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.
