[Monitoring of functional residual capacity by bedside real-time concentration via helium dilution technique]

To explore the accuracy, precision and repeatability of bedside real-time concentration monitoring via helium dilution (RHe) in ventilated dogs with and without acute respiratory distress syndrome (ARDS).

Functional residual capacity (FRC) measurements were performed with computer tomography (FRCCT) and RHe (FRCRHe) in 18 adult male beagle dogs. Blood gas analysis was conducted for baseline, post-lung injury and end-of-experiment. Vital signs were monitored continuously. And the differences were compared between two techniques and repeated FRCRHes.

For healthy lungs, FRCCT and FRCRHe were linearly correlated (R² = 0.89, P < 0.0001). Bias between FRCRHe and FRCCT was 6.3 ± 27.6 ml (1.5% ± 7.1%) with 95% confidence interval limits of -47.7 and 60.3 ml respectively. For ARDS lung, FRCRHe = 0.693 × FRCCT + 66.4 (R² = 0.507, P < 0.00 1). Bias between FRCRHe and FRCCT was 7.9 ± 271 ml (4.5% ± 13.6%) with 95% confidence interval limits of -45.3 and 61.1 ml respectively. And the differences of repeated FRCRHes were -0.1% ± 5.8% and 0.2% ± 9% in normal and ARDS lungs respectively.

The technique of bedside RHe may be used for measuring FRC with excellent accuracy, precision and repeatability.