BY GEORGE CRILE, M. D., CLEVELAND

In making our diagnosis, in estimating the operative risks, in the course of the operation itself, and throughout the after care of our patients, we have constantly to draw upon our knowledge of physiologic laws and factors. A thorough knowledge of normal physiologic action is of course essential, but this alone is not sufficient. Our cases present conditions in which the normal is altered and modified by physiologic changes, and it is through a familiarity with the reaction of the circulatory and nervous mechanisms to these abnormal conditions that we are enabled to foresee and forestall crises, or to meet them successfully when they do occur.

In surgical practice we are concerned chiefly with the integrity of the circulation and I shall mention in brief some of the factors that modify or effect the circulatory system.

Heart: As a muscle the heart is probably the most highly organized and performs the most important function of the various muscles of the body. It has a wider range of compensation and certain other characteristics and limitations that are of great importance surgically. In its response to trauma of various kinds it shows marked individuality. A stab or gunshot wound may in one instance cause only temporary alteration in function, while in another immediate death may ensue. Direct manipulation of the heart often has but slight effect, or it may cause inhibition and irregularity to appear at once. Experimental research has shown that the collapse or death following the short rib or so called "solar plexus" blow is in no way connected with the solar plexus, the diaphragm or the splanchnic nerves, but is

due to mechanical inhibition of the heart itself. No drug has as yet been found that will protect the heart against the important alterations in function that result from mechanical manipulation or trauma, neither are these phenomena modified by anesthetics. Therefore, in operations upon or about the heart prevention is the best treatment.

When the heart muscle is damaged or its nutrition impaired by acute infections, anemia, arteriosclerosis, advanced age, or when valvular lesions, fatty degeneration or the "athlete's heart" is present, physiologic research and clinical experience have shown that it is much more susceptible to trauma and mechanical interference than in the normal organ. One would hesitate much more to perform an operation on a senile heart than upon that of a young adult. Acute dilatation and paralysis of the heart presents a phase of surgical physiology that demands special attention. It is established that the output of the heart is dependent upon the blood pressure in the large venous trunks and not directly upon the arterial pressure. An increase in the amount of fluid entering the heart causes an increase in its work in geometric ratio, that is to say, trebling the amount of fluid causes nine times more work, not three times. This together with the fact that the heart is functionally impaired immediately upon the diminution of its own blood supply through the coronary arteries constitutes the most important group of physiologic factors relating to the heart in the operative part of surgical practice.

In an acute hemorrhage when the heart is functionally impaired by a lowered coronary pressure and by blood of poorer quality, if the amount of fluid is suddenly increased, as by a rapid intravenous infusion, the heart's work is increased out of proportion to its vitality, and it may suddenly suffer an acute dilatation and an immediate paralysis ending in death. So also if the intrapulmonary pressure is rapidly increased, as in certain methods of positive ventilation of the lungs in artificial respiration, the right heart may be unable to empty itself, the blood accumulates and the work of the right heart is doubled, trebled or quadrupled in a moment. This would cause a lowering of the nutrition of the cardiac muscle, would diminish its power of contraction, and might cause an immediately fatal dilatation and paralysis. When these crises arise, either from an increased amount of fluid, as by an unwise intravenous infusion, from obstruction of the pulmonary circulation or otherwise, the

removal of the cause is the first consideration. The patient should at once be put in the feet-down inclined posture. This causes the blood to gravitate from the heart into the splanchnic area and large venous trunks of the lower extremities, thereby partially relieving the over-distension of the vessels. Following this, rapid massage of the heart by rhythmic pressure upon the thorax over it, should be done and artificial respiration maintained. In addition, if it can be done quickly enough, extensive venous blood-letting from the jugular vein may be effective. The efficacy of these measures has been well established from both the experimental and clinical standpoints.

In one of my own cases, in the midst of an operation such a crisis arose. An acute dilatation was at once recognized by the extensive venous congestion, lividity and simultaneous collapse of the pulse. It was during an operation on the neck. The jugular vein lay in the field and was at once opened, and there was a gush of venous blood. During the same time vigorous heart massage was carried out. The heart, which had stopped in paralysis, within a few minutes again beat regularly. The operation was completed and the patient recovered.

This plan of treatment may be the means of saving a life in certain anesthesia accidents in which, as shown by Leonard Hill, the heart muscle being impaired by the anesthetic, acute dilatation and paralysis ensues.

Cerebral anemia has so long been regarded in surgical traditions as the one condition to treat that the rational management of the heart has not received the attention its importance deserves. The differential diagnosis between collapse of cerebral origin and the collapse of acute dilatation of the heart must be prompt and accurate, as the best treatment for the one is the worst treatment for the other.

The powerful influence which respiration exerts on the circulation must be borne in mind when performing operations on the thorax. The respiratory pumping action is of first importance in filling the right heart. In certain operations upon the thorax, when the respiration and hence the supply of oxygen is interfered with, it is well to take every precaution to see that the heart receives its normal quota of oxygen to meet the circulatory crises which thoracic operations so often entail.

Before every operation and every anesthesia, one must take as accurate a physiologic stock as possible of the cardiac reserve force. In the presence of any organic lesion or functional disor

der of the organ the margin for safe operative disturbance is proportionately diminished, and one must be prepared for sudden impairment or collapse. If the physiologic status is accurately determined and the operative effect perfectly controlled, the demand upon the heart may be made to fall within its physiologic margin of safety.

The factors that most greatly disturb the heart are sudden changes in blood pressure or sudden application of trauma or manipulation. In this connection, too, it is well to remember that the heart endures manipulation and trauma of its apex and ventricles much better than of its base, including the auricles and large venous trunks. Operative procedures directed against the heart should be gradually approached, allowing time for compensation and recovery from slight manipulation, and then should become gradually more extensive until the ultimate aim has been reached. In this way the heart is capable of withstanding a surprising amount of trauma and manipulation.

After collapse with sudden cessation of its beat, the heart may respond to proper treatment after a protracted quiescenceeven of fifteen minutes. It is during these crises that one is apt so often to fall into the error of administering an over-dose of saline infusion.

In any condition of impaired function or threatened breaks in compensation a preoperative treatment with digitalis or strophanthus with or without nitroglycerine may effectively improve the heart action, and thus increase the margin of physiologic safety.

Vasomotor System: The importance of the surgical physiology of the vasomotor system is worthy of a more detailed consideration and study than space will here permit. The height of blood pressure is due primarily to the action of the vasomotor center, which sends its impulses through the vasomotor nerves to the vascular periphery and controls the caliber of the vessels. The rise and fall in the blood pressure depends mainly upon the increase or decrease in the action of this center. The beat then, roughly speaking, energizes the blood stream, supplying artificial force to overcome the peripheral resistance and return the blood to the heart.

While cessation of the heart's action means death, it is no less true that cessation of the activity of the vasomotor center causes death quite as certainly but not so instantaneously. It is highly probable that from the vasomotor center more often than

from the heart arises the causes of surgical death. As a common example may be mentioned the paralysis of the center from operative or accidental trauma, usually designated as shock.

In many of the acute infections a toxic over-stimulation causes a break down in the center, and while it is true that in the majority of cases life is terminated by the combined effect of a number of factors, such as cardiac, renal, respiratory, etc., the vasomotor is probably the dominating factor.

In acute hemorrhage the vasomotor center is depressed on account of its diminished supply of nutrition and of oxygen. The short pulse wave is indicative of the relaxation of the vessels which in turn is caused by a diminished action of the vasomotor center. In a slow, continuous hemorrhage the nutrition of the heart muscle suffers more acutely and this enters later as an important factor in the causation of death.

In asphyxia of any grade the vasomotor center is stimulated, producing a higher blood pressure and a longer pulse wave, characterized clinically by a slow, full pulse. This is often deceptive, giving a false sense of security, so that what sometimes seems to be a marked improvement in the pulse is, when properly interpreted, a grave symptom.

The vasomotor system is the principal means of compensation in all the various circulatory crises occurring in the normal and pathologic state. When the blood pressure is falling in one territory an increased vasomotor action in another may compensate for it; dilatation in the skin area is compensated for by contraction in the splanchnic area and vice versa.

The splanchnic area and the brain have a certain and most important interrelation. To this subject Cushing has recently made, important contributions. When the intracranial tension is increased, threatening to cause anemia of the vasomotor center, this center sends out strong impulses to the splanchnic area, causing extensive vascular contractions there, which in turn produce a marked rise in the general blood pressure, thus reestablishing the amount of circulation in the vasomotor and other centers required for their normal function. In increased intracranial pressure from hemorrhage, abscess, depressed bone, tumors, and other causes, unless other factors interfere, the general blood pressure usually is increased. The blood pressure which normally is approximately 120 to 135 mm., has been raised in pathologic intracranial pressure to 425 mm. mercury. Thus the action of the vasomotor system may be seen to be one of the strongest