Tag Archives: #FOAM

Croup: Riding the Dex Express

Sooooo….this paper turned up at JC last week (thanks to Nicola P) and whilst I’m not sure that it meets all three of our criteria for a top JC paper it is relevant as a week barely seems to go by without someone questioning the dose/route/brand/colour/size/ethnicity of medicine for croup.
Rule of thumb chaps and chapesses ‘The greater the dogma, the greater the ignorance’. Someone cleverer than I said that, but I’m happy to plagiarise ‘cos it’s true.
Anyway, Croup arrives as a question once again in the journal Emergency Medicine Australia, but this time the question relates to speed of onset in mild to moderate croup.

 STOP! If you are in exam mode at this point you should read the paper. See what you think about it and give it a mark out of 10.

We’ve talked about this paper and it’s a tricky one. The first question is why has this paper been done (which we cannot answer, but can surmise privately). The use of steroids in the management of croup is very well established and is something we led on here in Virchester many years ago. It was even one of the very first BETs back in 2004 (amazing to think that we are still talking about this 8 years later).
I’ve also seen the Cochrane review and even examined some CTRs for FCEM on the subject. So, it pretty much seems to me that the question of whether we give steroids for croup is well made. The research that remains is, I suppose, about refining and polishing what is surely a well established fact.

STEROIDS WORK IN CROUP Click the link and read the Cochrane review.

So, what about the paper this week? Is there anything we can draw from it and learn? Well, the authors have done an RCT (good) on mild/moderate croup patients. Interesting this as for the mild ones would you give steroids or just let nature take its course? (Ed – depends on how mild as croup score 1-3 is mild) I’m not sure so there maybe an element of over-treatment in comparison to other practices. Whatever, the authors tell us that there is an effect of giving steroids that they can define and detect at  30 minutes following administration of steroid and that this counteracts the information given through Cochrane about a delayed effect taking up to 6 hours.

I have major concerns with this paper and I just don’t see how this is going to make a significant difference to our practice in PEM.  I don’t think a paper like this would appear in an exam, but if it did I would be pulling holes in it along the following lines.

1. What is the clinically important question here? It seems that we are looking to see the speed of onset of steroid meds in mild/moderate croup. The clinical importance of this is perhaps unclear except in logistical (admission) terms. What defines a significant difference in this low acuity group? Mild croup is not admitted anyway so what is the issue we are addressing?

2. Sample size. OK. An interest of mine, and if you share that interest (you sad person) then hop over to the podcast to hear more about how to understand and interpret sample size calculations. In this paper they appear to be using tests for continuous data for data which is unlikely to be so. Honestly, it seems as though these are the wrong tests for this data, but there is insufficient information in the paper for us to tell. Where is the clue? Well, the Wesley croup score is a categorical score (at best ordinal). It’s not continuous and is unlikely to be normally distributed, so a t-test is rarely going to be the right test. So hmm, not enough information to know but questions are there to be asked. If you want to know more about stats for Critical Appraisal then click here and here. Apart from anything else, a study of just 70 patients would have to show a massive effect if it is be valid and I don’t see that here. Similarly the graph shows average scores only, and I’m not sure that I’m just interested in the change in average score amongst 35 patients. I want to see the distribution as well. This is a common problem in papers as the mean score reporting removes the depth and character of the data.

3. Right, so we are unsure of the validity of the question and also of the sample size what else? Well,  do applaud the authors for defining the numbers of patients that they ‘could’ have recruited and the difference between that number (828) and the number recruited (70) is huge. This suggests a degree of patient selection which may well affect the results. Now, I don’t want to put a massive downer on this as it is an inevitable problem with EM research, but this ratio really asks questions as to whether this is a representative sample, or whether the results will be heavily skewed because it is a sample of convenience.

So, it sounds as though we were pretty down on this paper from a methodological point of view. We gave it a 3/10 to be honest which is clearly not high, but just wait is there ANYTHING we can take away from this piece of work at all. Well, it’s tricky to be honest. It’s likely (but I’m finding it difficult to tell) that oral dex starts working fairly quickly, but that was never a clinical dilemma for me before I read this paper so I’m not going to change practice. However, it’s a useful to use this as a vehicle to discuss Croup (again), to review the relevant BETs and to talk about how to spot flaws in papers.

 bw

Simon C

PS. If you are still in exam mode try answering the following questions…

1. What is meant by the term ‘double-blinded’ and why is it important in a trial like this?

2. Four patients in the placebo group worsened during the initial phase of the trial and were then given steroids. They were analysed in the placebo group despite getting steroids. What is this type of analysis called and is it the right approach?

Through the Looking Glass: Chirocaine vs Bupivicaine


I’ve seen a few paediatric femoral shaft fractures in the last couple of years, and while they always make my spidey-sense tingle for non-accidental injury, most (even the spiral fractures) have been explained away by plausible mechanisms of injury; they are usually late toddling age, have got their feet stuck, twisted and fallen over.

I’ve even seen a few which were pathological – undoubtedly the result of the vitamin d deficiency which stems from the miserable attempt at sunshine we have to put up with here in the North West.

The way I’ve managed these patients has changed with my experience and skill level; as an SHO I looked at them with sympathy while the oramorph, ibuprofen and paracetamol were absorbed slowly from their (no doubt static) GI tracts. As a registrar, they now get a squirt of intranasal diamorphine and an application of ametop over the ipsilateral groin, in anticipation of an ultrasound-guided femoral nerve block when they return from x-ray. I mix up a 50:50 solution of 1% lidocaine with 0.5% bupivacaine and, before ultrasound guidance, used 1mL per year of age. It works out as less than 2mg/kg of lidocaine (usually) and less than 1mg/kg bupivacaine – so relatively small doses. I’ve done it a few times, and it works pretty well, especially in combination with a Thomas splint. The great thing about ultrasound-guidance besides lower failure rates is that you can use even smaller drug volumes – it ends up more like 0.5mL per year of age.

So as I examined the two year old, who was refusing to weight bear, with little deformity to his leg but clear femoral tenderness, I reached for the trusty bupivacaine/lidocaine combination to make splint application less of an auditory assault. But shock! Horror! No bupivacaine!

Instead, there was chirocaine – which completely confused me, as I had no idea what it was (and there was apparently no bupivacaine to be had anywhere). I asked around – and no-one seemed to be entirely sure how the two drugs related to one another. So, after some research, I thought I’d share.

Chirocaine (levobupivacaine), as you may know (I didn’t), is “the pure S-enantiomer” of bupivacaine. The story is that some drugs exist in a 50:50 (racaemic) mixture of two stereo-isomers; molecules which are mirror images of one another. Where the mirror images cannot be superimposed, the molecules are said to be chiral, and the most common cause for this is an asymmetrical carbon atom. There is a right (dex-, or d-) and left (levo-, or l-) version of the molecules which cannot be made symmetrical no matter the orientation in the same way as your left foot just doesn’t fit in your right shoe [NB: an important differential in the non-weight bearing child]. Where drugs bind to receptors, one isomer may be able to bind, while the other cannot – or may generate alternative effects.

You probably knew this already, right? Every time you prescribe levothyroxine, esomeprazole, escitalopram or levofloxacin, you think proudly about how you are selecting out the correct isomer for your patient, yes? And how you are therefore giving half the dose, as they aren’t getting the 50% of isomers which don’t give a clinical effect? Well, it doesn’t quite work as predictably as that. In fact, in some cases the dose is significantly lower for the same clinical effect (notably escitalopram, 30 times more potent than citalopram) and in others confers no therapeutic advantage at equivalent doses (see esomeprazole) or may even be harmful (see thalidomide).

So what’s so special about chirocaine? It’s twice the price of standard bupivacaine per 10mL ampule, so it’s twice as good, isn’t it?

Well, no – it seems to be equivalent at providing analgesia in a variety of blocks (caudal, ilioinguinial, rectus sheath… The list goes on…), but every study is focussed on the reduction in adverse (cardiac) effects with levobupivacaine. It seems the rationale for selecting out this isomer is reducing cardiac toxicity. Where does this come from?

Most data comes from animal studies (in case you didn’t know, children are no more little adults than they are little rats, pigs, rabbits…).

You have to dig quite deep for original studies. All roads seem to lead back to this one paper. 14 healthy, adult, male subjects were injected with bupivacaine or levobupivacaine infusion and asked “do you have any symptoms?”. OK, let’s be fair, they’ve powered the study to detect a 10% difference in their primary outcome (stroke volume), but their bottom line conclusion is “that levobupivacaine may be a safer drug than rac-bupivacaine for procedures requiring high doses of local anaesthetic.” So not really our fractured femur toddlers, then.

Which brings us back to the beginning. Studies in children have suggested that levobupivacaine produces equivalent anaesthetic efficacy, but what they haven’t done is convince me that we should ditch bupivacaine when we are using such tiny doses. It’s cheaper, and with ultrasound guidance we can use a miniscule amount to achieve local anaesthesia long enough to reduce the fracture in a Thomas splint.

So the bottom line is this; use what you’ve got unless there’s specific cardiac risk for your paed patient, and using 50:50 with 0.5% chirocaine provides the same analgesia as bupivacaine (in our hospital the maximum dosing for ilioinguinal block is apparently 1.25mg/kg/side). Whatever you use, do the block; your patients will probably thank you (but we might have to wait to find out).

Natalie May

Ref

  • A comparison of the cardiovascular effects of levobupivicane and rac-bupivicane following intravenous administration to healthy volunteers. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1873676/pdf/bcp0046-0245.pdf
  • EPG data sheet on Chirocaine http://www.epgonline.org/drugs/chirocaine/
  • Regional anaesthesia for kids with femoral fractures at BestBets http://www.bestbets.org/bets/bet.php?id=130

#ICEM2012

Following on from the amazing twitterfest at the International Conference of Emergency Medicine in Dublin I think there will be many emergency physicians updating, revising and expanding their online presence.

There is no doubt that social media can have a positive effect in medical education and research and I think that I may have been lucky enough to be present at the start of something big…..or maybe it’s always been there but I’ve never realised it before.

So, what can we do in Manchester?

Ideas are overflowing after meeting such fantastic people in Dublin, but rather than create something entirely new the way forward will be to find a way to distribute the incredible learning that takes place behind closed doors at StEmlyns (1,2), and of course to find ways of disseminating the evidence from BestBets out to a wider audience.

Time for some distributed thinking.

S

1. http://classroom.stemlyns.org.uk
2. http://www.bestbets.org
3. http://www.stemlyns.org