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 validatethe V&C device for VD measurement in vitro (lung model) and in vivo(adult rabbits). Methods of measurement of VD using the V&C (automaticcomputation, interactive carbon dioxide-volume plot analysis, Bohrequation) were tested by comparing known added deadspace volumes (VDadd)with calculated VDadd. After producing a change in alveolar (VDalv) andphysiological (VDphys) deadspace by in vivo broncho-alveolar lavage, VDalvand VDphys computed automatically were compared with values calculated bythe Bohr-Enghoff equations. VDadd was slightly underestimated (absoluteerror in mean: automatically - 0.61 ml; interactively -0.55 ml; Bohr -0.54ml). The higher the VDadd, the lower the absolute errors and coefficientsof variation (cv). The highest cv occurred for automatic analysis(approximately 11%) compared with < 6% for interactive analysis or theBohr equation. Average differences between results calculated automaticallyand by the Bohr- Enghoff equation were -0.79 ml for VDalv (95% confidenceinterval -2.02 to 0.44 ml) and -0.23 ml for VDphys (-0.6 to 0.14 ml). Weconclude that the V&C can be used in newborn infants undergoingmechanical ventilation, if changes in VD are < 5 ml, interactiveanalysis or the Bohr equation should be used.