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Hyponatremia

Updated Oct 18, 2026Adults · ED management19 sources · 15 checked in PubMed2 figuresEuropean guideline 2014

Bottom line

  • Symptoms drive treatment, not the number alone. Vomiting, seizures, deep somnolence, cardiorespiratory distress or coma count as severe.1
  • Severe symptoms: 150 mL of 3% saline IV over 20 minutes, right away. Recheck sodium and repeat up to twice, stopping once sodium is up 5 mEq/L.1
  • Cap the rise. The European limit is 10 mEq/L in the first 24 hours and 8 mEq/L in each 24 hours after that. US experts use 8 for high-risk patients.1,4
  • Expect overcorrection. In 1,490 admissions with sodium under 120, 41% rose more than 8 mEq/L in 24 hours. A sudden urine output over 100 mL/h is the warning sign.9,1
  • How fast is too fast is now disputed. Large cohorts link slower correction to higher mortality, while guideline authors urge keeping the limits until better evidence arrives.14,15,16

Classify

Mild130–135mEq/L
Moderate125–129mEq/L
Profound< 125mEq/L

Bands from the European guideline (ESE, ESICM and ERA-EDTA), measured by ion-specific electrode. It uses "profound" for the lab value and keeps "severe" for symptoms.1 For sodium, 1 mmol/L equals 1 mEq/L.

Two dangers pull in opposite directions. Untreated acute hyponatremia can cause cerebral edema, and correcting chronic hyponatremia too fast can cause osmotic demyelination.2

  • Acute: documented to have developed in under 48 hours. The brain needs about 24–48 hours to adapt, so swelling is the main risk.1
  • Chronic: present for at least 48 hours. If you can't tell, treat it as chronic unless the history clearly says otherwise.1
  • Clues to acute onset: the postoperative period, prostate or uterine endoscopic resection, polydipsia, exercise, MDMA, colonoscopy prep, a recently started thiazide or desmopressin, oxytocin, IV cyclophosphamide, and terlipressin or vasopressin.1
Symptom gradeSymptoms
Moderately severeNausea without vomiting, confusion, headache
SevereVomiting, cardiorespiratory distress, abnormal and deep somnolence, seizures, coma (GCS ≤ 8)

Symptom grades from the European guideline. Other conditions cause the same symptoms. When sodium is only mildly low, the guideline accepts hyponatremia as the cause of severe symptoms only in exceptional cases.1

First steps

  1. Grade the symptoms using the table above.1
  2. Severe symptoms: don't wait for the workup. Give 150 mL of 3% saline IV over 20 minutes, whether the hyponatremia is acute or chronic.1
  3. Confirm it is hypotonic. Check glucose. Add 2.4 mEq/L to the measured sodium for every 100 mg/dL of glucose above 100 mg/dL. A measured serum osmolality under 275 mOsm/kg always means hypotonic hyponatremia.1
  4. Think of pseudohyponatremia when lipids or proteins are very high. Serum osmolality is then normal. A blood gas analyzer (direct potentiometry) gives the true sodium.1,3
  5. Send urine osmolality and urine sodium from a spot sample taken at the same time as the blood.1
  6. Stop fluids and drugs that may be causing it, where possible.1
  7. Set the ceiling before you start: no more than 10 mEq/L in the first 24 hours and 8 mEq/L in each 24 hours after that.1

Treatment

PresentationWhat to doCheck sodium
Severe symptoms (acute or chronic)
First hour3% saline 150 mL IV over 20 min. Repeat up to 2 more times until sodium is up 5 mEq/L. Consider 2 mL/kg instead in very small or large patients.1After each bolus (20 min)
Better after +5Stop 3% saline. Keep the line open with the smallest feasible volume of 0.9% saline. Start cause-specific treatment.16 h, 12 h, then daily
Not better after +5Continue 3% saline aiming for about +1 mEq/L per hour. Stop when symptoms improve, sodium is up 10 in total, or sodium reaches 130, whichever comes first. Look for another cause.1Every 4 h
Moderately severe symptoms
Nausea, confusion, headacheOne 150 mL bolus of 3% saline over 20 min. Aim for +5 mEq/L over 24 h. Find and treat the cause.11 h, 6 h, 12 h
No moderate or severe symptoms
AcuteStop the cause. If sodium has dropped more than 10 mEq/L, give one 150 mL bolus of 3% saline over 20 min.14 h, same method
Chronic, mildTreat the cause. Don't treat with the sole aim of raising sodium.1—
Chronic, moderate or profoundTreat the cause and respect the 10/8 limits.1Every 6 h

Doses and schedules from the European guideline; most carry very low-quality evidence (grade D).1 Symptoms may take time to resolve after the sodium rises. If you can't assess symptoms, for example in an intubated patient, follow the "better after +5" row.1

FIG 1The first 24 hours with severe symptoms. Drawn for this page from the European guideline's schedule. Each 150 mL bolus of 3% saline runs over 20 minutes, with a sodium check after each. The 3% infusion row applies only when symptoms persist after a 5 mEq/L rise. Times are targets, not measurements.1
Sources disagree

Bolus size and bolus vs infusion. The European guideline uses 150 mL over 20 minutes and a single bolus for moderate symptoms. The 2013 US panel uses 100 mL over 10 minutes, up to 3 times, and a continuous infusion of 0.5–2 mL/kg/h for moderate symptoms.1,4 In the SALSA trial (178 adults, sodium ≤ 125), boluses and slow infusion overcorrected at similar rates (17.2% vs 24.2%, not significant). Boluses needed relowering therapy less often (41.4% vs 57.1%).5 REBEL EM notes the confidence intervals were wide and no patient in either arm developed osmotic demyelination, so the trial cannot settle safety.6

  • In a non-randomized comparison, 100 mL boluses raised sodium faster at 6 hours than a 20 mL/h infusion (median 6 vs 3 mmol/L) and improved GCS sooner. A third bolus was linked to more need for dextrose or desmopressin to prevent overcorrection.7
  • Potassium counts as sodium. Correcting hypokalemia also raises the serum sodium, so include potassium replacement in your plan.1

By volume status (chronic, without severe symptoms)

  • Low circulating volume: restore volume with 0.9% saline or a balanced crystalloid at 0.5–1.0 mL/kg/h. With hemodynamic instability, resuscitation comes first, even if sodium rises faster than planned.1
  • Expanded volume (heart failure, cirrhosis): restrict fluid to prevent more overload. Don't treat mild or moderate hyponatremia just to raise the number.1
  • SIAD: fluid restriction first. Second-line options rated equal are urea 0.25–0.50 g/kg per day, or low-dose loop diuretic plus oral salt.1
  • Vaptans: the European guideline recommends against them in expanded volume and in profound hyponatremia.1 The tolvaptan label requires starting it in hospital with close sodium monitoring and warns that a rise over 12 mEq/L in 24 hours can cause osmotic demyelination.8 This is not an ED drug.

Find the cause

StepResultPoints toward
1. Urine osmolality≤ 100 mOsm/kgToo much water for the solute load: primary polydipsia, beer potomania, "tea and toast" diet
> 100 mOsm/kgGo to urine sodium
2. Urine sodium≤ 30 mEq/LLow effective arterial blood volume: true volume loss (such as diarrhea), third spacing, heart failure, cirrhosis, nephrotic syndrome
> 30 mEq/LCheck volume status and diuretic use. Renal sodium loss (diuretics, especially thiazides; primary adrenal insufficiency; kidney disease; cerebral salt wasting) or, if euvolemic, SIAD or secondary adrenal insufficiency

Sequence from the European guideline. Use it with caution in kidney disease and in patients on diuretics, because urine values no longer reflect the usual hormonal control.1

  • SIAD is a diagnosis of exclusion. Essential criteria: effective osmolality under 275 mOsm/kg, urine osmolality over 100, clinical euvolemia, urine sodium over 30 on normal salt and water intake, no adrenal, thyroid, pituitary or renal insufficiency, and no recent diuretics.1
  • Common SIAD triggers: nausea, pain, stress, anesthesia and drugs; small cell lung cancer; pneumonia and other lung disease; subarachnoid hemorrhage and other brain disease.1 SSRIs and MDMA are also listed causes.3
  • Always consider adrenal insufficiency, primary or secondary.1
  • Low solute intake (beer potomania, "tea and toast", anorexia) limits how much water the kidneys can clear.1

Overcorrection and osmotic demyelination

  • Overcorrection is common. In 1,490 patients admitted with sodium under 120, 41% rose more than 8 mEq/L in 24 hours.9
  • Osmotic demyelination is rare but serious. It occurred in 8 of those 1,490 patients (0.5%). Five had beer potomania, five had hypokalemia, and seven had risen more than 8 mEq/L in a day.9
  • Who overcorrects: in 623 ED patients with sodium under 116, predictors included reduced consciousness, vomiting, severe hypokalemia, dilute urine and a lower starting sodium.10 Younger age, female sex, schizophrenia and urine sodium under 30 also raised the risk.9
  • Watch the urine. A sudden urine output over 100 mL/h means free water is being cleared, so check sodium every 2 hours until it is stable. This is typical after volume repletion, cortisol replacement, or stopping a thiazide.1
  • Demyelination can occur within the limits. A review found 21 cases after correction of 10 mEq/L or less in 24 hours, mostly with starting sodium under 115 plus alcohol use disorder, malnutrition, liver disease or hypokalemia. The authors advise keeping these patients under 8 mEq/L per day and giving thiamine when intake has been poor.11

If sodium rises past the limit

  1. Stop the active treatment as soon as sodium rises more than 10 mEq/L in the first 24 hours or more than 8 in any later 24 hours.1
  2. Relower with an expert. Options are electrolyte-free water (such as D5W) 10 mL/kg over 1 hour with close urine output monitoring, and/or desmopressin 2 µg IV, repeated no more often than every 8 hours.1

The US panel starts relowering earlier for patients whose starting sodium was under 120.4 In 1,450 admissions with sodium under 123, most desmopressin was given reactively, after a change within the limits. The authors favor that reactive approach for average-risk patients and a limit of 8 mEq/L per day for high-risk patients.12

Axial T2-weighted brain MRI with a bright area in the center of the pons, consistent with central pontine myelinolysis
FIG 2Central pontine myelinolysis on MRI. Axial fat-saturated T2 image showing high signal in the central pons. According to the uploader, the patient had alcohol use disorder, presented with sodium 101 mEq/L, and was treated with hypertonic saline. He developed quadriparesis and dysarthria.Jto410 · Wikimedia Commons · CC BY-SA 3.0

How fast is too fast?

European guideline 2014US expert panel 2013
Upper limit, 24 h10 mEq/L (then 8 per day)10–12 mEq/L
High ODS riskSame limit8 mEq/L
Minimum riseNone4–8 mEq/L (4–6 high risk)
Start reloweringOnce the limit is exceededBaseline sodium < 120

European values from the guideline itself.1 US values as summarized in a side-by-side review of both guidelines; high-risk features in the US guideline include hypokalemia, alcoholism, malnutrition and liver disease.4

Sources disagree

Are the limits killing patients? In 3,274 patients with sodium under 120, correction under 6 mEq/L per day was linked to higher in-hospital mortality than 6–10.13 A meta-analysis of 16 cohorts (11,811 patients) linked rapid correction to fewer in-hospital deaths than slow correction (OR 0.67, moderate certainty) without a significant rise in demyelination.14 In 13,988 Kaiser Permanente patients with sodium ≤ 120, faster correction was linked to fewer deaths or delayed neurologic events at 90 days (−9.0 percentage points for > 12 vs < 8 mEq/L).15 All of these are observational and open to confounding by illness severity. Authors from 20 centers in 9 countries argue the limits should stay until better evidence exists.16 Even in the Seethapathy cohort, 5 of 7 patients with pontine myelinolysis had risen 8 mEq/L or less per day.13 Until trials answer this, follow the guideline limits and give extra care to high-risk patients.

Mild chronic hyponatremia

  • "Asymptomatic" may not be harmless. In ED patients with chronic hyponatremia (mean sodium 126), 21.3% came in after a fall, vs 5.3% of matched controls. Gait and attention testing worsened during hyponatremia.17
  • Correcting it in hospital did not change outcomes. In a 2,173-patient randomized trial (sodium under 130), targeted correction normalized sodium more often (60.4% vs 46.2%) but did not reduce 30-day death or rehospitalization (20.5% vs 21.8%).18
  • The European guideline suggests against treating mild hyponatremia with the sole aim of raising sodium.1

Disposition

  • Severe symptoms: manage where close biochemical and clinical monitoring is available.1
  • Hemodynamic instability with low volume: same requirement for close monitoring.1
  • Ongoing 3% saline: sodium every 4 hours. Moderate or profound chronic hyponatremia: sodium every 6 hours until stable.1 Plan the bed around that schedule.
  • Tolvaptan can only be started in hospital.8

Pitfalls

  • Delaying hypertonic saline in a seizing or obtunded patient to complete the workup.1
  • Treating a mildly low sodium as the cause of coma. Look for another cause first.1
  • Forgetting glucose. Hyperglycemia lowers measured sodium without hypotonicity.1
  • Not watching urine output after giving fluids to a volume-depleted patient or after stopping a thiazide. The water diuresis can raise sodium faster than any formula predicts.1
  • Ignoring potassium. Hypokalemia was common in patients who developed demyelination, and replacing potassium also raises sodium.9,1
  • Assuming the 10 mEq/L limit is safe for everyone. High-risk patients have developed demyelination within it.11,13

How strong is the evidence?

Nearly every European treatment recommendation is graded D, meaning very low-quality evidence.1 The US panel's recommendations rest on expert consensus and published data.2 There are only two relevant randomized trials: SALSA compared bolus with infusion delivery and was not powered for demyelination5,6, and the 2026 inpatient trial tested correcting chronic hyponatremia.18 The debate about correction speed rests entirely on observational data.14,15,16

On-shift teaching

Questions to ask a learner at the bedside. Tap a question to see the answer. Every answer uses facts cited above.

Q1A patient with sodium 118 is seizing. What do you give, and when do you stop?
3% saline 150 mL IV over 20 minutes, repeated up to twice with a sodium check after each, until sodium is up 5 mEq/L. Then stop hypertonic saline if symptoms improve.1
Q2What are the European correction limits, and what do US experts do differently for high-risk patients?
No more than 10 mEq/L in the first 24 hours and 8 mEq/L in each 24 hours after.1 The US panel uses 8 mEq/L per day for high-risk patients, such as those with hypokalemia, alcoholism, malnutrition or liver disease.4
Q3Which bedside sign warns that sodium is about to overshoot?
Urine output suddenly over 100 mL/h, as after volume repletion, cortisol replacement or stopping a thiazide. Check sodium every 2 hours until it is stable.1
Q4Sodium has risen 13 mEq/L in 20 hours. What are the options?
Stop active treatment. With expert input, give electrolyte-free water 10 mL/kg over 1 hour and/or desmopressin 2 µg IV, no more often than every 8 hours.1
Q5Urine osmolality is 80 mOsm/kg. What does that tell you?
At 100 mOsm/kg or less, the kidneys are diluting maximally. Think of too much water for the solute load: primary polydipsia, beer potomania or a "tea and toast" diet.1
Q6Did bolus therapy overcorrect more often than slow infusion in SALSA?
No. Overcorrection was 17.2% with boluses vs 24.2% with infusion (not significant), and boluses needed relowering less often (41.4% vs 57.1%).5 No patient developed demyelination, so the trial cannot prove safety.6

References

  1. 1
    Spasovski G, Vanholder R, Allolio B, et al.; Hyponatraemia Guideline Development Group. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transplant. 2014;29(Suppl 2):i1–i39. Also published in Eur J Endocrinol. 2014;170(3):G1–G47 and Intensive Care Med. 2014;40(3):320–331.GuidelinePMID 24569496DOIPMID 24569125Full text read (copy of the publisher's free PDF)
  2. 2
    Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013;126(10 Suppl 1):S1–S42.ConsensusPMID 24074529PubMed record; full text not openly accessible
  3. 3
    Nickson C. Hyponatraemia. Life in the Fast Lane, Critical Care Compendium; updated June 2025.FOAMlitfl.comPage read
  4. 4
    Hoorn EJ, Zietse R. Diagnosis and treatment of hyponatremia: compilation of the guidelines. J Am Soc Nephrol. 2017;28(5):1340–1349.ReviewPMID 28174217PMCPubMed; full text read on PMC
  5. 5
    Baek SH, Jo YH, Ahn S, et al. Risk of overcorrection in rapid intermittent bolus vs slow continuous infusion therapies of hypertonic saline for patients with symptomatic hyponatremia: the SALSA randomized clinical trial. JAMA Intern Med. 2021;181(1):81–92.RCTPMID 33104189PMCPubMed
  6. 6
    Rezaie S. The SALSA trial: symptomatic hyponatremia and hypertonic saline. REBEL EM; May 6, 2021.FOAMrebelem.comPage read
  7. 7
    Garrahy A, Dineen R, Hannon AM, et al. Continuous versus bolus infusion of hypertonic saline in the treatment of symptomatic hyponatremia caused by SIAD. J Clin Endocrinol Metab. 2019;104(9):3595–3602.CohortPMID 30882872PubMed
  8. 8
    SAMSCA (tolvaptan) tablets. Prescribing information, boxed warning. Otsuka America Pharmaceutical. DailyMed.Drug labelDailyMedLabel text read
  9. 9
    George JC, Zafar W, Bucaloiu ID, Chang AR. Risk factors and outcomes of rapid correction of severe hyponatremia. Clin J Am Soc Nephrol. 2018;13(7):984–992.CohortPMID 29871886PMCPubMed
  10. 10
    Woodfine JD, Sood MM, MacMillan TE, Cavalcanti RB, van Walraven C. Derivation and validation of a novel risk score to predict overcorrection of severe hyponatremia: the Severe Hyponatremia Overcorrection Risk (SHOR) score. Clin J Am Soc Nephrol. 2019;14(7):975–982.CohortPMID 31189541PMCPubMed
  11. 11
    Tandukar S, Sterns RH, Rondon-Berrios H. Osmotic demyelination syndrome following correction of hyponatremia by ≤10 mEq/L per day. Kidney360. 2021;2(9):1415–1423.ReviewPMID 35373113PMCPubMed
  12. 12
    MacMillan TE, Cavalcanti RB. Outcomes in severe hyponatremia treated with and without desmopressin. Am J Med. 2018;131(3):317.e1–317.e10.CohortPMID 29061503PubMed
  13. 13
    Seethapathy H, Zhao S, Ouyang T, et al. Severe hyponatremia correction, mortality, and central pontine myelinolysis. NEJM Evid. 2023;2(10):EVIDoa2300107.CohortPMID 38320180PubMed
  14. 14
    Ayus JC, Moritz ML, Fuentes NA, et al. Correction rates and clinical outcomes in hospitalized adults with severe hyponatremia: a systematic review and meta-analysis. JAMA Intern Med. 2025;185(1):38–51.Meta-analysisPMID 39556338PMCPubMed
  15. 15
    Mark DG, Alavi M, Nugent JR, Reed ME; Kaiser Permanente CREST Network Investigators. Sodium correction rates and associated outcomes among patients with severe hyponatremia: a retrospective cohort study. Ann Intern Med. 2026;179(3):330–339.CohortPMID 41587479PubMed
  16. 16
    Sterns RH, Rondon-Berrios H, Adrogué HJ, et al.; PRONATREOUS Investigators. Treatment guidelines for hyponatremia: stay the course. Clin J Am Soc Nephrol. 2024;19(1):129–135.ReviewPMID 37379081PMCPubMed
  17. 17
    Renneboog B, Musch W, Vandemergel X, Manto MU, Decaux G. Mild chronic hyponatremia is associated with falls, unsteadiness, and attention deficits (case-control study). Am J Med. 2006;119(1):71.e1–71.e8.CohortPMID 16431193PubMed
  18. 18
    Refardt J, Potasso L, Pelouto A, et al. A randomized trial of targeted hyponatremia correction in hospitalized patients. NEJM Evid. 2026;5(3):EVIDoa2500086.RCTPMID 41733398PubMed
  19. 19
    Farkas J. Hyponatremia. Internet Book of Critical Care, EMCrit. Further reading; not used for any claim above.FOAMemcrit.orgLink checked
How this page was made
  • Written from scratch. No source text was copied; facts are restated and cited.
  • The anchor is the 2014 European clinical practice guideline (ESE, ESICM and ERA-EDTA), published in three journals. Its full text was read from a copy of the publisher's free PDF of the Nephrology Dialysis Transplantation version; the publisher site itself blocked automated access. No newer guideline from these societies was found in PubMed. The 2013 US expert panel full text was not openly accessible, so its positions come from a peer-reviewed side-by-side review of both guidelines (full text read on PMC) and from its abstract.
  • Each PubMed citation was resolved through NCBI E-utilities, and each number was checked against that paper's abstract. The tolvaptan warning was checked on its FDA label. Doses for hypertonic saline and desmopressin come only from the European guideline.
  • Sources searched: PubMed, the European guideline, DailyMed, REBEL EM, LITFL, Wikimedia Commons. Adults only; children are not covered.
  • Figure 1 was drawn for this page from the guideline's schedule. Figure 2 is an openly licensed image from Wikimedia Commons, credited under it, and keeps its own license.
  • Not for clinical use until physician review.
Not for clinical use

AI-generated draft. Not reviewed by a physician. This page is for education only and may contain errors, including in doses. Do not use it to diagnose, treat or make decisions about any patient. Rely on your own clinical judgment, your institution's protocols and current drug labeling. Reading this page does not create a physician-patient relationship. Full terms