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Anaphylaxis

REF:   The Am J of Med Aug 2007: 120:664

Anaphylaxis is an acute and potentially lethal multisystem allergic reaction.  It most often results from immunologic reactions to foods, medications, and insect stings.

Clinical Manifestations of Anaphylaxis (at least 1 of the 3 following Sx within minutes or hours) Acute onset of illness within cutaneous and/or mucosal involvement and at least 1 of the following: respiratory compromise hypotension, or end-organ dysfunction Two or more of the following occur rapidly after exposure to a likely allergen: involvement of skin or mucosa respiratory compromise, hypotension or associated symptoms, or persistent gastrointestinal symptoms; Hypotension after exposure to known allergen for that patient: age-specific low blood pressure or greater than 30% decline from baseline BP. * Respiratory compromise and cardiovascular collapse are resonsible fro most fatalities. * Biphasic and prolonged Anaphylaxis:   Sx experiended during the recurrent phase may be equivalent to or worse than those observed in the initial reaction and may occur 1-72 hours (most occur within 8 hours) after apparent remission.   Neither biphasix nor protracted anaphylaxis can be predicted from the severity of the initial phase of an anaphylac reaction.  It may be necessary to monitor patients 24 hours or more after apparent recovery from the initial  phase.

Diagnosis of Anaphylaxis Anaphylaxis remains a clinical diagnosis based on probability and pattern recognition. Cause and effect often is confirmed historically in patients who experience objective findings of anaphylaxis o inadvertent reexposure to the offending agent. Elevated serum tryptase (reflect mast cell degranulation) may be helpful in confirming anaphylaxis.  It may peak 60-90 min after the onset of anaphylaxis and can persist as long as 5 hours after the onset of Sx.   Differential Diagnosis of Anaphylaxis The vasodepressor reaction is the condition most comonl confused with anaphylaxis. In vasodepressor reactions, however, urticaria and dyspnea are generally agsent, blood pressure is usually normal or elevated, and the skin if typically cool and pale.   Although tachycardia is the rule, bradycardia may occur during anaphylaxis. Flush syndrome Other forms of shock Systemic mastocytosis Panic attack, hyperventilation Scombroid fish poisoning

Management of Anaphylaxis  (managed in emergency facility) * Assessment and maintenance of airway, breathing, circulation, and mentation are necessary before proceeding to following Rx.    Elevate lower extremities in hypotensive patients. Administer oxygen supplement.  IV for normal saline fluid replacement. Epinephrine 1:1000 IM stat Dose: 0.2 - 0.5 mg IM in thigh (adult)  0.01 mg/kg (up to 0.03 mg) IM in thigh (child) Give immediately; repeat every 5-15 min as needed.  Monitor for toxicity. Epipen (0.3 mg dose) 0.1-0.5 mg Subc IM, may repeat every 10-15 min [The alpha-adrenergic effect of epinephrine reverses peripheral vasodilation, which alleviates hpotension and reduces urticaria/angioedema.  The beta-adrenergic properties of epinephrine increase myocardial outpout and contractility, cause bronchodilation, and suppress further mediator release from mast cells and basophils.] Volume expansion with normal saline Dose: 1-2 Liters rapidly IV in adults (5-10 mgL/kg in first 5 min); 30 mL/kg in first hour for children. Rate is titrated to blood pressure and pulse rate.  Monitor for volume overload. Antihistamines as Benadryl (Diphenhydramine) 25-50 mg IV (Adult); 1 mg/kg up to 50 mg (child) Zantac (Ranitidine) 1 mg/kg  IV infusion (adult), 12.5 - 50 mg infused over 10 mim (child) H1 and H2 antihistamine agents work better in combination than H1 agent alone. Methylprednisolone (Solumedrol) 1-2 mg/kg/day IV Prednisone 0.5 mg/kg/d PO * No role in acute anaphylaxis * It might benefit patients with asthma. Glucagon 1-5 mg slow IV, then 5-15 ug/min infusion in refractory anaphylaxis patients who are on Beta-blockers.

       2007