Serial changes of cerebral hemodynamics and prediction of cerebral ischemia in association with delayed cerebral vasospasm

Cerebral ischemia due to delayed cerebral vasospasm is still a major prognostic factor following intracranial aneurysm rupture. Serial changes of cerebral hemodynamics in association with cerebral vasospasm were investigated and reported using various methods for the prediction of cerebral ischemia. Measurement of regional cerebral blood flow (rCBF) using 133- Xenon intracarotid injection or inhalation technique have demonstrated that rCBF decreases along with the progression of cerebral vasospasm, and ischemic symptoms appear below approximately 20-25m1/100g/min (critical flow level). Hemispheric oxygen metabolism was calculated from rCBF and the difference between arterial oxygen content and jugular venous oxygen content. Patients with asymptomatic vasospasm (moderate degree) showed a decrease in delivery rate of oxygen (D-02) and an increase in oxygen extraction fraction (OEF) for keeping cerebral metabolic rate of oxygen (CMR02) over 2.0m//100g/min. On the other hand, patients with symptomatic vasospasm showed a decrease of CBF below critical flow level and a significant decrease of CMRO2 below approximately 1.5m//100g/min. Serial changes of D-02 and OEF values correlated with the chronology of cerebral vasospasm. Serial determination of OEF and jugular venous oxygen tension (Pj02) without CBF measurement may be predictable indicators for the progression of cerebral vasospasm. With the transcranial Doppler (TCD) ultrasound technique, it was possible to record flow velocity in main cerebral arteries through the cranium. The flow velocity was correlated with the diameter of each cerebral artery. In patients with symptomatic vasospasm, an increase of flow velocity in cerebral arteries was followed by a decrease of flow velocity in the extracranial ICA due to a reduction of flow volume. However, an increase of flow velocity in cerebral arteries did not necessarily correlate with a reduction of CBF; therefore, the flow volume has to be taken into consideration for the prediction of cerebral ischemia due to cerebral vasospasm. Despite this, TCD provides the most practica