A patient is being mechanically ventilated via the pressure-controlled CMV ventilation (PC-CMV) mode, and abruptly experiences an increase in airway resistance. How will the delivered tidal volume be affected by this development?

A. The patient's tidal volume will be virtually unaffected.
B. The delivered tidal volume will be increased.
C. The patient's tidal volume will decrease.
D. The delivered tidal volume will fluctuate.

?ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: Pressure-controlled ventilation (PCV) does not guarantee a volume, rather it controls inspiratory airway pressure. Volume is the dependent variable, and will change as lung mechanics or patient effort change. Sudden worsening of airway resistance with pressure targeted ventilation results in a loss of volume, but maximal airway pressures will not rise.
D. Incorrect response: See explanation C