In physiology and medicine, hypovolemia is a state of decreased blood volume.

Causes

Common causes of hypovolemia are dehydration, bleeding, and drugs such as diuretics or vasodilators typically used to treat hypertensive individuals. Rarely, it may occur as a result of a blood donation. Severe hypovolemia leads to hypovolemic shock.

Diagnosis

Hypovolemia can be recognized by elevated pulse, diminished blood pressure, and the absence of perfusion as assessed by skin signs (skin turning pale) and/or capillary refill on forehead, lips and nail beds. The patient may feel dizzy, faint, nauseous or very thirsty. These signs are also characteristic of most types of shock.

Note that in children, compensation can result in an artificially high blood pressure despite hypovolemia. This is another reason (aside from initial lower blood volume) that the even the possibility of internal bleeding in children should always be treated aggressively.

Also look for obvious signs of external bleeding while remembering that people can bleed to death internally without any external blood loss.

Also consider possible mechanisms of injury (especially the steering wheel and/or use/non-use of seat belt in motor vehicle accidents) that may have caused internal bleeding such as ruptured or bruised internal organs. If trained to do so and the situation permits, conduct a secondary survey and check the chest and abdominal cavities for pain, deformity, guarding or swelling. (Injuries to the pelvis and bleeding into the thigh from the femoral artery can also be life-threatening.)

Treatment

Minor hypovolemia from a known cause that has been completely controlled (such as a blood transfusion from a healthy patient who is not anemic) may be countered with initial rest for up to half an hour, oral fluids including moderate sugars (apple juice is good) and the advice to the donor to eat good solid meals with proteins for the next few days. Typically, this would involve a fluid volume of less than one liter (1000 ml), although this is highly dependent on body weight. Larger people can tolerate slightly more blood loss than smaller people.

More serious hypovolemia should be assessed by a nurse or doctor. When in doubt, treat hypovolemia aggressively.

First Aid

External bleeding should be controlled by direct pressure. If direct pressure fails, other techniques such as elevation and pressure points should be considered. The tourniquet should almost never be employed. If a first-aider recognizes internal bleeding, the life-saving measure to take is to immediately call for advanced medical help.

Field Care

Emergency oxygen should be immediately employed to increase the efficiency of the patient's remaining blood supply. This intervention can be life-saving.

The use of intravenous fluids (IVs) may help compensate for lost fluid volume, but IV fluids cannot carry oxygen in the way that blood can. See also emergency medical services for a discussion of techniques used in IV fluid management of hypovolemia.

Hospital Treatment

If the hypovolemia was caused by medication, the administration of antidotes may be appropriate but should be carefully monitored to avoid shock or the emergence of other pre-existing conditions.

Blood transfusions coupled with surgical repair are the definitive treatment for hypovolemia caused by trauma. See also the discussion of shock and the importance of treating reversible shock while it can still be countered.