• Martin Bennett - Photographer

Shock, the unrecognised killer

The body is a highly complex multi-cellular organism which has evolved to its present form over a very long period of time. This paper is to address one small but significant condition which affects the body and is the cause of over 50% of deaths : SHOCK.

Shock is a clinical condition brought about by trauma - a wound or injury. The two words are oft confused. Shock is a very complex reaction to a multitude of actions. Many of these, at some time, we are forced to deal with such as fires and burns, road accidents and injuries or heart attacks.

We refer to it in many ways and this often leaves some confusion as to what is actually happening. For instance, "some shock or injury can induce shock". For the sake of clarity, I will define the clinical condition known as Shock, its various types, its stages, its signs and symptoms and finally its methods of care and treatment.

Shock can be defined as a condition which produces a state of Inadequate Tissue Perfusion and because of this an inadequate oxygen supply to the whole body. Shock results from at least one of the three essential components of the circulatory systems.

1) Blood volume - i.e., the loss of blood or plasma from a burn or a wound.

2) Peripheral Resistance - the widespread blood vessel dilation caused by an injury, sepsis, nervous or allergic reaction.

3) Heart Output - a loss or reduction in heart output as volume or pressure from disease or from heart attack.

The term Shock is really a description for a syndrome which embraces many conditions, but most types of shock have inadequate tissue perfusion as their common denominator.

Tissue perfusion for the purposes of this paper is the end result of respiration and circulation. Each and every cell in our body requires a constant supply of oxygen, water, nutrients and elements, as well as a constant clearing away of waste products. This is done by a complex system of blood vessels. Tissue perfusion on a cellular level takes place from capillary vessels which are in intimate contact with every living cell in the body. The amount of capillary vessel is huge and provides sufficient surface area for cellular respiration to take place.


There are three major types of Shock - Hypovolaemic, Vasogenic and Cardiogenic - each type will be dealt with in order.

Hypovolaemic Shock

This is described as a loss of intravascular fluid volume. The intravascular fluids are whole blood and blood plasma. The loss of extra vascular fluids, plasma, and plasma proteins also causes hypovolaemic shock.

1) Haemorrhage - Loss of whole blood from internal or external bleeding.

2) Fractures - Both open and closed can lead to a considerable blood loss particularly with the major bones.

3) Multiple bruising - Severe or multiple bruising may damage many of the capillary vessels. With injury the permeability of the capillary wall increases, with this plasma escapes from the vascular system.

4) Burns - Burns damage the capillary vessels increasing their permeability and again plasma is lost from the body.

5) Severe dehydration - Such as from vomiting and diarrhoea. Normally we take in far more water than we need, the excess being excreted by the kidneys, skin, lungs and the gastro-intestinal tract. If, however, an abnormal amount of water is lost through these routes hypovolaemic shock will occur.

6) Hyperglycaemia or Diabetic Ketoacidosis - Glucose tends to draw water from the tissue cells, thus an excess of glucose as in hyperglycaemia will cause dehydration.

7) Sweating - Excess sweating such as is experienced at a serious fire or road accident when wearing heavy fire kit, or indeed any form of excess exercise, can induce hypovolaemic shock - excess water is lost through sweating as well as essential salts, used for the maintenance of the electrolyte balance.

Vasogenic Shock

Vasogenic shock is again brought about by a lack of circulatory blood volume, but here the volume of blood in the vascular system remains the same. However, because of certain nervous and hormonal reactions, depending on the cause, the arteries and veins dilate through a loss of control of the vessel wall and valve muscles. The arterioles which supply the capillary beds with blood rich in oxygen and nutrients etc., also give the highest resistance to flow and so with widespread vasodilation there is inadequate peripheral resistance (blood pressure). The vasodilation allows large amounts of blood to pool in the capillary beds. This reduces venous return and in turn cardiac output.

Vasogenic shock has a number of causes - neurogenic shock, anaphylactic shock and septic shock.

1) Neurogenic shock - This can be brought about by a disease, a drug, traumatic injury or pain. Certain nerve impulses from the brain (sympathetic from the vasomotor centre) are stopped, this allows another type of nerve pulse to react freely (runaway parasympathetic response). The result of this imbalance is a loss of vascular tone. The muscles controlling the blood flow through the arteries etc., this allows massive vasodilation. Venous return is severely reduced with decreased heart output and low blood pressure.

2) Anaphylactic shock - Anaphylactic shock is an allergic reaction to certain drugs, foods, bites or stings etc. Many drugs may induce it but the most common are antibiotics. Foods such as cheese, eggs, milk, oranges, nuts, sunflower or sesame seeds. Bites from snakes or insects. These actions cause tissue cells to release the hormone Histamine. Histamine causes an increase in the permeability of the capillaries.

3) Septic shock - Septic shock is caused by a bacterial infection probably of a wound or similar. The bacterial infection will affect the body in two ways - firstly the tissue cells will respond with the release of histamine and their associated messenger proteins, cytokines – this then leads to increased vasodilation and capillary permeability. Secondly the bacterial infection can inhibit the tissue cells from using the available oxygen and nutrients.

Cardiogenic Shock

This is probably the most commonly encountered type of serious shock, simply because of the number of people who have heart attacks. Cardiogenic shock occurs when for some reason the heart fails to pump sufficient blood to give adequate tissue perfusion. The various conditions which lead to this type of shock are: -

Myocardial Infraction. This is where a coronary artery becomes blocked by something such as a blood clot. There are no alternative routes for the blood to take in the heart so the muscle which was supplied by that artery dies.

Chronic heart disease, where for some reason the muscle cells of the heart become diseased, heart valve disease and arrhythmias. Arrhythmias are conditions where the heart is not pumping correctly.

1) Myocardial Infarction or heart muscle damage. This is probably the most common cause of Cardiogenic shock. As a result of the coronary artery blockage the heart muscle dies. The dead (or damaged) muscle tissue is unable to contract or to conduct electricity. Weakened by the damage, the atria or ventricle concerned (pumping chamber) cannot contract with its normal forcefulness. As a result, the heart pumps less blood to the circulatory system including the coronary arteries. Blood pressure and cardiac output drop. Because of the blocked coronary artery the heart muscles are already deprived of oxygen now, because of the reduced heart output these muscles receive even less.

1) Chronic Heart Disease. Where the muscle cells of the heart are diseased. The muscles of the heart become weak and ineffective and unable to pump enough pressure to overcome the pressure present in the major artery (the aorta). Because of this the pumping chambers of the heart fail to empty properly with each contraction.

2) Heart Valve Disease. This is where the inlet and outlet valves of the heart become diseased. When the heart contracts to pump some of the blood is forced back through a valve reducing the pressure and the output.

3) Arrhythmia. The speed at which the heart pumps is critical to our well being. If it is pumping to slowly it will fail to deliver enough blood to perfuse the tissues. If it is pumping to fast it will not allow enough time to fill the pumping chambers of the heart this results in reduced cardiac output.


Shock is a condition that is rarely stable, it is either getting progressively worse or better. Shock progresses at an unpredictable rate, depending on such factors as the patient’s general condition, age and the specific cause.

During shock's earliest stages the body mounts an elaborate counter attack designed to reverse the deadly process. This is known as the Compensatory Mechanism. The signs and symptoms may reflect the effects of shock, others may reflect the body's attempt to compensate and adapt.

The following three stages of shock are an attempt to classify the condition in order of its severity.

Stage 1 - Early or Compensatory Shock

The blood flow is inadequate to fulfil all of the body's nutritional needs adequate to maintain the vital functions. To restore normal blood flow to the vital organs the body puts into effect the Compensatory Mechanism. This constricts the peripheral blood vessels and increases the heart and respiratory rates. If this is successful the compensatory mechanism will raise the arterial blood pressure and improve the blood flow and the tissue perfusion to the vital organs.

Stage 2 - Progressive or Intermediate Shock

The compensatory mechanism put into effect by the body in Stage 1 of shock has now become ineffective. Unable to reverse the shock process, the compensatory mechanism now begins to contribute to the patient's deteriorating condition. The cardiac output and the arterial blood pressure begins to drop. Blood flow in the capillary beds becomes sluggish. Because of the sluggish blood flow the blood becomes saturated with many things, particularly carbon dioxide. This causes the blood to become unnecessarily acid, a condition known as metabolic acidosis. Eventually the blood flow will slow to a point where it begins to stagnate. Once the blood begins to stagnate or ceases to flow it will naturally begin to clot. This partial clotting is known as "Widespread Scattered Intravascular Coagulation".

Stage 3 - Irreversible Shock

A large volume of the patient’s blood is pooled in the capillary beds. If not already, the kidney's which require a very high blood pressure, will fail. Also, the blood flow to the lungs will be so slow as to result in respiratory failure. The arterial blood pressure is now too low to supply oxygen and nutrients to the brain, heart and other vital organs. The lack of tissue perfusion now causes multiple organ failure and the patients death.


Restlessness and Confusion

In early shock this may be a nervous reaction or a low blood oxygen level in the brain or both. In the later stages it is the result of inadequate tissue oxygen supply in the brain. This often shows as varying degrees of anxiety.

Rapid Breathing

In early shock this is again the response to low circulatory blood oxygen levels. In later shock however it is a mechanism to reduce the blood carbon dioxide level induced by the sluggish capillary blood flow. The carbon dioxide stimulates the medulla which increases the rate and depth of breathing.

Rapid Heart Rate - Weak Pulse

This is a common sign of shock and happens across all the various levels. The heart rate is increased to try and increase the arterial blood pressure. Because of the slow capillary return there will be slow pupil dilation/constriction.

Cold Pale Clammy Skin

The body constricts the peripheral blood vessels to move blood away from the skin and non vital parts of the body to try and improve the blood flow to the vital organs. The skin sweats continuously and without a supply of warm blood to drive it off the skin, the liquid (sweat) condenses on the surface giving rise to this clammy feeling.

Dry Mouth and Thirst

This again results from a reduced peripheral blood flow. The production of saliva is decreased. The increased respiratory rates contribute to the dry mouth and the movement of intravascular fluids causes dehydration.

Blood Pressure

In the early stages of shock, the blood pressure may be normal or even slightly higher as the compensatory mechanism has its effect. However, as the shock progresses, the blood pressure may fall. Also, as shock progresses the arterial blood pressure will fall and the venous pressure will drop slightly, again as an effect of the compensatory mechanism. This is known as a "narrowing of the pulse pressure".

Decreased Urine Output

Whilst this is not a useful indicator in the Pre-hospital phase, it is an indication of the blood flow to the kidneys and it is a useful indicator for monitoring the onset or depth of shock over a period of time.


The care and management of casualties suffering the early effects of shock is often a matter of contention. There are, however, certain clear cut steps we can take to reduce the unwanted effects of compensatory shock. With all stages of shock the casualty must be kept warm, but not heated. They must be treated very gently, but with confidence and oxygen can be given to help.

Again the treatment will be broken into the three stages of shock and must be adapted to suit the particular environment in which the casualty is found.

Stage 1 - Early or Compensatory Shock.

The casualty may well be fully conscious and reasonably aware of the situation. If they are not trapped, they should be lain down somewhere safe and comfortable, preferably on a stretcher. They should be kept warm with blankets or a casualty wrap. If the patient has to lie on the ground, the ground will always be cold and uncomfortable, therefore, some insulation must be provided between the patient and the ground. They should lie with their legs slightly raised to improve venous return.

The patient should be comforted as their psychological well being will have a profound effect upon the onset of the later stages of shock. The patient should be given high flow oxygen via the oxygen therapy.

If, however, the patient is trapped it makes things slightly more complex, particularly if it will be sometime before they are released. The patient should be comforted and kept warm, but not heated. Close consultation with the Paramedic or Flying Doctor is essential as metabolic acidosis in the trapped areas of the body, when released into the rest of the blood stream, will cause a very rapid deterioration of the patient. However, where necessary, drugs can be given to help this.

Hearing is one of the last senses to be lost when someone becomes unconscious, therefore, the trapped casualty will hear and may well remember a lot of what goes on around them. As with all injured patients, someone should remain with the casualty to monitor their condition - their pulse rate, colour, consciousness level and breathing. This applies to all to the treatments for shock as the situation can often deteriorate quite quickly.


From the available signs and symptoms each stage does not fall neatly under each set of symptoms, but gradually progresses and deepens.

STAGE 1 - Early and Compensatory Shock

10% blood loss or up to half a litre in an adult.

Dizziness on sitting up.

Heart rate increases (around 90 to 100 beats / minute).

Slightly cool skin.

10% to 20% blood loss or between half a litre and 1 litre in an adult.

Cool, sweating skin.



Heart rate 100 and more per minute.

Rapid rate of respiration.

Blood pressure beginning to fall.

STAGE 2 - Progressive or Intermediate Shock

20% to 40% blood loss or 1 to 2 litres of blood lost in an adult.

Anxiety and fear.

Pale and white.

Cold, clammy skin.

Heart rate 100 and more beats per minute.

Rapid rate or respiration.

Reduction in level of consciousness.

Narrowing of the pulse pressure.

Difficulty in finding a pulse.

STAGE 3 - Irreversible Shock

40% blood loss or 2 litres or more in an adult.

Deathly appearance.

Further reduction in consciousness level.

Rapid heart rate.

Respiratory distress.

Very low blood pressure

Very difficult to find a pulse.

STAGE 2 - Progressive Shock

Here the patient is less likely to be conscious and more likely to be trapped. The seriousness of the injuries is likely to be greater. If the patient is not trapped, they should be carefully lain down, preferably on a stretcher and kept warm, but not heated, with the legs slightly raised to improve venous return. Oxygen should be given at as close to 100% as possible. The increased amount is to cope with the deepening of the condition.

Where the patient is trapped the situation is again proportionally more serious. The risk of disseminated intravascular coagulation is high, as is organ damage. Peripheral constriction or "shutdown" is close now and the catastrophe that follows.

Great care is needed in the handling of patients in this condition as any bumps or knocks will cause severe bruising because of the lack of peripheral circulation.

STAGE 3 - Irreversible Shock

At this stage the patient's only hope of survival is intense medical treatment. If not trapped they should be conveyed to Hospital with the utmost urgency.

If trapped, they must have effective medical treatment before they are moved. The situation is very grave for someone in this condition - all haste should be made to release them. However, the casualty will be very prone to further damage from knocks or bumps. 100% oxygen should be given preferably through the best airway possible. The casualty should be kept warm and comfortable.

Do not heat a patient, there is no capillary flow to conduct any heat away (the same applies to cold). The body cells near to the heat source will burn with only a few degrees above normal body temperature.

Be very careful to avoid further bruising as there is no capillary flow to inflate the tissues and so they bruise very easily.

Give absolutely nothing to eat or drink as it may be likely that the patient will need to be anaesthetised on arrival at Hospital.


The treatments that can be given to someone “pre hospitaly” suffering from the effects of shock in its various stages is somewhat limited. However, the steps we can take are both positive and beneficial.

Oxygen should be given when appropriate as it improves the oxygen content of the available blood volume and gives confidence to the casualty and to the rescuer. The reduction of pain is a significant contribution, such as the immobilisation of fractures. the cooling of burns and the control of external bleeding. Reassurance really helps as people can still hear even when unconscious. Raising a casualty's legs, as said before, improves the venous return.

Co-operation with the available medical help will also be of great benefit. The drugs, such as tranexamic acid, and liquids available can go a long way to stabilising a patient and ensuring their viability on arrival at Hospital.

Ultimately the patient will require evaluation and treatment in hospital, our job is to get them there in as healthy a state as possible, as expeditiously as possible.

Author - Martin Bennett BSc Hons PHC, Post Grad Cert Al, M.I.FireE. (Exam)


Nancy Caroline - Emergency Care in the Streets 5th edition

John Eaton - The Essentials of Immediate Medical Care 2nd edition

Keith Porter - The Handbook of Immediate Medical care

ABC Major Trauma - BMJ various Authors 3rd edition

Giving Nursing Care Competantly - Nursing Skillbooks

Ambulance Service Basic Training - NHSTD

Textbook of Medicine - Souhami & Moxham 3rd edition

Ambulance Service Paramedic Training - NHSTD

Simple Guide to Trauma - Huckstep

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