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Hypovolemic Shock

Classification of Shock Based on Blood Volume and Pressure

There are several types of classification of shock. The functional classification of shock is based on the volume and pressure of blood. According to this classification, these categories include:

  • Hypovolemic shock - inadequate volume of blood to fill the vascular system
  • Cardiogenic sock - inadequate output of the heart due to heart muscle abnormalities
  • Vasogenic (distributive) shock_ - vasodilation in the presence of normal blood volume
  • Obstructive shock - inadequate heart output as a result of obstruction of blood flow in the lungs or heart

The shock syndromes of greatest importance in small animals include hypovolemic shock, systemic inflammatory response (septic shock), traumatic shock (surgical or blunt trauma) and cardiogenic (including obstructive) shock. 3

Hypovolemia is reduced blood volume. Hypovolemic shock results from acute blood loss. Such massive blood loss may result from gastrointestinal bleeding, internal bleeding caused by accidental or surgical trauma (hemorrhagic shock), or severe burns or crush injuries. Other underlying causes of hypovolemic shock include intestinal obstruction, acute pancreatitis, ascites, dehydration, severe diarrhea or prolonged vomiting, diabetes insipidus, or inadequate fluid intake.1

Extensive blood loss is required before animals develop hypovolemic shock. Healthy animals may lose one-fourth of their blood volume without showing immediate clinical signs and loss of one-half of blood volume may be required to result in death. When much blood is lost, the arterial blood pressure drops, and venous blood return to the heart decreases. Hypovolemic shock produces profound changes in all organs of the body: there is increased formation of blood clots in capillaries; liver cells degenerate and fail to detoxify harmful substances which are allowed to pass into the general circulation; blood vessels in the kidneys constrict which leads to small amounts of urine produced during shock; heart muscle undergoes damage caused by bleeding and lack of oxygen in heart muscle tissue; adrenal glands produce large amounts of neurotransmitter epinephrine and gradually degenerate; the gastrointestinal tract develops lesions due to decreased production of protective mucin which is part of mucosal barrier; skeletal muscles become pale.2

Signs of Hypovolemic Shock

Hypovolemic shock is characterized by low blood pressure; a rapid, thready pulse; cold, pale, clammy skin; intense thirst; rapid respiration; and restlessness.

Treatment of Hypovolemic Shock

Restoration of an effective circulating blood volume is the first priority in hypovolemic, traumatic and septic shock.

1. Professional Guide to Diseases. Lippincott Williams & Wilkins
2. Introduction to veterinary pathology. Norman F. Cheville
3. Textbook of small animal surgery. Douglas H. Slatter
4. Pathophysiology of disease: an introduction to clinical medicine. Stephen J. McPhee, William F. Ganong



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