A 68-year-old, 5-foot, 10-inch male patient with acute-on-chronic respiratory failure due to COPD has been placed on NIV with these settings: IPAP = 8 cm H2O, EPAP = 4 cm H2O, FIO2 = 0.28

The patient's measured exhaled volume is 350 mL with a spontaneous respiratory rate of 24 breaths/min. The resulting arterial blood gas values are: pH = 7.27, PaCO2 = 77 mm Hg, PaO2 = 64 mm Hg, SaO2 = 88%, HCO3? = 36 mEq/L. What action should the respiratory therapist take at this time?
a. Increase the FIO2 to 0.4.
b. Increase the EPAP to 6 cm H2O.
c. Increase the IPAP to 12 cm H2O.
d. Decrease the EPAP to 2 cm H2O.

ANS: C
This patient has an acute-on-chronic respiratory acidosis that has not been corrected by the NIV at the current settings. The resulting VT is 4.7 mL/kg, which is not enough to reduce the PaCO2 to an acceptable DIF for this patient (the pH should be about 7.37). Titrating the IPAP DIF to maintain an exhaled VT of 5-7 mL/kg can be accomplished by increasing the IPAP.