TIL in Medical School - Doctors have myths too.

post by ancientcampus · 2013-01-18T14:59:23.620Z · score: 2 (19 votes) · LW · GW · Legacy · 31 comments

Today I Learned in Medical School:

Doctors have medical myths too! According to my prof, many doctors believe that aspiration (having stuff go down into the lungs) causes anaerobic pneumonia, but that is rarely the case. He says that myth is often taught resident-to-student, but it isn’t actually backed up by any research, and isn’t true. The kicker - if the doctor would stop to think about it, it should jump out as unintuitive – it would take some serious changes inside the *lung* to make an *anaerobic* infection – an infection of bacteria that thrive in areas with no oxygen. In reality it takes frequent aspirations over a long period of time to block off an area of the lungs.

I think the moral of this story (though this just may be preaching to the choir here at LW) – all people, be they doctors or kindergarteners, don’t usually check facts they’re taught, especially when being taught by an authoritative teacher. Unless they’re lead to discover/derive a fact themselves, they usually assimilate it into their network of beliefs as a brute fact – “carbon has four valence electrons,” “don’t end a sentence with a preposition,” “in 1492 Columbus discovered America.”

Now, you frequently don’t have enough time to “learn it the hard way” or derive an answer yourself. If I had to read every single research publication that populated the facts in my textbooks, I might not ever graduate. However, it is important to remember that you’ve taken shortcuts for most of your education (and religion/lack thereof, and life in general) – and if some fact ever later strikes you as being odd, look into it. Otherwise, we’re just playing the telephone game.

31 comments

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comment by Scott Alexander (Yvain) · 2013-01-19T17:17:25.469Z · score: 31 (31 votes) · LW(p) · GW(p)

He says that myth is often taught resident-to-student, but it isn’t actually backed up by any research.

Lorber B, Swenson RM. Bacteriology of aspiration pneumonia. A prospective study of community- and hospital-acquired cases Ann Intern Med. 1974 Sep;81(3):329-31.

Brook I, Finegold SM. Bacteriology of Aspiration Pneumonia In Children, Pediatrics. 1980 Jun;65(6):1115-20.

Finegold SM. Aspiration Pneumonia Rev Infect Dis. 1991 Jul-Aug;13 Suppl 9:S737-42.

Bartlett JG. Anaerobic bacterial infections of the lung and pleural space Clin Infect Dis. 1993;16 Suppl 4:S248.

Yamashita Y et al. Anaerobic respiratory infection--evaluation of methods of obtaining specimens. Kansenshogaku Zasshi. 1994;68(5):631.

El-Solh AA et al. Microbiology of severe aspiration pneumonia in institutionalized elderly. Am J Respir Crit Care Med. 2003 Jun 15;167(12):1650-4. Epub 2003 Apr 10.

The kicker - if the doctor would stop to think about it, it should jump out as unintuitive – it would take some serious changes inside the lung to make an anaerobic infection – an infection of bacteria that thrive in areas with no oxygen. In reality it takes frequent aspirations over a long period of time to block off an area of the lungs.

The normal flora of the skin, mouth, and upper respiratory tract contains anaerobic bacteria; this alone should be sufficient to disprove overly simplistic "But there's oxygen, you can't have anaerobic bacteria there!" theories. Anaerobes are actually more common than aerobes in the mucus membranes of the mouth and URT and in fact outnumber aerobes in saliva about 10:1. According to The Anaerobic Microflora of the Human Body:

It is not surprising that anaerobes are present in large numbers in the flora of the intestinal and geintourinary tracts because oxygen concentrations are low in these regions. However, it appears unusual that they are also prominent members of the flora of the skin, mouth, nose, and throat - regions that are continuously exposed to air. The presence of anaerobes in these areas is explained first by the activity of the aerobic and facultatively anaerobic components of the flora that reside in association with the anaerobes and consume oxygen in their metabolism and second, by the colonization of anaerobes of microhabitats protected from air.

I think the moral of this story all people, be they doctors or kindergarteners, don’t usually check facts they’re taught, especially when being taught by an authoritative teacher.

Okay, here's what actually happened. In the 1970s and 1980s, a lot of people worked really hard studying the microbiology of aspiration pneumonia and all of them found lots of anaerobes. In the late 1990s, some other people, especially a guy named Paul Marik, tried the same thing using more modern techniques and found very few anaerobes. They concluded that the old studies had been wrong.

Some other people objected that anaerobes are really hard to detect and that maybe Marik and his supporters had just screwed up and not been able to find them even though they were there. This seems to be the view of Rene et al, who claimed to have repeated Marik's experiments using better technique and found lots of anaerobes just like the old theories would have predicted. It was then counterclaimed that Marik's experiment had been unusually rigorous and well-conducted, plus it was also easy to screw up the other way - that sometimes samples might have been contaminated by anaerobes in the upper respiratory tract that weren't responsible for the pneumonia at all. Everyone had a nice big fight about it which as far as I know still has not been fully resolved. UpToDate, which I tend to trust on this sort of thing, pushes the pro-anaerobe line, but emedicine, which is also pretty good, pushes the anti-anaerobe line. I do get the feeling the anti-anaerobe people now have the upper hand.

The rationalist thing to do would be to let the microbiologists fight it out among themselves and just study which antibiotics are most effective against aspiration pneumonia. The answer to that is very complicated, but the oversimplified answer as given by UpToDate is clindamycin, an antibiotic known for its efficacy against anaerobes, which seems to maybe suggest there was some kind of anaerobic component after all - but I am reading between the lines here on a subject I'm not really qualified to read-between-lines on and am probably completely wrong about this.

I agree that many doctors don't know anything about this (I hadn't heard of it until you brought it up and I checked the literature). The average doctor just checks every so often to see what antibiotic is recommended for aspiration pneumonia and then prescribes that one. As far as I know the antibiotic recommendations are still correct. This seems like a pretty efficient system, given how many things doctors have to know.

Anyway, as far as I can tell the real moral of this story is that medicine is really really hard and complicated and, like all science, often changes as technology improves and better experiments become possible. This is a less fun narrative than "Doctors are incredibly stupid and just by knowing about this one study I can totally outdo all of them" (YES, EVERYONE ON LESS WRONG, I AM TALKING ABOUT YOU) but fun narratives are wrong suspiciously often and this one is no exception.

comment by ancientcampus · 2013-01-19T22:49:26.759Z · score: 8 (8 votes) · LW(p) · GW(p)

Woah, nice, thanks for all that research! Yeah, it looks pretty much just how you described it. So, my statement, "no research backs it up" was wrong - there was research in the 70s and 80s that DID indicate it, so there WAS evidence. Thus, this is a case of "Old ideas in the process of getting overturned... maybe" and not "people doing it without science backing it up".

I don't have access to UpToDate here (because they recently skyrocketed their prices so my school is switching), so I only read emedicine.

EDIT: I can only read the abstracts, and nothing from the 70s article, so this input is limited. That said, the 80s article seemed to look at all aspiration pneumonias (most of which was are caused by chronic aspiration), while my professor's point was specifically about one-time aspiration (i.e. aspirating vomit). I did not make that distinction clear in my OP. So, you're right, though I wanted to defend my professor, because I think his point might still stand, though my post did not present the full story. I'd look more into the research, but I probably won't find the time. Yvain's a real trooper for wading through all those articles.

comment by Kawoomba · 2013-01-21T15:48:51.799Z · score: 0 (0 votes) · LW(p) · GW(p)

"But there's oxygen, you can't have anaerobic bacteria there!"

Also an easy mistake to make when not differentiating between facultative anaerobes and obligate anaerobes.

comment by MugaSofer · 2013-01-21T15:19:18.188Z · score: 0 (2 votes) · LW(p) · GW(p)

"Doctors are incredibly stupid and just by knowing about this one study I can totally outdo all of them"

That is a common attitude here, but I don't see how this post reflects it. Rather, the author fell prey to same thing they were highlighting, more or less.

comment by ancientcampus · 2013-01-21T23:27:36.990Z · score: 0 (0 votes) · LW(p) · GW(p)

The irony of that fact certainly wasn't lost on me. :) I though about checking up on the prof, but like I said, if I did that every time I'd never graduate.

But yes, thanks for saying that. I'm not often one to doctor-bash; my hubris often comes from being a "Future Doctor" rather "being a Rationalist."

comment by Wakarimahen · 2013-01-20T04:55:38.451Z · score: 0 (2 votes) · LW(p) · GW(p)

I've read a decent number of your posts, and it seems a bit out of character for you to generalize so heavily, and use all caps to describe everyone on LW as having a sentiment similar to, "Doctors are incredibly stupid and just by knowing about this one study I can totally outdo all of them."

I know you don't really mean it literally, but it may be worth pointing out that that sort of thing is just another one of those epistemically hazardous and unhygienic habits that should be done away with.

comment by shminux · 2013-01-20T06:06:22.830Z · score: 4 (4 votes) · LW(p) · GW(p)

it seems a bit out of character for you to generalize so heavily

Seems to me that Yvain is slightly fed up with those on the site who display the LW superiority attitude (I also complain about it on occasion, and so do others). The generalization and all caps probably indicate a certain amount of bitter sarcasm.

comment by Wakarimahen · 2013-01-20T06:20:23.592Z · score: -1 (5 votes) · LW(p) · GW(p)

Yeah. Slightly fed up is too fed up. It's never useful to be fed up, as far as I've ever seen. I've read a decent number of Yvain's posts, and he's always come off as rather immune to getting 'fed up' or 'annoyed' or anything, so I thought it was sort of out of character, and not in a good way.

comment by RomeoStevens · 2013-01-18T22:29:51.013Z · score: 4 (8 votes) · LW(p) · GW(p)

Doctors have epistemic hygiene just as terrible as the general populace. People sometimes point out that they have incentives such as legal liability to follow AMA/FDA best practices even when there is evidence that this is wrong. That's true, but many many doctors believe in AMA/FDA best practices.

comment by buybuydandavis · 2013-01-18T23:42:50.448Z · score: 0 (4 votes) · LW(p) · GW(p)

In general, I'd say worse.

It's not that doctors are ignorant; it's that they know so much that isn't so.

comment by ancientcampus · 2013-01-19T00:01:27.384Z · score: 3 (3 votes) · LW(p) · GW(p)

How so? I'd like to avoid such a fate if possible. (I will agree that, as a constantly changing field, many things doctors learn is later disproven. ACE inhibitors use to be contraindicated in congestive heart failure, but now they're first line. That's not so much irrationality, though, but a lack of data.)

comment by buybuydandavis · 2013-01-19T04:25:45.220Z · score: 3 (3 votes) · LW(p) · GW(p)

I was referring to mistakes in epistemic and decision theory.

Lack of a FDA supervised double blinded placebo controlled study evaluating a treatment does not mean "there is no evidence" the treatment works.

Failure to reject the null hypothesis for a statistic of a particular positive outcome measure over a particular set of patients for a particular treatment for a particular treatment regime does not imply that "the treatment does not work" or that "the treatment should not be tried". Besides the multitude of ways this fails predictively for a particular case, it completely ignores cost and risk of both sides of treatment/no treatment, and so is crap as decision theory.

To briefly summarize, most doctors replace what could be an exercise in decision theory, including causal inference, process modeling, and decision theory tailored to the information relevant for a patient with an officially blessed lookup tables based on general population statistics.

I would probably feel better if doctors admitted this wasn't a proper way to heal patients, but just the most convenientl way for doctors, the health care industry, and their government regulators, to dole out treatments to patients while protecting their income and control of patients. But I think they earnestly believe in this wholly suboptimal for the patient paradigm.

comment by ancientcampus · 2013-01-21T23:56:03.135Z · score: 0 (0 votes) · LW(p) · GW(p)

I'm sure many doctors do as you describe, but in my experience, most specialists physicians don't fall into that trap. They will prescribe "un-proven" and un-approved treatments if they think the risk-benefit relationship is favorable. However, it takes significantly more knowledge about the disease, your specific patient, and all the latest research to make a decision like that. Furthermore, if you're wrong, it's your hide on the line. If your family doctor knows all that, then they're a specialist.

The cost of treatment/no treatment: I'm going to disagree with you strongly there. That's drilled into our head every day in school. The cost to the patient, the cost to society, the side-effects the patient experiences, the risk of serious adverse reactions, the risk of going without treatment, the chance that the treatment doesn't even work at all (in the case of the unproven treatments)... we talk about this almost every day.

So, agreed: "Not proven beyond a wide margin of error" is not the same as "no evidence", however I don't think many doctors believe that. That is, it's not a flaw of rationality - it is either a convenience thing, a lawsuit thing, or most often limits to the doctor's knowledge.

comment by buybuydandavis · 2013-01-22T05:41:23.118Z · score: 0 (0 votes) · LW(p) · GW(p)

I'm sure many doctors do as you describe, but in my experience, most specialists physicians don't fall into that trap.

Specialists are a mixed bag. Some will think. Others will have their hammer, and every problem will be a nail on a conveyor belt. So some may be more adventurous, but I haven't met any who seemed to have a decent grasp of statistics or decision theory.

Furthermore, if you're wrong, it's your hide on the line.

Yes. Everyone involved, from payers to regulators to manufacturers to care institutions to care providers to patients protect their own interests first. The problem for the patient is that his power is only negative - not seeking treatment or refusing treatment. All other entities can and do legally limit his options based on their interests.

If your family doctor knows all that, then they're a specialist.

Or, maybe an old fashioned doctor in private practice who has some respect for the limits of his profession's knowledge and some respect for the autonomy of a patient. As one doctor expressed it to me, "Generally we don't know if a treatment is going to work. We try it and see." I've found that they seem much more open to more speculative treatments than institutional care facilities, as one would expect.

The cost of treatment/no treatment: I'm going to disagree with you strongly there.

Yes, people do a lot of talking. But the rubber meets the road in what people do, not in their talky talk. When the cost accrues to the patient alone, that cost is at best a secondary consideration to all other actors who have the power to limit the patient's options.

But I'd like to hear what's the approved theoretical procedure. A patient comes in reporting a chronic problem. He has tried all the "standard options". He is proposing an experimental treatment for it involving an off label use of a widely prescribed medication that is generally well tolerated but with potential side effects. He is basing this on anecdotal reports at web sites, pubmed articles, and wikipedia. In theory, what's the approved method for evaluating this request by a patient? How are the potential risks and rewards tallied up to make a decision?

You disagree with me strongly here. I'd like to hear the generally approved decisions theory applied to this case.

"Not proven beyond a wide margin of error" is not the same as "no evidence", however I don't think many doctors believe that.

Doctors, regulators, and some people who think they're being scientific will routinely say "there is no evidence for X" when there is plenty of evidence for X. When pressed on the matter by putting evidence in front of them they will disparage the evidence instead of admitting that they were making a false case that there was no evidence.

I have no doubt if they were strapped down in a chair, and had a gun held to their heads to find evidence, they could quickly come up with some evidence for X. When talking to other doctors, maybe they do say that the evidence is "not proven beyond a wide margin of error" instead of saying that there is "no evidence"". But it's so much more convenient to "shade" the truth when talking to patients since they know what's better for them anyway. That it simplifies their problem, evades effort on their part, hides their ignorance, and paints them as an all knowing authority is purely coincidental.

So with a gun to their heads, it's "the evidence isn't as convincing as I'd like". But in their practice, in life? "There is no evidence", and that's the belief that determines their actions. Which one do they really believe; the one they may never say, or the one they say a hundred times every day?

As you say, what's done is what's convenient. Convenience for doctors comes from simplified diagnoses and treatments, following his institution's procedures and guidelines, avoiding legal liability, and avoiding hassles with insurance companies, regulators, and patients. Much more convenient to everyone but the patient to turn the job of healing a patient into a job of following rules, procedures, and guidelines. Naturally, it's then convenient to convince the patient that all these rules, procedures, and guidelines are really the best way to heal him. They are not.

What is true is what is convenient to those in positions of power, and that extends to statistical, diagnostic, and treatment methods.

comment by ChristianKl · 2013-01-18T20:03:26.783Z · score: 2 (2 votes) · LW(p) · GW(p)

Even if you discover or derive the fact yourself you can still get it wrong. Truely knowing stuff is hard.

comment by Wakarimahen · 2013-01-20T04:51:10.873Z · score: 0 (2 votes) · LW(p) · GW(p)

What, you didn't think doctors had medical myths too? Although Yvain seems to have voided your particular example, it should be pointed out that there are a ridiculous number of doctors in any first-world country, and based on what we know about the sanity waterline it seems absurd to assume anything other than, "Most of them are probably rather irrational."

comment by MugaSofer · 2013-01-21T15:08:23.314Z · score: -2 (2 votes) · LW(p) · GW(p)

Irrational in general, sure. But people are generally at least somewhat more rational regarding subjects they are a domain expert in, correlated with the level of expertise.

That said, there's no level where you never make mistakes, so ...

comment by MixedNuts · 2013-01-18T16:55:52.078Z · score: 0 (2 votes) · LW(p) · GW(p)

What does actually happen to people who get food or water in their lungs, then get very sick or die, and are diagnosed with aspiration pneumonia?

comment by aelephant · 2013-01-18T23:40:35.971Z · score: 1 (3 votes) · LW(p) · GW(p)

I think his point was that they didn't just get food or water in their lungs once, but frequently over a long period of time, which caused damage & made an area of the lungs into a suitable environment for anaerobic bacteria to live.

comment by ancientcampus · 2013-01-19T00:33:36.788Z · score: 2 (4 votes) · LW(p) · GW(p)

Yep! Specifically, in a patient who is constantly aspirating food (say, someone who's throat muscles are messed up), sometimes remodeling occurs that blocks off a section of the lung, making an air-free area.

The problem is, if someone, say, has a seizure and inhales their own vomit (one time), some doctors might give antibiotics that specifically target anaerobes (as they were trained to), but they really shouldn't, and there isn't even any research saying that they should.

comment by Decius · 2013-01-19T03:57:53.180Z · score: 1 (1 votes) · LW(p) · GW(p)

Is there a difference between aspiration pneumonia and anerobic pneumonia?

comment by ancientcampus · 2013-01-19T14:28:47.470Z · score: 3 (3 votes) · LW(p) · GW(p)

Yes. Aspiration pneumonia is any pneumonia caused by aspirating fluids or solids. Anaerobic pneumonia is pneumonia caused by an infection of anaerobic bacteria.

I do not know of any anaerobic pneumonia that is not brought on by aspirating something, but there definitely are aspiration pneumonias that aren't anaerobic pneumonias, such as the vomit example I gave in my above comment.

comment by DanArmak · 2013-01-18T16:40:54.959Z · score: 0 (4 votes) · LW(p) · GW(p)

Now, you frequently don’t have enough time to “learn it the hard way” or derive an answer yourself. If I had to read every single research publication that populated the facts in my textbooks, I might not ever graduate.

Reading publications is the easy part. To really increase your degree of belief, you would have to repeat all the crucial experiments yourself. Including the experiments validating the instruments you use.

comment by ancientcampus · 2013-01-19T01:03:09.536Z · score: -1 (3 votes) · LW(p) · GW(p)

Shhh. My school administration might hear you!

comment by shminux · 2013-01-18T16:54:49.313Z · score: -2 (4 votes) · LW(p) · GW(p)

many doctors believe that aspiration (having stuff go down into the lungs) causes anaerobic pneumonia

The NIH seems to believe that, too:

Aspiration pneumonia is inflammation of the lungs and airways to the lungs (bronchial tubes) from breathing in foreign material.

comment by tgb · 2013-01-18T17:07:00.678Z · score: 2 (2 votes) · LW(p) · GW(p)

Does the NIH claim that aspiration causes anaerobic pneumonia? It's listed as a subtitle, but not in the content.

comment by shminux · 2013-01-18T17:16:19.198Z · score: -3 (3 votes) · LW(p) · GW(p)

It's the same thing.

comment by ancientcampus · 2013-01-19T00:51:49.671Z · score: 4 (4 votes) · LW(p) · GW(p)

No offense, but they're not. The NIH article lists various types of aspiration pneumonia. To quote directly from my textbook, "Robbins Basic Pathology":

"Although it is commonly assumed that anaerobic bacteria predominate, recent studies implicate aerobes more commonly than anaerobes".

(Reliability of the source: "Robbins Patholgy" is like the Grey's Anatomy of pathology. Robbins Basic Pathology is the mildly abridged version.)

(According to my professor, this was just assumed, but there weren't any studies supporting that assumption.)

comment by Decius · 2013-01-19T04:01:32.576Z · score: 1 (1 votes) · LW(p) · GW(p)

I'm not a doctor, but I would think that aspiration pneumonia would be from inhaling a foreign body, and anaerobic pneumonia would occur in the absence of oxygen.

comment by Kawoomba · 2013-01-18T18:30:15.495Z · score: -1 (1 votes) · LW(p) · GW(p)

Twist: the myth was the professor believing that to be a myth!

Also, it is indeed possible for contaminants to create a lung abscess with anaerobic conditions within. No idea regarding the frequency of such.

Lastly, not all of the alveolar tree is ventilated at all times, there are non-ventilated parts that do not even get perfusion (Euler-Liljestrand mechanism). Those could also provide a breeding ground for anaerobes.

comment by ancientcampus · 2013-01-19T00:56:27.732Z · score: 1 (1 votes) · LW(p) · GW(p)

You're right about the abscesses, hence my statement, "In reality it takes frequent aspirations over a long period of time to block off an area of the lungs." However, one aspiration usually won't cause such a scenario.