Intracranial hypotension results from decreased cerebrospinal fluid (CSF) volume, most commonly due to a CSF leak through a dural tear (post-lumbar puncture, post-epidural, spontaneous dural defect from connective tissue disorders). The reduced CSF volume decreases the buoyant support of the brain within the cranial vault; when the patient assumes an upright position, the brain sags under gravity, stretching pain-sensitive meningeal structures, dural arteries, and bridging veins, producing a characteristic orthostatic headache that worsens within minutes of standing and improves rapidly with recumbency. Compensatory venous engorgement occurs (Monro-Kellie doctrine: decreased CSF volume is compensated by increased blood volume), visible on MRI as diffuse pachymeningeal enhancement, engorgement of dural venous sinuses, and subdural fluid collections or hematomas. The nurse assesses headache characteristics (strictly positional is pathognomonic), maintains the patient in a supine or Trendelenburg position, encourages oral fluids and caffeine intake (which increases CSF production and causes cerebral vasoconstriction), monitors for complications (subdural hematoma, cranial nerve palsies from brain sagging), and assists with epidural blood patch procedure if conservative measures fail.