There are a few conditions which make the most experienced paeds anaesthetists take a deep breath in. Anterior mediastinal mass is right up there. Here’s a quick trawl through stuff that’s out there by Andrew Weatherall.
Imagine this patient. They are 7 years old. They’ve turned up to the emergency department with fevers. Quite high fevers and a cough. They did just return from an overseas trip to the sort of destination that makes people think about colourful infectious diseases worth a case presentation.
But then there’s an X-ray. The X-ray makes it seem like there’s a mass in the mediastinum. So people are going want to a diagnosis which will need some tissue. Plus maybe some imaging. And central venous access that will last a while.
So the request is going to be coming for a little bit of general anaesthesia to make that happen. So why would that request make people sweat?
What, me worry?
Well I kind of hope so. In a specialty area where we obsess over complications that happen every 1000 or so anaesthetics anterior mediastinal mass is in a different league. Depending on which series you read, complication rates are reported at anywhere between 11% (from the Stricker paper and all pretty low key) up to 20% (care of Hack et al).
Look at the serious complications and the picture can still be pretty scary.That same Hack paper quotes a serious complication rate (that takes in things like airway obstruction and cardiovascular instability) of 5% (which is only 3 patients in their series of 56 but still, yikes). Go back to Ng et al in 2007 and they include 7 of 48 patients (about 15%) who had issues with intubation, ventilation and cardiovascular collapse with one patient needing a tracheostomy and two patients dying.
So it doesn’t really matter how you cut it up being cautious makes a whole lot of sense.
But which ones should we particularly worry about?
Of course you don’t want to spend all your life worrying so maybe you should worry about particular ones more. In a series of reviews on the oncology patient Latham and Greenberg included this summary of ‘things that should freak you out just that little bit more’ (shockingly this was not the title they gave the table).
This seems like a pretty solid list. Dodge these and you’ll probably be OK, right? But wouldn’t you like to be even more specific? Pearson and Tan built on an earlier stratification from Blank and de Souza and came up with this:
Even better. It’s helped by getting imaging but it’s got percentages which must make it many percentage points more useful, right? And when it’s in a table like that it looks like you could probably allocate them into a risk group on your history because surely your symptoms will line up with those “signs” and imaging (and yes I used ” ” for “signs” because on my read those aren’t signs they’re findings from investigations… but let’s not get bogged down in words meaning what they’re supposed to mean).
Except there’s this annoying phenomena of the “not all risk factors” problem. In that look back at patients from about 8 years, Stricker et al. noted that of their 30 patients (from a total pool of 45) with investigations showing either respiratory tree or cardiovascular compression, 4 were asymptomatic. That’s a little over 13%.
At the same time, 8 patients with symptoms you’d be sure were due to mass effect (almost 18% of their pool) had no evidence of compression of either the breathing bits or the blood-filled bits. Symptoms just don’t necessarily match up that well.
So on these (pretty small) numbers we have risks of complications of some sort in 1 in 5 patients, more than 1 in 10 patients with compression turning up without symptoms and nearly 1 in 5 showing symptoms without imaging evidence of compression. Those are confusing numbers.
What does that mean for establishing risk? Well as Stricker and crew say “This discordance between symptoms and mediastinal compression underscores the importance of using a combination of history, physical examination, and diagnostic imaging studies when making perioperative management decisions.” More info helps. Who’d have thought?
So which anaesthetic technique?
Let’s say you’ve got your info. The patient does get short of breath when they lie flat. A lightning fast CT scan made the patient a bit uncomfortable but also showed they have around 50% compression of the distal trachea. Their vessels look pretty happy though. So they’re probably intermediate risk or just maybe high risk.
It’s a pity they’re not in the low risk group, right because the literature that’s out there suggests serious complications are unlikely even if you go with standard monitoring and positive pressure ventilation.
The question I’d ask is why bother? The consensus through the literature appears to be that spontaneous ventilation is a safer option for the higher risk patient. If that’s the case, what do I gain by trying to pick the lower risk patient and choosing a different technique when spontaneous ventilation is pretty likely to work just fine for those not so serious ones while still being the better choice if it’s high risk? I think I’d just stick with spontaneous ventilation.
Why spontaneous ventilation though?
Just like the last time you tried to cram a horse in an elevator (come on, we’ve all been there) squeezing something into a tight space that isn’t naturally occurring there causes problems. In the mediastinal space you’re already trying to cram in big vessels, multi-lobulated air cushions and the wind pipes that feed them.
When you add a general anaesthetic you drop functional residual capacity and that’s probably a result of loss of inspiratory muscle tone, changes in elastic recoil of the chest wall and a migration of the diaphragm towards the head. Losing spontaneous ventilation adds a fall in the transpleural pressure gradient to all of this. That gradient normally helps distend the airways in the chest and prevent collapse. Turn to positive pressure ventilation and you’re only exaggerating the increase in intrathoracic pressure.
Plus when you change intrathoracic pressure you alter the way the heart fills and works. The review by Blank and de Souza makes reference to canine work showing that in a model of anterior mediastinal mass and anaesthesia, cardiac index decreases. That was mostly due to an increase in RV afterload which then is associated with decreased LV stroke volume.
So spontaneous ventilation is likely to help maintain airway potency and may lessen the bad effects that might predispose to cardiovascular collapse. Is there one particular technique that you should use to keep that breathing going? There’s not enough out there to say. At the moment the key message is if they might be high risk, let them do as much of the work as possible. With some appropriate caution about agents that might influence cardiovascular status there is no one agent to support over others.
The Key Questions
So assuming we’re lining up to do a general anaesthetic, are there questions that we should really ask? Well yes, actually which is why I created a whole subheading here to break up the flow of words with a bold title and try and keep you skipping along. Well at least as far as the sub-subheading coming right now.
1. Can I get more info?
If the task is “give them a general anaesthetic” then you best go in with as much information as you can get before the general anaesthetic. Get that history, do that exam. You’ll probably have the CXR but ask long and hard about whether a bit of time to get extra info with an echo and CT could help (both of these probably will, but obviously getting the CT can be its own challenge) and whether investigations for airway flow dynamics are feasible.
2. Is there a better way to get your answer?
Choose a different spot and it might just be that a general anaesthetic is really not necessary. In a review of their approach put out there in 2015, Acker et al noted that in 81% of their 69 patients a diagnosis was made based on tissue from somewhere other than the mediastinum (like blood or bone marrow or a lymph node) or obtained using a minimally invasive approach. This makes it sound like it’s very worth asking if they really need an option incorporating quite so much of the sleepy-time adventures. A simple sample from a peripheral node might just need a little bit of local.
3. Can we treat first?
Well I’ve just been saying how terrible this whole setting is so why not just start treatment and shrink that tumour? The thing is not all tumours are the same and once you start treatment you can interfere with the tissue diagnosis or distort where the patient is in the whole chemo cycle. That’s a legitimate concern but diagnosis is still possible. In their series Hack et al describe 18 patients who received either steroids or chemotherapy before tissue diagnosis (but presumably after the oncologists had a good swing at stating what they were dealing with). In 17 of those 18 a clear diagnosis was still made.
Obviously this doesn’t mean there are no issues with starting treatment first, but it is at least reasonable to ask.
4. What’s my rescue move?
It might not be often that someone has to deploy the rescue manoeuvre but if it does happen don’t you want to know in advance what it’ll be? If you undertake the induction and it all goes bad (like the air won’t go in and out or blood doesn’t seem to be going round and round) what will you do?
The first thing to try and understand is the relationship between that big mass and vital structures on the imaging. Another tip might be to find out from the patient or their carers what their happy place is, at least when it comes to being positioned. If the patient’s best spot is lying up, or lying on one side you might want to consider starting or making it easy to get there if things go sideways. And always be prepared for the possibility that your best option might just be prone or that a little bit of cardiovascular compromise might need the aid of some volume expansion and a drug to support the blood pressure.[** Take note of also of the new, added link down in the notes – go on and check it out.]
5. What’s the plan for the “air goes in and out” bit?
One of the biggest fears of course is that the air we find so useful when it goes in and out will be denied that opportunity as the airway collapses entirely. Again risk stratification seems like the key here. Those in the low risk group seem to be unlikely to cause issues. For those in the intermediate and high risk groups it’s a different story. Your instinct might be to say “well once I get a tube past that obstruction I’ll at least be in charge of the “A” part of my alphabet”. Except no. There’s every chance you won’t find it that easy to get the tube down beyond the obstruction easily, or the problem will extend down the bronchus, or some other variant not fixed with a plastic pipe.
So for those in the intermediate or high risk group it’s worth at least discussing whether you should have someone with a rigid bronchoscope at your side. That way if the airway does become particularly compromised you might still have an option to re-establish airway patency and get back on top of things or evaluate the dynamic anatomy a bit more.
Perhaps a key point to take away way is that you need to think through your plan for each individual case though and not always assuming that you should do the same as that one other time, nor that you should persist with an option that is failing you. This links back to the need to have thought through a few rescue options and briefed them in advance.
[“But wait, what about a magical bypass option?” the keen-minded amongst you might say. Well this usually comes up in the reviews and there is a case report in an adult where they instituted bypass in an awake patient. Instituting bypass takes time though so if you were to reach for it as a rescue option, chances are things would be pretty dire for a pretty long time. So the advice seems to be to think about it early and consider as much prep as possible prior, though I couldn’t find anything in the paeds literature describing this being done. I did not check the magic literature in my “magical bypass option” search though.]
6. What other stuff should I have ready?
Invasive pressure monitoring would help with vigilance so some of the reviews stress institution before all attempts to get on with anaesthesia. Again I think a strong argument can be made that the necessity to place this before starting would be heavily influenced by the assessment of risk.
Apart from that reliable intravenous access, a way to expand the circulating blood volume and medications ready to support the blood pressure are a good start (I’m assuming the airway stuff has been prepared with the sections above in mind).
But the bits that are most important…?
Communication. It really comes down to communication.
This isn’t even an embedded ad for a telco desperate for you hard won cash in a crowded market who has not realised that people don’t actually talk on phones anymore. (Yes, look at me understanding the modern communications marketplace in the last few paragraphs of a fairly idiosyncratic blog site in 2016.)
All the assessment in the world goes to waste if you don’t tell everyone else your amazingly coherent plan. This is at least a little bit because having to say the plan out loud really makes you clarify what your plan (and the attached emergency plans) amounts to.
Even more important is communicating with the patient and their family. They need to understand what the state of play is and would probably feel a whole lot better knowing all the clever planning and precautions you’re putting into making it safer.
And that’s it. Anterior mediastinal masses are a bit scary. You might just be able to dial down the sort of horror that would leave you looking like this …
… if you take time for the assessment, figure out the level of risk, look for the least intrusive diagnostic option, keep that patient breathing and have your emergency plans ready to go.
And go home with that weight a little less on everyone’s chest.
Yes the wrap up of the last sentence was a slightly cheesy link back to the title of the post but I’ll be honest I was a bit thrown by the picture of the Aye Aye, which I found under Creative Commons as posted (and unchanged) by James Joel. Could be worse of course. I could have been in the room with it.
** Here is an update to the post contained within the notes, added about a month after the initial posting. Dr Johannes Huitink (Twitter handle @AirwayMxAcademy) who is a founder at the Airway Management Academy (and therefore part of a crew sharing interesting thoughts on all things airways) picked up the post and shared this link. It shows an example where an adult patient with tracheal compression was managed with emergency ventilation with a Frova catheter then an airway stent. In the tweets around the topic Hans made the excellent point that you need to make your management of the airway appropriate to the context of the particular case. If you continue with something that isn’t working, you could end up in a bad place.
To make this even clearer in the post I added the bit in key question 5 at the paragraph starting with “Perhaps a key point to take away…” and ending with “briefed them in advance.”
Anyway, that sort of insight tells you that there is probably some interesting stuff up there via the good Dr Huitink and the Airway Management Academy so here is the link to go and watch videos, right here. Or you can go to the home page here.
Now, to some literature … There are no big reviews of anterior mediastinal mass out there, just lots of relatively small series and review articles. This post can’t possibly do justice to all of them so going back to read the source literature comes with a strong recommendation.
In no particular order here are the ones that were helpful (or linked in the post):
And there you go. As it’s just before Christmas they’ll probably be a bit of a break in normal transmissions. We’ll have new stuff in 2017 (and still love hearing thoughts and comments in the meantime – that much we’ll be doing.)