Anne Katrin Torsheim

1 Introduction Sodium is a major determinant of osmotic pressure; hypernatremia is therefore a common cause of hyperosmolality. Clinically, subacute plasma hyperosmolality may manifest as confusion, dysphoria, drowsiness, convulsions or coma (1). In acute cases, it may cause substantial brain volume loss (2), increasing the risk of haemorrhage and irreversible brain injury (1).