Reliable tidal volume estimates at the airway opening with an infant monitor during high-frequency oscillatory ventilation

Objective., To assess the suitability of a hot-wire anemometer infant monit oring system (Florian, Acutronic Medical Systems AG, Hirzel, Switzerland) f or 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 dis tress. Intervention., The lung model was ventilated with a Sensor-Medics 3100A ven tilator. V-T was recorded from the monitor display (VT-disp) and compared w ith the gold standard (VT-adlab) which was calculated using the adiabatic g as 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%), an d F-IO2 (0.21-1.0) was used. Accuracy was determined by using modified Blan d-Altman plots (95% limits of agreement). An exponential decrease in V-T wa s 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 in creasing pressure amplitude and -0.2 mL (limits of agreement, -0.3 to -0.1) with increasing inspiratory time. Humidity and heating did not affect erro r, 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 pr ovides reliable measurements of V-T at the airway opening during high-frequ ency oscillatory ventilation when employed at frequencies of 8-13 Hz. The b edside application could improve monitoring of patients receiving high-freq uency oscillatory ventilation, favor a better understanding of the physiolo gic consequences of different high-frequency oscillatory ventilation strate gies, and therefore optimize treatment.