Measurement of carbon dioxide production in very low birth weight babies
C C Kingdona, F Mitchellb, O A F Bodamerc, A F Williamsa
a Department of Child
Health, St George's Hospital Medical School, Cranmer Terrace, London
SW17 0RE, UK, b Department of Medical Physics, St George's
Healthcare NHS Trust, Blackshaw Road, London SW17 0QT, UK, c Department of Molecular and
Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
Correspondence to: Dr Kingdon, Neonatal Unit, St Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK email: markeane{at}aol.com
Accepted 4 February 2000
BACKGROUND
CO2
production is most commonly measured by using indirect calorimetry to
quantify elimination of CO2 in breath
(VCO2). An alternative is to measure the rate
at which CO2 appears in the body pool
(RaCO2) by infusing a 13C labelled
bicarbonate tracer. VCO2 and
RaCO2 generally differ but are related by
c, a factor that adjusts for the incomplete recovery of infused tracer in the breath. The literature relating to
human studies cites a wide range of values for
c but the only neonatal study to determine
c empirically estimated a mean value of
0.77.
AIMTo estimate
fractional recovery rate, c, in very low
birthweight babies, and assess the feasibility of using the isotopic technique to measure CO2 production during mechanical ventilation.
METHODEleven
spontaneously breathing, continuously fed, very low birthweight infants
(median birth weight 1060 g, median gestational age 29 weeks) were studied.
RESULTSMean (SD)
VCO2 was 9.0 (2.0) ml/min (standard temperature
and pressure dry, STPD) and mean (SD) RaCO2 was
9.6 (2.1) ml/min (STPD). The mean (SD) value of
c was estimated as 0.95 (0.13). The 95%
confidence intervals of the mean were 0.87-1.03.
CONCLUSIONSThe
results emphasise the importance of measuring
c for a given study population rather than
assuming a value based on adult studies. The close approximation of
RaCO2 and VCO2 in this
group of babies implies that the labelled bicarbonate infusion
technique could be used to measure simply CO2 production
during mechanical ventilation.
Keywords: carbon dioxide; carbon isotopes; calorimetry; very low birthweight babies
© 2000 by Archives of Disease in Childhood
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