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KEY
🔍- Deep Dive
📌- Clinical Application
🔸 - Weak Evidence
🔹 - Strong Evidence
📑 - Evidence summaries
✅ - Recommended treatment
⚠️ - Critical Information
Hyponatremia is one of the most common ER diagnoses — and somehow still one of the scariest, thanks to the constant threat of ODS lurking like a jumpscare.
The European Journal of Endocrinology guidelines have become my go-to anchor. Whenever I feel that internal panic bubble up, I go back to these and they work every single time.
Let’s break it down the way I understand it at 2 AM on a busy shift.
1. First Things First: What Exactly Is Hyponatremia?
Very simple:
Serum sodium <135 mmol/L.
Before you do anything, always rule out the easiest mistake: Pseudohyponatremia
Check a capillary blood glucose. Severe hyperglycemia can give you a misleadingly low sodium.
Once that’s off the table, the real thinking begins.
2. Every Hyponatremia in the ER Comes Down to Two Questions
(1) When did this start?
This sounds simple, but it’s rarely clear in the ER.
Technically:
- Acute: <48 hours
- Chronic: >48 hours
But here’s the practical rule I use:
If you’re not sure, always assume chronic.
There are certain situations where the hyponatremia is almost always acute :
- Post-op
- TURP / hysteroscopy with irrigation
- Polydipsia
- Marathon runners
- Recently started thiazides
- MDMA use
- Colonoscopy prep
- IV cyclophosphamide
- Oxytocin, desmopressin, terlipressin, vasopressin
If you have any of these, then yes, call it acute.
(2) How sick is the patient?
Symptoms tell you everything.
Severe symptoms
These are the “no negotiation — act now” signs:
- Vomiting
- Cardiorespiratory distress
- Deep abnormal somnolence
- Seizures
- Coma (GCS ≤ 8)
Moderately severe
- Nausea
- Confusion
- Headache
Asymptomatic
Discovered incidentally.
3. What Are We Trying to Achieve?
No matter what the presentation, my goals are always the same:
- Stabilize the emergency problem
- Protect intravascular volume
- Avoid dropping the sodium further
- Avoid raising it too fast
- Start identifying the cause (or at least not miss obvious clues)
This framework keeps you grounded.
“Six in six hours for severe symptoms, then stop. Six a day makes
sense for safety.”
sense for safety.”
4. Start with your workup
In the ER, diagnosing the exact cause of hyponatremia is unrealistic , but you can set up the diagnosis for the admitting team.
- Serum osmolality
- Urine osmolality
- Urine sodium
- TSH, cortisol
- POCUS for volume status
Combined with a good history- any volume loss, drugs etc , this can narrow things down surprisingly well.
5. So… Should You Give 3% Saline?
The SALSA Randomized Clinical Trial : The RCT compared rapid intermittent bolus (RIB) vs slow continuous infusion (SCI) of hypertonic saline.
Both methods were safe and effective, and their overcorrection rates were similar.
But RIB had two key advantages: fewer cases needed relowering, and sodium correction was achieved faster—often in the first hour.
This makes RIB the preferred option for symptomatic hyponatremia and aligns with current guidelines.
doi:10.1001/jamainternmed.2020.5519
A. If the patient has severe symptoms
This is the easiest decision.
Recheck sodium after bolus (typically 20 minutes)
🔸If needed, repeat - up to three boluses or until the sodium rises by 5 mmol/L. (Weak recommendation)
If the patient improves:
👉 Stop.
Just keep a slow IV fluid running to keep the line patent.
Check serum sodium at 6 and 12 hours
If the patient still has symptoms:
- Start 3% saline infusion to increase sodium at 1 mmol/L/hr
Stop when:
- Symptoms resolve
- OR sodium rises by 10 mmol/L
- OR sodium hits 130 mmol/L
(Whichever happens first.)
Check serum sodium every 4 hours while infusion is running
B. Moderately Severe Symptoms
🔸Give 150 mL 3% NS over 20 minutes
🔹AND treat the underlying cause
Volume-specific care:
- Hypovolemic: Give 0.9% NS
- Hypervolemic: Fluid restriction + IV furosemide
Aim for:
A rise of 5 mmol/L (not more than 10 mmol/L in 24 hours)
Check serum sodium at 1, 6 and 12 hours
C. Asymptomatic Hyponatremia
Acute
If drop >10 mmol/L:
🔸Give 150 mL of 3% NS over 20 minutes.
Otherwise:
🔹Fix the cause
- Avoid overcorrection
Check serum sodium every 4 hours till sodium has stabilised.
Chronic
- Treat cause
🔸Restrict fluid intake in moderate to profound hyponatremia
🔹Defend volume with 0.5–1 mL/kg/hr 0.9% NS if hypovolemic
🔹No vaptans in the ER
Check serum sodium every 6 hours till sodium has stabilised.
Correcting hypokalemia raises sodium automatically.
If both Na⁺ and K⁺ are low, replacing potassium can bump up sodium even without hypertonic saline
Overcorrection?
RULE OF 100
Monitoring the urine output will be the deciding factor
in preventing overcorrection
in preventing overcorrection
- Insert a foley catheter and monitor
- If urine output >100cc/hour, send STAT urine Osmolarity
and sodium
- If urine osmolarity<100, consider IV 1mcg Desmopressin (after discussion with specialists)
🔹Re-lower serum sodium concentration if it increases 10 mmol/l during the first 24 h
Discontinue the ongoing active treatment.
Discontinue the ongoing active treatment.
Discuss with specialist about:
- Infusion of 10 ml/kg body weight of electrolyte-free water over 1 h under strict monitoring.
- IV Desmopressin 2 mcg
Consider DDVAP clamp technique
Administration of DDAVP prevents the kidneys from secreting free water. This takes the kidneys out of the equation, preventing the patient from auto-correcting.
Final Thoughts
Hyponatremia can be intimidating, but it doesn’t have to freeze you. Once you divide it into:
- acute vs chronic, and
- severity of symptoms
the treatment pathway becomes surprisingly straightforward.
The main enemy is overcorrection — not the initial low number.
If your actions raise sodium by 5 mmol/L and improve symptoms, you’ve already won more than half the battle.
Want to Read More?
Goce Spasovski, Raymond Vanholder, Bruno Allolio, on behalf of the Hyponatraemia Guideline Development Group, Clinical practice guideline on diagnosis and treatment of hyponatraemia, European Journal of Endocrinology, Volume 170, Issue 3, Mar 2014, Pages G1–G47, https://doi.org/10.1530/EJE-13-1020
Baimel, M, Etchells, E, Helman, A. Emergency Management of Hyponatremia. Emergency Medicine Cases. March, 2015. https://emergencymedicinecases.com/episode-60-emergency-management-hyponatremia/. Accessed [date].
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. doi:10.1001/jamainternmed.2020.5519
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