Subarachnoid hemorrhage (SAH) is a rare and serious form of stroke, mainly linked to the rupture of an intracranial aneurysm responsible for bleeding into the meningeal spaces. The main late serious complication is delayed cerebral ischemia (DCI), resulting in the appearance of new neurological deficits. Prevention of ICR involves in particular maintaining euvolemia, and early treatment of hyponatremia, itself dependent on the level of volume. Evaluation of water status and sodium balance is therefore essential. This assessment is complicated and relies on indirect parameters, both clinical and biological. Impedancemetry, making it possible to measure water volumes and sodium load, could be an aid in the management of blood volume and sodium intake.