Autoregulation is often impaired after SAH, even in patients presenting in good clinical grade [Voldby 1985]. An abnormal THRT response commonly develops either early during days 0 to 3 (primary), or late around days 7 to 14 (secondary) after the initial bleed. Primary abnormalities in THRT are far more common in poor grade patients, while secondary abnormalities occur more regularly in the initially good grade patients who later develop signs of DID with clinical deterioration [Ratsep 2002]. Routine and daily assessment of autoregulation with TCD helps to identify patients at higher risk for DID. This delay in the evolution of an abnormal autoregulation response in better grade patients presents an opportunity to introduce early therapeutic strategies designed to offset the potentially harmful effects. Indeed, routine use of plasma expansion is already adopted with this aim in mind [Origitano 1990].