Medical Aspects of Chemical Warfare (2008) - The Black Vault

Medical Aspects of Chemical Warfaresualty with peripheral damage will notice shortness ofbreath and tightness in the chest, which are symptomsof the development of noncardiogenic pulmonaryedema. These symptoms may initially be mild, butas the damage progresses, dyspnea on exertion willbecome resting dyspnea. Coughing is at first nonproductivewith chest tightness or discomfort describedas retrosternal burning, but if the damage is severe,the casualty will start producing clear to yellow frothysputum. This is caused by necrosis and inflammationof the lower airway and alveolar tissue and subsequentleakage of serum into the alveolar septa.The eventual severity of dyspnea is related to dose,concentration, and duration of the exposure. A casualtywith a very mild exposure will develop dyspnea6 to 24 hours after exposure, first noticed after heavyexertion. Later, however, the casualty becomes shortof breath after any activity. With proper care, completerecovery is expected. A casualty with a severe exposurewill notice shortness of breath within 4 to 6 hours afterexposure. Dyspnea, even at rest, results from inabilityof the pulmonary lymph system to eliminate the largeamount of fluid produced from the necrosis of the alveolar-capillarymembrane. This leads to the clinicalpresentation of noncardiogenic pulmonary edema,causing hypoxia and apnea. These casualties, evenwith intensive pulmonary care, may not survive.Many of the casualties exposed to lung-damagingagents are between these two extreme situations.When the onset of dyspnea is more than 6 hours afterexposure, there may be progression to dyspnea at rest.However, with good pulmonary care beginning earlyafter the onset of effects, the casualty should recovercompletely. Failure to consider the asymptomatic periodand delayed onset of peripherally acting lungdamagingagents may lead to early discharge fromthe emergency room, without an adequate period ofobservation, and possibly to a poor outcome. 1Diagnostic TestsNo commonly available laboratory tests exist forthe specific identification or quantification of exposureto lung-damaging agents; however, an increase in thehematocrit may reflect the hemoconcentration inducedby transudation of fluid into the pulmonary parenchymafrom the peripherally acting agents. Arterialblood gases may show a low Pao 2or Pac o 2, which isan early, nonspecific warning of increased interstitialfluid in the lung. Peak expiratory flow rate may decreaseearly after a massive exposure to peripherallyacting agents. This nonspecific test helps assess thedegree of airway damage and the effect of bronchodilatortherapy. Decreased lung compliance and carbonmonoxide diffusing capacity are particularly sensitiveindicators of interstitial fluid volume in the lung, butbecause of their complexity, these tests are usuallyperformed only in hospitals.Chest RadiographInitial findings on a chest radiograph may be normal;as the disease process progresses, the radiographmay demonstrate bilateral diffuse interstitial infiltrates.The early finding on a chest radiograph is hyperinflation,which suggests toxic injury of the smaller airwaythat results in air being diffusely trapped in the alveoli.The appearance of “batwing” infiltrates is caused bypulmonary edema secondary to the alveolar capillarymembrane damage. Pulmonary edema develops laterand without cardiovascular changes of redistributionor cardiomegaly. Radiological changes from centrallyacting lung-damaging agents may occur for hoursto days, so the use of a chest radiograph may be oflimited value.Arterial Blood GasesMeasuring carboxyhemoglobin and methemoglobinlevels can help determine whether the casualtieshave been exposed to methylene chloride or confirmsuspected carbon monoxide exposure; methemoglobinemiamay suggest other causes. Serial arterial bloodgases in cases of significant respiratory distress demonstratethe degree of hypoxemia. Hypoxia is often theresult of exposure to both centrally and peripherallyacting lung-damaging agents. The measurement ofthe partial pressure of oxygen (Po 2) can give insightinto the treatment of hypoxia, but it is a nonspecifictool in the diagnosis of exposure to a lung-damagingagent. 1Pulmonary Function TestsA variety of airway and pulmonary parenchymalfunction measures can be performed in rear-medicaltreatment facilities. Initial and follow-up measurementsof the flow-volume loop, lung volumes, andlung diffusing capacity for carbon monoxide are particularlyuseful in assessing and managing long-termeffects of a lung-damaging TIC exposure. Althoughsuch laboratory studies are of minimal value in anacute-care setting, flow-volume loop measures maydocument a previously unrecognized degree of airwayobstruction. A degree of reversibility may also360