A patient following head injury was admitted in Intensive care ward with signs of raised intracranial pressure. He was put on ventilator and staed on Intravenous fluids and diuretics. Twenty four hours later his urine output was 3.5 liters, serum sodium 156 mEq/1 and serum osmolality of 316 mOsm/kg. The most likely diagnosis based on these parameters is-

Ans is option 1 high output due to diuretics. Patient shows Increased serum sodium Increased serum osmolarity Polyuria History and the lab investigations suggests either diabetic insipidus or diuresis due to osmotic diuretics. Patient with head injury and increased intracranial pressure requires mannitol to reduce intracranial pressure Mannitol is an osmotic diuretic So the features of hypernatremia increased osmolality and polyuria indicates diuresis due to mannitol administration Ref Harrison 17/e p 274,279,290,2219,2210