Synopsis
Recognise dangerous postoperative hypo- and hypernatraemia, distinguish water-balance and endocrine mechanisms, and correct urgent symptoms while preventing overcorrection and missed adrenal insufficiency.
- Classify the emergency by symptoms, sodium level and rate of change, then obtain paired serum osmolality, urine osmolality and urine sodium without delaying resuscitation.
- After intracranial surgery, consider administered hypotonic or isotonic fluid, AVP deficiency, SIADH, glucocorticoid deficiency, osmotic diuresis, renal loss and less common natriuretic states.
- Severe or moderately severe symptomatic adult hyponatraemia uses monitored 3% saline boluses under the 2022 Society for Endocrinology pathway; target a small symptom-relieving initial rise, then prevent correction beyond 10 mmol/L in the first 24 hours and 8 mmol/L per 24 hours thereafter.
Key red flags
A seizure or falling consciousness with hyponatraemia needs symptom-led emergency therapy before the exact mechanism is fully resolved.
Rapid high-volume dilute urine with rising sodium after sellar or suprasellar surgery suggests AVP deficiency and can cause abrupt free-water loss.
Hyponatraemia around the first postoperative week can occur after discharge; headache, nausea, confusion, vomiting or seizure requires urgent sodium measurement.
Hypotension, hypoglycaemia, fever, abdominal symptoms or unexplained hyponatraemia after pituitary surgery may indicate cortisol deficiency and requires urgent endocrine assessment.
Headache, nausea, vomiting, confusion, seizure and falling consciousness reflect brain water shift; symptom severity and speed of fall matter more than a label alone.
Thirst, dry mucosa, tachycardia, hypotension, confusion and high-volume dilute urine indicate water deficit, especially when the patient cannot drink.
Falling urine output, weight gain and declining sodium after prior polyuria or desmopressin should trigger immediate fluid and medication reassessment.
Hypotension, hypoglycaemia, weakness, nausea or fever with hyponatraemia after pituitary-region surgery requires urgent consideration of secondary adrenal insufficiency.
Reasoning priorities
Define direction, rate and tonicity context while detecting hyperglycaemia-related translocational hyponatraemia.
Rapid change or neurological symptoms increase urgency; treatment is adjusted to measured correction rather than predicted response alone.
Worked reasoning
On postoperative day 7, an adult returns with headache, vomiting, confusion and serum sodium 119 mmol/L after taking desmopressin.
- Context: assess airway and neurological severity, repeat sodium and glucose, obtain paired serum and urine osmolality and urine sodium, examine volume status, review intake and output, desmopressin, glucocorticoids and other medicines.
- Reasoning: the timing and low output suggest an antidiuretic phase or excess desmopressin, but cortisol deficiency and other hypotonic hyponatraemia causes remain dangerous alternatives.
- Outcome: stop inappropriate free-water intake and reassess desmopressin, call critical care and endocrinology, and use the adult symptomatic-hyponatraemia hypertonic-saline bolus pathway while treating the confirmed cause.
- Verification: measure sodium after each intervention and frequently thereafter, document symptom response and total correction, prevent overshoot, and watch for later recurrence of dilute polyuria.