Repetition and the basics – #meded


Category : Medical Rants

Discussing a new patient recently, two important teaching points crystallized once again.  The patient was relatively young without any past medical problems.  He had dyspnea, first on exertion, and then at rest.  On exam he was tachypneic with crackles, wheezes and rales throughout his lungs.  After receiving nasal oxygen he “looked comfortable”.

His electrolyte panel:

135 90 8 103
4.8 30 0.6

So I asked why his bicarbonate was 30.

A fairly long discussion ensued.  The major point of the discussion was that an elevated bicarbonate here might be a danger sign.  I believed (as did a critical care attending in the audience) that this suggested hypoventilation.  The learners did not consider hypoventilation because the patient was tachypneic.

As Dr. Orhan Muren (one of my educator heroes taught me), pCO2 is a pure measure of ventilation.  Some tachypneic patients are actually hypoventilating, while some patients with “normal respirations” are actually hypoventilating.

The elevated bicarbonate made us worry about compensation for a respiratory acidosis – a danger sign in respiratory failure (unless the patient has chronic hypoventilation).

These learners had been taught this concept in the past, but they did not recall it in context.  This is a basic concept.

As medical educators we must reinforce and repeat basic medical concepts.  No matter how brilliantly we teach them, if the learners do not absorb the knowledge we have failed.  Our job is to repeat until the knowledge is virtually intuitive.

Teach the basics.


Comments (6)

Ventilation is a combination of respiratory rate and tidal volume. A tachypneic patient may indeed have an elevated CO2 if his or her tidal volume is low.

In fact in many conditions, patients pant- breathe rapidly but shallowly- you see this in marathon runners and in animals. They do this not because it is the most effective form of ventilation- it is not. But it is the most effective form of conserving oxygen in stressful situations. Normally breathing does not account for much of your total O2 consumption. in stressful situations it might. The minimal rise in Co2 that may occur is of no consequence because it will not impair arterial oxygenation.

In this patient a HCO3 of 30 might be a CO2 elevation or it may be a metabolic alkalosis. given the acute history and no known chronic illness I would still put my money on metabolic alkalosis- but the only way to tell is to do an ABG.

One of the questions you should be discussing with the residents is – at what level of HCO3 abnormality would you draw an ABG on initial evaluation. My general rule is 17 or less and 32 or more. Unless there is some clinical suspicion (and occasionally I would not draw on say in a CRF patient with a HCO3 of 15, where the cause is generally clear). So I don’t know if I would have gotten one here at 30 unless there was something else to look at – history of sleep apnea, obesity, suggestion of airway problem, chronic lung problem. At 32 always. At 30 I don’t know.
did you?

I was visiting a different hospital. The patient had an initial pulse oximetry of 90%. They had ordered an ABG – but it had not been done (I know, back in the day we would have done it ourselves). I could find no explanation for a metabolic alkalosis, therefore I wanted to see an ABG because I was worried the patient was “tiring out”.

Not your fault, I know- but this is why we aren’t going to get anywhere teaching them.
A patient who “looks comfortable” doesn’t sound like they are tiring out, and altho a rising CO2 would indeed be an ominous sign, I wouldn’t look for it so much in a venous HCO3, which is harder to interpret as a single value. But that’s besides the point – and that’s what your point is.
If they don’t get the ABG in a timely fashion to check whether the patient is tiring out, whatever happens with the patient, they will not learn much, in some cases not even enough to know what they are not learning.
I guess my point here is that in this case if tiring out is indeed an issue, an ABG is an acute test. so not only did they not learn what an increasing HCO3 might mean (if it is indeed increasing, we don’t know with one value) they didn’t know that it has to be evaluated right away.
So what exactly are they learning about acute physiology evaluation and who’s teaching them?

Lessons were learned during the discussion of why they should have gotten an ABG. The emergency department did not order it.

The ABG would have been very helpful.

When the patient came in he apparently did not look comfortable at all – was better with nasal oxygen.

“The emergency department did not order it.”
Shouldn’t those guys operate under the same rules? Shouldn’t they learn the same things?

Another problem with this, Dr. C., is that we don’t learn any more about the case, the clinical presentation and the ABG correlation either. And there is so much there. The ABG is such a valuable test in these situations.

It is likely that 30 years ago residents would have done the same thing – but the whole point is it is 30 years later and they are still doing the same thing – and if anything their expectations of learning from it haven’t changed (or perhaps are even lower).

Sorry for the rant (it is after all med rants) but this is too frustrating.

Your comments are “spot on”. Thanks for caring enough to leave the comment. Everyone should read and absorb it.

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