2011/05/19

About Shock

Shock is a state in which blood flow to peripheral tissues is inadequate to sustain life because of insufficient cardiac output or maldistribution of peripheral blood flow. Shock may due to inadequate intravascular volume, inadequate cardiac function, indaquate vasomotor tone, or combination of these factors.

Hypovolemic shock
Inadequate intravascular volume produces diminished ventricular filling and a reduction in stroke volume which, unless compensated for by increased heart rate, results in a decreased cardiac output. Acute hemorrhage following trauma is a common cause of hypovolemic shock, or hemorrhage may occur in a preexisting disease such as peptic ulcer, esophageal varices, aortic aneurysm.

Cardiogenic Shock
Although cardiac output is reduced as in hypovolemic shock, the reduction is secondary to ventricular failure in cardiogenic shock. Blood volume is adequate, and the cardiac output will not be significantly improved by fluid administration. Cardiogenic shock may result from mechanical interference with verticular filling, as during tension pneumothorax and pericardial tamponade, or from interference with verticular emptying, as in massive pulmonary embolism. Cardiac Shock also may result from a disturbance of heart rate, frequently associated with preexisting cardiac disease.

Vasodilation
Hypovolemic shock may be relative in that circulating blood volume is normal but insufficient for adequate cardiac filling. A variety of condition may cause widespread venous and or arteriolar dilation. If cardiac output does not increase commensurate with reduce vascular resistance, arterial hypotension develops, and if arterial pressure falls below critical level, vital centers will be inadequately perfused. The degree of hypotension necessary to cause the shock syndrome varies and often is related to the presence of preexisting vascular disease.

Symptoms and Signs
The manifestations associated with shock may due to the shock state itself or to the underlying disease process. Findings in patients with hypovolemic or cardiogenic shock are similar. Mentation may be preserved, but lethargy, confusion, and somnolence are common. The hands and feet are cold, moist and often cyanotic and pale. Capillary filling time is prolonged and, in extreme cases, a bluish reticalar pattern may appear over large areas. The pulse is weak and rapid unless there is associated heart block or terminal bradycardia; in some instances only femoral or carotid pulses can be felt.

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