The Nature of Irreversible Shock

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Abstract
When patients in shock respond temporarily or not at all to blood, plasma or plasma substitutes, they are thought to be in irreversible shock. Studies in the dog indicate that whether shock is induced by hemorrhage, bacterial endotoxins, epinephrine, or myocardial failure, there is a final common hemodynamic disturbance in the peripheral vascular bed. This disturbance is characterized at first by ischemic anoxia in which both the precapillary arterial sphincters (resistance vessels) and postcapillary venular sphincters (capacitance vessels) are tightly constricted, thus allowing little blood to enter the splanchnic bed. This is the period of reversible shock and lasts about 2-3 hours in the dogs, regardless of the original insult. Within 4-5 hours, irreversible shock supervenes and is characterized by stagnant anoxia in which the precapillary arterial sphincters have lost their tone while the postcapillary sphincters are still constricted. Now blood can get into the splanchnic bed but exits with difficulty, and hydrostatic capillary pressure increases. As a result, plasma begins to leave the vascular system at the venous end of the capillaries and circulating blood volume is progressively decreased. As shock is further prolonged, the capillary beds lose their integrity and slough, allowing whole blood to sequester outside of, as well as inside, the vascular system. Myocardial function is even more severely depressed by the acidosis attendant on the peripheral circulatory stagnation. In numerous animal experiments, the combination of the adrenergic blocking agent phenoxybenzamine (Dibenzyline), 1 mg/Kg intravenously, and plasma or low-molecular-weight dextran is an effective means for salvaging dogs from irreversible shock induced by various methods. Hydro-cortisone when given intravenously in doses of 50 mg/Kg acts also as an adrenergic blocking agent and restores normal relationships in the capillary bed even more effectively than Dibenzyline. Patients suffering shock from trauma, infection, myocardial failure or combinations of these insults, are being treated with a regimen including pharmacologic doses of hydrocortisone or phenoxybenzamine in combination with blood, plasma, or dextran. The results in these patients give added support to the belief that shock in man and animals is similar.