Comparing Fowler and Cotes dead space methods during single breath gas transfer.

<bold>Background:</bold> Anatomical dead space can be calculated using different methods. Cotes method estimates dead space utilising bodyweight (2.2 ml x kg). The Fowler technique measures dead space utilising the tracer gas washout curve. <bold>Aims:</bold> To assess the impact of different dead space methods on lung gas transfer measurements. <bold>Methods:</bold> Lung gas transfer was measured via the single breath method and rapidly responding gas analyser. Retrospective data analysis using the two dead space methods and discard and sample volumes of 900 ml and 600ml respectively were used. Gas transfer parameters and dead space values between methods were compared statistically using paired t-tests or Wilcoxon rank sum tests. Z-score classifications were also compared between methods. <bold>Results:</bold> Results are presented in table 1 comparing methods. TLCO and VA values were significantly different between methods. Several patients changed z-score severity class depending on method used. Anatomical dead space was significantly higher using the Fowler method compared with Cotes (p<0.001). <bold>Conclusion:</bold> Calculation of TLCO using Cotes and Fowler methods with set discard and sample volume resulted in different classifications of abnormality for several patients. Anatomical dead space was significantly greater using the Fowler method. Future studies should also explore the impact of automatic discard volume determination setting when using different dead space methods. <fig><object-id>erj;64/suppl_68/PA2328/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>