Smoke inhalation

Smoke inhalation is the primary cause of death in victims of indoor fires.

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Smoke inhalation injury refers to injury due to inhalation or exposure to hot gaseous products of combustion. This can cause serious respiratory complications[1]

It is estimated that "50-80% of fire deaths are the result of smoke inhalation injuries rather than burns."[2] The smoke injures or kills by a combination of thermal damage, poisoning and pulmonary irritation caused by carbon monoxide, cyanide and other combustion products.

Signs and symptoms

Symptoms range from coughing and vomiting to nausea, sleepiness and confusion. Burns to the nose, mouth and face; singed nostril hairs; and difficulty breathing / carbonaceous sputum (burned saliva) are also signs of smoke inhalation injury. Approximately one third of patients admitted to burns unit have pulmonary injury from smoke inhalation. The death rate of patients with both severe burns and smoke inhalation can be in excess of 50%.

Any person with apparent signs of smoke inhalation should be immediately evaluated by a medical professional such as a firefighter-paramedic or physician. Advanced medical care may be necessary to save the life of the patient, including mechanical ventilation, even if the person is conscious and alert. Pending advanced intervention, the patient should be brought into fresh air and given medical oxygen if available.

Mechanism

Smoke inhalation causes three complications:

1. Impaired or reduced levels of oxygen at the tissue level: This arises due to inhalation of carbon monoxide or cyanide and is an immediate threat to life. Immediate treatment with 100% oxygen is essential and is given till the level of carboxyhaemoglobin ( a product formed by combining of the haemoglobin molecule with carbon monoxide; reducing the amount of haemoglobin available to transport oxygen to tissues.) falls to less than 10% and the metabolic acidosis (a condition in which there is excess of acid in the body causing severe chemical imbalances and electrolyte disturbances) has resolved.

1. Thermal injury to the upper airway: Hot gases cause burns to the mucosal surfaces of the upper airway. Its complications become evident in 18-24 hours. They are: oedema, reduced ability to clear secretions, airway obstruction causing respiratory distress and noise on inspiration. In advanced stages respiratory failure can also occur. Treatment is humidified oxygen, head tilt to 30degrees, suction to clear secretions and medicines to reduce the swelling of the mucosa. Mixtures of Helium-Oxygen (Heliox) gas may be useful to reduce laboured breathing. Endotracheal intubation may be needed to maintain airway patency especially for deep facial burns or swelling of the pharynx. Investigations include arterial blood gas analysis, fibre optic laryngoscope or bronchoscope. Tracheostomy should be avoided if possible because of an increased risk of pneumonia and sepsis.

1. Chemical injury to the lung is due to inhalation of toxic gases and products of combustion which includes aldehydes and organic acids. It can present with symptoms of bronchospasm (narrowing of the airways), difficulty in breathing, an increased rate of breathing, wheezing and a fast heart rate initially. A day or two later, there might be swelling of the smaller airways which may start sloughing off causing airway obstruction and pneumonia in 5-7 days.

Treatment

Treatment consists of humidified oxygen, bronchodilators, suction, endotracheal tube and chest physiotherapy. Other measures include adequate fluids and control of infection by daily sputum stains and appropriate antibiotics.