Pressure and flow waveform characteristics of eight high-frequency oscillators

OBJECTIVES: The differences in performance of early generation high-frequency oscillators have been attributed to their distinct pressure and flow waveforms. Recently, five new oscillators have been commercially released. The objective of this study was to characterize the pressure and flow waveforms of eight commercially available oscillators.

DESIGN: In vitro benchtop study.

SETTING: Tertiary pediatric teaching hospital.

INTERVENTIONS: Eight oscillators were evaluated using a test lung; mean airway pressure 10 and 20 cm H₂O; frequencies 5, 10, and 15 Hz; pressure amplitude 30 cm H₂O (or equivalent); compliance 1.0 mL/cm H₂O; and endotracheal tube 3.5 mm. Ventilators tested were Sensormedics 3100A and B (Carefusion), SLE5000 (SLE), Fabian (Acutronic), Leonie+ (Heinen+Löwenstein), Sophie (Stephan), and VN500 and Babylog 8000 (Dräger).

MEASUREMENTS AND MAIN RESULTS: Pressure (airway opening, at oscillator and within the test lung) and airway opening flow waveforms were recorded. Airway opening waveforms were characterized by type (square or sine) and by determining power spectral density analysis. The Sensormedics A and B and the SLE5000 delivered square waves; all other oscillators generated sine waves. Sensormedics, the SLE5000, and the Sophie had a characteristic inspiratory slope (incisura). The pressure waveform within the test lung was a sine wave for all oscillators. Oscillators with square waves or an inspiratory incisura exhibited the highest number of nonfundamental frequency components on power spectral density analysis, suggesting more complex harmonic waveforms with potentially greater transmissive power to the lungs. At frequencies of 5 and 10 Hz, all ventilators, except Babylog 8000, generated airway pressure amplitudes greater than 28.6 cm H₂O and tidal volumes greater than 6 mL at the airway opening.

CONCLUSIONS: Current high-frequency oscillators deliver different waveforms. As these may result in variable clinical performance, operators should be aware that these differences exist.