Dear colleagues
Some nursing colleagues who I have been working with on
improving our EBP skills came up with the following EBP question.
In patients who are being fed by NG tube how good is pH testing at
determining whether the tube is in the Stomach or in the lungs ?
Practice at the hospital where they work is currently that the
position of all tubes when inserted is checked by a pH test and
also by X-Ray before feeding is commenced. They came up with
the following observations about this:
1) It seems strange to bother with the ph test if you are going to
x-ray the patient anyway.
2) Patients often pull on the tubes or the tubes get pulled and
therefore moved and often nurses just push the tube back and do a
ph test only.
3) If everytime patients pull on tube need to get it re x-rayed this
will results in patients having a lot of x-rays, and will be quite
expensive
4) Doing a only a pH test on insertion if sensitive enough would
reduce patient exposure to radiation and save a considerable
amount of resources
My recommendation to them (I hope its the correct one ) was that
they should treat this as a diagnostic test question. The evidence
they would need to find would therefore be a study whereby a group
of patients with ng tubes had the position checked by ph testing
(by your average nurse in real clinical setting (usually visual reading
of test reagent stick)) and by the gold standard (x-ray) and then
the sensivity and specificity, Pos predictive value etc. etc. for ph
testing could be established
They have been searching for this kind of study and no luck yet
(have found a lot of work by Norma Metheny and Colleagues from
St louis University which we are ploughing through but does not
seem to answer this particular question )
q.1 if anybody else knows of any other evidence sources for this
would be grateful to hear about them
reading so far has thrown up lots of questions about the various
methods of ph testing. Currently in this hospital they are using
litmus paper - Some of the evidence we have found on this
suggests that litmus paper is not good at discriminating between
gastric fluid and lung fluid because it can change colour for both
because of ph level at which it is sensitive (sorry can't remember
what this is at the moment) But evidence is not that good quality
q2. Anybody know of any other evidence on this
I have technical question about such a study. The risk of the tube
being in the lungs undetected appears to be quite small (4/605 in
one study). It would also be unethical if not impossible in practice
do a study where tubes were deliberately put into the lung as well
as put into the stomach.
q3. If in a study all the tests were on ph testing where all the tubes
were in the stomach would this answer our question - if not what
else could researchers do?
The risk of the tube being in the lungs undetected appears to be
quite small, However in the literature it seems to be regarded as
absolutely imperative that this is established before the feeding
started due to what are described as the grave consequences of
starting feeding with the tube incorrectly positioned.
q4. Does this mean that only a test which is 100% sensitive (or
whatever current gold standard level is - presumably x-ray is very
near this) is acceptable ?
That will give you something to chew during the festive season.
Look forward to hearing your replies which I will summarize for list.
seasons greetings
mark
***PLEASE NOTE ARCHWAY PHONE NUMBER CHANGED AGAIN*****
Mark Newman
Senior Lecturer:
School of Health, Biological & Environmental Sciences (HeBES)
Middlesex University &
Barnet & Chase Farm Hospitals NHS Trust
Furnival Building, Archway Campus
Highgate Hill
London N19 3UA
Tel: 0181 362 5000 (ex2281) or 0181 366 6600 ex 5775
Fax: 0181 362 6299
E-Mail: [log in to unmask]
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