Approach
Individuals with inhalation injury have typically been exposed to a multitude of potential insults, which has implications for the diagnostic approach. The type, intensity, and duration of exposure, obtained by history, are critical to focus attention on the most likely types of injury. However, the complexity of an explosion or fire often prohibits a clear identification of all toxins, even when a thorough history is obtained. The salient clinician should assume multiple exposures, pro-actively and vigilantly surveying the patient for evidence of injury from the upper airway to the lung parenchyma. Likewise, non-respiratory injuries such as trauma and cutaneous burns are common and complicate both diagnosis and management. Appropriate evaluation consists of at least a thorough history and physical examination, often involves serological and radiographical studies, and occasionally requires invasive diagnostics such as bronchoscopic evaluation. Finally, it should be noted that manifestations of inhalation injury may be delayed, and close observation and frequent reassessment are essential.
Assessing the upper airway
Thermal and toxic exposure can induce direct airway injury and oedema that can lead to airway compromise, leading to rapid clinical deterioration. The incidence of this type of injury varies greatly by exposure, but can occur in up to one third of patients hospitalised for burns.[18] A comprehensive evaluation to ensure that the airway is not threatened should be performed on all patients. Airway protection may obviously be threatened by a loss of consciousness, and obtundation should prompt rapid intubation to protect the airway. In alert patients, dyspnoea, hoarseness, dysphonia, stridor, and facial burns are suggestive of upper airway injury, oedema, and threatened patency.[19] These findings should minimally prompt evaluation with laryngoscopy or bronchoscopy to further evaluate airway patency. However, a more conservative approach is the immediate placement of an endotracheal tube to prevent progression and airway emergency.[20]
Assessing for cellular asphyxia
Carbon monoxide (CO) and hydrogen cyanide are by-products of residential fires that cause cellular asphyxia by disrupting cellular oxygen transport. CO is much more common, and some have questioned whether cyanide toxicity contributes to the morbidity of inhalation injury.[21] All patients exposed to an explosion or fire should be assessed for CO poisoning. Headache, dizziness, and confusion are common neurological symptoms, and myocardial ischaemia should also be evaluated with an electrocardiogram. Other symptoms suggestive of CO toxicity include nausea and seizures. Symptoms may be absent or obscured by other conditions; thus an arterial blood gas (ABG) with CO-oximetry should be performed to assess for carboxyhaemoglobin. If historical factors (burning home furnishings) or hypoxia suggest cyanide toxicity, the patient should be assessed for metabolic acidosis with an ABG, serum bicarbonate, and serum lactate level. However, these findings are not specific to cyanide toxicity, and are more commonly seen as a result of CO toxicity or shock. Cyanide levels can be considered; a rapid point-of-care test is not commercially available, but a simple optical analyser has been developed which accurately detects cyanide levels of imminent concern in around 2 minutes, as well as a paper microfluidic device that successfully measured cyanide ions in the blood samples of 20 fire survivors.[20][22][23]
Assessing for lower airway injury
There are numerous inhaled gases and particulates that can cause direct injury to the cells in the conducting airways, leading to bronchoconstriction, oedema, epithelial cell death with sloughing, diminished airway clearance, and airway obstruction.[10][12] Patients present with symptoms of cough and shortness of breath and demonstrate increased difficulty in breathing. Chest auscultation typically reveals wheezing from airway narrowing. Occasionally noted are diminished breath sounds or crackles from atelectasis due to poor airway clearance and obstruction. Crackles that fail to resolve with deep breathing may suggest lung parenchymal injury and oedema rather than atelectasis, and thus a chest radiograph should be obtained to determine the lung injury. If pulmonary function testing (PFT) is available, it may help characterise and trend airflow obstruction over time. Bronchoscopic evaluation has been suggested, but often provides redundant information more easily obtainable by examination, PFT, and upper airway examination.[19] Like upper airway injury, lower airway injury may be delayed, emphasising the importance of frequent reassessment.
Assessing for lung parenchymal disease
Inhalation injury and commonly associated conditions (cutaneous burns and trauma) are associated with acute respiratory distress syndrome (ARDS).[10][12][16] These complications may be evident on presentation, or may develop in the initial hours of treatment, unmasked by resuscitation of circulating volume. Patients will demonstrate an increasing oxygen requirement, and chest radiographs will commonly show diffuse airspace opacities. In common with ARDS in other settings, alternative diagnoses with specific treatments (CO toxicity, cardiac disease, infection, lung haemorrhage) must be considered.
Other considerations
Patients presenting with inhalation injury often suffer from other acute processes or exacerbations of chronic medical conditions. While it is reasonable to focus attention on the pulmonary system, general supportive care and organ surveillance should remain a priority. Cutaneous burns and trauma are common co-injuries that have significant overlap with symptoms and signs of inhalation injury. Likewise, epidemiological data suggest that alcohol or illicit drug intoxication is commonly associated with the accidents and fires that cause inhalation injury. Finally, pre-existing medical conditions (particularly cardiac and pulmonary disease) often complicate the course of these patients and should be carefully considered.
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