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CDHB

Anaphylaxis

Definition - a severe, life-threatening, generalized or systemic hypersensitivity reaction.

• Cardiorespiratory: shock, bronchospasm, laryngeal oedema.
• Skin: pruritus, urticaria, flushing, angioedema.
• Other: headache, vomiting, abdominal pain, diarrhoea, feeling of impending doom.

It is important to document the clinical features that support the diagnosis of anaphylaxis.

Not all symptoms may be present. Patients with only non-life-threatening symptoms (e.g., urticaria, external angioedema, abdominal pain) do not have anaphylaxis.

Immediate Management

Stop administration of precipitant if possible, assess reaction severity and treat accordingly.

• ABC:
  • High-flow oxygen - airway/ventilation support if needed.
  • Lie patient flat and elevate legs.
  • IV access - large bore.
• ADRENALINE:
  • 0.5 mL of 1:1000 IM (0.5 mg) to lateral thigh.
  • Repeat every three to five minutes if inadequate response, immediate life-threat or deteriorating.
  • If hypotensive give sodium chloride 0.9% bolus (20 mL/kg) under pressure (and repeat as necessary).
  • Bronchospasm: give nebulized salbutamol 5 mg.
  • Stridor: give nebulized adrenaline 5 mL of a 1:1000 solution (5 mg).
  • IV adrenaline is indicated if the situation is life-threatening with circulatory collapse, and the patient is unresponsive to the above initial treatment. Cardiovascular monitoring must be available. Begin with 0.5-1 mL of 1:10,000 (0.05 mg to 0.1 mg) and increase dose incrementally as required.
  • Call ICU.
  • Hydrocortisone 200 mg IV (onset of action 4-6 hours).

Notes:

• In early anaphylaxis (e.g., witnessed during desensitization therapy), 0.3 mg of adrenaline IM may be appropriate initial therapy; this dose is the same as in self-injecting adrenaline devices.
• Patients on beta-blockers are more likely to have severe anaphylaxis and may respond poorly to adrenaline, with side-effects resulting from unopposed alpha-adrenergic stimulation. Initial adrenaline doses should be halved if this is known. Hypotension in patients on beta-blockers may respond to IV bolus and/or infusions of glucagon.
• Antihistamines generally do not help with life-threatening anaphylaxis. They may be considered for treatment of urticaria. Likewise H2 blockers (e.g., ranitidine) are useful in urticaria not anaphylaxis.

Short-term Management

• Observation:
  • A minority of patients will experience biphasic reactions, with recurrence of symptoms 6-12 hours later. Steroids decrease this risk.
• Confirm diagnosis if this is in doubt:
  • Tryptase is released by activated mast cells. Levels peak 1-2 hours after anaphylaxis onset, and return to normal in 6-8 hours. Some patients with anaphylaxis will have normal tryptase levels, but an abnormal level is useful if there is doubt about the diagnosis. Ideally measure tryptase 60-120 min post-anaphylaxis and again at 8 hours.
• Antihistamines and prednisone, for example:
  • prednisone 40 mg daily for 3 days
  • cetirizine 10 mg BD for 4 days
• Advice to patient:
  • Anaphylaxis plans can be downloaded from www.allergy.org.au.
  • Self-administered adrenaline should be considered when the trigger for anaphylaxis is unknown or repeat exposure is not avoidable (e.g., food and venom, but not drugs).
  • Self-injecting adrenaline devices (EpiPens and Anapens) can be bought over the counter from pharmacies without a prescription; prices vary ($125-$200). ACC will reimburse costs in cases of anaphylaxis where the trigger is food or venom. ACC may not refund in cases where the trigger is unknown, and in this situation will not pay for patients to carry these devices prophylactically. Needles, syringes, and ampoules are cheaper but may be difficult for patients to administer accurately.
  • Adverse Drug Reactions (ADR) reporting guidelines (search for "ADR guidelines" on the CDHB intranet).
  • Centre for Adverse Reactions Monitoring (CARM) (national pharmacovigilance) ADR reporting form.
  • Consider MedicAlert.

Medium-term Management

• Referral to Immunology Service:
  • For all patients with anaphylaxis unless trigger known, and patient capable of managing attacks. Patients with severe and/or recurrent anaphylaxis should definitely be referred.
  • Management includes identification of trigger, education, advice re avoidance and (if possible) desensitization therapy.
• Further testing:
  • Skin prick testing cannot be performed for at least 4 weeks after anaphylaxis, as exhaustion of the mast cells can result in false negatives. False negative antibody tests (EAST/RAST) can also occur if done soon after the event.
• Anaesthetic reactions:
  • Patients with reactions related to anaesthesia should be referred to the Anaesthetic Department.

References:

Soar et al. (2008). Emergency treatment of anaphylactic reactions – guidelines for healthcare providers. Resuscitation, 77, 157-169.

Liberman et al. (2005). The diagnosis and management of anaphylaxis: an updated practice parameter. Journal of Allergy and Clinical Immunology, 115 (3), S483-523.

Brown et al. (2006). Anaphylaxis: Clinical concepts and research priorities. Emergency Medicine Australasia, Vol. 18, issue 2, 155-169

Immunology and Allergy: recommended referrals

Refer to Immunology and Allergy: recommended referrals.

Topic Code: 1271