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Chapter: Pathology: Circulatory Pathology

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Shock

Shock is characterized by vascular collapse and widespread hypoperfusion of cells and tissue due to reduced blood volume, cardiac output, or vascular tone.

SHOCK

Shock is characterized by vascular collapse and widespread hypoperfusion of cells and tissue due to reduced blood volume, cardiac output, or vascular tone. The cel-lular injury is initially reversible; if the hypoxia persists, the cellular injury becomes irreversible, leading to the death of cells and the patient.

Major Causes of Shock

·              Cardiogenic shock (pump failure) can be due to myocardial infarction, car-diac arrhythmias, pulmonary embolism, and cardiac tamponade.

 

·              Hypovolemic shock (reduced blood volume) can be due to hemorrhage, fluidloss secondary to severe burns, and severe dehydration.

 

·              Septic shock (viral or bacterial infection) causes cytokines to trigger vaso­dilatation and hypotension, acute respiratory distress syndrome (ARDS), DIC, and multiple organ dysfunction syndrome. Mortality rate is 20%.

 

·              Neurogenic shock (generalized vasodilatation) can be seen with anesthesiaand brain or spinal cord injury.

 

·              Anaphylactic shock (generalized vasodilatation) is a type I hypersensitivityreaction.

 

Stages of Shock

The stages of shock are arbitrarily defined as follows.

·              Stage I: compensation

Perfusion to vital organs is maintained by reflex mechanisms. Compensation is characterized by increased sympathetic tone, release of catecholamines, and activation of the renin-angiotensin system.

·              Stage II: decompensation

There is a progressive decrease in tissue perfusion, leading to potentially reversible tissue injury with development of a metabolic (lactic) acidosis, elec-trolyte imbalances, and renal insufficiency.

·              Stage III: irreversible tissue injury and organ failure This ultimately results in death.

 

The organs show various manifestations of shock:

·              Kidneys show fibrin thrombi in glomeruli and ultimately, acute tubular failure ensues, which causes oliguria and electrolyte imbalances.

 

·              Lungs undergo diffuse alveolar damage (“shock lung”).

 

·              Intestines show superficial mucosal ischemic necrosis and hemorrhages, and with prolonged injury, bacteremia may ensue.


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