Anaphylaxis
Written by – Dr Andrew Lam
Anaphylactic vs. Anaphylactoid Reactions
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| Anaphylaxis | Anaphylactoid Reaction | |
| Sensitisation Required? | Yes – Requires previous exposure to allergen for significant reaction to occur | No – reaction can occur on first exposure to the suspected substance |
| Pathophysiology | Mediated by IgE – triggers a reaction that stimulates degranulation of mast cells and histamine release along with other mediators | The substance causes a direct release of histamine and other mediators from mast cells – often complement-mediated |
| Amount of Allergen Required | Minimal | More than Anaphylaxis |
| Predicted by Allergen Skin Testing? | Yes | No |
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Management of Anaphylaxis
Immediate
- IM Adrenaline (0.3-0.5mg to the lateral thigh. If symptoms persist, can consider repeating dose every 5-15 minutes. However, if symptoms are refractory, prepare for an adrenaline infusion)
- If signs of bronchospasm present and refractory to adrenaline, consider 5mg of salbutamol through a nebuliser
- Deliver O2, up to 15L via a non-rebreather mask as required to maintain adequate SPO2
- Adequate fluid resuscitation with 20ml/kg of normal saline if the patient is shocked, and repeat as necessary
- Place the patient in the supine position, ideally with lower limbs elevated to support perfusion to vital organs
- Hydrocortisone 200mg IV for management of delayed immune reaction secondary to anaphylaxis
If Refractory
- Adrenaline infusion commencing at 1mcg/kg/min, titrating according to vital signs and clinical response of the patient
- Vasopressor support (in addition to adrenaline) for patients with for maintenance of blood pressure and prevention of shock
- Glucagon for a patient with beta-blocker therapy who may not respond to adrenaline, given as a bolus followed by infusion. Â
References:
Campbell, R.L., Kelso, J.M. (2021). Anaphylaxis: Emergency Treatment. UpToDate. Retrieved May 16, from https://www.uptodate.com.acs.hcn.com.au/contents/anaphylaxis-emergency-treatment
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