Effects of endotracheal tube leaks on functional residual capacity determination in intubated neonates.

The present study evaluates a new closed circuit helium (He) dilution technique for determination of endotracheal (ET) tube leakage and functional residual capacity (FRC) in neonates with ET tubes. By analytically relating the fall in He concentration due to mixing with that due to leakage, it is possible to predict the final equilibration concentration of He and, therefore, correct for ET tube leaks. The system (120 ml) contains an air pump, He meter, breathing bag in cyclinder, a strip chart readout, and solenoid valve. Continuous positive airway pressure (CPAP) or ventilator pressure can be applied during testing. FRC measurements were performed on 13 neonates (799--4500 g) on CPAP with ET tubes. Leak rates were significantly higher (P less than 0.001) on 3 cm H2O CPAP compared to O cm H2O CPAP. The mean measured FRC was 53.5 ml at 3 cm H2O and 46.3 ml at 0 cm H2O CPAP. If gas leakage had not been considered in FRC calculations, the error in FRC could have been as high as 39% at 3 cm H2O CPAP and 18% at 0 cm H2O CPAP.