Medical and endocrine disease15 / 30
Central diabetes insipidus on desmopressin and postoperative hyponatraemia32-year-old woman, 58 kg, for elective laparoscopic hysterectomy for fibroids
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Know this first
- Desmopressin for central DI: 2–4 mcg SC or 10–20 mcg intranasal; it can cause hyponatraemia.
- Postoperative water retention plus hypotonic fluid causes hyponatraemia; premenopausal women are at highest neurological risk.
- Seizure with hyponatraemia: 100 mL of 3% saline, repeated once or twice at 10-minute intervals if needed.
- Keep the sodium rise to 10 mmol/L or less over the first day; faster risks osmotic demyelination.
The patient
32-year-old woman, 58 kg, for elective laparoscopic hysterectomy for fibroids.
Central diabetes insipidus and panhypopituitarism since craniopharyngioma surgery 6 years ago.
Drugs: desmopressin tablets twice daily, hydrocortisone twice daily, levothyroxine.
Labs: Na 139 mmol/L, osmolality 288 mOsm/kg. Vitals: BP 118/72, HR 72, SpO2 99% on air, RR 12.
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Consider
What are your considerations?
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- A 32-year-old with central DI and panhypopituitarism after craniopharyngioma surgery, for elective laparoscopic hysterectomy. Patient
- She depends on three replacements, desmopressin, hydrocortisone and thyroxine, and all of them continue. Disease
- Desmopressin plus extra water risks hyponatraemia; stopping it risks polyuria and hypernatraemia.
- As a premenopausal woman, she's at particular risk of brain injury from postoperative hyponatraemia. Patient
- Her adrenal axis is absent, so she needs stress steroid cover. Disease
Prepare
How do you prepare her?
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- Morning desmopressin, hydrocortisone and levothyroxine all taken as usual. Disease
- Stress cover: her usual hydrocortisone, plus 50–75 mg IV that day, tapering to baseline in 1–2 days.
- Baseline sodium and osmolality, and first on the list to keep her fast short.
- Endocrinology agree a written plan for fluids and desmopressin. After surgery
Plan
How do you manage her fluids and desmopressin?
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- Isotonic fluid only; no hypotonic or plain dextrose infusions while desmopressin acts. Disease
- Strict input and output charting, with sodium and osmolality every few hours on day one.
- Once she's drinking, she drinks to thirst, without a drip on top. After surgery
- If she stays nil by mouth, desmopressin 2–4 mcg SC, guided by urine output and sodium. Disease
- If sodium falls, I check her volume: SIADH is euvolaemic, salt wasting leaves her dry.
Crisis
On day one she has a headache, vomits twice, then has a generalised seizure. Na 118 mmol/L. She's had 5% dextrose overnight and her desmopressin continued. What do you do?
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- Acute symptomatic hyponatraemia: desmopressin plus hypotonic dextrose made her retain free water. Crisis
- Airway, oxygen, on her side; midazolam 1–5 mg IV if the seizure continues.
- 3% saline 100 mL over 10 minutes, repeated once or twice at 10-minute intervals if she doesn't improve.
- The goal is a quick 2–3 mmol/L rise, then no more than 10 in the first 24 hours.
- Dextrose stopped; next desmopressin dose decided with endocrinology, with urine output watched closely.
- If she overcorrects, desmopressin 2–4 mcg IV slows the rise; too fast risks osmotic demyelination.
- HDU, sodium checked every few hours, endocrine team leading. After surgery
Fatal mistakes
- Hypotonic fluid while her desmopressin continues.
- Correcting her sodium too fast.
- Stopping desmopressin with no plan for her urine output.
Checked against: Miller 10e · Barash 9e · Stoelting 8e
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