CHANGES IN TCPCO2 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 TcPC O2 changes during the measurement of pulmonary function in 9 newborns subjected to mechanical ventilation. All newborns remained stable duri ng the 23 minutes of the test. The introduction of a low dead space pn eumotachometer (1.7 mt) 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 corre lated with the percentage of CO2 increas e were peak inspiratory flow and expiratory time/time constant. When t he pneumotachometer was removed, TcPCO2 fell but remained 0.99 +/- 2.1 3 mm Hg above basal TcPCO2. Final TcPCO2 tended to relate negatively w ith the minute volume. We conclude that this transient increase in PaC O2 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 v olume.