Which clinical history findings are characteristic of smoke inhalation caused by oxides of nitrogen?

Updated: Oct 15, 2021
  • Author: Keith A Lafferty, MD; Chief Editor: Joe Alcock, MD, MS  more...
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Because of their insolubility in water, NOx tend not to cause immediate upper airway irritation. Unfortunately, this may allow a significant exposure to remain undetected for prolonged periods. As with most toxic inhalations, severity of illness and presentation are related to the concentration of the smoke or fumes, length of time of exposure, manner in which the exposure was delivered, and the health status of the exposed individual.

Mild exposure to NOx results in upper airway and ocular irritation such as itching or burning eyes. Cough, dyspnea, fatigue, chest tightness, throat tightness, nausea, vomiting, vertigo, somnolence, and loss of consciousness also may occur from mild exposure.

At weaker concentrations of NOx, the individual may experience very little discomfort, quickly accommodating to the cough, mild choking, or upper airway irritation. Because of this, symptoms may appear quickly or remain unnoticed for a few hours. Although the symptoms of mild exposure may become quite dramatic, complete recovery is expected within 24 hours, once the patient is removed from the exposure.

In more severe exposures, the clinical response may be described as triphasic. During phase 1, an intense respiratory symptom complex may occur. Severe cough, dyspnea, and pulmonary edema may arise suddenly. Physical exertion may be a precipitating factor, quickening the progression to pulmonary edema. If the patient survives this episode, spontaneous remission occurs within 48-72 hours postexposure.

Phase 2 lasts from 2-5 weeks and is relatively uneventful. A mild residual cough with malaise and perhaps dyspnea may linger, but the chest radiograph typically remains clear.

In phase 3, which occurs 3-6 weeks after the exposure, symptoms may recur. Severe cough, fever, dyspnea, and cyanosis may develop in the setting of rales and increasing carbon dioxide retention.

More acutely severe exposures can result in immediate death from bronchiolar spasm, laryngeal spasm, reflex respiratory arrest, or simple asphyxia. Some exposures can progress from mild upper airway irritation to pulmonary edema in 3-30 hours.

Even in individuals with asthma or chronic obstructive bronchitis, NOx concentrations of 0.5 ppm or less generally have no effect. levels from 0.5-1.5 ppm begin to bother patients with asthma, who notice minor airway irritation. With concentrations greater than 1.5 ppm, people with healthy lungs experience decreases on pulmonary function tests and decreased carbon monoxide diffusing capacity (DLCO), with widening of the alveolar-arterial gradient on arterial blood gas measurement.

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