Effect of hyperventilation on cerebral blood flow in traumatic head injury: clinical relevance and monitoring correlates.


OBJECTIVE: To investigate the effect of hyperventilation on cerebral blood flow in traumatic brain injury. DESIGN: A prospective interventional study. SETTING: A specialist neurocritical care unit. PATIENTS: Fourteen healthy volunteers and 33 patients within 7 days of closed head injury. INTERVENTIONS: All subjects underwent positron emission tomography imaging of cerebral blood flow. In patients, PaCO2 was reduced from 36 +/- 1 to 29 +/- 1 torr (4.8 +/- 0.1 to 3.9 +/- 0.1 kPa) and measurements repeated. Jugular venous saturation (SjvO2 ) and arteriovenous oxygen content differences (AVDO2 ) were monitored in 25 patients and values related to positron emission tomography variables. MEASUREMENTS AND MAIN RESULTS: The volumes of critically hypoperfused and hyperperfused brain (HypoBV and HyperBV, in milliliters) were calculated based on thresholds of 10 and 55 mL.100g(-1).min(-1), respectively. Whereas baseline HypoBV was significantly higher in patients ( p