When patients suffer a subarachnoid hemorrhage (bleeding around the brain), they often develop hydrocephalus. This is an enlargement of the fluid-filled spaces (ventricles) in the brain. Standard-of-care treatment includes placing an external ventricular drain (EVD) to drain off fluid. Eventually the EVD is weaned with the goal of removing it. Occasionally a patient does not tolerate this and a permanent surgery needs to be done to internalize a shunt.

Though this is done commonly and routinely throughout the world, there are no good studies to address how to optimally set the EVD level and how fast to wean it. Most set the EVD to a level of around 15 mmHg. The investigators hypothesize that setting the EVD lower (which will allow higher volume Cerebrospinal Fluid (CSF) drainage through the EVD) will improve perfusion at the level of the microcirculation in the brain, and result in improved neurologic outcomes.

Inclusion Criteria

• Age ≥ 18 years
• Diagnosis of acute subarachnoid hemorrhage (SAH), confirmed with noncontrast head CT
• SAH is suspected to be aneurysmal in source
• Clinical management requires placement of EVD within 2 days of suspected time of hemorrhage

Exclusion Criteria

• Age < 18 years
• SAH of traumatic or non-aneurysmal etiology
• Patients treated with lumbar drains
• EVD placement ≥ 3 days after suspected time of hemorrhage
• Known contraindication to induction of relative intracranial hypotension (e.g. acute subdural hematoma)
• Pre-morbid mRS ≥ 3
• EVD that is suboptimally placed by CT obtained after EVD placement (i.e. EVD not in the ventricular system)