43. HAEMORRHAGE

The anaesthetist must always attempt to treat haemorrhage before giving an anaesthetic. Patients who need immediate surgery may need to have the haemorrhage treated at the same time as performing anaesthesia. These patients must be anaesthetised with extreme care.

Blood loss causes a reduction in blood volume, which causes a decrease in venous return, which causes a decrease in cardiac output and blood pressure. The fall in blood pressure activates baroreceptors, which increases sympathetic activity, causing tachycardia and peripheral vasoconstriction. Both general anaesthesia and spinal/epidural anaesthesia will reduce the sympathetic activity causing a fall in blood pressure. This can be severe. Spinal/epidural anaesthesia is best avoided in patients who have a large untreated blood loss. General anaesthetic induction drugs (e.g. thiopentone, propofol) must be given in small doses. Ketamine is a good alternative induction agent in patients with large blood loss. It will maintain the patients sympathetic activity.

Estimating Blood Loss

The anaesthetist must estimate the amount of blood loss and attempt to correct the hypovolaemia.

Early volume replacement is essential. Blood loss can be estimated by observing wounds, dressings and drain tubes and by the patient’s clinical condition.

The blood volume of an adult is 70 ml/kg, of a child is 80 ml/kg and of a neonate 90 ml/kg.

A healthy adult can loose 500 ml of blood without any clinical effect. With more blood loss the patient will develop signs and symptoms. The diastolic blood pressure changes before the systolic pressure due to active arterial vasoconstriction. Young fit adults can vasoconstrict so intensely that they can maintain a normal systolic blood pressure even after 1500 to 2000 ml of blood loss.

The anaesthetist must not rely only on the blood pressure as an indicator of the degree of blood loss. Similarly the anaesthetist must not use the systolic blood pressure as the only indicator of adequate fluid resuscitation. Other clinical signs and symptoms must also be assessed. The anaesthetist must also assess the heart rate, respiratory rate, urine output, skin colour and temperature, conscious state, capillary refill and postural hypotension.

(Capillary refill is assessed by squeezing the finger nail bed and observing how long it takes for the circulation to return. Normally it is less than 2 seconds).

The anaesthetist must take care in assessing patients who have significant medical disease and who are very young or very old. These patients may become hypotensive after relatively little blood loss.

Goals of Treatment

The treatment of blood loss aims to achieve an adequate blood volume and an adequate concentration of haemoglobin. It is not necessary to return the patient’s haemoglobin concentration to normal but it is essential to return the patient’s blood volume to normal. Blood transfusion is associated with potential risks and is rarely indicated if the haemoglobin concentration is greater than 100 g/litre (10 g/dl) and is almost always indicated if the haemoglobin concentration is less than 60 g/litre ( 6g/dL) in adults.

Choice of Intravenous Fluid

The choice of intravenous fluids will often be determined by what is available. Blood is the best volume expander and oxygen carrier but it takes time to crossmatch and is often in short supply. Colloids will correct hypovolaemia more quickly than crystalloids and will maintain intravascular oncotic pressure. Crystalloids require larger volumes to correct hypovolaemia but are equally effective as colloids and are cheaper. Crystalloids should be given at thee times the estimated blood loss as they rapidly distribute between the circulation and extracellular fluid.

In adults, blood loss of up to 20% (1 litre) can be safely treated with crystalloid or colloid. Check the haematocrit or haemoglobin and consider giving packed red blood cells.

Blood loss of 20% to 50% of blood volume (1 to 2.5 litres) may need a blood transfusion. Give packed red blood cells, check the haematocrit or haemoglobin and coagulation. Monitor the patient’s temperature and consider giving clotting factor replacement.

Blood loss of more than 50% of blood volume (more than 2.5 litres) will need packed red blood cells and clotting factors. Consider giving a platelet transfusion. Check coagulation, temperature and electrolytes.

If there is an abnormal response to blood replacement consider ongoing concealed bleeding, cardiac tamponade, tension pneumothorax, pulmonary embolism, neurogenic, cardiogenic and septic shock.

One unit of blood usually increases the haematocrit by 3 to 5%.

The anaesthetist must consider giving blood earlier in children and especially in neonates. It is wise to consider blood transfusions for greater than 10% blood loss.

Risks of Blood Transfusion

The greater the blood transfusion the greater the risk of complications. A massive blood transfusion in an adult may be considered as more than 10 units within 6 hours or more than 5 units in 1 hour or more than one blood volume within 24 hours. These patients are at risk of complications.

The potential risks of blood transfusions include coagulopathy (decreased platelets, factor V and V111 and disseminated intravascular coagulopathy), decreased oxygen delivery, hypothermia, hypocalcaemia, hyperkalaemia, metabolic acidosis, hypervolaemia, infection (hepatitis, HIV, malaria, syphilis, CMV), microaggregates and immunological reactions.

The anaesthetist can reduce blood loss by local infiltration with vasoconstrictors, tourniquets and positioning the bleeding site above the level of the heart. Deliberate hypotension will reduce bleeding but is dangerous with anaemic and hypovolaemic patients. Aim to keep the blood pressure within 20% of normal.

Management of Haemorrhagic Shock

When managing haemorrhagic shock the anaesthetist must remember the ABC of resuscitation (Airway, Breathing and Circulation). Give oxygen, intubate the patient if required, and control external bleeding by elevating the bleeding point and direct firm pressure. In massive bleeding, insert at least two large intravenous cannulae (preferably into different limbs), take blood for an urgent blood cross match, administer intravenous fluids, and monitor the patient’s response to fluid resuscitation (blood pressure, pulse rate, conscious state and urine output). Give boluses of fluid (200 to 500 mls) until the blood pressure and pulse rate are near normal. Perform blood investigations (coagulation, electrolytes, haematocrit/haemoglobin). Be prepared to transfuse blood and correct coagulation problems.

Vascular Access

Peripheral percutaneous cannulation is the procedure of choice.

Alternative vascular access includes surgical cut-down, central venous cannulation, femoral vein cannulation and interosseous needle.

Cut downs require surgical expertise, take longer and have complication rates similar to femoral vein and cental vein cannulation.

Central vein cannulation has few complications when performed by an experienced anaesthetist. Life theatening complications include haematoma, haemo/pneumothorax, cardiac tamponade, air embolism and arrhythmias.

Femoral vein cannulation has less immediate complications and can be performed at the same time as airway management.

Intraosseous needles can be used in all age groups but are most successful in children less than 6 years old. The needle is inserted in the upper third of the tibia with the point directed downwards (away from the epiphyseal plate).