Diagnosis

Several elements of the history and physical examination can alert the clinician to the possibility of an inhalation injury. Being burned in a confined space and having sensory impairment due to ethanol or drug ingestion, central nervous system trauma, or dementia place patients at high risk of this injury. Facial burns, singed nasal vibrissae, or burned eyelashes are commonly present in patients with inhalation injury. Even though the history of the event and physical examination of the patient can alert one to the possibility of inhalation injury, they are poor predictors of those patients who actually have that injury ( Shirani et al 1987) (Table 1). A chest radiograph, which is often normal in the acute setting, is also a poor indicator of inhalation injury.

The inaccuracy of history and physical examination in predicting inhalation injury has led to the use of early bronchoscopy and, if necessary in the face of a normal bronchoscopy, xenon-133 ventilation-perfusion lung scintiphotography. The accurate diagnosis of this condition allows these patients to receive therapies directed at reducing the comorbid effect of inhalation injury and allows for quantification of its effect on morbidity and mortality. Moreover, diagnostic bronchoscopy has the added benefit of identifying incipient upper airway obstruction due to edema elicited by the heat component of the smoke. Signs of upper airway edema upon initial fiber-optic examination warrant early intubation since edema and upper airway narrowing are typically progressive, usually peaking 12 to 24 h after injury. Carbonaceous debris and early changes of the respiratory epithelium such as hyperemia, edema, or superficial sloughing are consistent with inhalation injury. These findings often precede the clinical sequelae of inhalation injury such as hypoxia and declining pulmonary compliance. During the resuscitative phase early inflammatory changes may be absent owing to hypovolemia; therefore repeat bronchoscopy when the patient is 'fully resuscitated' will be more accurate.

A normal appearance of the upper airway on examination by fiber-optic bronchscopy does not always exclude inhalation injury. Distal airway and alveolar injury caused by finely particulate smokes which do not precipitate in the large-caliber airways can be missed by this modality. Therefore patients who are considered at risk for inhalation injury, yet have a negative bronchoscopic examination, should undergo xenon-133 scanning. Serial scintigraphs taken following intravenous injection of this radiolabeled inert gas document elimination via the lung. Retention of the isotope for more than 90 s after injection indicates injury of the small airways. Pre-existing chronic obstructive pulmonary disease or acute inflammatory processes such as bronchitis due to aspiration or infection can result in false-positive examinations. A combination of fiber-optic bronchoscopy with xenon-133 scanning detects inhalation injury with an accuracy to 93 per cent.

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