These data show that in normal human subjects measurement of dynamic autoregulation yields similar results as static testing of intact and pharmacologically impaired autoregulation.

is in persons 55 to 60 years old. 11 An estimated 5 to 15 percent of cases of stroke are related to ruptured intracranial aneurysms. 12 Aneurysmal subarachnoid hemorrhage, a form of hemorrhagic stroke, has a 30-day mortality rate of 45 percent. An estimated 30 percent of survivors will have moderate-to-severe disability. 13 Little is known about the cause of intracranial aneurysms or the process by which they form, grow, and rupture, although hypertension and smoking-induced vascular changes are thought to have a major role. 3 The most common histologic finding is a decrease in the tunica media, the middle muscular layer of the artery, causing structural defects. These defects, combined with hemodynamic factors, lead to aneurysmal outpouchings at arterial branch points in the subarachnoid space at the base of the brain (Fig. 1).

RECOMMENDATIONS(see Methodology) Indications for Surgery • An acute subdural hematoma (SDH) with a thickness greater than 10 mm or a midline shift greater than 5 mm on computed tomographic (CT) scan should be surgically evacuated, regardless of the patient's Glasgow Coma Scale (GCS) score. • All patients with acute SDH in coma (GCS score less than 9) should undergo intracranial pressure (ICP) monitoring. • A comatose patient (GCS score less than 9) with an SDH less than 10-mm thick and a midline shift less than 5 mm should undergo surgical evacuation of the lesion if the GCS score decreased between the time of injury and hospital admission by 2 or more points on the GCS and/or the patient presents with asymmetric or fixed and dilated pupils and/or the ICP exceeds 20 mm Hg. Timing • In patients with acute SDH and indications for surgery, surgical evacuation should be performed as soon as possible. Methods• If surgical evacuation of an acute SDH in a comatose patient (GCS Ͻ 9) is indicated, it should be performed using a craniotomy with or without bone flap removal and duraplasty.