Hyponatremia & Hypernatremia

at the bedside

escalate now if

hyponatremia

hypernatremia

causes

hyponatremia: workup

serum osmolality
- < 275 mOsm/kg → true hypotonic hyponatremia
urine osmolality
- < 100 → excess water intake (e.g. polydipsia)
- > 100 → ADH active → check urine Na
urine sodium
- < 30 mmol/L → hypovolemia (GI losses, dehydration)
- > 30 mmol/L → SIADH, diuretics, CKD / renal salt-wasting, adrenal insufficiency. Check diuretic use + renal function before assuming SIADH
determine acute vs chronic + volume status

hyponatremia: duration first, then symptoms

acute, known < 48 h (post-op fluids, water intoxication, MDMA, marathon) → any symptom is an emergency
chronic or unknown → boluses only for severe symptoms
severe < 120 · moderate 120–129 mmol/L
3% criteria met → bolus first, then the cause

acute, no symptoms

NaCl 3% 50 mL IV over 10 min to stop a further fall, unless already autocorrecting
autocorrecting = Na rising untreated, or brisk dilute urine with urine Na + K < serum Na → watch Na, bolus only if it falls

chronic, no severe symptoms

treat the cause; stop contributing drugs (thiazide, SSRI, carbamazepine, desmopressin)
cut electrolyte-free water → fluid restriction, no hypotonic IV fluids, more dietary salt
Na < 120, symptomatic, or known intracranial pathology → senior now

hypovolemic → NaCl 0.9% (or balanced crystalloid) IV 0.5–1 mL/kg/h; shock → resuscitate first, rate limits come second
euvolemic → fluid restriction 500–1000 mL/day; second line (senior): loop diuretic + salt tablets, or urea
hypervolemic → fluid restriction ± loop diuretic

edematous (heart failure, cirrhosis) → NaCl 3% 15–30 mL/h IV + furosemide 40 mg IV BD; Na every 2–4 h
rapidly reversible cause (true hypovolemia, adrenal insufficiency, transient SIAD) or high ODS risk → NaCl 3% 15–30 mL/h + desmopressin 1–2 micrograms IV/SC every 6–8 h to clamp water loss; Na every 2–3 h, then 4–6 h
otherwise → NaCl 3% 15–30 mL/h; Na every 4–6 h
all → aim +4–6 mmol/L per 24 h; stop the regimen at Na ≥ 125
self-induced water intoxication on a chronic low Na → general measures only; Na every 6–12 h

hypernatremia

shock or volume depleted → NaCl 0.9% until perfused; no hypotonic fluid in shock
estimate the deficit → FWD = TBW × (Na/140 − 1)
- TBW ≈ 0.6 × kg (men) · 0.5 × kg (women, elderly men, obesity) · 0.45 × kg (elderly women)
- estimate only → reassess against measured Na
add ongoing losses → urine output, GI, insensible, fever
route and fluid
- gut works → oral / NGT water (safest)
- pure water deficit, euvolemic → D5W IV
- still volume depleted, or ongoing hypotonic losses (diarrhea, diuresis) → NaCl 0.45% IV; switch to D5W once volume is restored
- hyperglycemia on D5W → NaCl 0.45% instead, or cover with insulin
- 0.9% saline: shock only, does not correct Na
- diabetes insipidus (dilute urine, high output) → desmopressin with senior / endocrine input
rate → deficit + ongoing losses, spread so Na falls ≤ 12 mmol/L per 24 h (~0.5 mmol/L/h) when chronic or unknown; roughly half the deficit in the first 24 h; too fast → cerebral edema; senior before starting

limits and monitoring

hyponatremia → ≤ 10 mmol/L in the first 24 h, then ≤ 8 mmol/L per 24 h until Na 130 (European / SfE); high risk of osmotic demyelination → stay ≤ 8 mmol/L per 24 h and aim for 4–6
- very low starting Na <105–110, chronic or unknown duration, alcohol use, malnutrition, advanced liver disease, hypokalemia
hypernatremia → ≤ 12 mmol/L per 24 h (~0.5 mmol/L/h) when chronic or asymptomatic

hyponatremia → Na on a gas after each 3% bolus and at 2 h, then at 6 h, 12 h and daily; every 2–4 h on a 3% infusion
hypernatremia → Na + RFT every 4–6 h while correcting
re-prescribe at every result
hand over → plan, next Na due, escalation trigger if correcting too fast

rising too fast

rise > 10 mmol/L in the first 24 h, or > 8 in any 24 h after → stop 3% saline and any active treatment; expect a water diuresis once the cause is treated
relower, with senior / nephrology: D5W 10 mL/kg IV over 1 h, strict urine output + fluid balance
ongoing free-water loss → desmopressin 2 micrograms IV, not more often than every 8 h
Na hourly until the trajectory is controlled
escalate early → senior / nephrology / ICU

source	type
European clinical practice guideline on hyponatraemia (ESE / ESICM / ERA-EDTA)	international guideline
Society for Endocrinology, emergency management of symptomatic hyponatraemia (2022)	specialty-society guidance
Hyperglycemic crises in adults with diabetes: consensus report (ADA / EASD / JBDS / AACE / DTS, Diabetes Care 2024)	consensus report

Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.

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reviewed Aug 2026updated Oct 2026file lab/rft-sodium