Allergy
1.1 Anaphylaxis
Cause: Aspiration, ingestion and/or parenteral use of drugs or other haptens including foreign antigens (insect stings), desensitization shots, semen, or polysaccharides.
Epidem: True anaphylaxis not common; the statistics are not well elucidated because this dx is too broad. Of note, no real crossreactivity between sulfonamide antibiotics and sulfonamide non-antibiotics (Nejm 2003;349:1628).
Pathophys: Respiratory distress due to both upper tract edema and lower tract bronchospasm, consider leukotrienes, also known as slow-reacting substance. Histamine release causes hypotension. Diarrhea and gi symptoms due to serotonin. Some reactions not IgE mediated, which is probably a function of clinical inclusion criteria being too broad.
Sx: Dizziness, dyspnea, pruritus, nausea, vomiting, diarrhea.
Si: Diffuse erythema (lobster red skin), tachypnea, decreased breath sounds, hypotension, altered mental status.
Crs: Onset in ½-3 min, death usually in 15-120 min; recurs in 28% if re-challenged.
Cmplc: Respiratory or vascular collapse, death.
Diff Dx: Differentiate from other forms of shock that include cardiovascular, septic, or neurogenic; and differentiate from other
causes of airway compromise that include asthma, COPD, airway foreign body, aspiration, near drowning, or pneumothorax.
causes of airway compromise that include asthma, COPD, airway foreign body, aspiration, near drowning, or pneumothorax.
Lab: Check for other reasons for respiratory and/or vascular collapse, and monitor vital functions—CBC with diff, ABG, serum tryptase level (Lik Sprava 1992:76) increases and helps distinguish from other forms of shock, EKG, pan culture, metabolic profile, CXR, ethanol level, urine toxic screen, O2 sat.
Emergency Management:
Secure airway, O2
Epinephrine 0.5-1.0 mg iv or im; peds dose 0.01 cc/kg of 1:1000 im (Ann EM 1995;25:785); Not sc (J Allergy Clin Immunol 1998;101:33). Despite prompt epinephrine treatment, some will still succumb to anaphylaxis and there will be the rare death from MI in those without true anaphylaxis—previous history of severe allergic reaction is not a good prognosticator for those who need home epinephrine kits (Clin Exp Allergy 2000;30:1144).
Trendelenburg if hypotensive, short term (J Trauma 1986;26:718) with potentially minimal effects (Ann EM 1985;14:641; Crit Care Med 1979;7:218).
Diphenhydramine 25-50 mg iv (peds 1 mg/kg) (J Appl Physiol 1988;64:210; J Allergy Clin Immunol 1990;86:684).
Methylprednisolone 125 mg iv (peds 2 mg/kg) (Ann Allergy 1989;62:201).
Nebs [β-agonists with equivocal data—patient pool with multiple diagnoses (Prehosp Emerg Care 2004;8:34), ipratropium].
Selective H2 blockers controversial, but may dose cimetidine 300 mg iv (Ann Allergy 1987;58:447).
Aminophylline controversial (9 mg/kg load, 0.7 mg/kg/hr) (Brit J Pharmacol 1980;69:467).
1.2 Angioedema
Cause: Genetic, autosomal dominant type (Clin Immunol Immunopathol 1991;61:S78); medications—eg, ACEIs; foods—eg, beer; environmental challenges; bacteria or viruses—eg, hep C, not H. pylori; drugs of abuse—eg, cocaine.
Epidem: Most Western races.
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