Restlessness, irritability, confusion; seizures when severe
Fluid, Electrolyte & Acid-Base · Topic 13 of 23
Hypernatremia
The confused elderly patient who "just stopped drinking water" after hip surgery may not have a neuro problem — they may have a sodium of 152 mEq/L that nobody checked.
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Hypernatremia
Na⁺SodiumPriority
K⁺PotassiumWNL
Cl⁻ChlorideH
Ca²⁺CalciumWNL
Mg²⁺MagnesiumWNL
PO₄³⁻PhosphateWNL
ECFVolume (ECF)L
pHpHWNL
Bedside monitor · pattern
Hypernatremia
Too little water relative to sodium raises serum tonicity, pulling water out of brain cells.
Direct physiology↑ serum tonicity→Water leaves neurons→Cellular dehydration
ECG responseNormal sinus rhythm
Neuronal excitabilityNormal
SuppressedBalancedHyper
BrainWater is being pulled out of brain cells. Expect thirst and restlessness first.
PerfusionHypovolemic
90%−1.4 kg
Orthostatic drop, flat neck veins, dry mucous membranes, BUN:creatinine climbing past 20:1. Fall precautions — they will be dizzy standing up.
What the nurse would notice
Hypernatremia across body systems
Also on this panel
Thirst, dry sticky mucous membranes, flushed skin
Weakness, twitching, hyperreflexia
Dilute urine in DI, concentrated urine with other water loss
Teaching model, not a clinical calculator. Patterns show high-yield directional relationships under the stated assumption. Real symptoms, ranges and treatment depend on cause, acuity, comorbidities and local protocols.
Signs & symptoms
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Fluids & Electrolytes · Na⁺
Hypernatremia
Too little water for the amount of sodium. The blood is concentrated — and the brain shrinks first.
Correction clock · example patient on D5W160Na⁺ mEq/L
Na⁺ 160 → 148 in 24 h. About 0.5 mEq/L per hour — lowered 12 is the day's limit.
01 · The numberNa⁺ above 145
mEq/L · normal 135 – 145 · usually too little water, not too much salt
02 · The dangerSeizures
Brain cells shrink → confusion, lethargy, seizures, coma · neuro checks + seizure precautions
03 · The fixReplace free water slowly
Water by mouth, or D5W / 0.45% saline IV · lower Na⁺ no more than 10 – 12 mEq/L in 24 h (≈ 0.5 per hour)
01
Slide the sodium. Watch the brain shrink.
Try it140Na⁺ mEq/LNormal
Brain vs skullFills the skullcells hold their normal size
140145150160170
Illustration. Water leaves the brain cells, so the brain pulls away from the skull and stretches the veins that bridge the gap. Correct too fast and water rushes back in — the brain swells.
02
What causes it
Watch forUsually a water problem (free water deficit), not a salt problem
Too little water in
Older adultsblunted thirstCan't reach or ask for watersedated, intubated, confusedTube feeds without water flushesPost-op patients
Too much water out
Diabetes insipidushuge amounts of dilute urineFever & heavy sweatingBurnsDiarrhea
Sodium added
Hypertonic IV fluidse.g., 3% saline
A missed or delayed desmopressin dose in central diabetes insipidus can cause life-threatening dehydration and hypernatremia.
03
What you'll see
SignsThirst earliestolder, sedated, intubated or confused patients may not feel or report it
Dry, sticky mucous membranes · dry, flushed skin early
Restlessness · irritability early
Confusion · lethargy (very sleepy)follow as the sodium climbs
Seizures · coma late
Urine clue: large amounts of pale, dilute urinepoints to diabetes insipidus — plain dehydration makes scant, dark urine
A fast rise causes symptoms at lower numbers than a slow one.FRIED SALT a common memory aidFFever (low-grade) · flushed skinRRestlessIIncreased fluid retention · increased BPsodium gain only (e.g., hypertonic IV fluid)EEdemasodium gain only (e.g., hypertonic IV fluid)DDecreased urine output · dry, sticky mouthdiabetes insipidus: large amounts of dilute urine insteadSSkin flushed and dryAAgitation · irritabilityLLow-grade feverfever and sweating also cause itTThirst — the earliest signI and E apply only when sodium was gained (hypertonic fluid). Most hypernatremia is water loss — no edema, and the BP is normal or low (low BP + fast pulse → 0.9% saline first).
04
Labs & diagnostics
CheckSerum Na⁺ > 145 mEq/L
Serum Na⁺ above 145 mEq/Lnormal 135 – 145 · mild 146 – 149 · moderate 150 – 159 · severe above 160 (an emergency)
Serum osmolality highnormal 275 – 295 mOsm/kg
Urine specific gravitynormal 1.005 – 1.030 · dehydration: high (concentrated) · diabetes insipidus: below 1.005 (dilute) despite the high Na⁺
Recheck Na⁺ about every 4 h during correctioncatches a fall that is too fast
05
Red flags
Act nowSeizure report nowprotect the airway · seizure precautions
New confusion or dropping LOC report now
During correction: new headache, falling LOC or seizure report nowcerebral edema from correcting too fast — stop the IV fluid, call the provider
Na⁺ falling too fast report nowmore than 10 – 12 mEq/L in 24 h (newer guidance: more than 10)
Low BP with a fast pulsevolume first — 0.9% saline before free water
Large volumes of dilute urinediabetes insipidus — check that desmopressin was given on time
06
Treatment: give back the water, slowly
Free waterReplace free water — lower Na⁺ no more than 10 – 12 mEq/L in 24 h
Do right now
1
→Seizure precautionsneuro signs or severe Na⁺
2
→Check BP and pulselow BP + fast pulse → 0.9% saline first
3
→Replace free waterby mouth, or D5W / 0.45% saline as ordered
4
Recheck Na⁺ about every 4 hreport a fall faster than the limit
Free waterThe fix for most patients
Oral water D5W 0.45% saline
Water by mouth when they can swallow safely; a hypotonic IV fluid as prescribed.
Lower ≤ 10 – 12 mEq/L in 24 hVolume firstLow BP · fast pulse
0.9% normal saline
Restore perfusion with isotonic saline, then replace free water.
Saline alone won't lower Na⁺Replace ADHCentral diabetes insipidus
Desmopressin (DDAVP)
Replaces the missing ADH so the kidneys hold water again.
Never miss or delay a doseHow fast to lower it
≈ 0.5 mEq/L per hour
About half a mEq/L per hour
recheck Na⁺ about every 4 h
≤ 10 – 12 mEq/L in 24 h
Speed limit for the whole day
newer guidance ≤ 10
Too fast → brain swells
Water rushes into shrunken brain cells
cerebral edema — headache, falling LOC, seizure
Special cases
0.9% saline and 3% saline don't lower sodium0.9% has no free water; 3% raises Na⁺ further
Severe (above 160) is managed as a medical emergency
How long to takerose within the last day → correct over 24 h · chronic or unknown → over about 48 h
Symptomatic and less than 48 h oldthe provider may lower it faster at first
07
Nursing priorities
In orderAirway and seizure precautionspadded rails, suction ready, bed low
Neuro checksLOC, orientation, restlessness — before and during correction
Check BP and pulselow BP + fast pulse → volume first
Give free water as orderedoffer water on a schedule if they can swallow
Recheck Na⁺ about every 4 hreport a fall faster than 10 – 12 in 24 h
Strict I&O · daily weightwatch for large volumes of dilute urine
08
Low or high sodium?
| The number | Na⁺ above 145 · severe above 160 |
|---|---|
| Usual problem | Too little water |
| Brain cells | Shrink |
| Early signs | Thirst, dry sticky mucous membranes, restlessness |
| Fix | Free water — D5W or 0.45% saline |
| Speed limit | Lower ≤ 10 – 12 mEq/L in 24 h |
| Too fast causes | Cerebral edema (brain swelling) |
09
Teach your patient
DischargeDrink on a schedule — don't wait for thirstfamilies of older adults: offer fluids regularly
Take desmopressin exactly as prescribeddiabetes insipidus — never skip or delay a dose
Report heavy urination, intense thirst or confusion
Tube feeds: give the ordered water flushes
High sodium = shrunken, dried-out brain. Give back free water, lower sodium slowly — too fast and the brain swells.
Sources · Correction limits and free-water replacement checked against StatPearls: Hypernatremia, the Merck Manual: Hypernatremia and the Society for Endocrinology diabetes insipidus guidance (2018); signs and nursing care from OpenStax Medical-Surgical Nursing 10.3 and OpenStax Pharmacology 5.2; lab ranges from MedlinePlus (urine specific gravity, osmolality); diabetes insipidus from the Merck Manual. Typical adult values — follow your protocol.
Hypernatremia
The confused elderly patient who "just stopped drinking water" after hip surgery may not have a neuro problem — they may have a sodium of 152 mEq/L that nobody checked.
Hypernatremia is serum sodium >145 mEq/L. The most common cause in hospitalized patients is free water deficit — the patient isn't drinking enough, has insensible losses (fever, burns, mechanical ventilation), or is receiving hypertonic solutions. Diabetes insipidus (central or nephrogenic) causes massive dilute urine output with rising serum sodium because ADH is absent or ineffective. The hallmark presentation is neurological: restlessness and irritability progress to confusion, lethargy, seizures, and coma as water shifts out of brain cells, causing cellular shrinkage. Thirst is a key early sign but is unreliable in sedated, intubated, or cognitively impaired patients. Assessment includes strict I&O, daily weights, urine specific gravity (elevated >1.030 in dehydration, paradoxically low <1.005 in diabetes insipidus), and monitoring serum osmolality (elevated >295 mOsm/kg). Correction must be gradual — sodium should decrease no faster than 10-12 mEq/L per 24 hours. Rapid correction causes water to rush into shrunken brain cells, producing cerebral edema. The primary nursing intervention is administering hypotonic IV fluids (0.45% NaCl or D5W) as prescribed and encouraging oral free water intake when safe. Seizure precautions are essential for significantly elevated sodium levels.
Key Distinctions
Don't confuse hypernatremia (dry, flushed, restless, thirsty) with hyponatremia (confused, nauseated, headache — which can be hypovolemic, euvolemic, or hypervolemic) — both cause neuro changes but the sodium and osmolality directions are opposite. Students mix up the correction danger: too-fast correction of hypernatremia causes cerebral edema, while too-fast correction of hyponatremia causes osmotic demyelination. In diabetes insipidus the urine is dilute despite high serum sodium — that mismatch is the diagnostic clue.
Clinical Pearl
Hypernatremia = dried-out brain cells. Think raisins. Correct slowly or those raisins swell into grapes too fast and you get cerebral edema.
Knowledge Check
3 quick questions on the must-knows for this topic.
Question 1 of 3
Which IV fluid is prescribed to treat hypernatremia?
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