Hypernatremia means there's too much sodium in the blood. Nurses see it often — especially in very sick and older patients in the hospital, who can't always respond to thirst.
Sodium keeps fluids balanced, helps muscles move, and supports nerve and brain function. When it climbs too high, water shifts out of cells and they shrink — and that's what drives the symptoms. This guide breaks hypernatremia down so you can spot it, find the cause, and correct it safely at the bedside.
Sodium keeps fluids balanced and helps muscles move. Normal serum sodium runs 135–145 mEq/L. Anything above 145 is hypernatremia and can be harmful to cells, graded by severity:
Normal
135–145
mEq/L
Mild
146–150
mEq/L
Moderate
151–159
mEq/L
Severe
> 160
mEq/L
Acute vs Chronic Hypernatremia
Before treating, you need to know whether sodium rose fast or slow — it changes how aggressively it can be corrected.
Acute (< 48 hours)
Sodium climbed quickly within the last 2 days. Brain cells don't have time to adapt, so this is treated more urgently.
Chronic (> 48 hours)
Sodium rose slowly over more than 2 days, so cells have time to adapt. It must be corrected slowly and carefully — nearly all hypernatremia is chronic.
Why it matters: in chronic hypernatremia, brain cells have adapted to the high-sodium state. Lowering sodium too fast pulls water back into those cells and causes cerebral edema — which can be deadly. Read more about osmotic demyelination and sodium correction here.
Causes of Hypernatremia
Hypernatremia always has an underlying cause, like every electrolyte abnormality. Most cases come down to losing water or not taking in enough. Here are the usual suspects:
Fluid Loss
Losing too much water drives sodium up: increased sweating, vomiting or osmotic diarrhea, and excessive urination — often from high blood sugar, certain medicines, or diabetes insipidus.
Decreased Water Intake
Some patients don't feel thirsty or can't drink enough. Older or very sick patients may simply not take in enough water, letting sodium climb.
Water Shifts
After heavy exertion or a seizure, water can shift into cells, transiently raising serum sodium.
Too Much Sodium
Rare, but eating or receiving excessive salt (e.g., hypertonic saline, sodium bicarbonate) can cause hypernatremia.
"Adipsic" Diabetes Insipidus
The body doesn't make enough ADH and the person doesn't feel thirsty. These patients become hypernatremic more often and may not notice symptoms because the change is gradual.
Nursing Assessment of Hypernatremia
Hypernatremia often comes with tell-tale signs. Many are neurologic, driven by brain cells shrinking as water leaves them.
Common symptoms
Thirst
Patients can feel intensely thirsty — the body is demanding water to dilute the high sodium.
Dry Mouth
Dry mouth and other mucous membranes — including dry eyes and nose — from too little body water.
Restless & Irritable
The nervous system is hypersensitive when sodium is too high, so patients may be restless or easily annoyed.
Muscle Twitching
Sodium is needed for normal muscle function; too much can make muscles twitch.
Altered Mental Status
Patients may get confused or disoriented. In severe cases they can become unconscious.
Seizure
When sodium is very high, brain cells get overactive, which can trigger a seizure.
Don't Forget Fall Risk
Restlessness, weakness, and altered mental status make these patients a fall risk. Put the bed alarm on and make sure they're in fall-risk socks.
Physical assessment
Vital Signs
Watch for hypertension and tachycardia as the body tries to compensate for dehydration.
Neuro Assessment
Hypernatremia affects the nervous system — check for restlessness, irritability, or confusion. Severe cases can cause seizures or coma.
Skin Assessment
Look for dehydration clues: dry skin, decreased skin turgor, or sunken eyes.
Treatment for Hypernatremia
Treatment depends on what caused the hypernatremia (similar to hyponatremia). In severe cases, nephrology is typically consulted. It also depends on whether it's chronic (developed over 48 hours ago) or acute (within the last 48 hours) — nearly all patients fall into the chronic category.
Address the Underlying Causethe actual treatment
Find what caused the high sodium. Assessing the patient's fluid balance guides whether they need more or less water. Correction goal: lower serum sodium by about ~10 mEq/L per 24 hours in chronic cases.
IV Fluidsreplace the water deficit
Managing water levels usually means giving more fluids — oral water or a hypotonic solution like 1/2 NS, which dilutes the sodium. A typical starting point is D5W at 100 mL/hr for a 70 kg patient (≈1.35 mL/kg/hr, max 150 mL/hr). Factor in any ongoing fluid losses. Rapid correction (aiming to drop sodium 1–2 mEq/L per hour) is reserved for serious, known-acute cases with seizures or unconsciousness — lowering sodium too fast can cause deadly cerebral edema.
Desmopressin (DDAVP)for central diabetes insipidus
In cases such as central diabetes insipidus, desmopressin (DDAVP) may be ordered to replace the missing ADH and reduce free-water loss.
Correct Too Fast = Cerebral Edema
In chronic hypernatremia the brain has adapted. Dropping sodium too quickly pulls water into brain cells and causes swelling that can be fatal. Stick to the slow correction goal unless the case is truly acute and symptomatic.
Monitoring of Hypernatremia
Monitor closely to confirm sodium is falling at the right rate and to catch complications:
Lab Tests
In acute cases, check sodium (and glucose if giving dextrose) every 1–3 hours. In chronic cases, every 4–6 hours, then every 12–24 hours. Watch patients with ongoing losses more closely.
Neuro Status
Reassess consciousness, orientation, strength, and coordination. Report new confusion, seizures, or loss of consciousness immediately.
Intake & Output
Document I&Os thoroughly to track the patient's fluid balance.
Summary of Hypernatremia
The big picture: hypernatremia is usually caused by dehydration and excess fluid loss. Healthy adults feel thirsty and drink; older or altered patients can't always respond to those cues, so sodium climbs. Symptoms include thirst, dry mouth, muscle twitches, irritability, altered mental status, and even seizures. Treat by addressing the cause and replacing the free-water deficit — usually with hypotonic fluids like D5W — while accounting for ongoing losses. Unlike potassium, magnesium, or calcium, sodium doesn't significantly affect the heart rhythm, so cardiac monitoring is less central here; the danger is neurologic.
Clinical Pearls
1
Hypernatremia is usually a water problem, not a salt problem. Most cases come from losing water or not drinking enough — think dehydration first.
2
Most hypernatremia is chronic. Correct slowly — about 10 mEq/L per 24 hours — to avoid cerebral edema from rapid water shifts.
3
The at-risk patient can't respond to thirst. The elderly, intubated, or altered patient can't ask for water — watch their sodium and I&Os.
4
Sodium rarely causes arrhythmias. Unlike potassium, magnesium, or calcium, the danger here is neurologic — cell shrinkage, not the ECG.
Yikes, thanks for catching that! I’ve updated it! 🙂
TSITSI MUDARE
3 years ago
Thankyou so much well explained i used to think that you can only become hypernatrimic when there is fluid overload not dehydration, so thank you for the insight
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I suppose this was supposed to read, mild, moderate, and severe hypernatremia not hyponatremia. Great teaching though! 👍
HYPERNATREMIA
Normal Levels: 135 – 145 mEq/L
Mild Hyponatremia: 146 – 150 mEq/L
Moderate Hyponatremia: 151 – 159 mEq/L
Severe Hyponatremia: > 160 mEq/L
Yikes, thanks for catching that! I’ve updated it! 🙂
Thankyou so much well explained i used to think that you can only become hypernatrimic when there is fluid overload not dehydration, so thank you for the insight
You’re welcome! Yes, hypernatremia and hyponatremia can both be tricky!
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