- Hypovolemic Shock is shock due to major reductions in effective circulating volume, that is hypovolemia.
- Hypovolemic shock may occur due to a major hemorrhage or severe dehydration. In either case, the effective circulating volume of the body is severely reduced resulting in inadequate volume to properly perfuse tissues. The SNS is intensely stimulated in severe hypovolemia and coordinates a number of important compensatory responses which aim to increase cardiac output. As described in Systemic Arterial Pressure - Autonomic Control, these include attempts to increase venous return and thus preload by causing venoconstriction as well as attempts to increase systemic vascular resistance by inducing vasoconstriction. Finally, intense sympathetic stimulation of the kidneys, as described in SNS - Renal Effects, result in reduced glomerular filtration and increased salt and water resorption of any fluid that is filtered. When such compensatory mechanisms fail, progression to death can be very rapid.