ANAPHYLAXIS DEFINITION Anaphylaxis is an immunological description of a type I hypersensitivity reaction mediated by IgE or IgG. Clinically, the term is used to describe a group of symptoms (see "clinical diagnosis" for complete description) irrespective of the mechanism. Where an immunological basis for the syndrome is unproven, the term "anaphylactoid" is used. Clinical expression of anaphylaxis is variable in severity but cardiovascular collapse is the most common life-threatening feature and bronchospasm occurs frequently. TOXIC CAUSES Innumerable substances may cause anaphylaxis. Common causative agents include: Antivenoms Blood products Chemicals Drugs: Antibiotics Antiinflammatory agents Analgesics Chemotherapeutic agents Local anaesthetic agents Neuromuscular blocking drugs Radiocontrast agents Foods: Nuts Shellfish Insect stings Latex Plants CLINICAL FEATURES History of exposure to a substance capable of producing anaphylaxis and appropriate clinical manifestations. These may include: hypotension, bronchospasm, upper airways obstruction, pulmonary oedema, angioedema, generalized oedema, pruritus, rash, vomiting, diarrhoea and abdominal pain. In some cases, there may not be a clear history of exposure. DIFFERENTIAL DIAGNOSIS Anxiety Asthma Bronchospasm or laryngeal oedema due to inhalation of irritant gases. Cardiogenic shock Foreign body in upper airway Hypovolaemia Pulmonary embolism Vasovagal episode RELEVANT INVESTIGATIONS In such an emergency situation, no biomedical investigations are required to commence treatment. TREATMENT Epinephrine (Adrenaline) Epinephrine is the preferred treatment for anaphylaxis and should be administered as soon as practicable while assessing and supporting vital functions. It is usually given intramuscularly but may be given subcutaneously in mild cases. Intravenous administration is only indicated in severe cases because of the risk of ventricular dysrhythmias. In the intubated patient, endotracheal installation is possible if intravenous access is unavailable. Doses of epinephrine: 1) Intramuscular/subcutaneous: Adult: 0.5 to 1.0 mg Paediatric: 0.01 mg/kg or Age Epinephrine 1:1000 solution < 1 year 0.05 mL 1 year 0.1 mL 2 years 0.2 mL 3-4 years 0.3 mL 5 years 0.4 mL 6-12 years 0.5 mL > 12 years 0.5 to 1 mL The appropriate dose should be repeated every 3 to 10 minutes until an adequate response in pulse and blood pressure is observed. 2) Intravenous: Adult: 0.1 mg (1 mL of 1:10000 solution made by diluting 1 mg of epinephrine in 10 mL of normal saline) over 2 to 3 minutes. Paediatric: 0.01 mg/kg over 2 to 3 minutes. The appropriate dose should be repeated until an adequate response in pulse and blood pressure is observed. Notes on epinephrine therapy: The dosage of epinephrine is NOT one ampoule. For the intubated patient, if intravenous injection is not possible, intratracheal instillation (1 to 3 mg) is an alternative. Patients on beta-blockers may require larger doses of epinephrine. Oxygen Supplemental oxygen should be administered to all patients. In severe cases, especially those with airways obstruction, establishment of an adequate airway (endotracheal intubation or tracheotomy) and/or assisted ventilation may be necessary. Fluids In patients presenting with hypotension, one to two litres of intravenous fluids should be given as soon as intravenous access is established. Colloid is preferable to crystalloid but either is acceptable. Persistent hypotension should be treated with further doses of epinephrine. Further administration of intravenous fluids should be cautious and ideally titrated against central venous pressure. Corticosteroids are not life-saving and are never the primary therapy of acute anaphylaxis. They may be useful in the treatment of bronchospasm and in the prevention of relapses. An intravenous dose of 200 to 300 mg of hydrocortisone (or equivalent dose of another corticosteroid) may be given. Nebulized salbutamol (albuterol) may be useful for refractory bronchospasm, particularly in children. CLINICAL COURSE AND MONITORING There is usually a rapid response to therapy and recovery is complete. Pulse, blood pressure, respiration and oxygen saturation must be monitored until full recovery. LONG TERM COMPLICATIONS Recurrent episodes of anaphylaxis. The agent that caused the anaphylaxis should be identified where possible and the patient adequately advised regarding the avoidance of further reactions. A warning device or letter should be issued. Patients who suffered life-threatening anaphylaxis should be instructed in the self-use of epinephrine. The need for desensitization to the allergen should be considered. AUTHOR(S)/REVIEWERS Author: Dr R. Fernando, National Poison Information Centre, Colombo, Sri Lanka. Reviewers: Cardiff 3/95, Berlin 10/95: A. Jaeger, R. Dowsett, J. Szajewski, V. Danel, A. Wong. Cardiff 9/96: V Afanasiev, T Della Puppa, J Huang, G Muller, L Murray, J Szajewski, C Warden.