Obligatory blog post about pain scores

PTR

So if you had to give your pain a score between 1 and 10, where 10 is the worst pain you've ever had, what would you pain score be right now?

Mrs Lumbago

10

PTR

So this is the worst pain you've ever felt?

Mrs Lumbago

No, it was worse this morning.

PTR

Ok, so if it was 10 out of 10 this morning, what score would you give it now?

Mrs Lumbago

10

PTR

So it's just as bad now as it was this morning?

Mrs Lumbago

No, this morning it was much worse.

PTR

Right. So the pain was at its worst this morning, 10 out of 10.  If 10 is the worst, what's it like now that it's a bit better?

Mrs Lumbago

10

PTR

Excellent. Excellent.

Just give three

Nurse

You've charted 450 mg of clindamycin for this patient.

PTR

Yes.

Nurse

Well we only have 150 mg tablets.  How are we supposed to do that?

PTR

...

Not really

Checkout Person
That'll be $87.76

Smaller Half
The register only says $28.76

Checkout Person
Oh, you know what I mean.

LD50

In my experience, when you poison someone you usually intend for them to die.  If you would rather that person did not die, it would make sense for you to not administer the poison in the first place.  This is why the concept of LD50 - the dose of a poison at which half the subjects will cark it - makes no sense to me.  If I'm going to go to the trouble of trying to bump someone off I don't want there to be any doubt about the outcome.  Fifty percent odds are unacceptable.  A measure such as LD99 would be more useful.

The reason I bring this up is because in anaesthetics there is a commonly used measure of anaesthetic potency called MAC.  It is defined similarly to LD50.  At the MAC dosage, half of all subjects won't leap off the operating table when you cut them open.  What a stupid measure.  I would prefer that none of my patients leap off the table.  Yet all the monitors and equipment and doctors and research papers talk about MAC.  ( I won't even get into how outraged I was when I found out that MAC stands for "minimum alveolar concentration" even though it's actually a median value.  The War On Innumeracy is long since lost on this front.)

I went looking for information about what the inter-person variability is for MAC.  In other words, how much anaesthetic would you have to give to ensure that everyone went under? It turns out that this information is surprisingly hard to track down.  Eventually I found a paper giving the 95% bands for MAC for one specific anaesthetic gas (desflurane) when used on - wait for it - llamas and alpacas.  Great.

Well it turns out that this paper is more useful than I thought because MAC is pretty much the same for all mammals.  For all animals, actually, just in case your pet starfish needs a hysterectomy some time soon.  Which makes me wonder why somebody bothered to do the experiments on llamas in the first place, noisy stinking beasts that they are.  Why not just assume that MAC in llamas is the same as in every single other species ever examined?

I suppose the researchers were hoping that somehow llamas and alpacas would end up being radically different from every other living being on earth and that this, combined with their intimate knowledge of llamoid physiology would enable them to deduce how the heck it is that anaesthetics actually work. Which would be nice because nobody really knows yet.

Think about that.  Nobody knows how anaesthetics really work.  For all we know they may work by destroying you and replacing you with a sinister mind-clone.  Controlled by sunflowers.

Good guessing

Hopefully the upcoming MCQ exam will have a lot of questions like this one I saw today:
Here is a medical investigation finding.  Which of the following statements is true?
A.  This can be found in normal people.
B.  This can be found in X syndrome.
C. None of the above.
D. All of the above.

Logically, the answer can't be D, since then the answer would be (A,B, and neither A nor B).  So my odds just improved from 1 in 4 to 1 in 3.  Sweet as bro!

Battle lines

Cry havoc and let slip the tubas of war!

It's been a long time since I reported from the front line in the War On Innumeracy.  But last Friday we had a marathon 7 hours straight of respiratory medicine from a Distinguished Physician, so of course after the first 3 hours my brain filled up and went to the happy place where all it does is trawl through my life looking for bloggable material. 

I was snapped back to reality when the Distinguished Physician said, "The terrible thing about asbestos and smoking in terms of your lung cancer risk is that they amplify each others' effects, making them synergistic.  For example, if asbestos made your risk ten times higher and smoking made your risk six times higher, then smoking and asbestos together make your risk sixty times higher."

Well, sorry to break it to you Dr Smart-Guy, but what you just described would mean that smoking and asbestos are independent risks rather than synergistic ones.  Did I stand up and blaze away at him with the Holy Machine-Gun Of Mathematics?  No, I kept my mouth shut, for two reasons:

1. In the War On Innumeracy I'm deep undercover.  So deep that sometimes I'm unsure if I'm fighting for the right side any more.
2. He's probably going to be marking us in the OSCE at the end of the year and the last thing I need is for him to write me off as that smart-arsed bastard who corrected his arithmetic the moment I walk through the door.

Still, I expect more of you, Gentle Reader.  If someone abuses mathematical jargon in your presence today, let them have it with both metaphorical barrels!

Transcendental numbers and you

Thanks to all 13 of you who completed my online personality quiz, a.k.a. the poll, "What's your favourite transcendental number?"  Here I present some feedback, based on the answer you chose:

e. You are a middle-aged, middle-class, moderately intelligent nobody, probably working in the finance department of a middle-size corporation.  You vaguely remember something about e from your commerce degree in the 80's, or was it high school mathematics?  Regardless, you knew it was smarter to choose this than pi, but didn't want to choose something too outlandish in case you got caught faking it and ended up being thrown out of the liberal party.

pi. You have a vivid memory of grade 6, mainly because you're still in it.  Wow!  A number that's so long you can't ever write it down!  You're unsure why 22/7 is so much more complex than 23/7, but maybe you'll find out in grade 7.

ln(2). You are a geek.  You always think in powers of two because you spend your life talking to computers, so ln(2) appealed to you because that's how you know how many megabytes you need for your Java blog mainframe uplink.

Chaitin's constant. You are a try-hard.  You went to look this up on wikipedia and what you read was baffling but you thought it would impress other people because it sounded so complicated.  Think again.

4. You are a moron.  You had to look up transcendental numbers on wikipedia, and you accidentally went to the page on transcendental meditation.  That didn't seem to have anything to do with numbers so you just chose 4 because you know it's a number and the other ones are letters or words.

Information underload

This is the bit where I complain (again) about being lucky enough to study medicine.

We had a lecture today which purported to be about the menstrual cycle. It was incomprehensible. Now, I appreciate that it's a complex topic, so it's unlikely that I was going to come out of that lecture unscathed. But the guy who presented it to us did us no favours either.

He may well know his stuff back to front and inside out, but I seriously think I could have given a better lecture than him with just five minutes preparation. He didn't ever seem to summarize or recap or explain or do any of those good pedagogical things.

It got even worse when someone asked him a question and it sounded like he was making up the answer. It went like this:

Q: Could you explain again how luteinizing hormone causes the follicle to release the ovum?

A: "Well it's simple, the way that, the thing is that, LH stimulates FSH, until it's high, and by high what I mean is that it's not dropping so fast as it was before, estrogen doesn't, I mean, how long have you got? I could give you a 200 page book on this stuff."

Not very convincing. He wouldn't last 2 minutes in my old PBL group. We could bullshit for 3 hours much more fluently than that.

Then later on today there was an outrage perpetrated by a different lecturer. In the course of trying to explain how to use trigonometry to find the distance from the beach in Chennai to the cricket stadium (the guy was ambitiously trying to distract us from the fact that his lecture was Content Free (tm) by weaving a line through Auckland, Mount Everest, surveying, Chennai, and antenatal oxygen tension, not necessarily in that order), he claimed that if you know the length of one side of a triangle and one of the angles that you can calculate the length of another side. Oh, sorry, I meant to end that sentence like this: "... another side!!!" I can tell you're shocked.

I shouted out to him that he needed to know two angles (yes, another side will also do, but that's not how you do geological surveying) but he chose to ignore me, clearly recognizing that I spoke with the Voice Of Authority and was not to be trifled with.

The War On Innumeracy rages on.

Get it right!

Here's another shot in the War On Innumeracy. I was reading an otherwise respectable textbook called Genetics At A Glance by Dorian J. Pritchard and Bruce R. Korf when I came across this doltish statement on page 27:

"Reassortment of paternal and maternal alleles within chromosomes creates an infinite potential for genetic variation between gametes."

This is just hogwash. The potential variation is not even close to being infinite - whatever that might mean...

I sat down with my pen and paper and made some basic simplifying assumptions such as there are about 30,000 genes in the human genome, and that the average gamete (ie: sperm or egg) has about 40 paternal/maternal crossovers, and concluded that the average person could conceivably (ho ho - pun intended) produce about 10 to the power of 160 different gametes. You should have seen how excited my tute group was when I told them!

Is that number really really large? Yes.

Is it infinite? No.

Shame shame shame.

Big Pedant

Oh, and one more thing. Today a lecturer told us that patients with kidney stones are "invariably" men. And then he told us that a quarter of them are women.

Obviously he was using the word "invariably" in some kind of specialized medical way to mean "variably". Right?

I'm changing the world!

Despite the morose tone of my previous post (two posts in one evening? I'm clearly putting off my Learning Issues!) I am feeling quite chirpy. Why? Because I'm Making A Difference.

You may remember that I was previously outraged at my lecturers mis-use of mathemathical terminology. Well, the message is getting through to them! Today in class the Learned Professor was describing the effect of smoking and asbestos together when considering their carcinogenic effect. And how did he characterize it? He said it was "multiplicative".

Please, please - no more applause. I did it for the children.

Crimes against nerdity

I just can't take it any more! The time has come for me to take a stand, to right a wrong, to speak out where there has been silence. Criminals are a cowardly and superstitious lot. In brightest day, in blackest night etc etc. I can no longer stand by while my lecturers describe curves as "exponential" when they merely have a positive second derivative. I know you're with me on this one.

Today it happened again. That makes twice this semester, and at least twice last semester. Today's curve described the ventilation/perfusion ratio of the lung. We were shown a graph of ventilation (litres per minute) versus distance from the base of the lung. The graph was a linear one, so y1 = ax+b. On the same graph was shown perfusion, again of the form y2 = cx+d. The ventilation/perfusion ratio was then shown and was described as being exponentially increasing. But if you let x = (z-d)/c, it's easy to see that (ax+b)/(cx+d) = a/c + (b - ad/c)/z, which is clearly a hyperbola! Outrageous!

If you think it's unimportant, consider the difference in the two cases as the size of your lungs approaches infinity!

Similarly, we were previously shown another example which was two linear curves multiplied together. Thus, it was simply a polynomial rather than exponential! How would you feel if you were a patient lying in hospital struggling for breath and you heard one of your treating physicians so egregiously confuse his high-school mathematics?

Every time it happens I feel like sticking my hand up and correcting them but part of my brain (I'm guessing the right hemisphere) tells me to be quiet. It is innate knowledge amongst medical students that any consultant that is corrected by a student would tear that student limb from stinking limb and I have no desire to be dismembered just yet. Nevertheless, ignorance breeds where wise men say nothing. If you are reading this I place upon you a most solemn duty. The next time a lecturer describes a curve as "exponential", you must raise your hand and enquire whether the gradient of the curve is proportional to its height or if it merely curves upward. And don't tell them I sent you.