CO2 is the most potent cerebral vasodilator.

Hyperventilation reduces PaCO2 (hypocapnia), which decreases CBV but also CBF. The goal is generally end-tidal CO2 (ETCO2) of 25–30 mm Hg with a correlating PaCO2 of 30–35. Use with care for stereotactic procedures to minimize the shift of intracranial contents when using this method to control ICP.