Objective: To assess the efficacy and reliability of neonatal high-frequency ventilators.
Design: Bench evaluation of neonatal high-frequency ventilators.
Setting: Physiology department and university hospital neonatal intensive care unit.
Interventions: HFV-Babylog 8000 (Dräger Medical), OHF 1 (Dufour), and SensorMedics 3100A (Sensor-Medics) ventilators were connected to a neonatal test-lung. Tidal volume, peak-to-peak pressure amplitude, and mean airway pressure were measured for several ventilator settings, endotracheal tube sizes, and lung compliances.
Measurements and results: Increasing peak-to-peak pressure resulted in a linear increase in tidal volume delivery in the 0-30% range of maximum amplitude. No significant increase in tidal volume was observed with the HFV-Babylog 8000 when pressure amplitude was above 50%. The maximum tidal volume delivered was substantially smaller with the HFV-Babylog 8000 than with the OHF 1 or SensorMedics 3100A. Tidal volume increased with endotracheal tube size with all three ventilators. Increasing test-lung compliance resulted in lower tidal volumes only with OHF 1. Decreasing mean airway pressure was responsible for a decrease in tidal volume delivery with HFV-Baby-log 8000.
Conclusion: We found that under our test conditions two of the three ventilators delivered adequate tidal volumes at the usual frequency of 15 Hz, regardless of the size of the endotracheal tube and of the mechanical properties of the respiratory system. When lung compliance increased or mean airway pressure decreased, both of which are common events during the recovery phase of hyaline membrane disease, we found that the intrinsic properties of two of the ventilators tested were responsible for a decrease in tidal volume. This decrease may account for some cases of heretofore unexplained hypercapnia.