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

Nerve Agentspatient. Decontamination is performed to prevent thecasualty from further absorbing the agent or to keepthe agent from spreading further on the casualty or toothers, including medical personnel, who may comeinto contact with the casualty.Ventilatory SupportVentilatory support is a necessary aspect of therapyto save a casualty with severe respiratory compromise.Antidotes alone may be effective in restoring ventilationand saving lives in some instances. In animalstudies, 160,161 antidotes alone, given intramuscularlyat the onset of signs, were adequate to reverse theeffects of agent doses of about 3 times LD 50, but theireffectiveness was greatly increased with the additionof ventilation. Pyridostigmine, given as pretreatmentand followed by the current therapy after challengeswith higher amounts of two agents, appears to preventapnea.Breathing impairment is an early effect of exposureto nerve agent vapor or aerosol. When the exposure issmall, the casualty may have mild to severe dyspnea,with corresponding physical findings, and the impairmentwill be reversed by the administration of atropine.If the distress is severe and the casualty is elderlyor has pulmonary or cardiac disease, the antidote maybe supplemented by providing oxygen by inhalation.In most other circumstances, supplementation withoxygen is unnecessary.Severely exposed casualties lose consciousnessshortly after the onset of effects, usually before anysigns of respiratory compromise. They have generalizedmuscular twitching or convulsive jerks and mayinitially have spontaneous but impaired respiration. Ina severely poisoned person, breathing ceases completelywithin several minutes after the onset of exposure.Assisted ventilation may be required to supplementgasping and infrequent attempts at respiration, or itmay be required because spontaneous breathing hasstopped. In addition to a decrease in central respiratorydrive, weakness or paralysis of thoracic and diaphragmaticmuscles, and bronchospasm or constriction,there are copious secretions throughout the airways.These secretions tend to be thick, mucoid, and “ropy,”and may plug up the airways. Postural drainage canbe used, and frequent and thorough suctioning of theairways is necessary if ventilation is to be successful.In one instance, efforts to ventilate a severely apneiccasualty were markedly hindered for 30 minutes untiladequate suction was applied to remove thick mucoidplugs. 66Initially, because of the constriction or spasm ofthe bronchial musculature, there is marked resistanceto attempts to ventilate. Pressures of 50 to 70 cm H 2Oor greater may be needed. After the administrationof atropine, resistance decreases to 40 cm H2O orlower, and the secretions diminish (although theymay thicken), creating less obstruction to ventilatoryefforts. Thus, in the unlikely but conceivable situationthat a lone first responder must treat a severelypoisoned casualty whose heart is still beating, IMatropine should be administered first (because it onlytakes a few seconds) before attempting to intubate andresuscitate the patient.There are numerous mechanical devices, includingsophisticated ventilators, that can be used to provideventilatory assistance in an apneic casualty. None ofthese is available to the soldier, and only a few—themask-valve-bag ventilation device, the RDIC (resuscitationdevice, individual, chemical), and a simpleventilator—are available at the battalion aid station.Whatever device is used, it must be able to overcomethe initial high resistance in the airways. If a casualtyis apneic or has severe respiratory compromise andneeds assisted ventilation, then endotracheal intubation,which will enable better ventilation and suctionof secretions, should be attempted.Mouth-to-mouth ventilation might be considered bya soldier who wants to assist an apneic buddy when noaid station is nearby. A major drawback to this is thelikelihood of contamination. Before even consideringthis method, the rescuer should be sure that there isno vapor hazard, which is not always possible, andthat there is no liquid contamination on the individualto be ventilated. The expired breath of the casualty isa smaller hazard. Studies 162–164 involving sarin haveshown that only 10% or less of inspired nerve agent isexpired, and that the toxicant is expired immediatelyafter inspiration of the agent.When managing a mass casualty incident, plannersneed to understand that the period of time thatventilatory support will be necessary in nerve agentcasualties is much shorter than that required for severeorganophosphate insecticide poisoning. This isbecause organophosphate insecticides tend to be morefat-soluble than nerve agents, disappear into the fatstores, and off-gas, causing symptoms, for days. Despitethe greater toxicity of nerve agents, ventilatorysupport should only be required for hours at most.Nerve agents also differ greatly in this respect fromboth pulmonary oedemagenic agents, such as chlorineand phosgene, and from sulfur mustard. Casualties ofboth of these types of agents may require ventilatorysupport for days to weeks.In the Aum Shinrikyo subway attack in Tokyo, onlyfour of 640 patients seen at Saint Luke ’ s InternationalHospital for definite or suspected sarin poisoning requiredintubation for ventilatory support. Of the fourpatients, one died with severe hypoxic encephalopathy181