Circulatory shock, commonly known as shock, is a life-threatening medical condition of low blood perfusion to tissues resulting in cellular injury and inadequate tissue function. The typical signs of shock are low blood pressure, rapid heart rate, and signs of poor end-organ perfusion (i.e.: low urine output, confusion, or loss of consciousness).
A clinical algorhythm for the collapsed hypotensive dog includes: cardiogenic shock, hypovolemic shock, or distributive shock. Cardiogenic shock is uncommon, and may be seen with acute severe heart disease or end-stage heart disease of many etiologies. Systolic myocardial failure and low output heart failure is seen with severe dilated cardiomyopathy. The most important diastolic disease leading to cardiogenic shock is pericardial effusion and cardiac tamponade. Other diastolic heart diseases that cause cardiogenic shock in cats includes hypertrophic cardiomyopathy and restrictive cardiomyopathy. Heart diseases that cause severe volume overload such as acute severe mitral regurgitation and a major chordae tendinae rupture, or acute infective endocarditis of the mitral or aortic valves may cause cardiogenic shock. Severe sustained tachyarrhythmias or bradyarrhythmias decrease cardiac output and can cause cardiogenic shock. Transient tachyarrhythmias or bradyarrhythmias may cause transient decreased cerebral perfusion and syncope (see below) rather than sustained collapse and shock. Hypovolemia may be secondary to hemorrhage or many diseases that cause severe dehydration and a volume underloaded state. Distributive shock occurs when there is inappropriate vasodilation, and main causes include sepsis and anaphylaxis.