Difference between revisions of "Shock"

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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

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.