The goal of this prospective multi-center observational study is to learn about the osmotic therapy in severe subarachnoid hemorrhage (SAH). The main question[s] it aims to answer are:

• whether the two osmotic therapy, 20% mannitol and 10% hypertonic saline(HTS), under the same osmotic equivalent, has similar influence on the outcome of SAH patients?

Participants will be given proper treatment according to local expert consensus, including the choice of osmotic medicine. Investigators just record and analyse the data, compare mannitol group and HTS group to see if the outcome of latter is not worse than the former.

Inclusion Criteria:

• ①age ≥18； ②aneurysmal subarachnoid hemorrhage; ③Hunt-Hess 3-5级

Exclusion Criteria:

• previous cranial decompression surgery, cerebrospinal fluid leakage or drainage,

  • bilateral pupils fixed or dilated,

    • hemodynamic instability,

      • hemoglobin < 8g / L,

        • serum osmolality > 320 mOsm / L,

          ⑥ combined with severe organ dysfunction (cardiac, pulmonary, hepatic, renal and so on);

          ⑦ serious electrolyte disorders (serum sodium concentration <125 mmol / L or >170 mmol / L), and difficult to correct within limited time;

          ⑧ serious acid-base balance disorders, and difficult to correct within limited time;

          ⑨ use of mannitol or HSS within previous six hours;

          ⑩ being pregnant.

Patients who meet inclusion and exclusion criterias will be consecutively included. Treatment will be given according to expert consensus of local center, including neurosurgical and intensive management.