Yandell Henderson suggested that shock was due to over oxy genation of the blood (acapnia) leading to insufficient respiration and deficient circulation, but the view has not gained general acceptance.
It is a fact that in shock there is a diminished alkalinity of the blood and some hold the view that acidosis is the cause of shock. It is much more likely a consequence than a cause.
Malcolm found that in the course of shock developing during operation there was a gradually increasing contraction of the peripheral arteries with a diminution of the volume but increase in the rate of the pulse. He stated that the fluid part of the blood was gradually reduced though he could only surmise the exact mechanism of the reduction. This view has been confirmed and to-day an essential fact is that the volume of the blood in circulation is greatly reduced in cases of shock. With an insuffi cient amount of blood in circulation, metabolism diminishes and all the vital centres are starved. For a time the blood-pressure is maintained by the contraction of the arteries, but ultimately vasoconstriction cannot maintain blood-pressure and final failure of the circulation follows.
Now fluid may be rapidly lost from the circulation not only directly by haemorrhage, but also by extreme diarrhoea as in cholera, profuse sweating as in some severe colics and toxae mias, or rapid effusion into the peritoneal cavity as in some cases of perforative peritonitis ; moreover certain poisons may in crease the permeability of the capillaries or possibly paralyse the contractile power of the minute blood vessels and thus cause local stagnation and loss to the general circulation of a large amount of blood.
It would appear therefore that shock and collapse are due to circulatory and metabolic failure consequent on a grave diminu tion of the amount of fluid in circulation. This fluid leaves the blood vessels either as the result of continuous and extreme reflex vasoconstriction, or as the result of toxins rendering the smaller blood vessels more permeable, or as a consequence of great loss of fluid by sweating, effusion or haemorrhage. In a few extreme cases toxins may paralyse the vasomotor centre. Shock which ensues immediately after an injury is called primary and is due to reflex nervous influence ; secondary traumatic shock comes on 24 hours after the infliction of an injury and is probably due to absorption of toxic products. Mental shock produced by severe
emotion may perhaps be due to temporary cardiac failure.
The treatment of shock depends upon an understanding of the main features of its mechanism. (I) Injurious stimuli must be avoided or diminished as much as possible; (2) the body heat must be maintained; (3) the fluid of the circulation must be re plenished; and (4) foci from which shock producing toxins are being absorbed must be dealt with. These four requirements hold for both prophylaxis and cure of the shocked condition.
(I) The greatest care has to be taken to avoid traumatism. In operations gentleness is essential. In giving anaesthetics it must be remembered that they intensify any shock. Nerve block ing to stop peripheral stimuli may be advisable. Pain is treated by adequate doses of morphia.
(2) The diminished metabolism shown by the subnormal tem perature is treated by applications of warmth and avoidance of further exposure. Warm blankets, radiant heat, hot water bottles, or any suitable source of heat can be tried.
(3) The fluid lost to the circulation is made good by injection of normal saline solution per rectum, subcutaneously or intra venously. A 6 per cent solution of gum acacia in saline was recom mended by Bayliss as being less rapidly lost again from the permeable vessels. Blood transfusion (q.v.) is very valuable when , much blood has been lost (4) Acute bacterial infection must be dealt with. A limb with gas gangrene must be amputated, the decomposition products in obstructed intestines must be drained by relief of obstruction or exteriorly, etc.
One of the latest methods of treating shock has for its aim the encouraging of metabolism. The patient is given an injection of glucose together with a proportionate amount of insulin to ensure the metabolism of the glucose in the body.
See W. B. Cannon, Traumatic Shock (New York, 1923, bibl.) ; Med. Research Council's Special Reports, Nos. 25 and 27; Proc. Roy. Soc. Med., vols. xii., 1918-19 and xv. 1921-22 (Sect. Obst. and Gyn.).
(V. Z. C.)