Humidifcation of base flow gas during adult high-frequency oscillatory ventilation: An experimental study using a lung model

In adult high-frequency oscillatory ventilation (HFOV) with an R100 artificial ventilator, exhaled gas from patient's lung may warm the temperature probe and thereby disturb the humidification of base flow (BF) gas. We measured the humidity of BF gas during HFOV with frequencies of 6, 8 and 10 Hz, maximum stroke volumes (SV) of 285, 205, and 160 ml at the respective frequencies, and, BFs of 20, 30, 401/min using an original lung model. The R100 device was equipped with a heated humidifier, HummaxII, consisting of a porous hollow fiber in circuit. A 50-cm length of circuit was added between temperature probe (located at 50 cm proximal from Y-piece) and the hollow fiber. The lung model was made of a plastic container and a circuit equipped with another Hummax II. The lung model temperature was controlled at 37 C. The Hummax II of the R100 was inactivated in study-1 and was set at 35 C or 37 C in study-2. The humidity was measured at the distal end of the added circuit in study-1 and at the proximal end in study-2. In study-1, humidity was detected at 6Hz (SV 285ml) and BF 201/min, indicating the direct reach of the exhaled gas from the lung model to the temperature probe. In study-2 the absolute humidity of the BF gas decreased by increasing SV and by increasing BF and it was low with setting of 35 C. In this study setting, increasing the SV induced significant reduction of humidification of the BF gas during HFOV with R100.