Anaphylaxis

Notes
  • Severe allergic reaction to drugs, food, insect stings and other substances that is potentially fatal.
  • It is a Type 1 Hypersensitivity reaction that is mediated by IgE in persons previously sensitized to the offending allergen.
  • When it is mediated by non-IgE, it is known as anaphylactoid reaction and it is treated in the same way as anaphylaxis
Symptoms

Flushing; pruritus; urticaria; hypotension; sneezing; rhinorrhea; respiratory distress (due to pulmonary edema); palpitations; dizzinness; dyspnea; diarrhea; nausea; abdominal cramps; syncope; seizure, cardiovascular collapse and death.

Diagnosis
  • It is mainly clinical.
Differential
  • Asthma
  • Pheochromocytoma
  • Vasovagal reaction
  • Foreign body aspiration
  • Angioedema
  • Panic Disorder
  • Malignant Carcinoid Syndrome
  • Acute COPD Exacerbation
  • Vocal Cord Dysfunction Syndrome
  • Postmenopausal Hot Flushes
  • Medullary Thyroid Carcinoma
  • Systemic Mastocytosis
  • Stroke
  • Pulmonary Embolism
  • Acute Poisoning
  • Myocardial Disorder.
Prevention
  • Avoiding the offending substance
  • Desensitization when possible
  • Where exposure is unavoidable give prednisolone 50mg PO 6hly (3 doses) starting 18hrs pre-exposure. This is given together with an oral antihistamine 1 hr pre-exposure.
  • Carrying “Allergy Card” as well as an adrenaline injection if highly predisposed.
Management
  • To avoid further exposure to the offending substance.
  • Lie patient flat with raised legs.
  • The key medicine for treatment of anaphylaxis is adrenaline (1:1000 solution) 0.3-0.5mL IM in adults or 0.01mL/kg in children, repeated after every 10-15 minutes (upto 3 doses). However, patients with collapsed CVS or severe respiratory obstruction are given 3-5 mL solution over 5 min or by infusion 15 - 60 mL/hr.
  • Nebulized bronchodilators such as salbutamol 5mg and /or ipratropium 0.5mg OR
  • Aminophylline 6mg/kg IV over 20 minutes in case of occurrence of wheezing and when it is not possible to nebulized.
  • Chlorpheniramine 10mg for adults and 0.1mg/kg in children IV slowly or IM or SC then repeat 8 hourly for 1-2 days
  • Hydrocortisone 100mg IV (to prevent delayed reaction) 2-6 mg/kg or dexamethasone 0.1-0.4 mg/kg intravenously.
  • Normal saline or Hartmann’s solution (20mL/kg) to treat hypotension and in case it is not successful give dopamine 5mcg/kg/min.
  • Intubation and oxygen are necessary in cases of wheezing and stridor that are not responsive to adrenaline.
  • Cricothyrotomy in case of upper airway edema that prevents endotracheal intubation.
  • In case the patient is on a beta-blocker, give glucagon 1mg bolus in adults and 20 - 30 mcg/kg in children to be followed by 1mg/hr infusion
  • H2-antihistamines such as ranitidine
  • NB: both antihistamines and corticosteroids play minor role in acute reactions.
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