Specific Forms of Shock

In its most severe form, heart failure can cause cardiogenic shock. When the cardiac output becomes too low, ischemia in the periphery occurs which begins the downward spiral associated with the shock state. What makes cardiogenic shock so difficult to treat is that often the primary lesion itself is often irreparable, as in myocardial infarction or end-stage heart failure. Cardiogenic shock can also result from the abrupt appearance of a valve lesion or filling of the pericardial space with fluid that constricts the heart and opposes diastolic filling (pericardial tamponade). Fluid resuscitation will obviously be less effective in cardiogenic shock, although further elevation of preload may still improve cardiac output in selected patients. A Swan-Ganz catheter is often used to make sure that only enough fluid is added to achieve an optimal ventricular filling pressure.

As mentioned earlier, hemorrhage reduces blood volume and sepsis causes peripheral pooling of fluids. In burn patients, fluid is lost at the site of the burn where raw tissue is exposed. In traumatic shock with extensive blunt tissue injury, internal hemorrhage and the release of toxic substances from the necrotic tissue cause vasodilation and peripheral pooling of blood.

Neurogenic shock may be caused by spinal cord or brain injury. It will be recalled that peripheral vascular control by the CNS is accomplished by varying the tone of the sympathetic nerves that constrict the peripheral vasculature (Chapter 17). Because the sympathetic nerves are unopposed, dilation is accomplished simply by reducing sympathetic tone. The sympathetic nerves course through the spinal cord; hence, transection of the cord will cause a profound vasodilation that will persist for weeks following the event. Hypotension due to a reduction of both filling pressure and peripheral resistance will occur immediately after the lesion, and the shock syndrome will soon follow unless aggressive resuscitation is instituted. Anaphylactic shock can occur when an antigen-antibody reaction occurs in the circulation. An example would be transfusion with an incompatible blood type. The reaction stimulates mast cells in the tissues to secrete histamine and related substances that cause vasodilation and increased capillary permeability. In these conditions, the hypotension can be so severe that circulatory collapse occurs within minutes.

Your Heart and Nutrition

Your Heart and Nutrition

Prevention is better than a cure. Learn how to cherish your heart by taking the necessary means to keep it pumping healthily and steadily through your life.

Get My Free Ebook

Post a comment