Animal Wrangling

If you are talking about things which don’t have a huge amount of evidence but need an answer you try to achieve consensus. Here’s a little thing from Andrew Weatherall (@AndyDW_) on a recent animal wrangling publication on paediatric regional anaesthetic hot topics. 

Creative people can be inspirational. They can be irritating. They can astonish and befuddle with their unique insights into things.

Take conspiracy theorists for example. The flexibility of thought to believe that climate change is part of a plot to establish a One World government run by the UN, or that the moon landings happened no further away than a film studio, or that research scientists can cure cancer they just don’t want to because they’re making money off tumours … so inventive.

How do these people manage to ignore the obvious flaw in their argument? Think back to the last time you went to a restaurant with a big group. How did the ordering go? Could you even agree on how to split the bill? Getting that many researchers to agree on anything with that much conspiratorial juice can’t possibly be realistic.


They’re All Cats

This makes a recent effort in kids’ anaesthesia equally noteworthy. A group of interested types got together to make a consensus statement on matters relating to regional anaesthesia in kids. A consensus statement. They agreed on things. It sounds too good to be true.

It wasn’t entirely a “let’s sit down and just chat it out” exercise either. They looked through the available evidence in a pretty comprehensive fashion. Then they sat down and talked it through.

This is about as impressive an effort as these heroes herding cats. For the purposes of this they looked most keenly at a few particular topics that keep exercising paeds anaesthetists: sleep, tests, something elemental (air vs fluid) and disguises.

Sleepy vs Wide Awake

Not that long ago I heard the claim that you could never do anything regional with the patient asleep because it would be indefensible if something went wrong. Yet in paediatric patients that’s what we do. As a routine.

This paper does a nice line in reviewing a bit of history around regional techniques and paeds anaesthesia. About the same time as such techniques started getting popular again there was a case report in an adult of a bad neurological result after multiple attempts at a thoracic epidural. This was later followed by a European publication describing complications after attempted epidural in 4 kids.

The theory is simple: when people are awake they would be able to warn the proceduralist of things that might matter like paraesthesia, pain on injection or motor responses that don’t quite fit.

However there’s now 4 big studies (as in > 10,000 patients in each study) that have looked specifically looked at complications in kids. None of them report any incidence of paralysis.

In the 2007 UK Prospective National Pediatric Epidural Audit one child had persistent paraesthesia at 12 months although they had a drug infusion error. Each study seems to get bigger too. The 2014 PRAN report included 53564 cases between 2007 and 2012. In that study there was no increase in risk of neurological complications when patients were under GA.

This doesn’t mean there is no risk when performing blocks under GA of course and there will always be some outliers that just couldn’t be picked up in these sorts of studies. We can’t remove risk entirely. But perhaps we can embark on these techniques in sleeping kids with a little bit of confidence. The same confidence we have when we go for a walk in the CBD of a big city that our heads are pretty safe from falling coconuts.


The main purpose of the neuraxial test dose is to have a little bit of adrenaline to give a warning if you’re giving agents into blood vessels. It’s the canary in the mine if you like.  A blood-soaked canary just for you.

The theory goes that for adults 3 mL of local anaesthetic with 15 mcg of adrenaline (or epinephrine if you prefer but I’ll go with adrenaline because it reminds me of extreme sports) should probably give you tachycardia, probably after a change in T wave morphology and maybe with a bit of a spike in blood pressure.

Great theory but does it work in kids? How much do you even give? Well the definition offered up is 0.1 mL/kg or a local anaesthetic solution with 5 mcg/mL of the crucial speed juice. There are additional challenges in kids too:

  1. A lot of them are under general anaesthesia (I feel like we went through this together recently).
  2. Little tackers tend to have a higher basal heart rate – perhaps a change will be harder to pick up?
  3. Maybe the reaction to adrenaline is different in different age ranges.
  4. What if they’ve had a premedication?
  5. What is the actual local anaesthetic used?

After the review most of these questions are still there little. There is probably still a roll for a test dose though. A positive test dose helps. False-positives are not a feature of the literature so if there is a change in T waves or heart rate within 90 seconds you’re best off believing it.

A negative test though? That probably shouldn’t alter your index of suspicion that a vessel could be in the picture. It could just be that your canary is asleep. In a deep and bloody sleep.


Look at that beady little eye. Don’t rely on the bird.

The Elements: Air and Water

Well here’s one people get passionate about: loss of resistance to air or salty water. I’ve certainly met people who swear by air as the better option for producing the feel of loss of resistance, particularly in the smaller kids where you don’t get the same feel for the connective tissues along the way. They’ll also sometimes say it’s hard to know when you get a dural puncture with a small needle using saline.

The problem is there are complications unique to air. At least there are when it comes to case reports – nerve root compression, pneumocephalus, incomplete analgesia and venous air embolism.  It is fair to say though that to produce those you probably need to inject a pretty decent amount of total air.

Is there an alternative to only using 0.5-1 mL of air if you want to make it a gas that you use? Well you can use carbon dioxide apparently, but 6 seconds of thought also makes you think the logistics would be such that you’d need a pretty compelling case to deploy a bubble of gas as your resistance checker.

Saline therefore minimises some of those other risks of complication, though it can cause a transit fall in cerebral blood flow in small infants if you get too volume happy. Volumes should still stay small. Then there’s the third way – one publication involving 500 paediatric epidural blocks suggests easy detection of the epidural space and less dural puncture than either saline or air alone. Win-win.


We’ve all had this one. The patient in a clinical situation where you’d really like to consider an epidural. A surgeon who is worried about compartment syndrome. A request to just go with things through the drip. After all it only takes about 4 hours of delayed treatment to result in irreversible limb damage.

The anaesthetist seeking to advocate for regional techniques would probably point to the idea that increasing analgesic requirements where the regional has previously been working well is actually a warning sign. They’d point to studies like that by Johnson and Chalkiadis where they reviewed 12 cases of compartment syndrome associated with epidural analgesia. The recurring message – don’t blame an epidural for things that don’t make sense as being caused by an epidural.

Case 1 for example – a patient complaining of limb paraesthesiae 18 hours after an orthopaedic operation where the epidural was deemed to be the culprit. The epidural hadn’t included local anaesthetic.

Then a patient spending 11.5 hours in the lithotomy position with a weak (0.0625%) bupivacaine infusion stopped before the end of surgery. 6 hours later a complaint of less leg sensation was treated with epidural opioids. And again another 6 hours later.

It goes on – patients in lithotomy position. Patients with leg splints in place. Patients in whom pain, remote to the epidural, kept getting worse with the issue of compartment syndrome missed. The song is so repetitive it gets boring quickly: people who happen to have an epidural in place have a risk of developing compartment syndrome if their actual symptoms are ignored.

So at the end of this review the comments are appropriately middle ground: they can’t find evidence that compartment syndrome is a significant clinical problem when it comes to numbers; probably use low concentration solutions.

Oh, and look at your patient. Yes, that one. Which, when it comes down to it is sort of the message of this whole article. Regional techniques are no more a case of “set and forget” than any other technique. They require close attention both to make them work and to keep them safe.

Perhaps the things to take from papers like this really are simple: think your way through a good safe technique; do it; then keep a close eye on your patients. Sounds easier than looking after a canary.



The image in this one came via Creative Commons flickr and was posted unaltered from the image by Patries 71.

Of course you should always go and read the source papers so you can figure out how to best apply the evidence to your own practice. Here are the references:

Ivani G, Suresh S, Ecoffey C, et al. The European Society of Regional Anaesthesia and Pain Therapy and the American Society of Regional Anesthesia and Pain Medicine Joint Committee Practice Advisory on Controversial Topics in Pediatric Regional Anesthesia. Reg Anesth Pain Med 2015;40: 526-32.

Llewellyn N, Moriarty A. The national pediatric epidural audit. Pediatr Anesth. 2007; 17:520-33.

Taenzer AH, Walker BJ, Bosenberg AT, et al. Asleep vs awake: does it matter? Pediatric regional block complications by patient state: a report from the Pediatric Regional Anesthesia Network. Reg Anesth Pain Med. 2014; 39:279-83. 

Johnson DJ, Chalkiadis GA. Does epidural analgesia delay the diagnosis of lower limb compartment syndrome in children? Pediatr Anesth. 2009; 19:83-91. 





One response to “Animal Wrangling

  1. Pingback: Animal Wrangling | Prehospital and Retrieval Medicine - THE PHARM dedicated to the memory of Dr John Hinds·

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