Source: Close, A. "Emergency Care", 2001.

Shock is "the loss of effective (blood) circulation." Effective circulation, or perfusion, is achieved when blood that is carrying sufficient oxygen is supplied to all cells throughout the body. Insufficient oxygen supply to the cells is called hypoxia. The causes of shock fit three main categories: Absolute, Relative and Cardiac. Although they have different causes, they all result in lack of sufficient oxygen to meet the body's needs.

Absolute Fluid Loss

Also known as hypovolaemic shock, absolute fluid loss can be caused by either bleeding, or dehydration from sweating. If not controlled it will result in inadequate oxygen supply to the tissues (shock). Blood loss can be external or internal.

Relative Fluid Loss

The blood volume remains the same but the size of the blood vessels in the system increases )similar to 1 litre of milk in a 2 litre carton). The effect of increasing the size of the blood vessels but not increasing blood volume may be a rapid and life-threateding drop in blood pressure. This may be caused by:
- Nervous control: the size of blood vessels are affected by pain, spinal injury, etc
- Chemicals and drugs: such as alcohol causing enlargement of blood vessels
- Severe Infections: (septic shock) toxins cause the size of blood vessels to increase
- Anaphylaxis: severe allergic reactions cause blood vessels to enlarge, the heart to beat too rapidly, and extreme difficulty in breathing as well as other detrimental effects on the body.

Heart Failure

This is also known as cardiac failure, or in severe cases cardiogenic shock. It is the failure of the heart to pump effectively due to injury or disease. If the heart's blood supply is intterupted by a coronary artery becoming narrowed or blocked (such as occurs in a heart attack) it's pumping ability may be reduced. If the damaged heart fails and cannot pump enough blood, the cells of the body will not be adequately perfused (oxygenated) causing shock.

Signs of shock appear when blood loss excedes 15%, or 750 mls (120 mls for infants). When the body suffers shock, the brain stem compensates with a combination of responses:
- Increasing heart and breathing (respiratory) rates to maximise blood oxygenation
- Constriction of the blood vessels to maintain blood pressure. This diverts blood away from teh skin, muscles, stomach and intestines to the vital organs such as heart, kidneys, and brain.

Signs and Symptoms of Shock

- Breathing rate and depth increase to supply more oxygen to the body
- Pulse rate increases and becomes more rapid and weak as shock progresses
- Pale, cool and moist (clammy) skin
- The skin will become blue (cyanosed) as oxygen supply decreases
- Blood pressure drops, heart and breathing rates try to increase
- Nausea and or vomiting
- Patient complains of excessive thirst
- Muscle weakness, due to poor flow of blood to the muscles
- Anxiety, restlessness and fainting due to the lack of oxygen to the brain
- Decreasing consciousness ending in unconsciousness
- Breathing failure due to hypoxia of the control center and muscles of respiration
- Heart failure due to a slowing, irregular and or chaotic pulse
- Loss of pulse and respiratory failure results in death

Normal Patient:
- Pulse: 60-80
- Skin Colour: Pale
- Skin Temperature: Warm
- Conscious state: Conscious, alert, responding
- Respiration: 12-14 Quiet Shallow

Early Shock
- Pulse: >100 increasing
- Skin Colour: Normal/Pink
- Skin Temperature: Cool, Moist
- Conscious State: Conscious, alert, responding
- Respiration: Increasing in rate (>20) and depth

Late Shock
- Pulse: Rapid >120 and weak (or no pulse)
- Skin Colour: Pale, cyanosed
- Skin temperature: Cold
- Conscious state: Unconscious
- Respiration: Increase in rate >30 or <6-8 breaths/minute or no breathing.

Treatment of Shock

In emergency, the only cause of shock that can be effectively treated by the First Aider is external bleeding and the patient who has simply fainted. While waiting for assistance, the First Aider can minimise the factors that contribute to, or accelerate, the shock process such as anxiety and pain. Fire Aid assists in reducing the pain and physical effects of shock.

- Carry out DRABC
- Control bleeding immediately
- Arrange urgent medical/ambulance assistance
- Reassure the patient
- Rest the patient by laying or sitting them down, if possible in position of least pain.
- Perform the secondary survey and establish history
- Dress any wounds and treat burns
- Manage fractures, to reduce pain and internal bleeding
- Place the patient in the shock position by elevating the legs if not fractured
- Keep the patient comfortable and maintain body temperature but don't overheat.
- Loosed any tight clothing
- Provide oxygen therapy if it is available and you have been trained to administer it
- Monitor and record pulse, breathing, skin and conscious level at regular intervals
- Inform emergency services of all information about the incident and patient(s)