Original ContributionPentane Measurement in Ventilated Infants Using a Commercially Available System
Introduction
The hydrocarbon pentane, formed by free radical mediated lipid peroxidation of w-6 fatty acids such as arachidonic acid, is excreted in breath and has been investigated as a noninvasive marker of lipid peroxidation. In neonates, lipid peroxidation may have a role in the aetiology of chronic lung disease (CLD), retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), and intraventricular haemorrhage (IVH),1, 2and the measurement of pentane concentration in the exhaled breath of ventilated preterm infants may help our understanding of these diseases.
Concerns exist over the accuracy of breath studies measuring pentane because of technical difficulties. Pitfalls cited include contamination with exogenous pentane, coelution of pentane with isoprene,[3]inadequate washout of exogenous pentane from airways and body stores,[4]bacterial sources of pentane,[5]metabolism of pentane by liver enzymes,6, 7intravenous lipid administration,[8]and influence of elevated oxygen concentration.[9]
We aimed to investigate and evaluate our method of breath collection and analysis, addressing these problems where possible and apply it to measure breath pentane in ventilated preterm infants.
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Study Population
The study was carried out on the Regional Neonatal Intensive Care Unit at Liverpool Women's Hospital; ethical approval and parental consent were obtained.
Infants included were preterm (23–33 weeks gestation, birthweight 520–1810 g) ventilated for respiratory distress syndrome (RDS). All measurements apply to infants who had not received Intralipid for at least 48 h prior to sample collection.
Breath Collection and Analysis
Hydrocarbon free air (HCFA) was prepared using an AS80 air purifier (Signal Instruments, UK). A washout
Gas Chromatography
The gas chromatography method was based on that published by Kneepkens et al.,[13]and provided satisfactory results without modification. Under these conditions, isoprene was shown clearly to be separated from pentane and cis-2-pentene in the calibration mixture, with retention times of 14.7 min, 11.0 min, and 13.1 min, respectively (Fig. 1).
Direct injection of the 1 vpm calibration mix produced intra- and interassay coefficients of variation of 3.6% (n = 11) and 1.7% (n = 5), respectively. The
Discussion
One of the major criticisms in the measurement of breath pentane exhalation is that many GC columns have been shown not to separate pentane from isoprene, and that frequently authors have mistakenly identified isoprene as pentane, resulting in grossly overestimated excretion rates for pentane, and implication of a role for lipid peroxidation in situations where it may not be justified.4, 14However, we have found that under the conditions described, we are able to separate pentane not only from
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