Shock

Shock is a pathologic state in which cellular injury results from an inadequate degree of effective tissue perfusion ⁵. It is commonly subcategorized by haemodynamic parameters into hypovolaemic, distributive, cardiogenic, and extracardiac obstructive shock ¹. Common causes include haemorrhage, cardiac tamponade and spinal cord injury in trauma patients, and sepsis in hospitalised patients.

Clinical presentation

The typical signs and symptoms of shock are non-specific and may depend upon the underlying aetiology. They may include:

• hypotension
• tachycardia
• cold, pale and/or clammy skin
• confusion
• loss of consciousness
• oliguria

Pathology

Aetiology

While the majority of shock encountered in clinical practice is mixed, it may broadly be categorised based on haemodynamic parameters as follows 

• hypovolaemic shock: reduction in intravascular volume with a resultant decrease in ventricular preload  
  • haemorrhagic
    • gastrointestinal haemorrhage
    • haemothorax
    • haemoperitoneum
    • retroperitoneal haemorrhage
    • external haemorrhage
  • non-haemorrhagic hypovolaemic
    • gastrointestinal fluid loss (e.g. vomiting, diarrhoea)
    • urinary fluid loss (e.g. iatrogenic diuresis, post-obstructive)
    • insufficient fluid intake
    • interstitial fluid loss (e.g. sepsis, thermal burns, pancreatitis)
• cardiogenic shock: primary anatomical or functional cardiac pump failure
  • myocardial disease
    • myocarditis
    • myocardial infarction
    • cardiomyopathy
    • blunt cardiac injury
  • mechanical
    • intracardiac shunt (e.g. atrial septal defect, ventricular septal defect)
    • valvulopathy
      • stenosis
      • regurgitation
    • left ventricular outflow tract obstruction
  • dysrhythmia
    • tachydysrhythmia
    • bradydysrhythmia
• obstructive shock: caused by impairment of ventricular filling or an increase in ventricular afterload primarily decreasing cardiac output
  • intravascular obstruction
    • acute pulmonary embolus
    • cardiac myxoma
  • extravascular obstruction
    • tension pneumothorax
    • cardiac tamponade
    • abdominal compartment syndrome
    • constrictive pericarditis
    • tension hydrothorax
• distributive shock: characterised by vasoplegia with a decreased in stressed venous volume and systemic vascular resistance 
  • neurogenic shock
  • anaphylactic shock
  • septic shock
  • thyrotoxicosis
  • adrenal crisis
  • toxic shock syndrome

Treatment and prognosis

Management of shock, regardless of aetiology, rests on resuscitation of the patient first, followed by definitive treatment of the underlying cause. These often have to occur concurrently, e.g. a bleeding patient will require fluids and blood to maintain cardiac output but also the exsanguination must be located and stopped. 

Mortality rates for untreated shock - regardless of aetiology - are very high.

See also

• approach to shock
• CT hypoperfusion complex
• focus‐assessed transthoracic echocardiography (FATE)
• rapid ultrasound in shock (RUSH)
• electrocution (electric shock)