Shock is a loss of effective circulation resulting in impaired tissue oxygen and nutrient delivery and causes life threatening organ failure. Any seriously ill or seriously injured person is at risk of developing shock.


Absolute fluid loss can result from either internal or external bleeding where there is damage to the circulatory system or loss of body fluids through severe burns, severe vomiting, or severe diarrhea, etc. This can lead to an inadequate supply of oxygenated blood to the cells and tissue. The onset of shock starts to occur when a casualty loses approximately 15% (approximately 750 ml for an adult) of the circulating blood volume.

Loss of circulating blood volume (hypovolaemic shock), e.g.:

  • Severe bleeding (internal and / or external)
  • Major or multiple fractures or major trauma
  • Severe burns or scalds
  • Severe diarrhoea and vomiting
  • Severe sweating and dehydration.
Cardiac Causes

Cardiac failure occurs when the heart is suffering from either injury or disease and is unable to pump effectively or efficiently. The heart has its own blood supply coming from the coronary arteries.

If this blood supply is interrupted by blockages or narrowing, as occurs in a heart attack, the heart will not be able to function correctly. The result is a lack of oxygenated blood to the cells and tissue.

Cardiac arrest occurs because of an electrical problem in the heart disrupts its normal rhythm. During cardiac arrest, the electrical signals to the heart become erratic. Blood flow to the brain is reduced and the victim loses consciousness. Death will follow unless emergency treatment is begun. 

Cardiac causes (cardiogenic shock), e.g.:

  • Heart attack
  • Abnormal heart rhythm.

Abnormal dilation of blood vessels (distributive shock), e.g.:

  • Severe infection (sepsis)
  • Severe allergic reactions (anaphylaxis)
  • Severe brain / spinal injuries
  • Fainting (generally short lived).

Blockage of blood flow in or out of heart (obstructive shock), e.g.:

  • Punctured lung causing increased pressure in chest causing reducing return of blood to the heart (tension pneumothorax)
  • Severe injury to the heart with weak heart muscle (cardiomyopathy) or blood around the heart reducing blood return to the heart (cardiac tamponade)
  • Blood clot in the lung (pulmonary embolus)
  • Compression of the large abdominal veins by the uterus in pregnancy.


Early recognition of the seriously ill or seriously injured person should alert the first aider to the risk of developing shock. The symptoms, signs, and rate of onset of shock vary depending on the nature and severity of the underlying cause. Shock is a condition that may be difficult to identify.

Symptoms may include:
  • Dizziness
  • Thirst
  • Anxiety
  • Restlessness
  • Nausea
  • Breathlessness
  • Feeling cold, shivering or chills.
  • Extreme discomfort or pain
 Signs may include:
  • Collapse
  • Rapid breathing
  • Rapid pulse which may become weak or slow.
  • Fever or abnormally low temperature
  • Cool, sweaty skin that may appear pale or discoloured.
  • Skin rash
  • Confusion or agitation
  • Decreased or deteriorating level of consciousness.
  • Vomiting
  • Decreased urine output