Confusion and a sodium of 118 after ten days of ibuprofen
A 68-year-old woman is brought to the emergency department in late autumn because of two days of nausea, one episode of vomiting, lethargy and confusion. Her daughter reports she has taken hydrochlorothiazide 25 mg daily for hypertension for eight years and began ibuprofen 400 mg three times daily ten days ago for knee osteoarthritis. On examination she is drowsy but rousable, oriented to person only, with no fever, no neck stiffness and no focal neurological deficit. Supine blood pressure is 118/70 mmHg, pulse 86/min regular, respiratory rate 14/min, temperature 36.8 °C; mucous membranes are moist, there is no oedema and no orthostatic fall. Serum sodium 118 mEq/L, potassium 3.6 mEq/L, chloride 88 mEq/L, bicarbonate 24 mEq/L, glucose 96 mg/dL, urea 14 mg/dL, creatinine 0.8 mg/dL, urine sodium 48 mEq/L, urine osmolality 520 mOsm/kg, serum osmolality 252 mOsm/kg, uric acid 3.1 mg/dL. Chest radiograph and urinalysis are unremarkable; TSH, free T4 and a morning cortisol are pending.
1. Is this true hypotonic hyponatraemia, and what is the single most likely mechanism? Which alternatives must be excluded before you accept that cause, and how?
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Confirm the tonicity first. Measured serum osmolality is 252 mOsm/kg, below 275, with a normal glucose of 96 mg/dL. That excludes pseudohyponatraemia (hyperlipidaemia or hyperproteinaemia, in which the measured osmolality is normal) and translocational hyponatraemia from hyperglycaemia.
Mechanism. She is clinically euvolemic: moist mucosae, no orthostatic fall, no oedema. The urine is inappropriately concentrated at 520 mOsm/kg, far above the roughly 100 mOsm/kg expected when ADH is suppressed, and the urine sodium is 48 mEq/L. Active ADH plus inability to excrete free water therefore explains the picture. Primary polydipsia would produce a maximally dilute urine (under 100 mOsm/kg); true volume depletion or renal salt wasting would give orthostasis, a high urea and a low urine sodium. The low urea (14 mg/dL) and low uric acid (3.1 mg/dL) fit the volume-expanded SIADH pattern rather than depletion.
The trigger is the pairing of a thiazide, which blocks distal dilution, causes sodium wasting and potentiates ADH action, with an NSAID started ten days ago, which removes prostaglandin-mediated free-water excretion. Either can cause this alone; together they are a classic combination, and the timing fits.
Still to exclude: hypothyroidism and adrenal insufficiency, both of which cause euvolemic hypotonic hyponatraemia with concentrated urine. Send TSH, free T4 and a morning cortisol, but do not delay treatment of symptomatic hyponatraemia waiting for them. The normal chest film argues against a pulmonary cause of SIADH.
2. She has a generalised tonic-clonic seizure in the emergency department. Give your immediate fluid orders with volumes and rates, the correction limits you must not exceed, and the complication you are preventing.
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Immediate: protect the airway, give oxygen, check capillary glucose, and give 3% hypertonic saline 100-150 mL as an intravenous bolus over 10-20 minutes. This usually raises serum sodium by 2-4 mEq/L and stops the seizure. If seizures persist, repeat the bolus up to two more times (total 300-500 mL) while preparing a continuous infusion, and treat the seizure with a benzodiazepine if it continues.
Limits. Target a rise of 4-6 mEq/L in the first 4-6 hours, which is enough to relieve cerebral oedema and symptoms, and never exceed 8 mEq/L in 24 hours. Because she is at higher risk of demyelination (older age, hypokalaemia at 3.6, likely chronic hyponatraemia), aim for the lower end, about 6 mEq/L in 24 hours. Check sodium every 2 hours during active correction, then every 4-6 hours.
Complication being prevented: osmotic demyelination syndrome, presenting days later with dysarthria, dysphagia, paraparesis or locked-in state.
Practical points: stop the thiazide and the NSAID, replace potassium, and once the acute symptoms have resolved and sodium is above 125 mEq/L, stop hypertonic saline and move to fluid restriction (about 800-1000 mL/day) with daily weights and sodium checks. If the sodium later overcorrects, do not simply observe: give desmopressin 1-2 micrograms with 5% dextrose to re-lower it into the safe range.
3. Twelve hours later her sodium is 132 mEq/L and she is more alert. What has gone wrong and what do you do now?
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She has risen 14 mEq/L in 12 hours, well beyond the 8 mEq/L per 24 hours limit, and beyond the 4-6 mEq/L target for a patient at risk of osmotic demyelination. The rise is probably from a combination of the hypertonic boluses, renal water loss once the thiazide was stopped and ADH fell, plus potassium replacement, since potassium entering cells moves sodium out.
Action. Stop all hypertonic saline immediately. Actively re-lower the sodium rather than just observing: give desmopressin 1-2 micrograms subcutaneously or intravenously to stop the renal free-water loss, together with 5% dextrose (about 10 mL/kg, i.e. 500-700 mL) over 1-2 hours, and recheck sodium hourly. The aim is to bring her back to no more than 8 mEq/L above the admission value of 118 mEq/L, that is about 126 mEq/L, within the first 24 hours and hold her there.
Monitor for the delayed signs of osmotic demyelination over the next 2-6 days: dysarthria, dysphagia, emotional lability, quadriparesis, and the locked-in syndrome. A normal level of consciousness now does not exclude it, because the injury is delayed. Document the event, review the fluid orders that caused the overcorrection, and avoid repeating hypertonic boluses without an explicit stop rule and interval sodium checks.