Gas Mixing Efficiency in Preterm Infants: Which Multibreath Nitrogen Washout Index is Best? 1740

Aims: We have recently shown that moment ratios (MR) and lung clearence index (LCI) of multibreath nitrogen washouts (MBNW) are sensitive indicators of gas mixing inefficiency in infants with mild chronic lung disease (CLD). The aim of the present study was to improve the calculation of MR and compare the improved index with the original and with other measures of gas mixing efficiency based on MBNW in preterm infants.

Subjects: We used records of MBNW from 15 healthy preterm infants and 15 CLD infants, studied at 35 weeks of postconceptional age. The identical records have been used previously for calculation of LCI and MR with classical methods (Ped.Research, in press).

Methods: MBNW was performed using a by-pass flow system. All infants were breathing spontaneously and the washout was accomplished by 100% oxygen. In order to compensate for approximations made when continuous data are substituted for by discrete ones in classical methods for calculating MR, we used the average of normalized end expiratory nitrogen concentration of adjacent breaths, and the same for dilution numbers, for the calculations.

The so refined MR were compared with our published data, calculated by classical methods, and with other indices which were assessed simultaneously by computerized methods: pulmonary clearance delay (Fowler), exponential fitting index (Merthen), nitrogen clearence and effective breath fraction(Sjöqvist). Calculations were based on two washouts per subject.

Results: Inter- and intrasubject variation was lowest with the modified MR but highest with the methods based on exponential fitting.

Conclusion: MR, calculated with the refined method, is the index to be preferred for assessing gas mixing efficiency with MBNW in preterm infants.

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(Spon by: Petter Karlberg)

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Shao, H., Sandberg, K. & Hjalmarson, O. Gas Mixing Efficiency in Preterm Infants: Which Multibreath Nitrogen Washout Index is Best? 1740. Pediatr Res 43, 297 (1998).

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