Veterinary Clinical Medicine-I (General and Systemic)

Causes and classifications of shock

CAUSES AND CLASSIFICATION OF SHOCK

• Multiple classification systems and etiologies of shock have been described. The classic approach will be used here

Hypovolemic shock

• It is one of the most common etiologies, and means that blood volume is low. This can be due to two major causes: hemorrhage (either external or internal) and dehydration. Dehydration does not always cause hypovolemia, but in severe cases can lead to it. The categories of hemorrhagic shock are listed below:
  Cardiogenic shock
• It occurs when the heart is unable to put enough blood forward to maintain perfusion and oxygen delivery. Examples of cardiogenic shock include dilated cardiomyopathy, mitral regurgitation and myocardial failure Obstructive shock
• It occurs when there is an obstruction to flow. Usually this is an obstruction to venous return, although arterial obstruction (such as with a saddle thrombus) can also cause obstructive shock. GDV, pericardial effusion, venous thrombosis and tension pneumothorax are all causes of obstructive shock.

Distributive shock

• It is a combination of various types of shock. (Mal)distributive shock usually occurs as a result of sepsis, although anaphylaxis can cause it as well. The hallmark of distributive shock is peripheral vasodilation and vascular pooling.
• The patient may have red instead of pale mucous membranes.
• Patients with septic shock may also have elements of hypovolemia (from fluid losses or tissue edema), cardiogenic (from myocardial dysfunction) and obstructive (from DIC) shocks.

Hypoxemic and anemic shock

• It occurs when there is insufficient oxygen content to meet tissue needs. This can be that there are not enough red blood cells to carry the oxygen (anemic), or that the oxygen cannot get into the blood (hypoxemic). Hypoxemic shock is usually the result of pulmonary pathology.

Neurogenic shock

• It is a specialized form of distributive shock. Massive sympathetic release causes severe systemic vasoconstriction, which results in decreased forward flow and signs of shock despite adequate blood volume.
• Causes are severe spinal cord or CNS injury, head trauma, status epilepticus, strangulation and airway obstruction.

Metabolic shock

• It is caused when the cells have sufficient oxygen for normal metabolism, but are unable to use that oxygen. This is usually the result of disruption of the Krebs cycle or the electron transport chain.
• Causes include hypoglycemia, cyanide toxicity or mitochondrial dysfunction (as occurs with sepsis).