For patients enrolled in the study, cerebrospinal fluid will be collected by either lumbar puncture or external ventricular catheter. Specimens will be collected immediately pre-operatively if an external ventricular drain is in place or intraoperatively if an external ventricular drain is not present. We will also collect cerebrospinal fluid post operatively after placement of an external ventricular drain regularly from the excess cerebrospinal fluid that has been collected in the drainage bag. CSF will be collected in a serial fashion at multiple time points: immediately post operatively, during vasospasm and before the external ventricular drain is removed.