Hyponatremia & Hypernatremia
at the bedside
- check vitals
- assess → neurological status + volume status
- confirm sodium, compare with previous levels
- correct for hyperglycemia
- every ↑ glucose 5.6 mmol/L → Na ↓ ~1.6 mmol/L
escalate now if
- seizures, coma, or depressed consciousness
- rapid or large change in Na
- Na <120 or >160 mmol/L
focused check
hyponatremia
- mild: fatigue, weakness, nausea
- moderate: confusion, ataxia
- severe: seizures, coma
hypernatremia
- confusion, altered mental status · weakness, fatigue · nausea, vomiting
causes
- water loss (most common), GI losses, insensible (fever, burns)
- renal loss, diabetes insipidus, osmotic diuresis
- sodium gain, hypertonic fluids, NaHCO₃
send now
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
treat
hyponatremia, by volume status
| volume status | treatment |
|---|---|
| hypovolemic | IV normal saline 0.9% |
| euvolemic | fluid restriction 500–1000 mL/day |
| hypervolemic | fluid restriction ± loop diuretic |
severe symptomatic hyponatremia: give 3% saline now
- seizures, coma, or depressed consciousness → treat immediately, do not wait for cause
- bolus (local protocol sets which)
- 100 mL over 10 min · up to ×3
- or 150 mL over 20 min · up to ×2
- goal: controlled rise of 4–6 mmol/L to stop dangerous symptoms
- normalizing Na is not the goal → stop boluses once symptoms improve
- recheck Na and reassess neurology after each bolus
- emergency rise counts toward 24 h limit below
- call senior / ICU, do not run this alone
hypernatremia
unstable or volume depleted? restore perfusion first
- shock or significant intravascular depletion → 0.9% saline until perfusion restored
- do not start hypotonic fluid in shock
then replace free water
- 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)
- a starting estimate, not a prescription → reassess against measured sodium
- add ongoing losses: urine output, GI, insensible, fever
- route: oral / NGT water where it can be absorbed (safest); IV if not, fluid chosen by volume state and ongoing losses, not a fixed sequence
- rate: set by duration (acute vs chronic or unknown); limits in recheck below
correct slowly
- avoid rapid shifts → risk of cerebral edema
- consult senior before initiating correction
calculator Na correction rate · MDCalc ↗︎
recheck
correction limits, do not exceed
- hyponatremia: ≤ 8 mmol/L per 24 h; ≤ 4–6 mmol/L per 24 h if high risk of osmotic demyelination
- very low starting Na <105–110, chronic or unknown duration, alcohol use, malnutrition, advanced liver disease, hypokalemia
- hypernatremia: ≤ 10 mmol/L per 24 h (~0.5 mmol/L/h)
- recheck sodium + RFT every 4–6 h while actively correcting; reassess the prescription each time
before leaving
- document: sodium value + trend, correction strategy, rate limit for next 24 h
- pending: repeat sodium / RFT due
- hand over: ongoing plan, next recheck due, escalation trigger if correcting too fast
if not improving / further escalation: sodium rising too fast
- too-fast hypoNa correction → osmotic demyelination risk; too-fast hyperNa correction → cerebral edema risk
- stop driver: stop hypertonic saline, watch for water diuresis once cause treated
- relower with free water → D5W where indicated
- desmopressin where appropriate to stop ongoing free-water loss
- Na hourly until the trajectory is controlled
- escalate early → senior / nephrology / ICU
MOC pearl
sodium is a water problem, not a salt problem. Check osmolality first, let volume status drive treatment, correct slowly: osmotic demyelination if you over-correct low Na, cerebral edema if you over-correct high Na.
evidence
| 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 |
Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.
free the on-call checklist covers the whole shift on one printable page.
More clinical resources in the MOC+ Library →
reviewed Aug 2026updated Sep 2026file lab/rft-sodium