Inclusion Criteria:  Sevoflurane administration >24h 18 years and older  Exclusion Criteria:  < 18 years old Pre-existing diabetes insipidus Use of drugs at risk for diabetes insipidus (including lithium, cisplatin) Hypercalcemia (persistently >2.75 mmol/L) Pituitary or acute brain surgery Patients requiring continuous renal replacement therapy Pregnancy