Headache, confusion, lethargy; seizures under about 120
Fluid, Electrolyte & Acid-Base · Topic 12 of 23
Hyponatremia
A confused postoperative patient with a sodium of 128 mEq/L doesn't need more fluids — they likely need less.
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Hyponatremia
Na⁺SodiumPriority
K⁺PotassiumWNL
Cl⁻ChlorideL
Ca²⁺CalciumWNL
Mg²⁺MagnesiumWNL
PO₄³⁻PhosphateWNL
ECFVolume (ECF)WNL
pHpHWNL
Bedside monitor · pattern
Hyponatremia
Excess water relative to sodium lowers serum tonicity, so water moves into brain cells.
Direct physiology↓ serum tonicity→Water enters neurons→Cerebral edema
ECG responseNormal sinus rhythm
Neuronal excitabilityNormal
SuppressedBalancedHyper
BrainWater is moving into brain cells. Neuro checks and fall precautions.
PerfusionEuvolemic
106%+0.8 kg
Extracellular volume at baseline. The dashed line marks euvolemia.
What the nurse would notice
Hyponatremia across body systems
Also on this panel
Cramps, weakness, poor coordination
Nausea and vomiting with an acute fall
Concentrated urine if ADH is the cause
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
Present on this panel. Tap any sign to see which values produce it.
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Fluids & Electrolytes · Na⁺
Hyponatremia
Too little sodium for the amount of water. The blood is watered down — and the brain swells first.
Example patient · SIADHSevere · Na⁺ 116
Low sodium swells the brain — raise it slowly
Nurse sees: Na⁺ 116 — below 120: seizures, coma.
Nurse doesSeizure precautions, protect the airway, call now. 3% saline is likely — a small rise of 4 – 6 first, then slow down.
Illustration — one example patient. Speed matters as much as the number: a fast drop to 125 can seize; a slow drift to 125 may barely show.
01 · The numberNa⁺ below 135
mEq/L · normal 135 – 145 · severe below 120
02 · The dangerSeizures
Water shifts into brain cells → cerebral edema (brain swelling)
03 · The fixRaise Na⁺ slowly
No more than 8 – 12 mEq/L in 24 h — faster injures the brainstem
01
What causes it
Watch forClassic exam cause: SIADH
Too much water kept
SIADHlung cancer, head injury, medsHypotonic IV fluids#1 in the hospitalHeart failureCirrhosisPsychogenic polydipsiadrinking huge amounts
Sodium lost
Thiazide diureticsVomiting & diarrheaNG suctionHeavy sweatingAddison's disease
Meds that raise ADH
SSRIsCarbamazepine
Low sodium usually means too much water, not too little salt — so the fix is often less water.
02
What you'll see
SignsOften nothingmild · Na⁺ 130 – 134
Nausea, headache, muscle cramps early
Confusion · lethargy (very sleepy) earlymoderate · Na⁺ 120 – 129
Seizures latesevere · usually Na⁺ below 120
Coma · respiratory arrest late
Volume clues: orthostatic hypotension (BP drops on standing) and dry mouth — or edema (swelling) and JVD (bulging neck veins)tells you which type it is
A fast drop causes symptoms at higher numbers than a slow one.
03
Labs & diagnostics
CheckSerum Na⁺ < 135 mEq/L
Serum Na⁺ < 135 mEq/Lnormal 135 – 145 · severe below 120
Serum osmolality lownormal 275 – 295 mOsm/kg · below 275 = watered-down blood
Urine osmolality and urine Na⁺ high in SIADHthe kidneys hold water they should let go
Volume statusturgor, edema, JVD, orthostatic BP, daily weight — decides the treatment
Repeat Na⁺ during correctionoften every 2 – 4 h on 3% saline — catches overcorrection
04
Red flags
Act nowSeizure report nowprotect the airway · seizure precautions
Na⁺ below 120 or falling fast report now
New confusion or dropping LOC report now
Na⁺ rising too fast report nowmore than 8 – 12 mEq/L in 24 h (newer guidance: more than 10)
Bradycardia (slow HR) with rising BPrising pressure inside the skull
Days after correction: dysphagia (trouble swallowing), slurred speech, weaknessosmotic demyelination — shows up 2 – 6 days later
05
Treatment: match the volume
Volume decidesSame sodium, opposite fixes — volume decides
Do right now
1
→Seizure precautionsif Na⁺ < 120 or neuro signs
2
→Assess volumedry, normal or overloaded?
3
→Stop the causehypotonic IV fluids, thiazides — as ordered
4
Recheck Na⁺often, during correction
Low volumeHypovolemic · Na⁺ lost
0.9% normal saline
Replace the volume and the sodium.
Na⁺ can jump once volume is backNormal volumeEuvolemic · SIADH
Fluid restriction
1,000 – 1,500 mL/day — first line for the watered-down type.
Restrict water, not saltHigh volumeHypervolemic · HF, cirrhosis
Fluid restriction Loop diuretic
Pull off the extra water.
Daily weightsSevere symptoms (seizures, coma) — any volume type
3% saline
Hypertonic NaCl in small IV boluses
on a pump, frequent Na⁺ checks
+4 to 6 first
A small rise stops the symptoms
then slow down
≤ 8 – 12 / 24 h
Speed limit for the whole day
newer guidance ≤ 10 (≤ 8 if high risk)
Doses & special cases
3% NaCl bolus, e.g., 100 – 150 mL over 10 – 20 minrepeated if still symptomatic · recheck Na⁺ after each
High risk for osmotic demyelinationalcohol use, malnutrition, low K⁺, liver disease, Na⁺ below 105 → the slower limit
Rose too fast?the provider may give D5W or desmopressin to bring it back down
Tolvaptan for SIADH or heart failurestarted in hospital — can raise Na⁺ too fast
06
Nursing priorities
In orderAirway and seizure precautionspadded rails, suction ready, bed low — Na⁺ below 120 or neuro changes
Neuro checksLOC, orientation, headache
Assess volume statusdecides fluid restriction vs saline
Fluid restriction as orderedspread across the day · ice chips count
Recheck Na⁺ during correctionreport a rise past the limit
Strict I&O · daily weight
07
Which kind of low sodium?
| What happened | Water kept by ADH |
|---|---|
| Causes | SIADH, hypotonic IV fluids |
| Exam | No edema, normal BP |
| Fix | Fluid restriction |
08
Teach your patient
DischargeStick to the fluid limitall liquids count — soup, ice, gelatin
Don't cut salt unless you're told tothe problem is water, not salt
Report headache, confusion, nausea or muscle cramps
Check meds with your providerthiazides, SSRIs and carbamazepine can lower sodium
Low sodium = swollen, waterlogged brain. Restrict water when it's dilutional, replace sodium slowly — correcting too fast is the real danger.
Sources · Correction limits and 3% saline dosing checked against the Society for Endocrinology emergency guidance (2022) and the European clinical practice guideline (2014). Brain cell drawn from “Complete neuron cell diagram” (LadyofHats, Wikimedia Commons, public domain). Typical adult values — follow your protocol.
Hyponatremia
A confused postoperative patient with a sodium of 128 mEq/L doesn't need more fluids — they likely need less. Correcting hyponatremia too fast can be more dangerous than the imbalance itself.
Hyponatremia is serum sodium below 135 mEq/L. Sodium is the primary extracellular electrolyte controlling water balance, so low sodium really means too much water relative to sodium — the blood is diluted. The most common cause in hospitalized patients is excessive hypotonic IV fluid administration or SIADH (syndrome of inappropriate antidiuretic hormone), where the body retains free water inappropriately. Other causes include diuretic use (especially thiazides), heart failure, and psychogenic polydipsia. Symptoms track with how fast sodium drops, not just how low it goes. Mild (130–134): often asymptomatic. Moderate (120–129): nausea, headache, confusion, lethargy. Severe (<120): seizures, coma, respiratory arrest. Assessment findings reflect cellular swelling from water shifting into cells via osmosis — the brain is most vulnerable because it's confined by the skull. Fluid restriction (typically 1,000–1,500 mL/day) is the first-line nursing intervention for dilutional hyponatremia. For severe symptomatic cases, hypertonic saline (3% NaCl) is given via IV pump with frequent sodium monitoring — correction must not exceed 8–12 mEq/L per 24 hours to prevent osmotic demyelination syndrome (central pontine myelinolysis), an irreversible neurological injury.
Key Distinctions
Don't confuse hyponatremia (confusion, seizures, cellular swelling) with hypernatremia (thirst, dry mucous membranes, cellular shrinkage) — both cause neurological changes but the fluid shift direction is opposite. Students often think hyponatremia means 'give sodium,' but dilutional hyponatremia is treated by restricting water, not adding salt. Osmotic demyelination comes from correcting too fast, not from the low sodium itself — the treatment is the danger.
Clinical Pearl
Low sodium = swollen cells. Think of waterlogged brain tissue pushing against the skull — that's why seizures happen. Restrict water first, replace sodium slowly.
Knowledge Check
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Question 1 of 3
What is the first-line treatment for dilutional hyponatremia?
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Go further
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- GuideFluid and Electrolyte NCLEX Questions: The 7 Patterns the Exam Keeps TestingThe priority is the organ, not the number. Anything changing the ECG comes first. Magnesium before potassium and calcium. Volume before the electrolyte. The lab that is lying. Slow is the rule for correction. The assessment that gates the drug. Learn the seven patterns and the individual questions stop being surprising.
- GuideHyperkalemia ECG Changes in Order: Peaked T Waves to Sine Wave, and What the Nurse Does FirstThe fixed sequence — peaked T, long PR, wide QRS, sine wave — with approximate potassium levels, what IV calcium actually does (protects the heart, does not lower the potassium), the stabilize–shift–eliminate treatment order, and what the nurse monitors. Includes a live ECG you can drag.
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