Map of life expectancy at birth from Global Education Project.

Tuesday, September 19, 2006

Now they tell me . . .

I happened to be reading the British Medical Journal yesterday and I came across the information -- apparently sufficiently unfamiliar to your average physician that it required a major warning article with a lot of very basic background in one of the world's foremost generalist medical journals -- that sodium phosphate can be very dangerous for some patients. (Y Mun Woo, Susan Crail, Graham Curry, Colin C Geddes. A life threatening complication after ingestion of sodium phosphate bowel preparation. BMJ 2006;333:589-590) Not for me, as it turns out -- the major risk is to people with malfunctioning kidneys -- but they never actually asked me about my kidneys before they sent me the instructions to drink the industrial waste.

It turns out that ingesting sodium phosphate causes a transient spike in phosphate in the blood, and probably more important, a drop in calcium concentration. People with kidney failure can't excrete the phosphate and as a result can't get their serum calcium back up. Very bad news, because serum calcium is an essential electrolyte and without it the nervous system doesn't function right and the heart doesn't beat right. These authors say that mortality after ingesting sodium phosphate among people with damaged kidneys may be 33%. But the low calcium (hypocalcaemia) may also be dangerous for people with heart disease, liver disease, and known electrolyte imbalances, and people who are just plain old and frail. That would seem to include a fair proportion of people who get colonoscopies.

They go on to state that "Evidence shows that many endoscopists may not be aware of groups of patients who are at high risk and their potential for complications after ingestion of sodium phosphate."

So, what are we to make of this? Many endoscopy providers, as a default, tell all their patients to prepare using sodium phosphate. It definitely works,* and it's cheap. But there are also several alternatives which are safer for some patients. This is an obvious example of a practice which needs to be embedded in systems to prevent recommending it to people for whom it is not appropriate.

If I did have kidney failure, or heart disease, or for some other reason should not have ingested sodium phosphate, whose fault would it be if I were injured or killed? The triage nurse who called me ahead of time and didn't find out about my counterindications? The doctor who performed the procedure? Whoever developed the protocols used in the clinic? And maybe the protocols are stronger, but they just weren't followed -- but then whose fault is that? Who should my survivors have sued? Would they have won?

As I mentioned a couple of days ago, doctors are thinking hard about these sorts of questions, as are people like me who are not real doctors (I'm a doctor of philosophy). I'll try to review some of the common thinking shortly.

*For those of you who are fans of Dr. Science, the way it works is pretty simple -- it has extremely high osmolarity, so it just sucks water out of your body and into your colon. Whooosh, you're a human fountain. No fun, but mighty impressive.

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