Objective., To assess the suitability of a hot-wire anemometer infant monitoring system (Florian, Acutronic Medical Systems AG, Hirzel, Switzerland) for measuring flow and tidal volume (V-T) proximal to the endotracheal tube during high-frequency oscillatory ventilation.Design. In vitro model study.Setting. Respiratory research laboratory.Subject., In vitro lung model simulating moderate to severe respiratory distress.Intervention., The lung model was ventilated with a Sensor-Medics 3100A ventilator. V-T was recorded from the monitor display (VT-disp) and compared with the gold standard (VT-adlab) which was calculated using the adiabatic gas equation from pressure changes inside the model.Measurements and Main Results. A range of V-T (1-10 mL), frequencies (5-15 Hz), pressure amplitudes (1104A cm H2O), inspiratory times (30% to 50%), and F-IO2 (0.21-1.0) was used. Accuracy was determined by using modified Bland-Altman plots (95% limits of agreement). An exponential decrease in V-T was observed with increasing oscillatory frequency. Mean DeltaV(T-disp) was 0.6 mL (limits of agreement -1.0 to 2.1) with a linear frequency dependence. Mean DeltaV(T-disp) was -0.2 mL (limits of agreement, -0.5 to 0.1) with increasing pressure amplitude and -0.2 mL (limits of agreement, -0.3 to -0.1) with increasing inspiratory time. Humidity and heating did not affect error, whereas increasing F-IO2 from 0.21 to 1.0 increased mean error by 6.3% (+/-2.5%).Conclusions. The Florian infant hot-wire flowmeter and monitoring system provides reliable measurements of V-T at the airway opening during high-frequency oscillatory ventilation when employed at frequencies of 8-13 Hz. The bedside application could improve monitoring of patients receiving high-frequency oscillatory ventilation, favor a better understanding of the physiologic consequences of different high-frequency oscillatory ventilation strategies, and therefore optimize treatment.