Saturday, 22 January 2011

My first chest x-ray

Another sick person; another likely pneumonia: He?s got a fever,
coughing up green spit and has a white count of 20. ( He was advised,
not by anyone European, to take diamox as prophylaxis against acute
mountain sickness and he had a reaction to their formulation, so was
given second line dexamethasone 4mg bd instead. But logistical delays
meant he was on it for five days waiting to come up to altitude. He
started coughing the day after he stopped the dex, funnily enough)
His sats are low, his respiratory rate and his heart rate are up but
he?s actually pretty well with it. But mindful that our last HAPE
/ pneumonia   patient deteriorated shockingly rapidly and in the space of
36 hours  ended up with oxygen saturations of 56%, we are being
very careful with this guy.
The lack of atmospheric pressure means our blood carries less oxygen -
both dissolved in the blood and attached to the haemogmobin molecules.
At sea level, about 97% of our haemoglobin molecules will pick up a
molecule of oxygen at the lungs and carry it to supply our body?s
cells (it?s what we refer to as oxygen saturation, or sats, measured
by a photospectrometer in a clip that goes on a fingertip). But at
altitude the air is thinner and although O2 is still present in the
same proportion, there is numerically less, and so it is harder for
our blood to get fully saturated. I?ve found that stepping off the
plane from sea level we will typically have sats of 80 to 85 % and so
we all feel rough because of the lack of oxygen. Headaches, poor
sleep and nausea are almost universal and all recover fairly quickly
as we acclimatize and our sats rise. Lots of people, including me,
have cheyne-stokes breathing for a while. That's due to the
physiology of the situation, not imminent departure.
I?ve been told, but I?m not convinced, that 2,3 DPG is the sole
cause for improvement. 2,3 DPG has a shift effect on the dissociation
curve. But as both sats rise, and unloading must improve as symptoms
get better, it seems to me the curve must change it?s shape and spread
out rather than just shift.
But high altitude pulmonary oedema (HAPE) is something else. It?s the
second time I?ve seen it, and it seriously needs to be respected.
Our capilliaries are slightly leaky, we know this, and our bodies have
ways of dealing with the fluid that leaks out and returns it to the
main circulation. Reduce the atmospheric
pressure and it seems the resulting reduction in available oxygen causes
the blood pressure in the lung's circulation to rise. In some people
fluid will leak out and coat the lungs'
surfaces, reducing the movement of oxygen into the blood. This is
HAPE. Patients get severely hypoxic and it can be life threatening.
The treatment is simply to get down to a lower altitude, i.e. a higher
atmospheric pressure. Other things help. Inhaled oxygen from a
cylinder, salbutamol, diamox and nifepidine
all help. If you can't get them down and these measures don't work we
have a pressurised bag we can put them in.
But there?s more to it. Infection generally causes
capilliaries to become more leaky, to let white blood cells out to
fight the invaders; and inevitably therefore anyone with a lung
infection is seriously at risk of HAPE as they are more likely to leak
fluid. But the converse is also true, standing fluid in the lung is an
infection risk and so HAPE can lead to pneumonia. In our first
patient a few weeks ago, pneumonia, mild and not troubling at sea
level led to a life threatening situation within 36 hours at altitude.
We got him down rapidly and he stepped off the plane at sea level
much better. This time, this guy is not so badly affected, and it?s
harder to say which came first; It could have been either.
I do my first ever chest X ray, shown how to do it by the base doctor
Andrea and Antonio the nurse; Compared to a hospital film it?s very
poor quality, the costophrenic angles are cut off, its rotated and
there are scratches all over the film from my terrible development
technique. But it?s enough; there is patchy consolidation in the
left midzone confirming the diagnosis; We take a digital photo of it
so we can alter the contrast and thank goodness we did, I recognize
subtle but unmistakable fattening of the left hilum revealing batwing
pulmonary oedema. I have to admit, I?m quite proud of it.
So on the oxygen, antibiotics, diamox, salbutamol and nifepidine he
goes and by morning all his numbers are going the right way, he has a
better colour, the breath sounds are louder throughout his chest, and
we?re satisfied he?s getting better. It takes 48 hours for
antibiotics to really have an effect and he?s getting better too fast
for that, the HAPE is a good catch we might have empirically treated
but wouldn?t have diagnosed without the chest x-ray.
Great. Now what do we do?
If it?s pneumonia, treating the infection could resolve the HAPE and
he could stay at altitude. If it's HAPE alone, given time and a little oxygen,
and he might acclimatise.  He seems to be stable anyway. Shall we
keep him and see if it works? Absolutely not. Firstly, we?ve got
good weather, a plane nearby and the opportunity. What if we let the
chance slip and then in two days time he deteriorates? There?s no ICU
here, no opportunity for higher level care if he deteriorates.
Patients that even the most remote rural hospital would be happy to
keep and treat pose a serious risk out here. Remember even the
nearest high dependency unit even is ten solid hours of flying away.
So we have an exceptionally low threshold for choosing to transfer
unwell people out. Why risk anything? He can come back and do his
research another time.
And there?s another thing, something that I promise you we do
not allow to alter our care one bit, but is nevertheless on our minds.
He?s using up our supplies. We have a store of antibiotics, oxygen,
and all the other acute treatments a hospital needs, predicted to be
enough for the winter. But so close to the winter, it?s not so easy
to get us up replacements from Australia. If he sits here taking a
week to recover he will seriously eat into our supplies. So down
he?ll go. We didn?t even hesitate over the decision. Handily he?s a
US citizen, and McMurdo base email back saying they want him, without
even a debate.

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1 comment:

  1. I finally managed to find some articles to read on HAPE. It seems that it is associated with high pressure in the blood flow from the heart to the lungs and back to the heart again, rather than directly because of an atmospheric pressure effect. Low oxygenation causes the pressure to rise, and that excessive pressure forces fluid out of the lung's capilliaries. It pools in the spaces where gas transfer should occur and prevents the lungs from working properly