INITIAL TREATMENT OF SHOCK
Cardiovascular failure, or shock, can be caused by (1) depletion of the vascular volume; (2) compression of the heart or great veins; (3) intrinsic failure of the heart itself or failure arising from excessive hindrance to ventricular ejection; (4) loss of autonomic control of the vasculature; (5) severe untreated systemic inflammation; and (6) severe but partially compensated systemic inflammation. If the shock is decompensated, the mean blood pressure or the cardiac output (more precisely, the product of the pressure and output) will be inadequate for peripheral perfusion. In compensated shock, the perfusion will be adequate but only at the expense of excessive demands on the heart. Depending on the type and severity of cardiovascular failure and on response to treatment, shock can go on to compromise other organ systems. This chapter discusses the cardiovascular and pulmonary disorders associated with shock.
Hypovolemic shock (shock caused by inadequate circulating blood volume) is most often caused by bleeding but may also be a consequence of protracted vomiting or diarrhea, sequestration of fluid in the gut lumen (eg, bowel obstruction), or loss of plasma into injured or burned tissues. Regardless of the etiology, the compensatory responses, mediated primarily by the adrenergic nervous system, are the same: (1) constriction of the venules and small veins in the skin, fat, skeletal muscle, and viscera with displacement of blood from the peripheral capacitance vessels to the heart; (2) constriction of arterioles in the skin, skeletal muscle, gut, pancreas, spleen, and liver (but not the brain or heart); (3) improved cardiac performance through an increase in heart rate and contractility; and (4) increased sodium and water reabsorption through renin-angiotensin-aldosterone as well as vasopressin release. The result is improved cardiac filling, increased cardiac output (both directly by the increase in contractility and indirectly through increased end-diastolic volumes), and increased blood flow to organs with no or limited tolerance for ischemia (brain and heart).
The symptoms and signs of hypovolemic shock are many and can be caused either by the inadequate blood volume or by the compensatory responses. Some signs manifest themselves early, in mild forms of shock. Some present late and only in severe forms of shock. The goal is to pick up on the early signs. Doing so can save a life.
As early signs of shock, the physician might find it difficult to gain intravenous access. The skin might be cold (a nonspecific sign, but an early sign). But, by far and away, the most important, that is, most sensitive, of all the early signs of hypovolemic shock is diminished blood flow to the skin and subcutaneous tissues. It is a sign that needs to be elicited with care. It can be missed. It is best detected in the skin on the plantar surface of the foot, an area without pigmentation, with the color determined solely ...