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Inhalation is the most common exposure route in reports to national poison control centers and the most common cause of fatalities related to toxic exposures. Acute inhalational injury occurs via two basic mechanisms. Inhaled substances are either absorbed leading to systemic toxicity or they directly injure the pulmonary epithelium at various levels of the respiratory tract. Many exposures (or exposure situations) produce both effects. Systemic toxins include asphyxiants (substances that interfere with oxygen delivery or utilization) and other toxins whose primary effects are on distant organ systems. This chapter will not discuss inhalational toxins whose main effects are on distant organ systems but limited examples are shown in Table 35–1.

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Table 35–1. Systemic Toxins Absorbed Via Inhalation.
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The degree of injury after acute inhalational exposure is determined by multiple host and exposure factors. Elderly patients and those with underlying debilitating illness, particularly underlying lung disease that impairs host defense mechanisms, typically fare worse. Important environmental factors include the intensity and duration of exposure as well as the quality of ventilation in the space in which exposure occurs. In general, greater exposure dose (defined as the product of the concentration of exposure and duration of exposure) is associated with greater potential harm.

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Essentials of Diagnosis

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  • • Patients may be unaware of asphyxiant exposure, as many do not have warning properties.
  • • Consider asphyxiants in patients with a history of working in enclosed spaces prior to symptom onset.
  • • Consider asphyxiant exposure in patients with a history of smoke inhalation.
  • • Consider chemical asphyxiant exposure in patients with unexplained lactic acidosis.

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General Considerations

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Asphyxiants are divided into two classes, simple and chemical. Simple asphyxiants act by displacing oxygen from inspired air. Any gas can act as a simple asphyxiant if present in high enough concentration. Typical exposure scenarios include release of compressed gas and work in enclosed spaces. Chemical asphyxiants act by interfering with oxygen delivery or utilization. Examples of both simple and chemical asphyxiants are shown in Table 35–2. The potential number of exposed workers in the United States is unclear, but the National Occupational Exposure Survey estimated that more than 500,000 workers may ...

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