• Hypovolaemic shock - This is the most common type of shock and based on insufficient circulating volume. Its primary cause is loss of fluid from the circulation from either an internal or external source. An internal source may be haemorrhage. External causes may include extensive bleeding, high output fistulae or severe burns.

• Cardiogenic shock - This type of shock is caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large myocardial infarction. Other causes of cardiogenic shock include arrhythmias, cardiomyopathy, congestive heart failure (CHF), contusio cordis or cardiac valve problems.

• Distributive shock - As in hypovolemic shock there is an insufficient intravascular volume of blood. This form of "relative" hypovolemia is the result of dilation of bloodvessels which diminishes systemic vascular resistance. Examples of this form of shock are:
  • Septic shock - This is caused by an overwhelming infection leading to vasodilation, such as by Gram negative bacteria i.e. Escherichia coli which releases an endotoxin which produces adverse biochemical, immunological and occasionally neural mechanisms which are harmful to the body.
  • Anaphylactic shock - Caused by a severe anaphylactic reaction to an allergen, antigen, drug or foreign protein causing the release of histamine which causes widespread vasodilation. Leading to hypotension and increased capillary permeability.
  • Neurogenic shock - Neurogenic shock is the rarest form of shock. It is caused by trauma to the spinal cord resulting in the sudden loss of autonomic and motor reflexes below the injury level. Without stimulation by sympathetic nervous system the vessel walls relax uncontrolled, resulting in a sudden decrease in peripheral vascular resistance, leading to vasodilation and hypotension.

• Obstructive shock - In this situation the flow of blood is obstructed which impedes circulation and can result in circulatory arrest. Several conditions result in this form of shock.
  • Cardiac tamponade in which blood in the pericardium prevents inflow of blood into the heart (venous return). Constrictive pericarditis, in which the pericardium shrinks and hardens, is similar in presentation.
  • Tension pneumothorax. Through increased intrathoracic pressure, bloodflow to the heart is prevented (venous return).
  • Massive pulmonary embolism is the result of a thromboembolic incident in the bloodvessels of the lungs and hinders the return of blood to the heart.
  • Aortic stenosis hinders circulation by obstructing the ventricular outflow tract

Recently a fifth form of shock has been introduced:

• Endocrine shock based on endocrine disturbances.
  • Hypothyroidism, in critically ill patients, reduces cardiac output and can lead to hypotension and respiratory insufficiency.
  • Thyrotoxycosis may induce a reversible cardiomyopathy.
  • Acute adrenal insufficiency is frequently the result of discontinuing corticosteroid treatment without tapering the dosage. However, surgery and intercurrent disease in patients on corticosteroid therapy without adjusting the dosage to accommodate for increased requirements may also result in this condition.
  • Relative adrenal insufficiency in critically ill patients where present hormone levels are insufficient to meet the higher demands.

Signs and symptoms

• Hypovolaemic shock
  • Anxiety, restlessness, altered mental state due to decreased cerebral perfusion and subsequent hypoxia.
  • Hypotension due to decrease in circulatory volume.
  • A rapid, weak, thready pulse due to decreased blood flow combined with tachycardia.
  • Cool, clammy skin due to vasoconstriction and stimulation of sweat glands.
  • Oliguria (low urine output) due to renal artery vasonconstriction.
  • Rapid and deep respirations due to sympathetic nervous system stimulation and acidosis.
  • Hypothermia due to decreased perfusion and evaporation of sweat.
  • Thirst and dry mouth, due to fluid depeletion.
  • Fatigue due to inadequate oxygenation.
  • Cold and mottled skin (cutis marmorata), especially exteremities, due to insufficient perfusion of the skin.

• Cardiogenic shock, similar to hypovolaemic shock but in addition:
  • Distended jugular veins due to increased jugular venous pressure.
  • Absent pulse due to tachyarrhythmia.

• Obstructive shock, similar to hypovolaemic shock but in addition:
  • Distended jugular veins due to increased jugular venous pressure.
  • Pulsus paradoxus in case of tamponade

• Septic shock, similar to hypovolaemic shock except in the first stages:
  • Pyrexia and fever, or hypothermia, due to overwhelming bacterial infection.
  • Vasodilation and increased cardiac output due to sepsis.

• Neurogenic shock, similar to hypovolaemic shock in its presentation.

• Anaphylactic shock
  • Skin eruptions and large weals.
  • Localised edema, especially around the face.
  • Weak and rapid pulse.
  • Breathlessness and cough due to occlusion of airways and swelling of the throat.

Treatment

First aid

• Immediate reassurance and comforting the casualty if conscious.
• If alone, go for help. If not, send someone to go for help and someone stay with the casualty.
• Ensure the patency of the airway and assess breathing. Position in the recovery position if able.
• Attempt to stem any obvious haemorrhaging.
• Cover the patient with a blanket or jacket, but not too thick to cause vasodilation.
• Do not give a drink, moisten lips if requested.
• Prepare for cardiopulmonary resuscitation.
• Give as much information when the ambulance arrives.

The management of shock requires immediate intervention, even before a diagnosis is made. Re-establishing perfusion to the organs is the primary goal through restoring and maintaining the blood circulating volume ensuring oxygenation and blood pressure are adequate; achieving and maintaining effective cardiac function and preventing complications. Patients attending with the symptoms of shock will have, regardless of the type of shock, their airway managed and oxygen therapy initiated. In case of respiratory insufficiency (i.e. diminished levels of consciousness, hyperventilation due to acid-base disturbances or pneumonia) intubation and mechanical ventilation may be necessary. A paramedic may intubate in emergencies outside the hospital, whereas a patient with respiratory insufficiency in-hospital will be intubated usually by a physician.

The aim of these acts is ensure survival during the transportation to the hospital; they do not cure the cause of the shock. Specific treatment depends on the cause.

A compromise must be found between:

• raising the blood pressure to be able to transport "safely" (when the blood pressure is too low, any motion can lower the heart and brain perfusion, and thus cause death);
• respecting the golden hour. If surgery is required, it should be performed within the first hour to maximise the patient's chance of survival.

In-hospital management

Hypovolaemic shock