Abstract
Measurement of FRC in distressed neonates on continuous positive airway pressure (CPAP) with endotracheal (ET) tubes presents special problems. Since neonatal ET tubes are uncuffed they permit leakage of gas around the tube during respiration and, therefore, introduce errors in FRC determination. The present study evaluates a new 60 second closed circuit helium (He) dilution technique for determination of FRC independent of small gas leaks. 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 cylinder, a strip chart readout, and solenoid valve. CPAP or ventilator pressure can be applied during testing. Fifty in vitro measurements of FRC ranging from 5-50 cc in both leak and non-leak models were accurate to 7.2 and 5.2% respectively. Seventy-two FRC measurements were performed on 15 neonates (700-4400 g) on CPAP with ET tubes. Leak rates wera significantly higher (P<.001) on 3 cm H2o CPAP compared to 0 cm H2O CPAP resulting in a mean (±SEM) total helium loss in 60 seconds of 16.2 (± 1.1)% and 9.1 (± 0.5)% respectively. The mean measured FRC was 53.5 ml at 3 cm H2O CPAP and 46.3 at 0 cm H2O CPAP. If leak calculations were not considered the error in FRC could have been as high as 76.7 and 42.7%. This method permits accurate calculation of FRC in neonates on CPAP with ET tubes.
Article PDF
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Fox, W., Schwartz, J., Shaffer, T. et al. A NEW APPROACH FOR MEASURING FUNCTIONAL RESIDUAL CAPACITY (FRC) IN THE INTUBATED INFANT. Pediatr Res 11, 570 (1977). https://doi.org/10.1203/00006450-197704000-01201
Issue Date:
DOI: https://doi.org/10.1203/00006450-197704000-01201