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

Medical Aspects of Chemical Warfarebuddy system was used because any soldier able toself-administer diazepam does not need it. Medics andunit lifesavers were issued additional diazepam autoinjectorsand could administer two additional 10 mgdoses at 10-minute intervals to a convulsing casualty.Current policy states that diazepam is given followingthe third Mark I or ATNAAs when the conditionof the casualty warrants the administration of threeMark I kits or ATNAAs. The United Kingdom usesa drug similar to diazepam known as Avizafone. 132Avizafone is a water-soluble, prodrug formulation ofdiazepam that is bioconverted to diazepam followinginjection.If a convulsing or seizing casualty is being treatedin a medical treatment facility, research has shown thatother anticonvulsant benzodiazepines (eg, lorazepam[Ativan, Wyeth, Madison, New Jersey]), midazolam[Versed, Roche, Basel, Switzerland]) are just as effectivein stopping nerve-agent–induced seizure as diazepam.138 Experimental work has also shown that midazolamis twice as potent and twice as rapid in stoppingnerve-agent–induced seizures compared to diazepamwhen the drugs are administered IM, the route ofadministration for immediate field treatment. 107,211For these reasons, efforts are currently underway forFDA approval of midazolam as treatment of nerveagent–inducedseizures and the eventual replacementof diazepam by midazolam in the convulsive antidotenerve agent injectors.Therapy for Cardiac ArrhythmiasTransient arrhythmias occur after nerve agent intoxicationand after atropine administration in a normalindividual. The irregularities generally terminateafter the onset of atropine-induced sinus tachycardia(see discussion of cardiac effects above).Experimental studies 156,215 have shown that whenanimals are poisoned with ChE inhibitors and thenallowed to become cyanotic, rapid IV administration ofatropine will cause ventricular fibrillation. This effecthas not been reported in humans.After severe intoxication from exposure to an organophosphateinsecticide, a 20-year-old patient wasstabilized with atropine and ventilatory support, buther ECG showed depression of the ST segment and flatteningof the T wave, presumably because of persistentsinus tachycardia secondary to large doses of atropine(287 mg in 4 days; total of 830 mg). She was givena β-adrenergic blocking agent (propranolol), whichslowed the heart rate to 107 beats per minute, normalizingthe ST-T changes. The normal ECG pattern andheart rate of 107 beats per minute persisted, despiterepeated doses of atropine. In effect, this produced apharmacologically isolated heart, with both cholinergicand adrenergic blockade. The authors reporting on thecase suggested that propranolol might be of value inprotecting against the effects of atropine and organophosphorusintoxication. 216SPECIFIC TREATMENT BY EXPOSURE CATEGORYThe goals of medical therapy of any poisoningare, in most cases, straightforward: to minimize thepatient ’ s discomfort, to relieve distress, and to stopor reverse the abnormal process. These goals are thesame in the treatment of a patient with nerve agentintoxication.Therapy should be titrated against the complaints ofdyspnea and objective manifestations, such as retching;administration of the contents of Mark I kits (or atropinealone) should be continued at intervals until reliefis obtained. Seldom are more than two to three MarkI kits required to provide relief. Topical application ofatropine or homatropine can effectively relieve eye orhead pain not relieved by Mark I injections.The signs of severe distress in a fellow soldier, suchas twitching, convulsions, gasping for breath, andapnea, can be recognized by an untrained observer.A casualty ’ s buddy will usually act appropriately, butbecause a buddy ’ s resources are few, the level of assistanceis limited: a buddy can administer three MarkI kits and diazepam and then seek medical assistance.In a more sophisticated setting, adequate ventilationis the highest priority, but even the best ventilatorsprovide little improvement in the presence of copioussecretions and high airway resistance. Atropinemust be given until secretions (nose, mouth, airways)are decreased and resistance to assisted ventilation isminimal.The goals of therapy must be realistic. Current medicationswill not immediately restore consciousnessor respiration or completely reverse skeletal muscleabnormalities, nor will IM or IV drug therapy reversemiosis. Muscular fasciculations and small amountsof twitching may continue in a conscious patient longafter adequate ventilation is restored and the patientis walking and talking.Although in practice exposure categories are neverclear-cut, different therapeutic measures are recommendedfor treating nerve agent casualties at differentdegrees of exposure severity. Treatment is based onthe signs and symptoms caused by the particular exposure(Table 5-7). The following suggested exposurecategories are based on the casualty presenting signsand symptoms.190