This study aims to investigate the inner mechanism during different dehydration therapies such as mannitol injection and hypertonic saline. The investigators used a self-made near infrared spectroscopy (NIRS) instrument to monitor the physiological changes noninvasively including oxyhemoglobin ([HbO2]), deoxy-hemoglobin ([Hb]), the derived change in blood volume ([tHb]) and water concentration on the forehead of brain edema patients.

Cerebral edema, as an acute head injury along with high intracranial pressure, has been of great interest over decades in clinical neurosurgery research. Dehydration therapy is a common clinical method to decrease intracranial pressure. This study aims to investigate the inner mechanism during different dehydration therapies such as mannitol injection and hypertonic saline. The investigators used a self-made near infrared spectroscopy (NIRS) instrument to monitor the physiological changes noninvasively including oxyhemoglobin ([HbO2]), deoxy-hemoglobin ([Hb]), the derived change in blood volume ([tHb]) and water concentration on the forehead of brain edema patients. Then the investigators compared the changes process of multiple physiological parameters during different dehydration therapies.

Inclusion Criteria:

• Patients who had brain edema and need dehydration therapy to decrease intracranial pressure.

Exclusion Criteria:

• AIDS, Active Hepatitis, Tuberculosis, Syphilis
• Patients who regularly take anticoagulants, antiplatelet drugs
• Anemia, thrombocytopenia
• Hemorrhagic disease like hemophilia