Ask: Is she symptomatic — confused, vomiting, headache, seizure, drowsy? What was the previous sodium and when?
That is the whole triage. Symptomatic acute hyponatraemia is an emergency treated with hypertonic saline. Asymptomatic chronic hyponatraemia is a puzzle you must solve slowly, and correcting it fast causes osmotic demyelination.
- Under-treating severe symptoms. Seizure, obtundation or serious vomiting needs hypertonic saline now, in a monitored setting, with a senior involved — not fluid restriction and a morning review. Protocolised 3%: European practice is commonly 150 mL over 20 minutes, aiming for an initial rise of about 5 mmol/L to take the pressure off the brain. You are treating cerebral oedema, not normalising a number
- Over-correcting. Exceeding the safe rise per 24 hours risks osmotic demyelination, which is irreversible and which you will have caused with a bag of fluid. Highest risk: chronic hyponatraemia, a sodium in the low 100s, alcohol, malnutrition, hypokalaemia, liver disease. Unless a specialist protocol says otherwise, the ceiling is 10 mmol/L in the first 24 hours and 8 mmol/L in each 24 hours after — 8 from the start in anyone with those risk factors. Know your local number, write it in the notes as a limit, and set an actual alarm for the repeat sodium
FIRST MOVES Symptoms first, then volume status, then the biochemistry that actually answers it: paired serum and urine osmolality plus urine sodium, taken before you give anything — unless she is fitting, in which case the samples go off alongside the saline and not instead of it. Rule out the impostors before you start categorising: hyperglycaemia and pseudohyponatraemia are not this disease. Volume status splits it — hypovolaemic (losses, diuretics), euvolaemic (SIADH, hypothyroid, adrenal insufficiency, drugs), hypervolaemic (heart failure, cirrhosis, nephrotic). Check for thiazides, SSRIs, antipsychotics, carbamazepine and oxcarbazepine, cyclophosphamide, desmopressin, PPIs, recreational drugs, and the litre of hypotonic fluid somebody kindly prescribed. Then schedule the repeat sodium — this is the single most important order you will write on this call.
Critical result: sodium [X] mmol/L; previous [X] on [DATE] — so this is [ACUTE <48h / CHRONIC / UNKNOWN DURATION]. [AGE]-year-old [SEX], admitted for [REASON]. Symptoms: [NONE / NAUSEA / HEADACHE / CONFUSION / DROWSY / SEIZURE]. Volume status: [HYPO / EU / HYPERVOLAEMIC] based on [FINDINGS]. Serum osmolality [X], urine osmolality [X], urine sodium [X] — [TAKEN / NOT YET TAKEN]. K [X], glucose [X], TSH [X], cortisol [X] if known. Drugs: [THIAZIDE/SSRI/CARBAMAZEPINE/PPI/DESMOPRESSIN/OTHER]. Risk factors for demyelination: [ALCOHOL/MALNUTRITION/LIVER/HYPOKALAEMIA]. First tell me whether this needs hypertonic saline tonight and why. Then the diagnostic algorithm from volume status and the urine studies. Then give me the maximum safe correction over 24 hours for THIS patient given the demyelination risk factors, the monitoring interval, and what I do if I overshoot. Flag which of these drugs is the likely culprit.