We currently use our CDU to do this. Once CT normal the patients go there
to wait for 12 hour LP. CSF checked for bilirubin spectrophotometrically.
So far out of about 300-400 we have (I think) had one positive that the
neurosurgeons deided was not likely to be from an SAH. This protocol only
applies to patients without neurology.
I wonder as to the need to do these LPs in this group. The pre-test prob
must be fairly low given they have had their CT within 12hours. Furthermore
no one actually knows the sens /spec of CSF analysis.
One study looking at spectrophotometry of CSF samples taken at spinal
anaesthetic found a 20% positive rate in this group with no suggestion of
SAH (but they were looking at oxyhaemaglobin - which can be formed in vivo)
The biochemists are very keen on this approach however (see recent 'Lesson
of the Week' in BMJ).
Anyway, I'll stop wittering as I can be very boring on this subject (and
indeed many others too..)
Jon Jones
Leeds
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