An adult patient with ARDS is being ventilated with VC-CMV. The settings are: f = 14 breaths/min; VT = 375 mL; PEEP = 16 cm H2O; and FIO2 = 0.8

The patient's ABG values are: pH = 7.40; PaCO2 = 56 mm Hg; PaO2 = 48 mm Hg; and SaO2 = 83%; the mean airway pressure is 18 cm H2O. The patient's physician decides on a trial of HFOV. What initial ventilator settings should be used?
a. Bias flow = 30 L/min; mPaw = 23 cm H2O; set power to obtain ?P = 76 cm H2O; f = 6 Hz; TI = 33%; FIO2 = 1.0
b. Bias flow = 35 L/min; mPaw = 76 cm H2O; set power to obtain ?P = 33 cm H2O; f = 10 Hz; TI = 50%; FIO2 = 1.0
c. Bias flow = 20 L/min; mPaw = 18 cm H2O; set power to obtain ?P = 76 cm H2O; f = 8 Hz; TI = 33%; FIO2 = 1.0
d. Bias flow = 30 L/min; mPaw = 30 cm H2O; set power to obtain ?P = 56 cm H2O; f = 6 Hz; TI = 50%; FIO2 = 1.0

ANS: A
The initial settings should be as follows: (1) the initial bias flow for an adult is 25-40 L/min; (2) the mPaw is set at 3-5 cm H2O above the observed during conventional ventilation (typically starting between 25 and 30 cm H2O); (3) the power is set to result in an amplitude 20 greater than the PaCO2 before HFOV; (4) the initial frequency for an adult is 5-6 Hz; (5) the initial inspiratory time percent is 33% or 50% to improve CO2 removal.