Anaphylaxis
From Ganfyd
Anaphylaxis (aka anaphylactic shock) is an overwhelming allergic response to an allergen. Common allergens include such things as:
- Food stuffs (e.g. peanuts, shellfish, strawberries)
- Allergenic materials (e.g. latex)
- Drugs (e.g. intravenous contrast media, penicillins, streptokinase, more rarely vaccines.)
- Insect stings (bees / wasps)
Anaphylaxis can be fatal and must be respected. People still die in the UK from this disease.
Contents |
Mechanism
Priming
Sensitisation usually occurs by prior exposure to the allergan. Sensitisation can occur without prior obvious exposure. This has now been well described via the oral route for wasps, where food contminated with wasp allergens has the potential for Hymenopptera sensitisation[1].
The anaphylatic reaction
IgE cross-binds the offending allergen to mast cells causing degranulation of the mast cell and release of its contents (histamine and other vasodilatory inflammatory mediators). This results in massive systemic vasodilation causing circulatory failure (shock) and, if untreated, death.
Asphyxia may also occur in anaphylaxis secondary to upper airways obstruction.
Clinical Features
The onset of symptoms can be very rapid (minutes) but may take up to 2 hours to become apparent.
Respiratory
- Upper airways obstruction (swelling of lips, tongue, pharynx and epiglottis)
- Lower airways involvement (dyspnoea, wheeze, hypoxia, hypercapnia)
Skin
Cardiovascular
- Tachycardia
- Hypotension
Gastrointestinal
Management
Anticipation
Where treatments are to be given that may precipitate anaphylaxis, suitable drugs and equipment should be available before the treatment is given.[2][3]
Treatment
As with all medical emergencies, the principles of ALS (Advanced Life Support) apply:
- Airway
- Breathing
- Circulation
If the allergen is known, remove the patient from it (e.g. stop the infusion of the offending drug). If the offending allergen is a sting then remove the sting from the patient with forceps.
Lie the patient down and consider raising their legs / lowering their head ("Trendelenburg position").
Secure the airway. This may require an airway adjunct (such as a Guedel airway) or tracheal intubation. Give 100% oxygen via a face mask with a reservoir bag.
Give Adrenaline. The dose is 0.5mg of 1 in 1000 solution. It is given intramusclarly. It can be repeated.
Get IV access. Insert the largest cannula possible in the antecubital fossa. Try to insert at least a green venflon. If the patient is hypotensive (or if young, tachycardic) give IV fluids.
If the patient is wheezing or there is poor air entry on auscultation despite an adequate airway suspect lower airways involvement and give nebulised Salbutamol (5mg, can be repeated multiple times).
Give 10mg IV Chlorpheniramine (an antihistamine).
Give 200mg IV Hydrocortisone.
If true anaphylaxis, the patient should be admitted for at least 24 hours as relapses can occur. The patient should be discharged with IM Adrenaline in the form of an EpiPen. If the allergen is unknown, attempts should be made by the patient, GP and / or an Immunologist to discover it.
See also
References
- ↑ Armentia A, Pineda F, Fernández S. Wine-induced anaphylaxis and sensitization to hymenoptera venom. The New England journal of medicine. 2007 Aug 16; 357(7):719-20.(Link to article – subscription may be required.)
- ↑ Salisbury D, Ramsay M, Noakes K. Chapter 8: Vaccine safety and the management of adverse events following immunisation. Immunisation against infectious disease. 3rd Edition ed. London: HMSO, 2006:53-64.
- ↑ UK Guidance on best practice in vaccine administration (from the Association of Occupational Health Nurse Practitioners, the British Travel Health Association, the Community Practitioners and Health Visitors Association, the Royal College of General Practitioners, and the Royal College of Nursing
