Between 5 and 10% of patients develop enough cerebral oedema to cause obtundation or brain herniation. Oedema peaks on the second or third day but can cause mass effect up to the tenth day. Water restriction and intravenous mannitol may be used to raise the serum osmolality but hypovolumia should be avoided as this may contribute to hypotention and the worsening of infarction1 .