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diagnostics

LP post-seizure – do white cells indicate infection?

5 Jun, 11 | by Bob Phillips

Obviously, I’m excluding the rather large proportion of my workload where the presence of white cells in the CSF indicate metastatic disease … but in normal children, if you did an LP on a child after a seizure and got a total white cell count of 19, would you be treating for meningitis?

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Do neonates produce CO2?

4 May, 11 | by Bob Phillips

Well, I know that they do to some extent, but do they do it enough to make those expensive little burp-detector kits turn yellow when you intubate correctly? They do in grown ups, and in proper children with big breaths, but what about teeny tiny children?

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What’s a normal CSF opening pressure?

19 Apr, 11 | by Ian Wacogne

Bob has kindly let one or two of us into his Archimedes blog to write about some of the papers we’ve consider for Picket in E&P

This letter in the NEJM (Avery RA, Shah SS, Licht DJ, et al. Reference range for cerebrospinal fluid opening pressure in children. N Engl J Med 2010;363:891-3.) gives us, potentially, a new set of reference ranges for CSF opening pressures in children and young people.  It’s got a bottom line as follows:

a post-hoc analysis of opening pressure percentiles was calculated for the 52 subjects who received minimal or no sedation and were not classified as obese, resulted in a 90th percentile of 25 cm of water

There are a number of things which are of note.

  1. Sedation does not seem to alter the CSF opening pressure.  This is at odds with what we’ve been led to believe previously.
  2. If the 90th centile is 25 cm of water, that’s a pretty big cut off for diagnosing and then treating raised intracranial pressure.  Are the authors seriously suggesting that 10% of all children have raised intracranial pressure?
  3. In their larger population, which includes sedated and obese children the 90th centile is at 28 cm water.  That’s a pretty high pressure, in the context of what I’ve previously understood.
  4. Their way of determining obesity is very strange indeed.  They seem to have taken an adult approach, with the assumption that a certain value of BMI indicates obesity.  However, we know that BMI normal range changes with age, and that in order to compare children over time and between ages, you need to look at BMI SDS – ie a mathematical representation of the centile for the age.
  5. BMI was only available on 131 of the 197 patients.
  6. The other bit they don’t give enough data on – even in the appendix – is the actual discharge diagnosis.  These are a series of diagnostic LPs, and they’ve done their best to exclude what would be reasonably expected to alter intracranial pressure – or specifically raise it.  However, the range discharge diagnoses is quite broad, from “headache” to “undiagnosed white matter disease”.

So, I think this is a flawed paper, and as such it doesn’t reach the threshold of quality we’d apply to Picket it.  However, it does give us some interesting information and food for thought.  Does it change my practice?  I suspect I might be a bit more permissive about slightly raised opening pressures.  In those children with “barn door” raised pressure, this will still be straightforward, but it doesn’t help me in treating children with some symptoms, but with an opening CSF pressure of, say, 27 cm water.  What would I do if I saw this tomorrow?  Probably an n=1 trial of therapy, and see what happened…

Diagnostic tests: as easy as I, II, III

21 Sep, 10 | by Bob Phillips

Diagnostic testing keeps coming back to bite Archi, and that’s not just because of a probability-based failure about a small relative and a missed diagnosis of congenital heart disease. No, the problem with diagnostic tests and their use and abuse remains difficult because the methods of research, the quality of research and the consequence of bad research aren’t generally as high-profile as therapeutic failures. Perhaps we could help with a bit of this by adopting a similar approach to evaluating diagnostic tests as we do new drugs: go for phase I, II and III studies.

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Natural frequencies “keeping it real”

8 Sep, 10 | by Bob Phillips

So, on hearing Matthew Thompson open up a mini-session with natural frequencies my mind turned to the healing power of crystals, and I become acutely concerned that the open-minds approach of the Teaching EBM Conference had gone too far.

But this was quashed quickly by his description: more…

Squiggly lines and tea leaves

13 Jun, 10 | by Bob Phillips

My grannie-in-law knew a lady who would look at your tea leaves and tell you the future (younger readers – see here – tea is not always bagged & tagged).

I had a similar experience with a neonatologist who would look at the seismograph attached to a babies head and declare the child needed more (or less) phenobarbitone.  Exactly how the dose alterations were related to who’d just knocked the incubator, and what they did for the babe, I have yet to understand. But there is a London doctor who is reviewing just how much those ‘cerebral function monitors’ really do tell clever tiny baby docs anything at all. more…

Q: Echogenic bowels and new babies

31 Jan, 10 | by Bob Phillips

Bias plotIt was a vogue around the start of regular antenatal ultrasound scanning to note everything, associate wildly and some up with ‘antenatal markers of disease’, as I recollect. Some of these things turned out to be quite useful (nose bones, for instance, or their absence) and others still confuse me … like the ‘echogenic focus of bowel’ more…

Q: Parental presence and lumbar punctures

4 Apr, 09 | by Bob Phillips

Scar from LPDoes having the a worried mum or fretful dad in the room with you make a lumbar puncture less likely to succeed? It’s an interesting question, and one that has been posed following an evening on call in Yorkshire. What’s the opinions of folk out there – and any evidence that you can quote to substantiate them?

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Why (wo)men always think they are right.

2 Apr, 09 | by Bob Phillips

Life on MarsHave you ever been involved with a debate with a partner or colleague, travelling from one place to another, and when the course they took has got you to the destination safely, they turn to you and say “So, [add endearment here], you see my way was right.”? If you have, I doubt that you took the opportunity to explain that they may be suffering from a methodological reasoning problem, of which the conterfactual argument and the possibility of differential verification bias may be important to consider. more…

Making science of art

22 Oct, 08 | by Bob Phillips

Timourous Beasties Wellcome WindowIn the window of the Wellcome Collection in London artists work to interpret and explain science: it’s an impressive experience to the irregular visitor. When faced with the presenting problems of a child & family, we are faced with trying to do the reverse. We have the sometimes inaccurate recollections of history, the variable responses of clinical examination and our own bias-riddled minds to bash, through the ‘art of diagnosis’ into a suitable explanation for the predicament and onwards into a management strategy. Can this really be evidence based?

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