In vitro and in vivo assessment of the Ventrak 1550/Capnogard 1265 for single breath carbon dioxide analysis in neonates.

The Ventrak 1550/Capnogard 1265 (V&C) enables deadspace (VD) measurements to be made in neonates. The aim of our studies was to validate the V&C device for VD measurement in vitro (lung model) and in vivo (adult rabbits). Methods of measurement of VD using the V&C (automatic computation, interactive carbon dioxide-volume plot analysis, Bohr equation) were tested by comparing known added deadspace volumes (VDadd) with calculated VDadd. After producing a change in alveolar (VDalv) and physiological (VDphys) deadspace by in vivo broncho-alveolar lavage, VDalv and VDphys computed automatically were compared with values calculated by the Bohr-Enghoff equations. VDadd was slightly underestimated (absolute error in mean: automatically -0.61 ml; interactively -0.55 ml; Bohr -0.54 ml). The higher the VDadd, the lower the absolute errors and coefficients of variation (cv). The highest cv occurred for automatic analysis (approximately 11%) compared with < 6% for interactive analysis or the Bohr equation. Average differences between results calculated automatically and by the Bohr-Enghoff equation were -0.79 ml for VDalv (95% confidence interval -2.02 to 0.44 ml) and -0.23 ml for VDphys (-0.6 to 0.14 ml). We conclude that the V&C can be used in newborn infants undergoing mechanical ventilation, if changes in VD are < 5 ml, interactive analysis or the Bohr equation should be used.