Dr IH Wilson,
Consultant Anaesthetist.
Dr PJF Baskett,
President, Association of Anaesthetists of Great Britain & Ireland.

Pathophysiology		Choice of intravenous fluids
Classification of blood loss		Life saving surgery
Management of haemorrhagic shock		Summary

Pathophysiology.

Shock produces a reduction in tissue perfusion resulting in hypoxic metabolism, acidosis and deterioration in organ function. The body responds to hypovolaemia through the sympathetic nervous system which causes tachycardia and vasoconstriction in an attempt to maintain cardiac output and blood pressure. To preserve blood flow to the vital organs (brain, heart, kidneys and liver), there is marked vasoconstriction of cutaneous and other peripheral blood vessels. Oliguria (defined as a urine output of less than 0.5ml/kg/ hour) occurs as the body actively retains fluid. The patient feels thirsty. As blood loss progresses there is increasing organ failure shown by dyspnoea (lungs), aggression or drowsiness (brain) and myocardial depression.
 
Classification of blood loss.

Haemorrhage may be classified according to the actual amount of blood lost, or as a percentage of the circulating blood volume.

The circulating blood volume may be estimated using the formula in figure 1.		Figure 1. Calculating the circulating blood volume
		Circulating blood volume @ 70mls/kg e.g. A 70kg man has: 70 x 70 = 4,900mls e.g. A 20kg child has: 70 x 20 = 1,400mls

After haemorrhage the diastolic blood pressure changes before the systolic, due to active arterial vasoconstriction. The capillary refill test indicates the condition of the peripheral circulation. It is assessed by squeezing the finger nailbed and observing how long it takes for the circulation to return. Normally it is less than 2 seconds. Note that patients who are drowsy or unconscious due to shock have lost at least 2000mls, or 40% of their blood volume.

Young fit adults can vasoconstrict intensely in response to blood loss maintaining a relatively normal systolic blood pressure even after 1500-2000mls. Therefore always assess the systolic blood pressure in conjunction with the other clinical signs of shock. Remember that during resuscitation with intravenous fluids, the restoration of systolic blood pressure does not mean that the blood volume has returned to normal-there may still be class 2 shock with severe volume depletion.

Not all clinical signs are present in every patient. For example elderly people may not develop a tachycardia, especially if they are taking a beta adrenergic blocker such as propranolol. Like patients with heart disease (ischaemic or valvular) they may become hypotensive after relatively little blood loss. In patients with pre-existing hypertension care must be taken when interpreting blood pressure. For example a systolic blood pressure of 110mmHg would be normal in a young person, but may reflect serious hypotension in the adult with hypertensive disease. Pain and cold may also produce some of the clinical signs of shock. Patients with extensive tissue damage lose a considerable amount of their circulating volume by oedema formation.
 
Management of haemorrhagic shock.

Remember the ABC of resuscitation. Check and correct any problems with the airway and breathing. Give oxygen in a high inspired concentration by face mask. Intubate patients who are unconscious. Control external haemorrhage by elevating the limb and by direct firm pressure with a clean pad over the bleeding site.

Insert a large cannula (14 gauge) into a suitable vein, use two when shock is worse than class one. When it is difficult to find veins, cannulate the external jugular or femoral vein or perform a cutdown at the ankle or antecubital fossa. In small children the intra-osseus route has been used with success. Do not use leg veins when intra-abdominal haemorrhage is suspected, or cannulate veins in an injured arm or shoulder. Take a sample for blood crossmatching when the first cannula is inserted.

(Continued...)

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