Ch 42 Anaesthesia And Burns

CHAPTER 42

ANAESTHESIA AND BURNS

Outline: Points of importance to the anaesthetist Indications for surgery in the burned patient Initial management of the burned patient Anaesthesia for the burned patient

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POINTS OF IMPORTANCE TO THE ANAESTHETIST • • • • • • •

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Reduced circulating blood volume. There is a loss of water and protein from the circulation, so IV fluids, both crystalloids and colloids, may be required. A fall in body temperature due to the loss of a large amount of skin. Anaemia. Deep burns result in haemolysis of red blood cells. Hypotension may be associated with the hypovolaemia and may also be due to the toxins released from the damaged tissues. Renal failure may follow hypovolaemia and hypotension. There is a constant danger of infection in the burned patient. If infection occurs the patient becomes debilitated. Airway damage, which may involve the upper or lower airways. It may be due to the inhalation of hot gases, fumes, steam, smoke, etc. Upper airway obstruction will increase over 6 to 24 hours, so intubate the patient or consider early tracheostomy depending on nursing care facilities. Pulmonary oedema may be caused by inhalation of noxious fumes especially if the patient was in a closed space. Face, neck, nose and mouth burns are commonly associated with this type of trauma. Pulmonary oedema may also occur during resuscitation from fluid overload. Dyspnoea and tachypnoea are early signs. Respiratory infection. The danger of hyperkalaemia. Burned patients should not be given suxamethonium compounds after 48 hours and for up to 1 year after a significant burn injury. The rapid rise in serum potassium during the depolarisation of the muscle with suxamethonium has been known to produce cardiac arrest. Venepuncture is difficult. Using a mask is difficult in patients with facial burns. Maintaining a clear airway is difficult in patients with neck contractures. Monitoring is difficult in patients with burns to the upper half of the body. The problem of multiple anaesthetics and the danger of repeated use of the same anaesthetic agents. Fear and depression. The anaesthetist needs to establish rapport with the patient and reassure them.

INDICATIONS FOR SURGERY IN THE BURNED PATIENT • • • • •

Debridement Tracheostomy Fasciotomy Skin grafts Reconstructive surgery to improve function and cosmetic appearance.

INITIAL MANAGEMENT OF THE BURNED PATIENT •

Assess the depth of the burns First degree burns affect the epidermis (superficial tissues). The burns are painful, red and dry but they do not blister. Second degree burns blister and are painful, mottled, red and moist. Third degree burns reach the subcutaneous tissue. Fat, muscle and even bone may be destroyed. The critical burn area is that percentage of the body surface above which the patient cannot compensate for fluid loss. When the burn area is greater than 15% in an adult or 10% in a child the patient can no longer compensate and IV fluids will be required.

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Assess the extent of the burns The “Rule of Nines” is commonly used to obtain the percentage of the surface area affected. Area children

Adults

Whole head 9% Each upper limb 9% Front of trunk 18% Back of trunk 18% Each lower limb 18% Perineum 1%

Infants and young 18% 9% 18% 18% 14% 1%

In an adult the palm of the hand is approximately 1% of surface area.

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Fig 42.1 The “rule of nines” for rapid assessment of % body surface area

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Weigh the patient if possible, otherwise estimate weight.

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Calculate intravenous fluids according to the formula 2ml x body weight in kilograms x percentage of surface area burnt. This gives the requirement for the first 24 hours. Half of the calculated volume can be given as colloid and half as crystalloid solution. Half the calculated volume can be given in the first 8 hours and the rest in the next 16 hours. In addition to these, the volume lost by nasogastric suction is replaced with 0.9% saline or 0.45% saline. Give extra fluid to compensate for fluid loss from diarrhoea, vomiting and pyrexia. Use a large bore cannula, inserted under sterile conditions, for administering the fluid. Re-assess fluid requirements at regular intervals. Maintain a urine output of 1ml /kg /hour. After 24 hours the volume of fluid given may be reduced to about half that given during the first 24 hours. Anaemia may be corrected by the use of blood after the blood volume is first restored with other fluids.

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Give analgesics if the patient is in pain: − Give the drugs IV, not intramuscularly. The muscle blood flow is reduced in the shocked patient. − Use adequate doses of drugs. These patients often develop tolerance and have increasing requirements for opioids, which should not be withheld. Sedatives and anxiolytics may also be useful. − Clean and manage the burn with a dressing or by open exposure. Ketamine 0.5- 1.0 mg/kg IV is useful for dressing changes. − Use silver sulphadiazine cream to reduce bacterial contamination.

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Continue to monitor the following: − Pulse − Blood pressure − Temperature − Urine output − Serum electrolytes − Haemoglobin and haematocrit

ANAESTHETIC TECHNIQUES FOR BURNS PATIENT General Anaesthesia Intubation with a muscle relaxant and IPPV. Endotracheal anaesthesia is useful for surgery in the area of the head and neck. It is also useful for prolonged surgery and surgery performed in abnormal positions. It ensures adequate ventilation. Care is needed however with the use of muscle relaxants such as suxamethonium. Rapid sequence induction is not advised because of the dangers of suxamethonium. Once healing of burns has begun fibrosis and strictures may make laryngoscopy impossible. Tracheostomy is not desirable because of the danger of infection and awake intubation using local anaesthesia may be necessary.

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Mask (inhalational) anaesthesia. Inhalational anaesthesia is useful for short procedures performed in the supine position, in a patient with a secure airway but may be difficult in patients with facial burns. Remember that peripheral vasodilatation increases heat loss and postoperative shivering may cause movement of the graft. However, peripheral vasodilatation may help with venepuncture. Ketamine (Bolus or Infusion) The choice of the technique will depend on the site of the burn, the posture required for surgery and the nature and duration of surgery. Absorption of the ketamine (IM) may be delayed in burns resulting in a slower than normal recovery. The use of ketamine has been described under Techniques of anaesthesia in Chapter 14. Ketamine is useful for debridement and grafting of facial burns, where the use of a mask is impossible. It is also useful for the division of neck contractures prior to intubation. The burned patient with neck contractures and therefore possible airway obstruction will have to be treated with special care. This is discussed under anaesthesia in the presence of respiratory obstruction in Chapter 8 (The Airway and its maintenance).

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