The Effect of Total Sympathectomy on the Occurrence of Shock from Hemorrhage.

Shock has been differentiated from hemorrhage on the basis of hemoconcentration, negative reaction to blood transfusions, and pathological changes in the tissues (1). In hemorrhage, dilution of the blood occurs while concentration takes place in shock. After simple loss of blood, prompt recovery follows transfusion, whereas in severe shock, the administration of blood is frequently unavailing. It has been held that the tissues are anemic after hemorrhage while the pathological picture of shock is that of " dilatation and engorgement of capillaries and vessels " (2). Blalock, however, in a convincing series of experiments (3), showed that the classical picture of shock with hemoconcentration, negative reaction to transfusion, and pathological changes in the tissues, could be produced by hemorrhage alone. In his experiments on dogs under local anesthesia, the blood pressure was maintained at a low level for several hours by means of hemorrhage. At the end of this time, in spite of the fact that all the blood which had been removed was reinjected, the blood pressure continued to fall and the animal died. The present experiments were performed to investigate further the mechanism through which shock was produced by hemorrhage. It is recognized that vasoconstriction takes place after hemorrhage and this reaction has been described as protective (4). By means of contraction of the vessels in the presence of hemorrhage, the blood pressure is maintained at a level compatible with life. After removal of the vasoconstrictors by complete sympathectomy, cats under anesthesia are unable to tolerate as great a loss of blood as normal animals (5). In a former communication (6), it was shown, on the other hand, that intense and prolonged vasoconstriction caused a reduction in blood volume and