• Heart failure is a condition in which the heart is unable to adequately propel blood through the circulation.
• The cardinal sign of heart failure is elevated venous pressure on the side of the heart that is failing. If both sides are failing, venous pressure rises on both sides.
• Increased venous pressure causes distension of the veins and edema (venous congestion). Pulmonary edema can occur quickly, sometimes with fatal consequences.
• Compensations such as increased venous pressure may keep the cardiac output normal in mild failure; however, the ability to increase cardiac output (reserve) is lost.
• An abrupt increase in venous pressure can cause the heart to dilate, which further weakens it due to the law of LaPlace.
• Increased workload causes the heart to hypertrophy; hypertrophy invariably leads to failure.
• In circulatory shock, an inadequate cardiac output causes damage to the organs.
• Causes of shock include low blood volume, loss of autonomic tone, and impaired cardiac function.
• Injury to the periphery occurs in a progressive manner when the cardiac output is reduced. As injury continues, the capillaries become permeable to plasma proteins which causes fluid loss into the tissues. Decreased circulating volume causes decreased venous filling of the heart and a further fall in cardiac output.
• Signs of shock include pale, cool skin; oliguria; thirst; and mental confusion.
• Treatment is directed at restoring the cardiac output as soon as possible, often with fluid resuscitation.
Essential Medical Physiology, Third Edition
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