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

Objective: 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).
Methods: 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.
Results: 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.
Conclusion: The technique of bedside RHe may be used for measuring FRC with excellent accuracy, precision and repeatability.