Description/Etiology
Hypovolemic shock is a potentially fatal medical emergency caused by a large drop in intravascular fluid volume that leads to a disruption of homeostatic mechanisms, hypotension, cardiovascular collapse, and impaired end-organ perfusion. Causes of hypovolemic shock include severe fluid or blood loss (e.g., in traumatic blood loss) and severe internal fluid shifts (e.g., as occur in patients with severe dehydration, edema, or ascites). Depending on the magnitude of blood loss, hypovolemic shock is classified as class I, loss of less than 15% of the blood volume; class II, loss of 15–30% of the blood volume; class III, loss of 30–40% of the blood volume; and class IV, blood loss > 40%. Loss of more than 30% of total blood volume, which may be life-threatening, results in hypotension, reduced urine output, and changes in mental status.