Anaphylaxis

Related clinical tool - Angioedema

Definition

Anaphylaxis is:

any acute onset illness with typical skin features (urticarial rash or erythema/flushing, and/or angioedema) PLUS involvement of respiratory and/or cardiovascular and/or persistent severe gastrointestinal symptoms.

OR

any acute onset of hypotension or bronchospasm or upper airway obstruction where anaphylaxis is considered possible, even if typical skin features are not present.

Australasian Society of Clinical Immunology and Allergy (ASCIA)

Signs and symptoms of allergic reactions

Mild or moderate reactions

  • Swelling of lips, face, eyes
  • Hives or welts
  • Tingling mouth
  • Abdominal pain, vomiting (these are signs of anaphylaxis for insect allergy)

Anaphylaxis

Watch for any one of the following signs of anaphylaxis:

  • Difficult / noisy breathing
  • Swelling of tongue
  • Swelling / tightness in throat
  • Difficulty talking and / or hoarse voice
  • Wheeze or persistent cough
  • Persistent dizziness or collapse
  • Pale and floppy (young children)
  • Vomiting and / or abdominal pain (for insect stings)

Treatment

  • Remove allergen (if still present)
  • Call for assistance
  • Lay patient flat – do not allow them to stand or walk; if airway compromise or breathing is difficult, allow patient to sit up;  if vomiting, then place patient in left lateral position
  • Give adrenaline IM without delay (can use autoinjector if available)
  • Supplemental oxygen
  • Fluid resuscitation - IV fluid bolus of normal saline (20mL/kg) and repeat as needed
IM adrenaline
  • Use 1:1000 adrenaline IMI into lateral thigh
  • Dose: 0.01mg/kg up to max 0.5mg per dose
  • Repeat every 5 minutes as needed
  • If multiple doses are required or ongoing severe reaction, consider IV adrenaline infusion

IM Adrenaline dosage chart

Age (years)

Weight (kg)

Volume adrenaline 1:1000

Adrenaline autoinjector

<1

5 – 10

0.05 – 0.1 mL

 

1 -2

10

0.1 mL

10-20kg (1-5 yrs)

0.15mg (green device)

2 – 3

15

0.15 mL

4 – 6

20

0.20 mL

7 – 10

30

0.30 mL

> 20kg (> 5yrs)

0.30mg (yellow device)

10 – 12

40

0.40 mL

> 12 & adult

> 50

0.50 mL

  • In pts with known asthma and allergy to food, insects or medications, if there is sudden breathing difficulty (such as wheeze, persistent cough or hoarse voice) always give IM adrenaline before asthma reliever, even if there are no skin symptoms.
IV adrenaline infusion
  • IV boluses of adrenaline are not recommended due to risk of cardiac ischaemia or arrhythmia unless the patient is in cardiac arrest
  • IV adrenaline infusion may be used if there is an inadequate response to IM adrenaline
  • A suggested protocol for IV adrenaline infusion is:
    • Mix 1mL of 1:1000 adrenaline in 100mL normal saline
    • Start rate at 0.5mL/kg/hr and titrate to response
    • Should only be given by infusion pump
    • Requires continuous monitoring – ECG, pulse oximetry & frequent NIBP measurements
Additional measures to consider if IV adrenaline infusion is ineffective:
  • Persistent stridor – may respond to nebulised adrenaline (5mg in 5mL)
  • Persistent bronchospasm – may respond to bronchodilators; if intubation is needed, continuous puffs of salbutamol into the circuit may help to relieve severe bronchospasm;
    • Corticosteroids may also be useful – oral prednisolone 1mg/kg (max 50mg) or IV hydrocortisone 5mg/kg (max 200mg) – these should not be used as first line
  • Persistent hypotension – may be due to profound vasodilation or cardiac failure; vasodilation may respond to vasopressors such as metaraminol or vasopressin
    • In patients who are taking beta-blockers, IV glucagon may be tried
    • Start with IV glucagon bolus of 1-2mg in adults; 20-30mcg/kg (max 1mg) in children
Advanced airway management – key points
  • Oxygenation is more important than intubation per se
  • Always call for help from the most experienced person available
  • Use airway manoeuvres (e.g. jaw thrust, Guedels or nasophargyneal airway) with high flow oxygen - even in patients with airway swelling, most patients have stopped breathing due to circulatory collapse rather than airway obstruction
  • Anticipate a difficult airway and consider early intubation if signs of upper airway oedema are present; consider options such as awake intubation with a flexible scope or rigid video laryngoscope
  • Do not make prolonged attempts at intubation – continue to oxygenate the patient
  • If needed, a surgical airway (cricothyroidotomy) may be required
Cardiac arrest – overwhelming anaphylaxis
  • Usually due to massive vasodilatation and fluid extravasation
  • In this case, IM adrenaline is unlikely to be absorbed due to poor peripheral circulation
  • IV adrenaline boluses (cardiac arrest dose, 1mg every 2-3 mins) and aggressive fluid resuscitation may be required in addition to CPR – follow cardiac arrest protocol
Other treatments in anaphylaxis
  • Antihistamines have no role in treating or preventing the systemic symptoms of anaphylaxis; they may help treat skin manifestations such as itching and hives.
    • Second generation H1 antihistamines (e.g. cetirizine) are preferred.
    • Avoid sedating antihistamines as they may mimic some signs of anaphylaxis
    • IV promethazine should not be used – it may worsen hypotension and cause muscle necrosis
  • Corticosteroids have no proven benefit in acute severe settings – they are given to theoretically reduce the risk of biphasic reactions or symptom recurrence, though evidence for this is lacking  (see article below for more details)
Investigations
  • Investigations are usually of little value in cases of mild or moderate anaphylaxis
  • Serum tryptase levels may be considered if the diagnosis is unclear (useful retrospectively)
    • Take levels at 1, 6 & 24 hours post event (levels peak at 1-2 hrs post event)
Disposition
  • Patients who have responded to IM adrenaline should be observed for at least 4 hours after the last dose of adrenaline
  • Be aware that relapse, protracted and/or biphasic reactions may occur
  • Patients will require overnight observation if they meet any of the following:
    • Required repeated doses of adrenaline or fluid resuscitation
    • Have a history of asthma or severe / protracted anaphyalxis
    • Have other concomitant illness, e.g. asthma or arrhythmia
    • Live alone or are remote from medical care
    • Present for medical care late in the evening
  • Incidence of biphasic reactions is estimated to be 3-20% post anaphylaxis reactions
Follow up treatment
Adrenaline autoinjector

If there is a risk of re-exposure (e.g. stings, foods, unknown allergen) then prescribe an adrenaline autoinjector prior to discharge or provide one from the hospital pharmacy– teach patient how to use it and give action plan.

Be aware adrenaline auto-injectors (EpiPen) are expensive from the pharmacy without a Pharmaceutical Benefits Scheme (PBS) which an emergency physician cannot provide without discussion with an Immunologist, Allergist, Paediatrician or Respiratory physician. Consider providing in the ED from hospital pharmacy prior to discharge.

Allergy specialist referral

All patients who present with anaphylaxis should be referred for specialist review.

Further References and Resources

ASCIA website

The Australasian Society of Clinical Immunology and Allergy (ASCIA) website has lots of great resources for health professionals and consumers:

  • ASCIA Guidelines – Advanced acute management of anaphylaxis
  • Clinical resources for health professionals – includes action plans and patient information
  • E-learning modules for health professionals
  • Anaphylaxis patient factsheet for parents (also available in other languages)
  • Adrenaline Autoinjectors (EpiPen®) - Frequently asked Questions

Australian Prescriber - Anaphylaxis – Emergency management for health professionals wallchart

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