Changes in TcPCO 2 regarding pulmonary mechanics due to pneumotachometer dead space in ventilated newborns

The aim of this study was to analyze the effect of added dead space on PaCO2 after application of a pneumotachometer during the measurement of pulmonary mechanics. The study was based on 24 observations of TcPCO2 changes during the measurement of pulmonary function in 9 newborns subjected to mechanical ventilation. All newborns remained stable during the 23 minutes of the test. The introduction of a low dead space pneumotachometer (1.7 mL) for 10 minutes led to an increase in TcPCO2 of 5.40 +/- 2.66 mm Hg, from 39.76 +/- 8.69 to 45.17 +/- 9.22. Pulmonary mechanics indexes that correlated with the percentage of CO2 increase were peak inspiratory flow and expiratory time/time constant. When the pneumotachometer was removed, TcPCO2 fell but remained 0.99 +/- 2.13 mm Hg above basal TcPCO2. Final TcPCO2 tended to relate negatively with the minute volume. We conclude that this transient increase in PaCO2 should be born in mind in neonates with a high basal level and can be prevented by maintaining a long expiratory time and a high minute volume.