Pathophysiology & Risk Factors

Serum sodium >145 mEq/L. Water shifts out of cells down the osmotic gradient, shrinking brain cells ("dried-out raisins") and driving the neurologic picture. The usual mechanism in hospitalized clients is a free water deficit — not enough water in, too much water out, or hypertonic fluids in.

152 · Symptomatic

168 · Severe / chronic

Hyponatremia

Normal Na+

Hypernatremia (>145)

120

135

145

175

mEq/L

Signs & Symptoms

EarlyProgresses →

Intense thirst Hallmark

Unreliable if sedated or cognitively impaired

Restlessness

Irritability

Dry, flushed skin

Dry, sticky mucous membranes

Poor skin turgor

Late / Severe

Confusion

Lethargy

Decreased level of consciousness

Seizures

Late in hypernatremia (lethargy/confusion come first)

Coma

Diagnostics & Labs

Diagnostic

Serum sodiumNa+ > 145 mEq/L

Symptomatic ~152; severe ~168

Serum osmolality> 295 mOsm/kg

Should fall with effective treatment

Urine specific gravity

Elevated >1.030 in dehydration

Dilute urine despite high serum Na+SG < 1.005

Mismatch is the clue to diabetes insipidus

Monitor

Serial serum sodiumevery 4-6 hr during correction

Strict intake and output

Daily weights

Neurologic status

Earliest sign of overcorrection cerebral edema

Interventions & Priorities

Administer prescribed hypotonic IV fluid Hallmark

0.45% NaCl or D5W

Limit correction to 10-12 mEq/L per 24 hr

Faster shift risks fatal cerebral edema

Neuro checks every 2 hr during infusion

Deteriorating LOC = earliest overcorrection sign

Recheck serum sodium every 4-6 hr

Encourage oral free water when safe to swallow

Give scheduled free water flushes for tube feeds

Corrects the underlying free-water deficit

Seizure precautions

Aspiration precautions for altered LOC

Treatments & Medications

0.45% sodium chloride

Hypotonic — supplies free water

D5W

Free water once dextrose is metabolized

Desmopressin (DDAVP)

Central diabetes insipidus only — replaces deficient ADH

Avoid 0.9% normal saline for correction

Isotonic; no free water, will not lower serum Na+

Avoid 3% hypertonic salineHold

Raises sodium further — contraindicated here

Patient Teaching

Maintain consistent daily fluid intake

Offer fluids proactively to at-risk elders

Thirst is blunted with age

Report decreased urination or dark urine

Take desmopressin exactly as prescribed in DI

Report new confusion or marked drowsiness

Complications

Cerebral edema from rapid correction Hallmark

Water rushes into shrunken brain cells

Severe dehydration

Permanent neurologic injury

Coma

Report Nowescalate immediately

New or worsening seizures

Declining level of consciousness

May signal overcorrection cerebral edema

Sodium falling faster than 10-12 mEq/L per 24 hr> 12 mEq/L/24 hr drop

Serum sodium ≥ 160 mEq/LNa+ ≥ 160 mEq/L

Massive dilute urine output

Ongoing free water loss — suspect diabetes insipidus

Rising serum osmolality on treatment

Hypernatremia worsening despite therapy

Clinical Pearl

Hypernatremia = dried-out brain cells — think raisins. Correct slowly (no more than 10-12 mEq/L per 24 hr) or those raisins swell into grapes too fast and you get cerebral edema.

Hypernatremia