The ventilator mode that would be most appropriate to iatrogenically induce hyperventilation to manage a closed head injury patient with severely elevated intracranial pressure (ICP) is which of the following?

a. Volume support ventilation (VSV)
b. Airway pressure release ventilation (APRV)
c. Pressure-controlled continuous mandatory ventilation (PC-CMV)
d. Volume-controlled intermittent mandatory ventilation (VC-IMV)

ANS: C
To deliberately hyperventilate a patient, each breath needs to be a machine breath (either volume or pressure). The only mode from the choices given that does that is the pressure-controlled con-tinuous mandatory ventilation (PC-CMV) mode. Volume support ventilation (VSV) is a patient triggered, volume targeted, flow cycled mode of ventilation that has no backup rate and there-fore is a purely spontaneous mode. Airway pressure release ventilation (APRV) is designed to provide two levels of continuous positive airway pressure (CPAP) and to allow spontaneous breathing at both levels when spontaneous effort is present. If the patient is not breathing spon-taneously, APRV resembles pressure-controlled inverse ratio ventilation (PCIRV) and could po-tentially elevate the patient's already elevated intracranial pressure (ICP). Volume-controlled in-termittent mandatory ventilation (VC-IMV) actually could be made to hyperventilate the patient if the rate is set high enough. The IMV mode is actually used to reduce the effect of patient hy-perventilation on acid-base balance. This happens because only the set rate is a ventilator breath; the rest are patient triggered with the patient's own tidal volume.