What treatment is indicated for a patient who develops polyuria after clipping of an aneurysm, suggestive of diabetes insipidus (DI)?

Post-Aneurysm Clipping Polyuria: Treatment Protocol

Administer desmopressin (DDAVP) immediately for central diabetes insipidus, which is the most likely diagnosis in this post-neurosurgical setting.

Immediate Diagnostic Confirmation

Before initiating treatment, rapidly confirm the diagnosis with:

• Simultaneous measurement of serum sodium, serum osmolality, and urine osmolality to establish the characteristic triad: polyuria with inappropriately dilute urine (osmolality <200 mOsm/kg) and high-normal or elevated serum sodium 1, 2
• Plasma copeptin levels can help distinguish central from nephrogenic DI, with levels <21.4 pmol/L suggesting central DI 1, 2
• However, do not delay treatment if clinical presentation is clear—polyuria developing 1-4 days post-aneurysm surgery is pathognomonic for central DI 3

Primary Treatment: Desmopressin

Central DI following neurosurgery requires desmopressin replacement therapy 4, 5:

• Initial route: Subcutaneous or intravenous desmopressin is preferred in the immediate postoperative period, starting at 2-4 mcg in divided doses 1
• Rationale for parenteral route: The intranasal route may be compromised by nasal packing, congestion, surgical trauma (especially transsphenoidal approaches), or impaired consciousness 4
• Continuous infusion option: For severe, uncontrolled polyuria, aqueous pitressin at 1-1.5 IU/hr via slow continuous infusion is more effective than intermittent intramuscular injections 3

Transition to Long-Term Management

Once the patient is stable and able to take oral medications:

• Oral or sublingual desmopressin can replace parenteral forms 5
• Intranasal desmopressin (0.01% solution) is indicated for long-term management of central cranial DI, particularly effective for polyuria following head trauma or pituitary surgery 4
• Dose titration: Patients typically find their own effective minimal dose to maintain normal urinary frequency without excessive polyuria, particularly at night 5

Critical Supportive Management

Fluid Management

Free access to water is absolutely essential 1, 2:

• Never restrict fluids—this is a life-threatening error that leads to severe hypernatremic dehydration 1
• Allow drinking to thirst rather than calculated requirements, as osmosensors are more sensitive than medical calculations 1
• For IV rehydration: Use 5% dextrose in water (hypotonic fluid) at maintenance rates, NOT normal saline 1

Monitoring Protocol

Serum sodium must be checked within 7 days of starting desmopressin, then at 1 month, then periodically 1:

• Primary risk: Hyponatremia from water intoxication is the main complication of desmopressin therapy 1, 5
• Initial monitoring: Check serum sodium every 2-3 days initially, then weekly as patient stabilizes 6
• Ongoing assessment: Monitor urine volume, urine osmolality, and plasma osmolality to evaluate treatment efficacy 2

Expected Clinical Course

Post-aneurysm clipping DI typically follows a monophasic pattern 3:

• Onset: 1-4 days after surgery 3
• Duration: 6-9 days in most cases 3
• Plasma ADH levels: May drop below 0.6 microunits/ml in the days preceding overt polyuria 3
• Mechanism: Likely due to vascular spasm of branches supplying the paraventricular and preoptic nuclei (especially with anterior communicating artery aneurysms) combined with direct surgical trauma 3

Common Pitfalls to Avoid

Do not confuse with nephrogenic DI—desmopressin is ineffective for nephrogenic DI and may cause dangerous hyponatremia 6, 4:

• Central DI responds to desmopressin with increased urine osmolality (>50% increase) 1
• Nephrogenic DI does not respond and requires thiazide diuretics plus NSAIDs instead 2, 6

Avoid delayed treatment—once plasma ADH values drop, patients should receive replacement therapy promptly to prevent severe dehydration and hypernatremia 3

Patient education is essential to prevent water intoxication and hyponatremia from excessive desmopressin dosing 5

Alternative Diagnosis Consideration

While central DI is most likely post-aneurysm clipping, rule out other causes of polyuria 7:

• Mannitol-induced diuresis: Mannitol is commonly used intraoperatively for brain relaxation and is a potent diuretic that can cause hypovolemia 7
• Hypertonic saline effects: Has minimal diuretic effect compared to mannitol 7
• Distinguishing feature: DI presents with dilute urine (<200 mOsm/kg) and elevated serum sodium, whereas osmotic diuresis from mannitol presents with higher urine osmolality 1