Fig. 2
From: Regulation of the cerebral circulation: bedside assessment and clinical implications
CO2 reactivity after TBI. CO2 reactivity is a measure indicating how well vascular responses in the brain are preserved. Mild hyperventilation (PaCO2 challenge from 35 to 31.5 mmHg) is applied temporarily (1 h) in the patient after TBI. Right CBF velocity (FVR) in the middle cerebral artery decreased from 120 to 100 cm/s. CO2 reactivity is calculated as ∆CBF velocity (%)/∆ PaCO2 and in this case reactivity is ~ 5 %/mmHg—very good. However, at the same time ICP decreased from 32 to 27 mmHg and blood pressure (ABP) increased from 120 to 125 mmHg. Therefore, CPP increased from 88 to 98 mmHg. The formula for cerebrovascular CO2 reactivity does not take into account the possible interaction between chemoregulation and autoregulation. ABP arterial blood pressure, ICP intracranial pressure