Tasty Morsels of EM 084 – #FRCEM Local Anaesthetic Doses and Toxicity

27 Jul

(featured image, JL Johnson 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.


  • Amide
    • Lignocaine
    • Bupivacaine
    • Priolcaine
  • Esters
    • Cocaine
    • Benzocaine
    • Tetracaine

How do they work?

  • All work by
    • “inhibiting sodium influx through sodium-specific ion channels in the neuronal cell membrane, in particular the so-called voltage-gated sodium channels.” (Wiki)
    • Different pain fibres are affected in  different ways with sympathetic fibres being most sensitive followed by pain fibres. Hence the sensory block without motor block that we often see.

Max Doses

  • Bupivacaine 2mg/kg
  • Lignocaine 3mg/kg
  • Lignocaine with Adrenaline (1:200000) 7mg/kg
  • Prilocaine 6mg/kg (of note remember the MetHb risk with this – I’ve seen it and been responsible for it!)
  • NUH have a lovely table with patient weights and different concentrations all worked out.
  • Also of note if you’ve given your 2mg/kg of bupivacaine you can’t just have a go with lignocaine

Discuss Local Anaesthetic Systemic Toxicity

(From the AAGBI 2010)

  • Signs
    • altered mental staus
    • CV collapse, brady, conduction blocks, asystole and VF/VT
    • apparently you can also get a rash (if you need a third body system for an exam question…)
    • of note can be delayed
  • Management
    • Stop injecting the stuff dummy
    • HELP!!!
    • ABCs
    • Stop the seizure with your agent of choice (benzo, prop, thio…)
  • If cardiac arrest
    • CPR
    • Lipid Emulsion
    • May take >1 hr for recovery so keep going!
    • From the realms of the obvious
      • propofol not a suitable substitute for intralipid despite being made from it
      • don’t give lignocaine for arrhythmias
      • (sigh… eye roll… repeat)
  • If no cardiac arrest
    • supportive yadda yadda
    • consider lipid emulsion

How to give the intralipid

From the AAGBI 2010 Click image for full PDF

  • Bolus
    • 20% intralipid 1.5ml/kg over 1 min (eg about 100mls in a 70kg patient)
    • Can be repeated twice (once every 5 mins)
  • Infusion
    • as soon as the 1st bolus given
    • infusion of 15ml/kg/hr (1000ml/hr of 20% solution in a 70kg patient)
    • if repeating the bolus then double the infusion rate
  • 12ml/kg of the 20% is the maximum dose


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