This document discusses peri-operative fluid management during neurosurgical procedures. It notes that fluid management aims to reduce cerebral edema and intracranial pressure while maintaining hemodynamic stability. Neurosurgical patients often receive diuretics which can cause complications like bleeding and diabetes insipidus, requiring large fluid volumes. Goal-directed therapy is recommended to maintain circulating volume and tolerate anesthesia-induced changes. The document then discusses factors influencing brain water content like osmolarity and the blood-brain barrier, which is semi-permeable and regulates fluid movement between blood and brain tissue.