On successfully completing this topic, you will be able to:
understand the impact of a thermal injury on the airway, breathing and circulation
describe the immediate management of airway breathing and circulation in a patient with burns
assess the severity of burns
discuss the management of the fetus in the pregnant patient with burns.
Introduction
The incidence of pregnancy in women admitted to hospital with burn injuries has been found to be 6.8–7.8%. The burned pregnant woman should be managed jointly by the burns team and obstetricians. This may necessitate transfer to a burns centre with appropriate transfer of care to a local obstetrician. Most burns are caused by thermal injury but chemical, electrical and radiation burns also occur.
The severity of the injury is chacterised by the area and depth of the burn and the effect on the vital functions (the ‘ABCs’). Burns may cause immediately life-threatening problems that need to be identified and simultaneously treated in the primary survey. A surface area burn of 25–50% has a mortality rate of 63% for both mother and fetus.
Pathophysiology of burns
Airway obstruction
Airway burns may result in airway obstruction due to oedema as a direct response to thermal injury (heat). Obstruction of the lower airways may be caused by deposition of soot particles. Airway injury from burns can be immediate or delayed, so the airway must be continually observed and early intubation should be considered, particularly if the patient is to be transferred. The maximum oedema is likely to occur at 24 hours after injury, but changes in airway patency can be rapid and disastrous. Clinical changes of impending airway obstruction will be seen, i.e. stridor, increased work of breathing with falling SaO2 and decreasing conscious level. Stridor is therefore a ‘red flag’ symptom in the context of burn injury.
Impaired gas exchange
Respiratory injury to the lung parenchyma may be caused directly by hot gas or steam and may result in critically impaired gas exchange. However, impairment of respiratory function can occur in the burns patient in the absence of obvious respiratory injury. The mechanism for this may be unclear, but can involve ventilation/perfusion mismatch, secondary infection or adult respiratory distress syndrome (ARDS) and may occur up to 2 weeks after the initial injury.
Inhalation of carbon monoxide
Inhalation of carbon monoxide is common if the burn has been sustained in an enclosed area. It can occur without any burn injury due to inhalation from, for example, exhaust fumes or faulty household heaters. Oxygen delivery relies on haemoglobin binding to oxygen. Carbon monoxide has a greater affinity for haemoglobin than oxygen so displaces oxygen from the binding sites on the haemoglobin molecule, resulting in reduced oxygen delivery to the tissues.
A carboxyhaemoglobin level of greater than 10% indicates significant inhalation of carbon monoxide. There are, however, usually no physical symptoms at less than 20% hence the danger in this condition, and the risk of failing to make a diagnosis. Carboxyhaemoglobin levels should be measured routinely in patients exposed to burning materials in an enclosed space. In addition, a reversible period of relative hypoxia for the mother may have consequences for the fetus, depending on the period of time and the gestation, as for any other cause of inadequate fetal oxygen delivery. Carbon monoxide levels of 60% are likely to result in death.
Circulatory effects
Localised tissue damage causes oedema and fluid leak into the tissues. In addition, circulating inflammatory mediators cause an increase in systemic capillary permeability. This leads to a generalised extravasation of fluid from the intravascular compartment into the tissues, producing massive peripheral and pulmonary oedema. These inflammatory mediators can have a direct effect on cardiac function, which, when combined with relative hypovolaemia, vasodilatation, vascular stasis and tissue oedema, produces a marked reduction in tissue perfusion. A summary of these effects can also be simply defined as ‘shock’, which in the case of a severe burn may be classified as hypovolaemic, cardiogenic and distributive shock.
Immediate first aid
The burning process must be stopped: extinguish the flames by laying the affected patient on the ground and wrapping them in a blanket or equivalent. Gently remove burned clothing and any jewellery, unless stuck to the burnt skin. Small burns can be cooled with clean, cold water. Burns should be covered to avoid hypothermia. Nonsterile, domestic cling film is useful as a first aid dressing: it allows visualisation of the wound, but protects it from contamination and fluid loss while reducing pain.
Primary survey and resuscitation
Airway and breathing
Airway and breathing injuries should be suspected particularly if:
the burn was sustained in an enclosed space
there is hoarseness, loss of voice, stridor or wheeze
there is evidence of burns around the lips, mouth and nose
there is singeing to the nasal hair or eyebrows
there is soot around the mouth or nose, or the patient is coughing up carbonaceous sputum
there is respiratory distress and alteration in level of consciousness
in the presence of carbon monoxide poisoning.
If there is a suspicion of an airway and breathing problem, or in the presence of carbon monoxide poisoning, advice from an anaesthetist is required as early intubation and ventilation may be indicated.
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