[Physiological basis of the clinical course and treatment of shock]

Shock occurs when the circulatory system fails to maintain adequate cellular perfusion, with widespread reduction in delivery of oxygen and other nutrients to tissues. Irreversible cellular injury and multisystem organ failure develop if the condition is not promptly remedied. In cardiogenic, hypovolemic and vascular obstructive shock, systemic vascular resistance is elevated and pulmonary artery oxygenation is decreased. Distributive shock is caused primarily by vasomotor dysfunction resulting in excessive venous pooling, loss of arteriolar tone, and redistribution of blood flow. Cardiac output and intravascular volume may be low, normal or increased in the presence of hypotension in distributive shock. The characteristic pattern of cardiac performance of septic shock is reduced left and right ventricular ejection fractions, increased end-diastolic and end-systolic volumes of both ventricles and normal stroke volumes.