CHAPTER XVIII

.

DISTURBANCES OF BLOOD PRESSURE; SHOCK AND COLLAPSE.

The maintenance of the normal pressure of the blood is a material factor in the welfare of surgical cases. Deviations in the direction of lowered pressure constitute the most important features of _shock_ and _collapse_. Prevention of loss of blood is but one of several complex indications in prophylaxis and after-treatment.

Blood pressure is maintained in large part by the vasomotor system of nerves, whose prime centre is in the gray matter of the fourth ventricle, with subsidiary centres in the spinal cord and great ganglia. Stimulation of these centres causes contraction of the peripheral arterioles and increases intravascular pressure. If, however, it be long-continued or excessive, these centres become exhausted, vasomotor paralysis results, the arterioles dilate, and pressure is lowered.

Three factors coöperate to maintain this pressure:

1. Regular and normal rhythmic heart action;

2. Normal vascular contractility;

3. Normal quantity of suitable fluid in the vascular system.

Departure from the normal in any one of these factors causes perceptible disturbance, but when in all three of them it may prove fatal. Whether this be caused by emotion, accidental injury, or deliberate operation is of slight concern, as the effect is essentially the same.

The pulse will usually tell its own story to the experienced observer, but scientific accuracy in measuring blood pressure can only be obtained by certain instruments of precision, such as the _tonometer_ or the _sphygmomanometer_, consisting of an air-containing armlet which encircles the arm, a bulb by which the pressure of air can be regulated, and the whole connected with a manometric gauge and mercury tube. These instruments can be procured of the dealers, and their employment during an operation gives the operator a continuous record of the blood pressure, by which he may judge at any moment of the degree of shock.

The normal blood pressure in healthy adults is 130 to 140 Mm. of mercury in the tube. In children it ranges from 90 to 110 Mm. Females have an average lower pressure of 10 Mm.

Excitement or slight stimuli will send the pressure up thirty or forty points. It is also higher than the above average in arteriosclerosis. In uremia it is always high. In cases of intracranial tension it is also high, as the brain alone of all the organs of the body has no complete vasomotor apparatus of its own; when it needs more blood this has to be contributed from the general supply. When pressed upon by a clot, depressed bone, or foreign body it becomes anemic, and on effort to furnish the needed blood from other parts the vascular tonus is increased. Cushing has shown the value of these estimations in cases of _head injury_, for the rise of blood pressure may be regarded as an indication for operation. In typhoid fever a sudden rise of pressure is associated with perforation, or perhaps with the peritonitis which is its immediate result. On the other hand, in this disease a sudden fall of pressure is an indication of hemorrhage.

The course of events in surgical shock is about as follows: Injury to afferent sensory nerves acts as a vasomotor stimulus after it reaches the centre in the fourth ventricle; a reflex impulse is then sent out which produces arterial contraction and raises the blood pressure. When the abdomen is concerned the opening and handling of its contents produce the same result through the splanchnic centres. If, however, the stimulus is excessive, too often repeated, or too prolonged the vasomotor grip is lost, the arterioles dilate, and the blood pressure is reduced. A severe injury to any part of the body may produce this effect without the preliminary rise. The popular impression that a patient “bleeds to death into his own veins” has this to justify itself, that the arterial tonus is lost and the blood is pumped through the arterioles to accumulate in the capillaries and veins, especially the abdominal, thus overloading the right side of the heart and giving it a disproportionate amount of work.

Accompanying these circulatory disturbances are others, secondary and unavoidable, as of respiration, which becomes rapid and enfeebled in proportion to the degree of shock.

Any factor which tends to weaken the heart’s force favors both phenomena. So important is the respiratory action that patients die from cessation of respiration rather than from impairment of the circulation. This shows the importance of maintaining artificial respiration in cases of severe shock.

Cushing and Crile have studied the subject exhaustively in animals. They have shown that certain injuries are likely to be followed by well-marked reduction of blood pressure; for example, those of the brain, the interior of the larynx, the abdomen and testicle, are often followed by a marked reduction of pressure without any preliminary rise. In other words, vasomotor paralysis is sometimes an almost instantaneous effect of certain injuries. When most of the blood is collected in the venous system and the central nervous system fails, because of lack of blood supply, to respond to those normal stimuli which are essential to heart action and respiration, the heart weakness or heart failure is due, not alone to failure of its innervation, but to its reduced output and its diminished content of blood on the left side.

Crile has shown that the more abundant the blood supply to a given part the more it contributes to production of shock; hence, the value of cocainizing the interior of the larynx and the nerve trunks.

Aside from emotional causes--which are sometimes inseparable from even surgical cases--the principal agencies in the production of surgical shock and collapse are those which make a sudden and deep impression through the medium of the sensory nerves upon the central nervous system or the large sympathetic ganglia; ultimately upon the latter in all serious cases. _Loss of blood, then, need not play a very important role._

Weakened, anemic, or neurotic patients are predisposed by virtue of these conditions, and also the young and aged. Fright combined with injury increases the degree of the effect. Crile has shown that trifling lesions of the interior of the larynx will cause symptoms which do not occur in animals if the superior laryngeal nerves be divided or if the parts be cocainized.

The upper portions of the abdomen are more sensitive in this respect than are the lower, testicles particularly. The skin is more impressible than the muscles or tissues beneath, save the nerve trunks, which are very sensitive; the bones and large joints slightly so. After shock has been once produced further injury causes a disproportionate lowering of blood pressure.

So-called “concussion of the brain” is essentially a condition of shock following injury to this particular part of the body. (See Head Injuries.)

_Shock and hemorrhage are often closely associated_, and loss of blood is doubtless a powerful factor in the production of the former, especially in those already reduced or whose blood contains a lowered percentage of hemoglobin. There are, therefore, great advantages in entrusting an assistant with the duty of watching blood pressure during serious operations.

The terms _shock_ and _collapse_ are nearly interchangeable, but, by common consent, the latter is usually the name given to conditions that are more sudden and overwhelming. Shock may be of all degrees--from temporary faintness, from which the patient recovers within a few moments, up to a condition of vital depression which terminates fatally, there being no reaction in spite of all efforts to produce it.

=Symptoms.=--These vary to a considerable extent according as the patient is or is not under a general anesthetic. The description of _types_ and _symptoms_ includes an expressionless face, pallor of the skin and mucous membranes, with corresponding coldness of the same, _i. e._, reduction of surface circulation and heat; dilated pupils, reacting slowly to light; irregularity of the heart’s action, with a weak, irregular, thready, or almost imperceptible pulse; irregular respiration, _i. e._, irregular both in rate and depth; mental inactivity and apathy; loss of voluntary muscle movement; impairment of superficial sensibility; reduction of body temperature; and nausea or actual vomiting. These at least constitute the symptoms and form the apathetic or torpid type of shock.

In the so-called erethistic type (Travers) the patients are restless and excited, uncontrollable, with irregular pulse and breathing, often with dilated pupils.

In a third type, described by Travers as the _delayed_, the symptoms are as above detailed, but do not appear until some hours after the cause which has produced them, which may be a concealed (internal) hemorrhage. The delayed type is also seen in those who escape serious accident with a minimum of physical harm.

As shock becomes more pronounced, mental depression deepens into coma, or mental excitement subsides into it; the surface becomes colder and bathed with perspiration, and death follows. These symptoms are those generally noted, whether following injury to the head and denoting so-called concussion of the brain, loss of blood, wound of the abdomen with injury to the viscera, blows upon the testicles, gunshot wounds or other accidents which are causes of shock. They follow also after perforation of the bowel, as in typhoid fever or appendicitis; depression following the receipt of bad news, or fright, etc.; in other words, the physical condition is practically the same no matter what the exciting cause.

=Diagnosis.=--Shock is mainly to be diagnosticated from fat embolism; concealed hemorrhage as well as pulmonary edema and suppression of urine are to be suspected. It is unquestionable that many patients have died of fat embolism in whom the actual cause of death has not been ascertained, yet has been ascribed to shock. (See Fat Embolism,