Shock

What is Shock?

• "Shock" is a clinical term to describe a condition in which:
  • The body temperature is subnormal.
  • Reflexes are subnormal.
  • Respiration is shallow.
  • There is a rapid thready pulse.

Cause of Shock

• The cause of shock is circulatory failure.
  • This leads to impaired perfusion of tissues, resulting in inadequate cellular oxygenation.

Types of Shock

Hypovolaemic shock

• This is caused by massive reduction in circulating blood volume.
  • For example, due to loss in
    • Severe haemorrhage.
    • Extensive body burns.
      • There is excessive loss of tissue fluid from the injured areas.

Trauma, pain and major surgery

• Trauma, pain and minor surgery affect the vasomotor control of the peripheral circulation.
• The capillaries become dilated and blood pools in the peripheral circulation.
  • A secondary hypovolaemia occurs.

Endotoxic shock

• Endotoxic shock occurs in severe infections by Gram negative bacteria.
• The toxins produced by the bacteria are thought to induce clotting of the blood in very small vessels.
  • The flow is blocked and blood pools in the peripheral tissues.

thereby blocking the flow and causing pooling of blood in the peripheral

• The condition is known as Disseminated Intravascular Coagulation.

Cardiogenic shock

• Cardiogenic shock occurs when a suddenly developing cardiac failure causes circulatory collapse, e.g.
  • Myocardial infarction
  • Severe arrhythmia
  • Sudden failure of the valves.

Pathophysiology of Shock

• In haemorrhagic and burn shock, there is reflex vasoconstriction of the peripheral and splanchnic blood vessels.
  • The body becomes starved of oxygen.
  • There is no constriction of the cerebral or coronary blood vessels - this protects the brain and the heart.
• The fall in blood pressure stimulates the release of renin from the kidney.
  • Angiotensin from the liver is activated.
    • Causes an increase in blood pressure.
    • Stimulates the adrenal cortex to secrete aldosterone, which causes the kidney to retain sodium and water.
    • The flow of urine may cease.
• The kidney is particularly vulnerable to shock.
  • If the condition is prolonged, acute tubular necrosis will develop.
• After a sustained period of oxygen deficit, the vasomotor control over the blood vessels is lost.
  • Blood becomes pooled in the capillary beds.
  • This state is termed "irreversible shock" and is quickly followed by death.

Post-Mortem Findings

• Post-mortem findings are non-specific.
• The lungs are wet and heavy, showing congestion and oedema.
  • The alveolar capillaries are distended with blood.
  • The alveoli are filled with haemorrhage and oedema fluid.
• A degree of atelectasis (collapse) also develops.
• In the intestine, the blood vessels are congested and there is patchy haemorrhage of the mucosa due to localised anoxia.
  • There is also a considerable amount of blood stained fluid within the lumen.
    • May be mistaken for inflammation.
• The kidneys cortex appears pale due to tubular necrosis, while the medulla is darkened by congestion.
  • Histologically, the tubular epithelial cells die and fall into the lumen, the basement membranes rupture and irritant material escapes into the interstitium.