Anaphylaxis
Introduction
Anaphylaxis is the exaggerated response of a previously sensitized individual to foreign (antigenic) material. There are three types of reaction.
A. Hypersensitivity, IgE mediated
- Prior sensitisation e.g. with peanuts, bee stings or to penicillin
- Histamine (and other vasoactive mediators) released from mast cells & basophils
- Producing respiratory, circulatory, cutaneous and gastrointestinal effects.
- Increased vascular permeability and peripheral vasodilatation reduce venous return and cardiac output.
- ommonest agents - Radiologicals, Anaesthetics, Antibiotics, Dextrans
B. Complement mediated
- Hereditary angio-oedema - functional C1 esterase inhibitor.
C. Anaphylactoid.
- Occurs on first contact with antigen
- Due to histamine release, e.g. aspirin, morphine, N-acetyl cysteine (parvolex)
- No previous sensitization
- IgE is not involved
- The treatment is the same.
Diagnosis
- a feeling of faintness or impending doom (aura)
- nausea, vomiting, diarrhoea
- a rash for example urticaria or erythema
- facial swelling (angio-oedema) involving upper airway
- bronchoconstriction
- ß BP = vasodilatation & Ý vascular permeability
Treatment
Please follow the Resuscitation Council 2008 Anaphylaxis guidelines (local copy right)
A & B
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The airway should be opened, cleared and maintained.
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100% oxygen should be administered using a reservoir bag to assist ventilation if necessary.
C
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After assessing the circulation, commence chest compressions if there is no detectable cardiac output.
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Connect an ECG monitor
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Treat non-perfusing arrhythmias according to standard protocols
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Treat bradycardia with atropine
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If hypotensive - Administer 0.5 mg adrenaline intramuscularly (or the equivalent paediatric dose[10ug/kg = 0.1ml of 1/10,000 per kg]) as early as possible
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If hypotensive do not sit the patient up
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Repeat adrenaline as necessary (every 5 minutes)
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Consider adrenaline infusion 1:100,000 [10ug/ml], starting at 30 - 60 ml / hour
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Intravenous fluids to counteract hypovolaemic shock
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Rarely (in extremis) titrated intravenous doses of dilute adrenaline may be required.
Once cardiac output has been restored, treat according to the regime
below.
- The patient must be admitted to hospital
- IV fluids, (1000ml in an adult 20ml/Kg in a child) as a bolus
- Bronchodilator by nebulizer
- Consider IV aminophylline, 250 mg over 5 mins. (or IV salbutamol @ 250ug slow loading dose followed by 5-10ug per minute)
- Antihistamines (e.g. chlorpheniramine 10 mg IV over two minutes)
- H2 antagonist ( PO or IV ranitidine) are unproven
- Hydrocortisone 200 mg IV. These will have no immediate effect but may well be beneficial later and prevent recurrent collapse.
- Resuscitation Council 2008 Anaphylaxis guidelines (local copy of flow diagram above)
Patients who present with simple urticaria, minimal airway involvement and who have a rapid response to piriton or Histek (certirizine), ranitidine and hydrocortisone can be discharged.
Troubleshooting
- Patient on ß blockers and not responding? - consider IV Glucagon [BestBets] (10mg IV bolus then infusion)
Patients must be admitted if:
- there is any degree of bronchospasm
- any hypotension
- any airway oedema, such as tongue swelling
Even with good initial responses these patients are at risk of a biphasic anaphylactic response where the same problems can arise again.
Links
Emerg Med J 2004; 21:149-154 Patient advice simple urticaria ;Hereditary Angioneurotic Oedema
