Anesthesia for Casualties of Nerve Agents Dr. Daniels

Chemical Warfare: Don Daniels, M.D. Chief Anesthesiologist Brooke Army Medical Center Fort Sam Houston, Texas Anesthesia for Casualties of Nerve Agents DON DANIELS COL MC 1 Anesthesia for Casualties of Nerve Agent: Objectives    Discuss problems posed to military Anesthesiologist and CRNAs by casualties exposed to nerve agents who require anesthesia intervention Discuss management of patients undergoing anesthesia who received pyridostigmine prophylaxis Discuss interaction with agricultural insecticide and anesthesia DON DANIELS COL MC 2 Chemical Warfare: Anesthesia for Casualties of Nerve Agents  Alleged Uses of Chemical Warfare  Egypt in South Yemen 1963-68  Vietnam in Laos 1975-78  Ethiopia against Eritrean & Somalia backed rebels 1976 Vietnam in Cambodia 1978 China & Vietnam 1979  Iraq against Iran 1984-88  Iraq against Kurds 1988 DON DANIELS COL MC 3 Chemical Warfare: Anesthesia for Casualties of Nerve Agents  Terriorist Attacks  1995 Tokyo subway attack (Sarin) DON DANIELS COL MC 4 Chemical Warfare: Anesthesia for Casualties of Nerve Agents      GA: GB: GD: GF: VX Tabun Sarin Soman no common name DON DANIELS COL MC 5 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Lessons Learned from Iran-Iraq War  Troops with organophosphate exposure fell into 4 groups     1. Greatest exposure died in the field 2. Severely injured who reached medical aid were unconscious and in respiratory arrest 3. Seriously intoxicated had dizziness, disorientation, anxiety, salivation and respiratory difficulty 4. Patients with mild symptoms were physically difficult to manage due to disorientation DON DANIELS COL MC 6 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Lessons Learned from Iran-Iraq War    Largest number of casualties required no treatment other than decontamination Comatose casualties of nerve agents who did not have cardiovascular problems were treated with large doses of atropine, 50 200 mg IV. Most received 2 mg q 8 hrs Comatose casualties with significant cardiovascular deterioration (such as bradycardia after 2 mg atropine) were most often found not to survive DON DANIELS COL MC 7 Chemical Warfare: Anesthesia for Casualties of Nerve Agents  Mechanism of Action: Organophosphorous compounds  Inhibit acetylcholinesterase  Accumulation of acetylcholine leads to CNS stimulation then depression, finally paralysis  DON DANIELS COL MC 8 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Clinical Effects  Exposure to either liquid or vapor nerve agent can cause  Muscarinic - increase in secretions from the nose, eyes, mouth, airways and intestines. Bradycardia  Nicotinic - muscle fasciculations, twitching, weakness and paralysis. Tachycardia  CNS - generalized seizures DON DANIELS COL MC 9 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Clinical Effects  Nerve agents are liquids, skin entry    small droplet effects onset 18 hr large exposure onset 1-30 min At high temps or aerosolized by explosion, they may be inhaled   Small vapor exposure onset seconds - miosis, rhinorrhea, ocular pain, conjunctivitis, visual changes, bronchoconstriction & bronchial secretions Large exposure- unconsciousness in seconds, convulsions, paralysis and apnea in minutes DON DANIELS COL MC 10 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Treatment     Decon - Hypochlorite or soap & water Atropine: blocks the action of excess acetylcholine at muscarinic sites  2 mg mild, 6 mg severe  q 5 min until secretions minimal  15-20 mg if necessary  Miosis may persist Pralidoxime Chloride - releases the inhibiting agent from acetylcholinesterase. Acts at the nicotinic site to normalize skeletal muscle activity  I gram over 20 min, then q 1 hr max 3 gram Anticonvulsants: 5 - 10 mg diazepam DON DANIELS COL MC 11 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Pretreatment  Pyridostigmine     Essential when GA or GD is considered imminent Reversible cholinesterase inhibitor, it binds 2030% cholinesterase so that it cannot be irreversibly inactivated by nerve agent. The bound cholinesterase is returned to normal activity after 12 hrs Alone will not entirely protect soldier from lethal effects of nerve agents 30 mg po q 8 hrs. DON DANIELS COL MC 12 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Pretreatment  Pyridostigmine Side Effects  Muscarinic - gastrointestinal hypermotility, cramping, nausea, vomiting, diarrhea, salivation, lacrimination, urination, sweating, increased tracheobronchial secretions, bronchoconstriction, miosis, bradycardia and atrioventricular conduction slowing  Nicotinic - muscle cramps, fasciculations and weakness DON DANIELS COL MC 13 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Preoperative Assessment and Examination    History of toxic exposure  Type of agent, route of contamination, when and proximity  Pretreatment with pyridostigmine and treatment with antimuscarinics and oximes Examination  Respiratory  Cardiovascular  Nervous system Laboratory  Dibucaine number DON DANIELS COL MC 14 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Preoperative Preparation      Cimetidine has no interactions with Pyridostigmine Diphenhydramine has antinicotinic activity and reverses organophosphate induced neuromuscular blockade Hydroxyzine does not have antinicotinic actions Promethazine anticholinergic effects should be offset by the pyridostigmine muscarinic effects. However, should use cautiously in combination with succinycholine and organophosphorous compounds Glycopyrrolate - may require larger doses to decrease oral secretions, protect against larygngeal mediated vagal reflexes and bradyarrhytmias DON DANIELS COL MC 15 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Anesthetic Induction   Thiopental can provoke asthma and pyridostigmine through its muscarinic activity may aggravate even more Ketamine will antagonize muscarinic effects DON DANIELS COL MC 16 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Anesthetic Maintenance   Nondepolarizing blocking agents will be antagonized. Minimal clinical experience. Depolarizing blocking agent may be prolonged. DON DANIELS COL MC 17 Anesthesia for Casualties of Nerve Agents: Anesthetic Maintenance & Opioids    Morphine vasodilation may be accentuated in presence of pyridostigmine Meperidine tachycardia may counteract some bradycardia Fentanyl bradycardia can be treated with antimuscarinic DON DANIELS COL MC 18 Anesthesia for Casualties of Nerve Agents: Anesthetic Maintenance & Inhaled Agents  Halogenated anesthetics potentially beneficial effects in nerve injured patients Bronchodilation  Skeletal muscle relaxation   Nitrous oxide has no reported interactions with pyridostigmine DON DANIELS COL MC 19 Chemical Warfare: Anesthesia for Casualties of Nerve Agents: Postoperative Complications  Ventilatory 2 support will be required if all acetylcholinesterase is removed - 3 hours with nerve agent  Days with insecticide poisoning  High peak pressures (50-70 cm H2O) due to bronchoconstriction DON DANIELS COL MC 20 Anesthesia for Casualties of Nerve Agents: Persian Gulf Experience       # casualties to allied forces low No nerve agent casualties 3 casualties anesthetized after pyridostigmine Ketamine, midazolam, vecuronium No extension of succinylcholine Possible increased vecuronium usage DON DANIELS COL MC 21 Anesthesia for Casualties of Nerve Agents: Conclusions      Be prepared to deliver anesthesia to patient exposed to nerve agents Be aware of prior treatment received and its potential to affect patients physiology or influence anesthetic care Be prepared for post operative ventilation Remember Anesthesia experience is virtually nonexistent Document experience in literature for others to use DON DANIELS COL MC 22 QUESTIONS? DON DANIELS COL MC 23