Endocrine · Year 2 · from Endocrine
Case 3: Post-Operative Diabetes Insipidus - Triphasic Response
Patient Demographics
- Age: 41 years
- Sex: Female
- Occupation: Nurse
Chief Complaint
Post-operative monitoring after transsphenoidal surgery.
History of Present Illness
A 41-year-old woman underwent transsphenoidal resection of a non-functioning pituitary macroadenoma 36 hours ago. Surgery was uncomplicated. She is being monitored in the neurosurgical ICU. Over the past 12 hours, nursing staff have noted dramatically increased urine output (averaging 400-500 mL/hour) with dilute-appearing urine. She reports intense thirst and has been drinking large amounts of water. Prior to this, her urine output in the first 24 hours post-operatively was normal.
Physical Examination
- Vital Signs: BP 108/68 mmHg, HR 98 bpm, Temp 36.8°C
- General: Alert, thirsty
- HEENT: Nasal packing in place
- Cardiovascular: Tachycardia, regular rhythm
- Neurologic: Alert, oriented, no visual complaints
Workup
- Laboratory Studies:
- Serum sodium: 148 mEq/L (elevated)
- Serum osmolality: 305 mOsm/kg (elevated)
- Urine osmolality: 95 mOsm/kg (dilute)
- Urine specific gravity: 1.001
- Urine output: 5.2 liters over past 12 hours
Diagnosis
Post-operative central diabetes insipidus - Phase 1 of the triphasic response
Treatment
- Phase 1 (DI phase - current):
- Desmopressin (DDAVP) 1-2 mcg IV or 10 mcg intranasally
- Careful fluid replacement (match output with hypotonic fluids)
- Frequent sodium monitoring (every 4-6 hours)
- Anticipate Phase 2 (SIADH phase):
- Typically occurs days 2-7 post-operatively
- Hold desmopressin, fluid restrict if sodium drops
- Monitor for hyponatremia
- Anticipate Phase 3:
- Permanent DI vs. recovery
- May need long-term DDAVP or may resolve completely
- Strict intake/output monitoring
Clinical Pearl
The triphasic response after pituitary surgery reflects the dynamic changes in ADH release from damaged neurons: Phase 1 (DI) occurs when surgical trauma causes acute dysfunction of ADH-secreting neurons; Phase 2 (SIADH) occurs 2-7 days later when dying neurons release stored ADH in an uncontrolled manner; Phase 3 represents permanent DI if >90% of neurons are destroyed, or recovery if sufficient neurons survive. Not all patients experience all three phases - some have only transient DI, isolated SIADH, or permanent DI. Careful monitoring of sodium and urine output, with thoughtful use of DDAVP and fluids, is essential to avoid both severe hypernatremia and dangerous hyponatremia during this period.
Clinical Image
Schematic representation of the triphasic response after pituitary surgery showing patterns of urine output and serum sodium over time.
Image Source: Radiopaedia - "Triphasic response pituitary surgery" License: CC BY-NC-SA 3.0 URL: https://radiopaedia.org/articles/triphasic-response-of-diabetes-insipidus