Evaluation of performance of two high-frequency oscillatory ventilators using a model lung with a position sensor

High-frequency oscillatory ventilation (HFOV) is thought to protect the lungs of acute respiratory distress syndrome (ARDS) patients. The performance and mechanical characteristics of high-frequency oscillatory ventilators, especially with regard to delivering appropriate tidal volume (V(T)) to compromised lungs, might affect the outcome of patients. We evaluated the performance of two such ventilators using a model lung with a position sensor.

We tested the Metran R100 and SensorMedics 3100B. V(T) was measured using the model lung with the compliance set at 20 or 50 ml/cmH₂O and the resistance at 0 or 20 cmH₂O/l/s. Oscillator frequency was set at 5, 7, and 9 Hz, and amplitude was set at 25%, 50%, 75%, and 100% (100% being maximum amplitude available at each setting configuration).

At each model lung setting, R100 delivered greater V(T) at 5 Hz. V(T) differences between the ventilators decreased as frequency increased and were negligible at 9 Hz. At each model lung setting and frequency, as amplitude increased from 25% to 100%, V(T) increased proportionally more with R100. With an I:E ratio of 1:1, 3100B delivered greater V(T) than with 1:2.

Because it is able to deliver comparably greater V(T), R100 may be a better choice for HFOV in critical ARDS patients. Better proportionality may be a result of more effective amplitude titration for adjusting PaCO₂ during oscillation.