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Anaphylaxis and its treatment

Incidence: Anaphylaxis is a severe systemic allergic reaction which occurs quickly and is extremely frightening for all involved. Incidence is very approximately 1 - 3 in 10000 per annum. The allergen reacts with specific IgE antibodies on mast cells and basophils and results in the rapid release of stored histamine and the rapid synthesis of newly formed mediators. These cause capillary leakage, mucosal oedema and ultimately shock and asphyxia. Anaphylactic reactions can vary in severity. They may progress rapidly or slowly (occasionally in a biphasic manner). Rarely manifestations may be delayed by a few hours (adding to diagnostic difficulty), or persist for more than 24 hours.

Aetiology: Most commonly foods, bee and wasp stings; and drugs (eg antibiotics, opioids, NSAI's, iv contrast media, muscle relaxants and other anaesthetic drugs). Foods implicated include peanuts and similar pulses, tree nuts (eg, brazil nut, almond, hazelnut), fish and shellfish, eggs, milk and sesame. 1 Beta blockers may increase the severity of an anaphylactic reaction and antagonise the response to adrenaline.2

Presentation: Skin symptoms include generalised itching, urticaria and erythema, rhinitis, conjunctivitis and angio-oedema. Signs that the airway is becoming involved include itching of the palate or external auditory meatus, dyspnoea, laryngeal oedema and bronchospasm (asthma). General symptoms include palpitations and tachycardia (as opposed to bradycardia in simple vasovagal at immunisation time!), nausea, vomiting and abdominal pain, feeling faint - with a sense of impending doom; and ultimately collapse and loss of consciousness. Airway swelling, stridor, breathing difficulty, wheeze, cyanosis, hypotension, tachycardia and reduced capillary filling suggest impending severe reaction.2

Differential Diagnosis Vasovagal collapse, panic attacks.

Emergency Treatment:2

ANAPHYLACTIC REACTIONS
Treatment by First Medical Responders and for Community Nurses


Consider when compatible history of severe allergic-type reaction with respiratory difficulty and/or hypotension especially if skin changes present
Oxygen treatment when available (high flow 10-15 l/min)
Lie flat ± leg elevation for hypotension unless this increases breathing difficulties.
If Stridor, wheeze, respiratory distress or clinical signs of shock a
Give Epinephrine (Adrenaline) 1:1000 solution IM b,c
Recommended doses
(Half doses of adrenaline (epinephrine) may be safer for patients on amitriptyline, imipramine, MAOI or betablocker)
Age ml of 1:1,000
Adult 0.5 ml (500 microgram) IM
>12 years 500 micrograms IM (0.5 mL)
250 micrograms if child is small or prepubertal
6 - 12 250 micrograms IM (0.25 mL)
6 months to 6 years 120 micrograms IM (0.12 mL)
<6 months 50 micrograms IM (0.05mL)d
Repeat in 5 minutes if no clinical improvement
Antihistamine (Chlorpheniramine)
Recommended doses
Age Dose
Adult 10-20 mg IM/or slow IV
>12 years 10-20 mg IM
>6 - 12 years 5-10 mg IM
1 - 6 years 2.5-5 mg IM
In addition:
For all severe or recurrent reactions and patients with asthma give Hydrocortisone
Adult 100-500 mg IM/or slowly IV
>12 years 100-500 mg IM or slow IV
>6 - 12 100 mg IM or slow IV
1 - 6 50 mg IM or slow IV
If clinical manifestations of shock do not respond to drug treatment give 1-2 litres IV fluid (adult) or 20 ml/kg body weight IV fluid (child) e
Rapid infusion or one repeat dose may be necessary

  1. An inhaled beta2-agonist such as salbutamol may be used as an adjunctive measure if bronchospasm is severe and does not respond rapidly to other treatment.
  2. For profound shock judged immediately life threatening give CPR/ALS (child: PBLS/PALS) if necessary.
    Consider slow intravenous (IV) epinephrine (adrenaline) 1:10,000 solution. This is hazardous and is recommended only for an experienced practitioner who can also obtain IV access without delay.
    Note the different strength of epinephrine (adrenaline) that may be required for IV use. Never give 1:1000 intravenously.
  3. If adults are treated with an Epipen, the 300µg will usually be sufficient. A second dose may be required. Half doses of adrenaline (epinephrine) may be safer for patients on amitriptyline, imipramine or betablocker.
    For children who have been prescribed Epipen, 150µg can be given instead of 120µg, and 300µg can be given instead of 250µg or 500µg.
  4. Absolute accuracy of the small dose is not essential.
  5. A crystalloid may be safer than a colloid. 3

After Emergency Treatment: Attempts should be made to confirm diagnosis: After 45-60 minutes (must be <6 hrs), take 10 mls clotted blood for mast cell tryptase and IgE which confirms mast cell activation (anaphylaxis or anaphylactoid reaction) - but tells nothing of cause. Record peak flow if possible. Take full history (especially details of previous episodes) and perform examination, paying particular attention to skin, pulse rate, upper airways and auscultation of the chest.2. Patients with moderate and severe reactions can have early recurrence of symptoms so may need observation for 8-24 hrs - particularly if the onset was slow and idiopathic; previous "biphasic" reaction, prominent asthmatic component or there remains the possibility of continued absorption of allergen.

Longterm Management: Refer to an allergist or allergy clinic to try and identify allergen so that it may be avoided in future. Organise self-use of pre-loaded pen injections for future attacks (eg EpiPen ®; containing 0.3 ml of 1 in 1000 strength (that is, 300 µg) for adults; and for children 0.3 ml of 1 in 2000 (150 µg)). This again may be best done in allergy clinics. Give a written self-management plan and arrange to teach patient and relatives how to use syringes. 1 Encourage patient to wear a Medic alert bracelet/necklace endorsed by doctor.

References, footnotes and further reading:

  1. Ewan P; Anaphylaxis. (Review) ABC of allergies BMJ 1998 316(7142):1442-5. [Full Text]
  2. Project Team of the Resuscitation Council; The Emergency Medical Treatment of Anaphylactic Reactions for First Medical Responders and for Community Nurses Updated 2005 (UK). Originally published in J Accid Emerg Med 1999 16:243-247 (Algorithm reproduced with permission of the Resuscitation council and BMJ publishing group)
  3. Schierhout G, Roberts I.; Fluid resuscitation with colloid or crystalloid solutions in critically ill patients: a systematic review of randomised trials. BMJ 1998 316:961-4. [Full Text]
  4. Hughes G, et al; Managing acute anaphylaxis. New guidelines emphasise importance of intramuscular adrenaline. BMJ 1999 319(7201):1-2. [Full Text]

Internet

Acknowledgements EMIS is grateful to Dr Huw Thomas for checking and updating this article. The final copy has passed peer review of the independent Mentor GP authoring team. ©EMIS 2005.

Last issued 30 Aug 2006


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