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[Percentile curves of functional residual capacity of newborn infants].

BACKGROUND
Helium dilution or nitrogen washout techniques are commonly used to measure the functional residual capacity (FRC) in newborn babies. For both techniques equipment is available. Its clinical application, however, was difficult since there were no FRC reference ranges for the different weight groups of newborn infants; reference studies are very time consuming and cause several technical and ethical problems.


METHODS
Statistical methods were used to evaluate several results from the literature and to exclude significantly differing data of some authors. Measured values of FRC were related to body weight, and the percentiles of FRC/kg were estimated by the smoothed cumulative distribution function of the pooled data.


RESULTS
No significant differences were found between the results of helium dilution and nitrogen washout techniques. The distribution of 178 results showed a significant skewedness (x5% = 18.3 ml/kg; x50% = 27.5 ml/kg x95% = 42.8 ml/kg), which could also be seen in the percentile curves calculated approximately, assuming a linear development of functional residual capacity with body weight.


CONCLUSION
Percentile curves describe best the development and interindividual variability of FRC in newborn babies as our evaluation could show. We conclude that the nonparametric estimation of percentiles is more adequate for the description than the use of simple regression models.