3 days after pituitary surgery: urine 300 mL/h, thirsty; Na⁺ 154, serum osmolality 318, urine osmolality 120 (or an elderly, bed-bound patient with poor water intake and Na⁺ 160)
Red flags
Na⁺ >160
Seizures
Absent thirst
Post-op hyponatraemia swing (triphasic)
Differential diagnosis
Osmotic diuresis (glucose, urea, mannitol)
Primary polydipsia
Nephrogenic DI (lithium, hypercalcaemia)
Poor water intake / insensible losses
When to admit, call ICU or discharge
Admit: Na⁺ >150 with symptoms, polyuria after pituitary surgery/head injury, unable to drink
ICU: GCS low, seizures, haemodynamic instability
Key points
"Diabetes insipidus" is now called AVP deficiency (central) and AVP resistance (nephrogenic).
Patients with intact thirst and access to water rarely become hypernatraemic — the elderly, unconscious and post-op are at risk.
Adrenal insufficiency can mask DI; starting hydrocortisone may unmask polyuria.
Never
Lower chronic hypernatraemia by >10 mmol/L in 24 h (cerebral oedema)
Give desmopressin and then keep pushing IV fluid (water intoxication)
Forget cortisol — treat adrenal insufficiency before or with DI
Use 0.9% saline alone to correct pure water loss in a stable patient
Common mistakes
Too-fast correction
Water intoxication after desmopressin
Missing hypocortisolism
Confusing central and nephrogenic
Disposition and follow-up
HDU/ICU if GCS low; ward with 4–6-hourly Na⁺ otherwise. Endocrinology follow-up.
ICU Decoded — original critical-care and internal-medicine pathways by
Dr Javed Akhtar, each cited to a current guideline. For education and quick
reference; verify every dose against local protocols before prescribing.