Recurrent vomiting and lethargy in an infant—just another viral illness?
BMJ 2010; 341 doi: https://doi.org/10.1136/bmj.c1037 (Published 04 August 2010) Cite this as: BMJ 2010;341:c1037
All rapid responses
We don't know much about hyperammonaemia, but the blood gas results
quoted in Cheung's case report seem improbable (1). The patient is either
in an hyperbaric chamber or breathing supplementary oxygen rather than
room air as stated in the text.
It is impossible to have an arterial partial pressure of oxygen which
is higher than that of the inspired air. The alveolar gas equation,
assuming a respiratory quotient of 1 for simplicity, gives an alveolar
partial pressure of 17.4 kPa if the patient is breathing room air at
normal atmospheric pressure.
(1) BMJ 2010;340:c2189
Competing interests:
None declared
Competing interests: No competing interests
Cheung and colleagues note that symptoms in this case study began
when the patient was aged a month. A good question to ask would have been
'was this baby breastfed at all? Either before or after the start of
symptoms?'
We get information on weaning, so diet is clearly thought relevant to
the picture of recurrent vomiting and failure to grow normally.
Breastfeeding was dubbed the 'invisible feeding method' in a rapid
response to a '10 minute consultation'(1) published last year in the BMJ
where questions on a hypothetical infant who was continually 'bringing
back feeds' did not allow for the possibility the baby might be breastfed.
In the current (actual) case study, it seems that whether this infant
was/is breastfed is to remain invisible too!
(1) BMJ 2010;340:c2189
Competing interests:
None declared
Competing interests: No competing interests
Response to comments
We are grateful for the responses to our case report. We would like
to provide clarification on the issues raised in those responses and
apologise for those important omissions.
We acknowledge that the feeding method of our patient, breastfed or
otherwise, should have been explicit and was relevant when considering the
differential diagnoses at presentation. This infant was solely bottle-fed
till weaning.
We agree with Clark and Jefferson on the improbable blood gas results
on air with a partial pressure of oxygen at 22.191 kPa. We can confirm
that our patient was indeed nursed in room air. We interpret such an
erroneously high result as being due to an air bubble trapped in the
sample tube. It still remains that the low partial pressure of carbon
dioxide and alkalotic pH are entirely consistent with the metabolic
picture we have described in the case report.
Competing interests:
None declared
Competing interests: No competing interests