In order to prevent cerebral vasospasm after a subarachnoid hemorrhage (SAH), the so-called triple H therapy (hypertension, hypervolemia, hemodilution) could be applied. In these cases, colloidal solutions containing Hydroxyethyl starch (HES) are used to induce hypervolemia. The administration of HES is very much under debate for the mentioned use because in general the application of HES for the treatment of critically ill patients has been reduced tremendously in the last years due to its nephrotoxic effects. In this context, there are limited data investigating the influence of HES on the blood-brain barrier.