Inhalation injury to the lower respiratory tract
A lower respiratory tract inhalation injury is often caused by the inhalation of burning substances, such as chemicals in smoke. Physical signs and symptoms include burns to the face and difficulty breathing. Here you can find information on the causes and signs of an lower respiratory tract inhalation injury, as well as treatment approaches.
Etiology and pathophysiology
An inhalation injury to the lower respiratory tract is often caused by the inhalation of burning substances, such as chemicals in smoke. Inhalation of hot gases may also cause damage to the airway distal to the larynx. However, this only occurs after exposure to extreme heat, as the airway proximal to the larynx is efficient at dissipating heat.
There are two types of lower respiratory tract inhalation injury: tracheobronchial and parenchymal.
Inhalation of noxious chemicals and particulates, which are present in smoke from a fire, cause oxidation and reduction of compounds containing carbon, sulfur, phosphorus and nitrogen. Acids and alkalis are produced when these compounds dissolve in the moisture of the airways and alveoli, resulting in a chemical burn of the tissues of the lower respiratory tract.
The lung parenchyma is involved in cast formation and plugging that may result in distal airway obstruction. Atelectasis and alveolar collapse are characteristic of damage to the lung parenchyma. This results in the inactivation of surfactant, formation of inflammatory exudates and a loss of hypoxic vasoconstriction.
Assessment of inhalation injury
During the clinical assessment, an inhalation injury to the lower respiratory tract should be suspected if findings are consistent with the following history, physical findings and further diagnostics.
The patient would have a history of exposure to flames, smoke, an explosion or chemicals. Ascertain the duration of exposure and find out if it was in an enclosed space, as exposure in an enclosed space would indicate this type of injury. The patient may also have a history of a loss of consciousness.
The physical findings that indicate this type of injury include burns to the face (specifically the mouth, nose and pharynx); singed nasal hairs; soot in the oropharynx, nasal passages or proximal airways; carbonaceous sputum; and edema formation in the head and neck.
The patient may also have difficulty breathing, indicated by tachypnoea (>30 breaths per minute) or signs of increased respiratory effort, including flared nostrils, tracheal tug, chest indrawing and use of the accessory muscles of ventilation.
When examining the patient, listen for hoarseness, stridor, a productive cough and croup-like breathing.
In all patients with a suspected inhalation injury, measure their carboxyhemoglobin (COHb) levels. An initial chest X-ray is helpful in the diagnosis, but a bronchoscopy is most useful to get the best information regarding the level and the severity of the injury.
Larynx. Most critical area, an inspiratory or biphasical stridor is the symptom of a threating obstruction
Trachea. An expiratory or biphasical stridor may be heard
Right and left main bronchus. Obstruction of only one long may be overlooked because of temporary compensation
Treatment of inhalation injury
Treatment is based mainly on respiratory support. Administer high flow oxygen at 15L/min via a non-rebreathing mask. If higher levels of oxygen need to be administered, or if a toilet bronchoscopy is required to remove secretions, use intubation and mechanical ventilation.
Prophylactic antibiotics and corticosteroids are not indicated for the treatment of smoke inhalation injury.
Patients should be nursed in a semi-upright position with a moderate elevation of the head and trunk. The ability to provide optimal care for patients with inhalation injuries depends on the availability of intensive care facilities and clinical expertise.