Anaphylaxis is the exaggerated response of a previously sensitised 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 e.g. tryptase, leukotrienes) released from mast cells & basophils.
- Producing respiratory, circulatory, cutaneous and gastrointestinal effects.
- ↑ Vascular permeability and peripheral vasodilation, ↓ venous return and ↓cardiac output.
- Commonest agents - radiologicals, anaesthetics, antibiotics, dextrans.
B. Complement mediated
- Hereditary angio-oedema - functional C1 esterase inhibitor.
- Occurs on first contact with antigen
- Due to histamine release, e.g. Aspirin, Morphine, N-Acetyl Cysteine (Parvolex)
- No previous sensitisation
- IgE is not involved
- The treatment is the same.
- A feeling of faintness or impending doom (angst)
- Nausea, vomiting, diarrhoea
- A rash for example urticaria or erythema
- Facial swelling (angio-oedema) involving upper airway
- ↓BP = vasodilation & ↑ vascular permeability
Please follow the Resuscitation Council 2008 Anaphylaxis guidelines (local copy right)
A & B
- The airway should be opened, cleared and maintained.
- 100% oxygen should be administered using a reservoir bag to assist ventilation, if necessary.
- After assessing the circulation, commence chest compressions if there is no detectable cardiac output.
- Connect an ECG monitor.
- Treat non-perfusing arrhythmias according to standard protocols.
- Treat bradycardia with Atropine.
- If hypotensive - Administer 0.5 mg Adrenaline intramuscularly (or the equivalent paediatric dose[10µg/kg = 0.1ml of 1/10,000 per kg]) as early as possible.
- If hypotensive, do not sit the patient up.
- Repeat Adrenaline as necessary (every 5 minutes).
- Consider Adrenaline infusion 1:100,000 [10µg/ml], starting at 30 - 60 ml / hour.
- Intravenous fluids to counteract hypovolaemic shock.
- 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 fluid, (1000ml in an adult 20ml/Kg in a child) as a bolus.
- Bronchodilator by nebuliser.
- 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.
- 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.
Patients requiring Adrenaline resuscitation warrant admission (CDU) for 12 hours (rebound phenomenon has been reported - but rare).
Prescribe an epinephrine auto-injector on discharge (15-30Kg = 150µg dose, >30kg = 300µg dose).
All patients who require Adrenaline should attend their GP for on-going referral and management.