Hypovolemic shock most commonly results from acute blood loss (approximately 20% of total volume). Massive blood loss may result from GI bleeding, internal or external hemorrhage, or any condition that reduces circulating intravascular volume or other body fluids.

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

Without sufficient blood or fluid replacement, hypovolemic shock may lead to irreversible damage to organs and systems. Without immediate treatment, hypovolemic shock can cause adult respiratory distress syndrome, acute tubular necrosis and renal failure, disseminated intravascular coagulation, multisystem organ failure, and death.

The patient’s history will include conditions that reduce blood volume, such as GI hemorrhage, trauma, and severe diarrhea and vomiting. A patient with cardiac disease may report anginal pain.

Inspection may reveal pale skin, decreased sensorium, and rapid, shallow respirations. Urine output usually falls below 25 ml/hour. Palpation may disclose rapid, thready peripheral pulses and cold, clammy skin. Auscultation of blood pressure usually detects a mean arterial pressure below 60 mm Hg and a narrowing pulse pressure. In patients with chronic hypotension, the mean pressure may fall below 50 mm Hg before signs of shock appear. (See Abnormal hemodynamic values in hypovolemic shock, page 466.)

Orthostatic vital signs and the tilt test may also detect shock.