Hypovolemic shock is a potentially life-threatening situation in which reduced intravascular blood volume causes circulatory dysfunction and inadequate tissue perfusion. Tissue anoxia prompts a shift in cellular metabolism from aerobic to anaerobic pathways. This produces an accumulation of lactic acid. resulting in metabolic acidosis.

Without sufficient blood or fluid replacement. hypovolemic shock may lead to irreversible cerebral and renal damage. cardiac arrest and. ultimately. death.Hypovolemic shock necessitates early recognition of signs and symptoms and prompt. aggressive treatment to improve the prognosis.

Causes of Hypovolemic Shock

Hypovolemic shock most commonly results from acute blood loss - about one-fifth of total volume. Massive blood loss may result from GI bleeding. internal hemorrhage (such as hemothorax or hemoperitoneum). external hemorrhage (caused by accidental or surgical trauma). or any condition that reduces circulating intravascular plasma volume or other body fluids such as in severe burns.

Other causes of hypovolemic shock include intestinal obstruction. peritonitis. acute pancreatitis. ascites and dehydration from excessive perspiration. severe diarrhea or protracted vomiting, diabetes insipidus, diuresis. and inadequate fluid intake.

Signs & Symptoms of Hypovolemic Shock

Hypovolemic shock can cause the following:

cold, pale skin
fainting
low blood pressure
confusion
reduced urine output
rapid heartbeat

Diagnostic Tests

Characteristic laboratory findings include:

low hematocrit and decreased hemoglobin levels and red blood cell and platelet counts .
elevated serum potassium. sodium, lactate dehydrogenase. creatinine. and blood urea nitrogen levels . increased urine specific gravity (greater than 1.020) and urine osmolality.
decreased urine creatinine levels .
decreased pH and partial pressure of oxygen in arterial blood and increased partial pressure of carbon dioxide in arterial blood.

In addition, X-rays, gastroscopy. aspiration of gastric contents through a nasogastric tube, and tests for occult blood identify internal bleeding sites. Coagulation studies may detect coagulopathy from disseminated intravascular coagulation.

Treatment

Emergency treatment measures include prompt and adequate blood and fluid replacement to restore intravascular volume and to raise blood pressure and maintain it above 60 mm Hg. Infusion of normal saline solution or lactated Ringer's solution and then possibly plasma proteins (albumin) or other plasma expanders may produce adequate volume expansion until packed cells can be matched. A rapid solution infusion system can provide these crystalloids or colloids at high flow rates.

In severe cases, an intraaortic balloon pump, ventricular assist device, or pneumatic antishock garment may be helpful.

Treatment may also include oxygen administration, bleeding control by direct application of pressure and related measures, dopamine or another inotropic agent, and possibly surgery to correct the underlying problem. To be effective, dopamine or other inotropic agents must be used with vigorous fluid resuscitation.

Prevention Tips

Preventing shock is easier than trying to treat it once it happens. Prompt treatment of the underlying cause will reduce the risk of developing severe shock. Early first aid can help control shock.

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