In categorizing the causes of shock, it is helpful to consider the components of the cardiovascular system that determine blood flow to the tissues: the heart (the pump), the blood vessels, and the volume of blood in the system. Shock can be caused by a failure of, or deficit in, any of these components. Hypovolemic shock occurs when circulating blood volume is decreased because of loss of whole blood (hemorrhagic shock), loss of plasma volume (e.g., burn), or loss of fluid and electrolytes (e.g., vomiting, diarrhea). Cardiogenic shock is caused by myocardial impairment (e.g., myocardial infarction, congestive heart failure). Mechanical obstruction to blood flow can occur anywhere in the circulatory system and cause a local decrease in blood flow. Neurogenic shock (e.g., deep general anesthesia, spinal anesthesia, spinal cord injury) involves loss of vasomotor tone, which leads to venous pooling of blood. Septic or anaphylactic shock involves increased filtration across capillary walls, which leads to decreased circulating blood volume.