Rare Birds and First Principles

Ever noticed how things that are potentially scary often have the smallest evidence-base to help guide the clinician? Today’s example is congenital lobar emphysema,  from Dr Andrew Weatherall

Every day I get to make hundreds of little shortcuts. There are things that over generations and generations have gone from being things that we sweat the sweet sweat of good manual work over, to things that require as much thought as a sleepy morning ceremonial dragging of the comb through short hair.

The same can be true of anaesthesia. A lot of our experience lets us choose the best option to get things done almost without thought. Then a clinical situation comes along which shakes that right up because it really does require a good plan because otherwise it can get pretty scary.

And because this has all come to a head through a particular clinical situation I had to think through recently, this post will be about just one such clinical scenario – the kid with congenital lobar emphysema who really needs that fixed up. Now.

 

Rare Birds

A quick refresher on this rare bird. This is an anomaly within the lower respiratory tract related to development, not the sort of emphysema babies get from smoking. The reason it’s likely to turn up for the paediatric anaesthetist is that it can be associated with overinflation of the emphysematous bit of lung. It’s rare though with a prevalence of around 1 in 20000-30000. It’s more common in boys than girls.

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This came up when I searched for ‘rare bird’ and I have to say it is true that would be a particularly rare type of bird that would scare me when expecting any type of bird.

The reasons for development of this aren’t always entirely clear, although obstruction of the developing airway is one of the more common associations. Sometimes this is associated with deficiencies in the bronchial cartilage, or other forms of obstruction or extrinsic pressure. The end-result is airway collapse during expiration. Gas that doesn’t get out doesn’t just hang around quietly of course. Air trapping can cause all sorts of problems.

The classic picture is the kid developing tachypnoea and increased work of breathing. Up to a third present around birth, about 50% by 1 month and most of the rest by 6 months.

It seems like the assumption used to be that these patients were almost all symptomatic and would require resection of the affected bit of lung. There is actually a group of patients where the lesion is discovered but it’s asymptomatic or has minimal associated symptoms. There’s an argument that watching these patients is a reasonable first option, as long as you really mean close watching.

 

Rare Birds Also Like Special Attention

So the problem as an anaesthetist would appear to be that air trapping. Even more than other lung pathologies like congenital cystadenomatous malformation, the fear is of precipitous hyperexpansion of that floppy bit of lung causing compromise. So if it’s such a scary cave of devilry, everyone who had braved it would have scrawled something on the wall for the next unfortunate traveller, right?

Well, not as far as I can tell. Clearly it’s rare enough, and the patients needing surgery are generally sick enough, that prospective studies aren’t much of an option. When you search though it seems like you’ll find a few case reports with a clear anaesthetic interest which frequently lean on something published by Coté back in 1978.

This is one of those cases where evidence-based medicine, originally defined as needing to apply both the literature and the experience of the clinician as crucial elements to choose the best course, relies a lot more on the fleshy clinician bit than the ‘things written in black and white’ bit.

For situations like this could it be that there’s a looming problem? You might have noticed that it seems to be getting harder rather than easier to publish case reports, even with some new spots opening up. All too often the journals will say “it would have to add something amazingly new” and describing a case of CLE is only as new as 1978.

In the meantime for CLE that number of case reports I could count on my digits. In fact I could probably have a couple amputated in an unfortunate lawn bowls accident and still count them off.

Anyway, enough pointing out the pitfalls of the literature while I ask for help with a question – what should we do for the anaesthetic?

Plurals

Yep, I used the plural version because there may well be a request to provide anaesthesia for the CT scan as well. That’s the sort of imaging we’ve discussed before where you really want an excellent breath hold on inspiration to get nice expanded lung segments. Except for here I guess. So let’s keep in mind these broad thoughts also need to be considered for that CT scan.

Things that Seem to Make Simple Sense

In looking at things written by those who were kind enough to scrawl tips on the cave wall, there seem to be a few points to keep in mind:

1. Think about the fluid status

Look I thought I was going to start with airway pressures too. The thing is that once you start adding any airway pressure at all, you need to be prepared for gas trapping and rising intrathoracic pressure. Patients with respiratory issues who have potentially been on high flow oxygen or treatments such as non-invasive ventilation, while also not able to feed normally may well have issues with dehydration. If you do get a rise in intrathoracic pressure, don’t you think you’d rather have that fluid on board?

A low threshold for starting with a fluid bolus (maybe 10 mL/kg of an appropriate crystalloid) seems like a good start.

2. What have they had so far?

Some of these patients turn up with respiratory distress and a CXR that looks like there’s a big area of gas and a bit of shift and get treated for pneumothorax. Some develop infection on top of it all and have secretions everywhere. Some will have had either non-invasive ventilation or been intubated to treat those other things. This could mean you have a ready-made guide for what ventilation settings work for this child. Or it could mean that positive pressure has brought things to the brink of not great. Either way, it’s important to know what treatment they’ve had up until now.

3. Don’t get going without the surgeon right there

We all know that often the best bit of anaesthesia is the bit before the surgeons start making life difficult by embarking on the cutting with steel or scorching the earth adventures. This is not one of those occasions to keep them away. Whether it’s for the scan or in the theatre, there is a chance the patient will deteriorate very rapidly and one of the steps to deal with that actually does need a decisive surgeon. I’d argue it’s worth having one around.

4. Don’t use nitrous oxide

I was worried this might seem too obvious, but it’s the sort of easy slip we’re all prone to making if we live up to the standards of being human. There’s no doubt though that these patients aren’t the ones to plan to demonstrate what happens when your agents start making the ‘big pocket of air’ problem bigger.

5. Breathe.

You should breathe. It makes things easier. But there’s a strong argument for keeping the patient breathing too. This is certainly the case for any scanning. Assisted ventilation keeps popping up in the case reports and the rationale seems obvious – why command a machine-driven pressure to keep air going in and out when you can give a gentle nudge of air drawn in by the patient?

The challenge might be a bit more profound for any thoracotomy. Techniques for doing this are described though (see the Arora reference below). Given that we have options including volatile anaesthesia, local anaesthetic, ketamine, dexmedetomidine and the occasional gentle opioid, it does seem like you should be able to get there.

Having the patient do some of the respiratory driving should allow use of lower patient-friendly airway pressures. Oh, that brings me to …

5. Patient-friendly airway pressures

One of the clinical challenges is trying to pick the magic number. What is the critical pressure at which you’ll start over inflating that annoying bit of lung?

Well no one can tell you that. So in all the case reports you’ll see a line about trying to limit peak airway pressures to something like 20-25 cmH2O. Sounds sort of sensible. It probably first started sounding sensible back in 1978 when it appeared in the Coté paper. Maybe it is the best pragmatic bit of advice you can cling to. Let’s just not pretend it’s a super-robust number.

The available case reports have cases with controlled ventilation throughout, manual ventilation until the surgeons have taken care of the lobe, or even high frequency oscillation ventilation for such a case.

I’d personally be trying to keep the patient breathing. I’d be providing minimal pressure support to decrease work of breathing. I’d consider manual ventilation with those pressures not too high and I’d try to remember the other key rule in ventilating these kids:

  • CO2 is allowed to be high for a bit.

Seriously, don’t chase it.

6. Send that lobe to Siberia

I don’t mean transfer the patient to an inhospitable land in which it will definitely be someone else’s problem. I mean consider isolation. Obviously it can be tricky in small kids, but endobronchial intubation may well do the job. Even better, the commonest lobe to be involved is the left upper lobe. Maybe you can just get a medical student to put the endotracheal tube and they’ll be so excited they’ll helpfully push the tip down the right main bronchus.

Disclaimer: Don’t actually get the medical student involved in a hands on fashion of course.  Unless they’re delegated to make sure there’s coffee around to keep the troops happy.

7. What if they crash in a heap?

If they crash to me it would suggest one of two urgent things:

  • You need to stop air getting into that lobe.
  • You need to stop that lobe being inside the chest to cause problems.

What does that mean in the real world terms? Well stopping air getting into that lobe really means trying for lung isolation. That way you’d hope the problem didn’t get worse while you were getting things ready.

The second feature here relevant bit of lung making a visit to the world outside the chest wall. If there’s a rapid deterioration you want the thoracotomy to happen quickly because it’s hard to rectify from anaesthetic point of view. You can certainly make it worse. If the surgeon gets that bit of lung outside then air trapping becomes much less of a problem.

 

So there’s the combination. A key feature here is that this is just the stuff you can glean from a handful of case reports and a bit of chat amongst colleagues over the years.

These cases can be scary. They are less scary if you have colleagues to share the load. That’s why there is still space for case reports so we can all learn from others’ experience. Or of course you could mention it here. Colleagues can be anywhere you find them.

Notes:

This is exactly the sort of case where we’d love to hear clever insights from those far and wide. So please consider leaving a comment. You can also follow the blog and you’ll hear when new posts pop up.

That busy tiger was on flickr Creative Commons by Steve Wilson with no modifications.

We would always advocate going to the source literature. Blog posts have their place but it’s the literature that really needs meshing with local practice and expertise.

So here’s links to references (or papers where possible):

Tempe DK, et al. Congenital lobar emphysema: Pitfalls and management. Ann Card Anaesth. 2010;13:53-7. 

Celik M, et al. Anesthetic Management in Children with Congenital Lobar Emphysema. Acta Chir Belg. 2015;115:279-83.

Arora MK, et al. Combination of inhalational, intravenous, and local anesthesia for intubation in neonates with congenital lobar emphysema. 2006;16:998-9.

Gojia AR et al. Anaesthetic management of a case of congenital lobar emphysema. J. Anesth Clin Pharm. 2011;27:106-8.

Goto H, et al. High-frequency jet ventilation for resection of congenital lobar emphysema. Anesth Analg. 1987;66:684-6.

 

 

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