injuries poisoning
Pulmonary Chemical Warfare Agents
Pathophysiology of Pulmonary Chemical Warfare Injuries
Toxic chemical-warfare agents that affect the respiratory tract are divided into 2 types depending on which part of the tract is predominantly affected (see table Representative Type 1, Type 2, and Mixed-Effect Chemicals With Acute Local Effects on the Respiratory Tract ): Type 1 agents: Affect large airways Type 2 agents: Affect terminal and respiratory bronchioles, alveolar sacs, and alveoli Mixed-effect agents: Affect large airways and small airways and alveoli Type 1 agentsusually are those with inhaled particles (eg, smoke), which tend to settle out before reaching the alveoli, or highly water-soluble and/or highly reactive chemicals, which dissolve into respiratory mucosa before reaching the alveoli. Type 1 agents cause necrosis and sloughing of the respiratory epithelium in the large airways, which may cause partial or total airway obstruction. Chemical pneumonitis and secondary bacterial pneumonitis may occur as a consequence of type 1 local damage. High doses of type 2 agents also can cause type 1 (large-airway) effects, although the type 1 effects are more likely to be transient. Type 2 agentsusually are lower-solubility and/or less-reactive chemicals, which travel to the alveoli before dissolving. These agents damage pulmonary capillary endothelium, causing fluid leakage into interstitial spaces and alveoli; pulmonary edema may result. With some type 2 agents (eg, oxides of nitrogen and HC smoke [hexachloroethane pluszinc oxide]), acute pulmonary edema may be followed days to weeks later by progressive and potentially irreversible pulmonary fibrosis. The mechanism is presumed to be immunologic. High doses of type 1 agents can also cause pulmonary edema. Mixed-effect agentsinclude most inhaled chemicals with local effects on the respiratory tract. Mixed-effect agents lie in the middle of the spectrum of aqueous solubility and chemical reactivity and have both type 1 and type 2 effects. They act in both large airways and alveoli although one effect or the other usually predominates except at high doses. 