Modification of the open circuit N2 washout technique for measurement of functional residual capacity in premature infants
✍ Scribed by Roland Hentschel; Andreas Suska; Andreas Volbracht; Thomas Brune; Gerhard Jorch
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 157 KB
- Volume
- 23
- Category
- Article
- ISSN
- 8755-6863
No coin nor oath required. For personal study only.
✦ Synopsis
We compared the standard nitrogen (N 2 ) washout technique for measuring functional residual capacity (FRC) with a modified technique that uses a helium/oxygen mixture (heliox) at different ratios instead of pure oxygen. The tests were made with a standard lung function system equipped with an ultraviolet (UV) analyzer for measurement of N 2 concentrations in the expired gas. We examined models of ''spontaneous breathing'' and ''mechanical ventilation,'' each with volumes of FRC in the range of a premature and a newborn lung (20-80 ml), using both techniques at different baseline inspired oxygen concentrations (FiO 2 ). Correlations between known and measured volumes were high and identical for the two techniques (r = 0.996), and the mean error was not significantly different from zero (P = 0.111). Measurements of FRC in 6 infants gave a correlation coefficient of r = 0.989 between the two techniques; reproducibility, as measured by the coefficient of variation, was high, showing no significant differences between both techniques (P = 0.792). However, values of individual infants were different (P = 0.011), and the slope of the regression line relating measurements by the 2 techniques was 1.04, with an intercept on the y-axis at 1.46. We conclude that FRC can be measured with the modified N 2 washout technique, using heliox as a washout gas. Volumes can be measured with high precision and reproducibility, even in premature infants with low lung volumes and/or high baseline FiO 2 . A correction factor may be necessary to equate FRC measurements made by oxygen-N 2 vs. heliox-N 2 washouts. Hyperoxemia and hypoxemia can be avoided by admixing different flows of oxygen to a standard heliox mixture.