produce a state resembling that of fainting. This is clearly produced through the nervous system and is recovered from more or less rapidly, supposing that the injury is not in itself sufficiently severe to be fatal. This “primary shock,” as it may be called, does not show itself to any important degree in the case of operations done under an anaesthetic. But it has long been familiar to surgeons that another kind of shock may appear during or after an operation. This “secondary shock” was of frequent occurrence during the war of 1914-8 and the cause of many deaths. To define it, Cowell suggested the name “wound-shock.” The symptoms are very difficult to distinguish from those of mere loss of blood, but it became obvious that it might be present although actual haemorrhage had been very slight. This fact is of significance in the interpretation of the actual pathology of the condition, as will be seen later. As indicated above, it does not show itself at once; it may, however, develop in less than an hour if the injury has been great, and primary shock may sometimes pass into it gradually without a period of recovery. It shows itself by a state of general collapse, with pallor, coldness, thirst, low blood pressure and the various consequences of this, such as vomiting, sweating and sometimes rapid shallow breathing. No evidence of heart failure or of paralysis of vasomotor centres has been obtained. The higher nerve-centres do not suffer until the late stages. Pain is not a prominent factor. If the state has not been of long duration nor of severe intensity, it may pass off on warming and rest, but if left alone death nearly always ensues.

Observations made by Sir Cuthbert Wallace in operations before the war suggested to him that the actual injury to the tissues, and especially to muscle, played an important part. This surgeon noticed that operations involving much section or removal of tissues were more liable to produce shock. The fact might, of course, be also interpreted as the result of the irritation of nerves, acting subconsciously on the centres; but Quénu, a French surgeon, at an early date in the war, propounded the view that the serious effects of wounds are due to an absorption into the blood of toxic products arising in the injured cells. This view was confirmed by the recognition of the importance of early removal of the injured parts; operative procedure was pushed nearer and nearer to the fighting line as the war progressed. It was also noticed that, even after shock had developed, a marked improvement was frequently brought about by excision of the damaged structures. Experimental work by Bayliss and Cannon showed that it was possible to produce in anaesthetized cats a condition similar to that of wound-shock. This could be done by extensive injury to the muscles and skin of the legs. It was found that the results were identical whether the nerve channels from the injured tissues were severed or not, but that they were absent if the blood returning from the tissue was prevented from passing into the general circulation. Thus the name “traumatic toxaemia,” proposed by Quénu, is an appropriate descriptive title for the state under consideration.

But what is the nature of the poison and how does it act? These are important questions in dealing with appropriate methods of treatment. The possibility of bacterial toxins has been definitely excluded, and although it cannot be stated that we have yet found the actual substance produced in wounded tissues, the work of Dale and his colleagues on the properties of a base called “histamine,” which is formed by removal of carbon

dioxide from one of the component amino-acids found in the proteins of tissues, namely histidine, shows that we have to deal either with this compound or with a very closely related one.

Dale and Laidlaw found, in fact, that a small amount of histamine injected into the veins of cats or dogs produced a large fall of blood pressure, accompanied by the other signs of shock, which increased progressively until death. The heart was unaffected and continued to beat powerfully, although nearly empty of blood. Now, until the work of Dale and Richards, it was believed that to produce a fall of blood pressure without removal of blood or depressing the heart it was necessary that the muscular coat of the arterioles should be relaxed and thereby the peripheral resistance decreased. But the previous work had shown that histamine has the effect of causing contraction of all smooth muscle, including that of the arterioles. The fall of pressure produced by a very small dose of histamine remained a paradox until the work mentioned, which was published in 1918. In this research it was shown that the effect was due to a wide-spread dilatation of the capillary blood vessels. In order to appreciate the significance of this discovery, a few words are necessary on the reactions of the capillaries and on the importance of the volume of blood in circulation. Although various observations had been made indicating that the capillaries are not merely inert channels, but that their walls are capable of contraction and dilatation in response to chemical stimulation or nervous influence, there seemed to be difficulty in realizing how protoplasmic cells such as those of the capillary wall succeed in doing this. The changes of shape in amoeba and in pigment cells, nevertheless, show the possibility. Dale and Richards, by an ingenious series of experiments, demonstrated that histamine does actually cause a marked widening and opening-up of the capillaries of the body generally. It may also be pointed out that Krogh has recently shown the existence of a nervous regulation of these vessels, which appears to be of an antidromic nature, like that of the dorsal roots described by Bayliss. Now, when we observe how enormous a share of the total vascular system the capillaries make up, we realize what a large volume of the total circulating blood may be penned up or pooled in these vessels when they are dilated, leaving very little to be sent round by the heart to supply the organs with oxygen obtained by its flow through the lungs. The whole of the body is therefore suffering from want of fresh blood containing the oxygen necessary for its existence.

These facts have caused renewed attention to be paid to the question of the volume of blood in circulation. By the injection into a vein of an innocuous dye, which does not quickly diffuse out of the blood vessels, such as “vital-red” or better “congo-red” (Harris), the degree of dilution of the amount injected indicates the volume of the fluid part of the blood. When observations of this kind were made by N. M. Keith on men suffering from shock, it was found that, even when they had lost little or no blood, the volume actually in circulation was greatly reduced. Hence we are justified in postulating the presence of a toxic action dilating capillaries, an action similar to that of histamine.

It was early recognized that shock might be greatly exaggerated or even brought on by various conditions incidental to the state of the wounded man, or to the treatment necessary afterwards. Some of these throw additional light on the subject.

Anaesthetics.—Dale observed that a dose of histamine highly toxic to a cat under ether was innocuous to a normal animal. Thus there are processes in the healthy organism which either destroy the poison rapidly but are inactive under ether, or the anaesthetic itself makes the capillaries more sensitive. In any case, it was often noticed in the war that a state of shock came on during an operation under ether and that there was less risk with nitrous-oxide and oxygen.

Haemorrhage.—Since the serious nature of shock is due to the deficiency of circulating blood, it is obvious that when blood has actually been lost a lesser degree of capillary stasis will suffice to induce shock. This was also found to be the case, experimentally, by Dale and by Bayliss and Cannon. A practical conclusion as regards operations seems to be that loss of blood should be avoided as far as possible and that means for replacing it by intravenous injection should be at hand in case shock makes its appearance.

Thirst.—There was always a notable demand for water by the wounded soldier. If he was already suffering from thirst when