Tasty Morsels of EM 105 – #FRCEM Anaphylaxis

3 Aug

(featured image: Greg Friese on Flickr, CC License)

I’m entering a few months prep for the UK and Ireland exit exam in Emergency Medicine: the FRCEM. I’ll be adding lots of little notes on pearls I’ve learned along the way. A lot of my revision is based around the Handbook of EM as a curriculum guide and review of contemporary, mainly UK guidelines. I also focus on the areas that I’m a bit sketchy on. With that in mind I hope they’re useful.

You can find more things on the FRCEM on this site here

i think we’re all happy to manage this when we see it. But there’s some subtlety surrounding pathophysiology and follow up that is very testable, plus i’ve never really understood anything to do with immunology…

From NICE 2011 and Resus Council UK

Define anaphylaxis and its pathophysiology

Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction

  • Anaphylaxis is likely when all of the following 3 criteria are met:
    • Sudden onset and rapid progression of symptoms
    • Life-threatening Airway and/or Breathing and/or Circulation problems
    • Skin and/or mucosal changes (flushing, urticaria, angioedema), (of note I’ve heard people describe abdo pain/diarrhoea has a mucosal change too)
    • (note the US guidelines differ somewhat from this)
  • In the OHEM 4th P42 they describe it as either
    • IgE mediated
    • Complement mediated
  • Either way there is
    • mast cells and basophils release exciting stuff like
      • histamine
      • prostaglandins
      • thromboxanes
      • leukotrienes

How do you dose your adrenaline?

  • 12-Adult – 500mcg
  • 6-12 – 300mcg
  • <6 – 150mcg
  • They have a little section on IV adrenaline titration but the number to remember is 50mcg for adults and 1mcg/kg for kids
  • give IM anterolat mid third of thigh
  • note the autoinjectors are either 150 or 300 mcg

What tests do NICE and the resus council recommend?

  • mast cell tryptase
    • released as part of mast cell degranulation
    • rise about 30 mins after exposure and peak 1-2 hrs and have a short half life (in other words get your sample early)
    • there’s some advice from NICE about timing of follow up samples
      • ASAP after reaction
      • 1-2 hrs after (and not beyond 4 hrs)
    • can go in your standard serum bottle, make sure it’s timed

how long should we observe these folk for?


  • 6 hrs post treatment
  • note NICE recommends admission for kids given emergency treatment
  • consider anti histamine and steroid for 3 days
  • consider an autoinjector prescription
    • ideally following discussion with allergist
    • venom and food reactions are higher risk of recurrence (given difficult avoiding the exposure). It’s usually easy to avoid getting the drugs again




Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.