Cite this article as:

Andrew Tagg. Topical anaesthetic creams, Don't Forget the Bubbles, 2015. Available at:

https://doi.org/10.31440/DFTB.7762

Six year old Angela comes into your department with a three day history of diarrhoea and vomiting. You determine that she needs cannulation both to assess her renal function and to begin treatment. You know that cannulating children can be a painful and traumatic experience and are keen to make it as stress-free as possible. The nurses ask you what you would like them to put on the child?

Bottom line pearls: IV cannulation can be a painful experience for children; by making it less distressing we can reduce potential anxiety if further cannulation is required

A variety of local anaesthetic creams are available

Topical amethocaine seems to work better than EMLA

It should be liberally applied to a number of potential cannulation sites but has uses beyond just cannulation

Do children really need something to make cannulation less painful? Of course they do! By reducing both pain and anxiety we can make life much easier for ourselves and our colleagues in future visits.

What local anaesthetic creams are available in the Emergency Department? The three commonly available topical anaesthetic creams are EMLA (5%), AmetopTM/AnGelTM (4% amethocaine) and LMX-4.

How do they work? For a beautiful video reminder of how local anaesthetics work watch this video by Armando Hasudungan. The cream should be placed on normal, intact skin on a minimum of two (ideally four) possible cannulation sites and covered with an occlusive dressing. This does two things: it improves absorption; and it also stops the cream covering everything the child comes into contact with. They are rapidly absorbed from inflamed skin, highly vascularised areas and the mucous membranes and should be avoided in these areas.

I’ve got to get this patient out of the department in four hours. How long do they take to work? Both work very quickly with amethocaine taking 30 minutes before any clinically significant analgesia is obtained. EMLA takes a little longer, up to an hour. If you think a child is going to need cannulation then get some cream on them sooner, rather than later.

What is EMLA? EMLA is an acronym for Eutectic Mixture of Local Anaesthetic. The science geeks amongst you will know what this means but in lay terms this ‘eutectic’ mixture displays unique physical properties different from its composite parts. Both prilocaine and lignocaine are crystalline solids at room temperature but when combined in an oil:water base have a much lower melting point and act as an oil.

Enough about the science. What do I really need to know? EMLA is a mixture of lidocaine 2.5% and prilocaine 2.5%. It is licensed for use in all children from the neonatal period but care must be taken in dosing as with all medications. There is the theoretical risk of inducing methaemoglobinaemia if its use is combined with other agents that may precipitate such a state e.g. sulphonamides or dapsone. It should be left on for a minimum of an hour prior to removal and may cause noticeable skin blanching around the application site. The numbness will last one to two hours. It can be stored at room temperature.

What is AnGel™? The active ingredient in AnGel™ or Ametop™ is amethocaine (tetracaine) 4%. It can be used in children over one month of age. Clinically acceptable analgesia is achieved in about 30 minutes. The numbness lasts up to six hours. It may cause erythema and vasodilatation around the application site. It should be stored below 8°C.

What about LMX-4? The active ingredient is 4% lidocaine. A proprietary liposomal formulation leads to rapid onset of action and like AnGel™ it is effective within 30 minutes of application. It appears to have some of the advantages of EMLA in that it does not require refrigeration coupled with the speed of onset of AnGel™. It is only approved for use in children over two years of age.

So is one better than the other? Theoretically topical amethocaine should be better. It has a faster onset of action and may cause less vasoconstriction than the alternative. A BestBets review in 2008 revealed a paucity of quality literature around the subject with many heterogenous trials involving small numbers of participants. The overall trend did seem to favour topical amethocaine though some hospitals are moving towards the newer LMX-4.

Other than IV cannulation what else can we use these topical anaesthetics for? They can be used for any potentially painful invasive procedure such as lumbar puncture, nerve block and SPA.

What non-pharmacological alternatives are available? Locally, we have had some success using Buzzy – an electronic device that utilizes both cold and vibration to distract from the discomfort if cannulation.

For some expert level tips on paediatric cannulation read this blog post by a paediatric anaesthetist, Andrew Weatherall.

Also please consider using bedside ultrasound to help find those elusive veins in chubby toddlers.

Scenario conclusion

You ask the nurses to liberally apply AnGelTM to both cubital fossae and to the backs of the hands. When you go back 30 minutes later she lets you expertly place a 22g cannula without flinching. Job done with three hours left before she has to leave the department.

References

Morgan‐Hughes, N. J., and C. B. Kirton. “EMLA–is one hour long enough?.” Anaesthesia 56.5 (2001): 495-496. full text

Boyd, Russell, and Michelle Jacobs. “EMLA or amethocaine (tetracaine) for topical analgesia in children.” Emergency medicine journal: EMJ 18.3 (2001): 209. full text

Speirs, A. F., et al. “Anaesthetics: A randomised, double-blind, placebo-controlled, comparative study of topical skin analgesics and the anxiety and discomfort associated with venous cannulation.” British dental journal 190.8 (2001): 444-449. full text

Pywell, Alison, and Andreas Xyrichis. “Does topical Amethocaine cream increase first-time successful cannulation in children compared with a eutectic mixture of local anaesthetics (EMLA) cream? A systematic review and meta-analysis of randomised controlled trials.” Emergency Medicine Journal (2014): emermed-2014

Young, Kelly D. “Topical anaesthetics: What’s new?.” Archives of disease in childhood-Education & practice edition 100.2 (2015): 105-110.

Browne, John, et al. “Topical amethocaine (Ametop™) is superior to EMLA for intravenous cannulation.” Canadian Journal of Anesthesia 46.11 (1999): 1014-1018.

Moadad, Nemat, et al. “Distraction Using the BUZZY for Children During an IV Insertion.” Journal of pediatric nursing (2015).

McNaughton, Candace, et al. “A randomized, crossover comparison of injected buffered lidocaine, lidocaine cream, and no analgesia for peripheral intravenous cannula insertion.” Annals of emergency medicine 54.2 (2009): 214-220.

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