HYPERNATREMIA

HYPERNATREMIA - Fae Gwen B. Ganiron, BS, PharmD; Joshua M. V. Mammen, MD
BASICS
DESCRIPTION
• Serum sodium (Na) concentration level >145 mEq/L and usually represents a state of hyperosmolality. Hypernatremia results from primary Na+ gain or water deficit.
• Hypernatremia may exist with hypo-, hyper-, or euvolemia.
• Hypovolemic hypernatremia: Most common type; occurs with a decrease in total body water (TBW) and a lesser decrease in total body Na.
• Euvolemic hypernatremia: Increase in TBW with normal total body Na.
• Hypervolemic hypernatremia: Increase in total body Na and a lesser increase in TBW.
ALERT
Geriatric Considerations
• More common in the hospitalized patient, resulting in a higher morbidity or mortality.
• Hypernatremia may be caused by dehydration due to administration of loop diuretics.
• Increased risk occurs because of impaired renal function and decline in thirst mechanism.
• Chronically ill patients are at higher risk due to consumption of high-solute formulas.
Pediatric Considerations
• May occur in low-birth-weight newborns.
• May result from improper preparation of infant formula or high concentration of Na in breast milk.
GENERAL PREVENTION
• Treatment or prevention of underlying cause
• Avoid preparing infant formula at home, and never add salt to any commercial infant formula.
• Keep well hydrated.
EPIDEMIOLOGY
Incidence
• Common in elderly, infants, and children
• Gastroenteritis with diarrhea is the most common cause of hypernatremia in infants.
Prevalence
Females are at an increased risk due to their decreased TBW.
RISK FACTORS
• Children
• Elderly
• Patients who are intubated or have altered mental status
Genetics
Some diabetes insipidus may be hereditary.
ETIOLOGY
• Excess Na (increase in total body Na) resulting from
- Incorrect infant formulary preparation
- Salt given as punishment or as a prank
- Sea water ingestion
- Excessive use of NaHCO3 as an antacid
- IV NaCl or NaHCO3 during cardiopulmonary resuscitation, metabolic acidosis, or hyperkalemia
- Intrauterine NaCl for abortion
- Excessive Na in dialysate solutions
- Disorders of the adrenal axis (Cushing syndrome, Conn syndrome, congenital adrenal hyperplasia)
• Water deficit (total body Na normal) resulting from
- Adipsia (e.g., impaired thirst regulation, decreased access to water)
- Increased urine water loss (e.g., diabetes insipidus)
- Increased insensible water loss (e.g., fever, hyperventilation, hypermetabolic state, sweat, severe burns, heat exposure, newborns under radiant warmers)
• Hypotonic fluid loss (total body Na decreased) resulting from
- Loss of fluid containing Na without adequate water replacement
• Urinary loss
- Osmotic diuretics
- Diabetes mellitus
- Diuresis from acute tubular necrosis (ATN) or from relief of acute urinary obstruction
• GI loss
- Diarrhea, especially in children


DIAGNOSIS
SIGNS AND SYMPTOMS
• Varies with the underlying disorder and extent of hypernatremia
• Cardiovascular: Sinus tachycardia, hypotension, orthostatic hypotension
• Dermatologic: Decreased skin turgor, cool skin, dry sticky mucous membranes, gray skin, fever
• GI: Excessive thirst, nausea and vomiting (common in infants and children), diarrhea
• Musculoskeletal: Muscle cramps and weakness
• Neurologic: Altered mental status, restlessness, mania, irritability, lethargy, coma, hemiparesis, seizures (symptomatic when Na >160 mEq/L), hyperreflexia, high-pitched cry, chorea, muscle twitching
• Ophthalmic: Sunken eyes
• Respiratory: Dyspnea
• Urologic: Oliguria or anuria, polyuria (suspect diabetes insipidus in the absence of osmotic diuresis)
History
• Obtain list of current and recent medications.
• Obtain history of recent illnesses and activities.
TESTS
• Serum Na and osmolality
• Urine Na and osmolality
• Urinalysis
• Serum glucose
• Special tests
- Water deprivation (with diabetes insipidus, urine osmolality does not increase when hypernatremic)
- Antidiuretic hormone (ADH) stimulation (with nephrogenic diabetes insipidus, urine osmolality does not increase after ADH or DDAVP)
Lab
• Serum Na >150-170 mEq/L (>150-170 mmol/L): Usually dehydration
• Serum Na >170 mEq/L (>170 mmol/L): Usually diabetes insipidus
• Serum Na >190 mEq/L (>190 mmol/L): Usually chronic salt ingestion
• Diabetes insipidus
- Urine osmolality less than serum osmolality
- Urine Na usually low
- Polyuria
- Neurogenic vs. nephrogenic diabetes insipidus
• Hyperosmolar coma
- Blood sugar elevated
- Decreased urine output
- Increased urine osmolality
• Salt ingestion
- Increased urine Na
- Increased urine osmolality
• Hypertonic dehydration
- Decreased urine Na
- Increased urine osmolality
ALERT
A variety of medications may raise or lower Na levels. Refer to a laboratory test reference.
Imaging
CT or MRI in diabetes insipidus to rule out craniopharyngioma, tumor, or median cleft syndrome
Diagnostic Procedures/Surgery
History, physical, laboratory studies, family history for neurogenic diabetes insipidus
DIFFERENTIAL DIAGNOSIS
• Diabetes insipidus
• Hyperosmotic coma
• Salt ingestion
• Hypertonic dehydration
TREATMENT
GENERAL MEASURES
• Appropriate healthcare: Inpatient (many patients are already hospitalized, and hypernatremia develops after admission)
• Treat hypovolemia 1st, then treat hypernatremia.
• Water replacement orally, if patient is conscious
• Restore intravascular volume with IV fluids to normalize serum Na levels
• Calculated water deficit (liters) = [(0.6  wt)  (Na - 140)]  140
- Note: wt = weight in kilograms; Na = current serum Na.
• Dialysis: Especially with serum Na >200 mEq/L (200 mmol/L)
• Speed of correction depends on severity of symptoms or rate of development of hypernatremia.
Diet
• Ensure proper nutrition during acute phase.
• After resolution of acute phase, may want to consider Na-restricted diet for patient
• Severe salt restriction in nephrogenic diabetes insipidus
Activity
Bed rest until stable or underlying condition resolved or controlled
MEDICATION (DRUGS)
First Line
• Hypovolemia
- Isotonic saline (normal saline or Ringer's lactate): 10-20 mL/kg IV over 1-2 hours. May repeat if 10% dehydration
- Isotonic fluids: 5% dextrose with half-normal saline until urine output established
• Hypernatremia
- Hypotonic fluids (NaCl or dextrose 5% in water)
- Decrease serum Na by 0.5 mEq/L/hr (0.5 mmol/L/hr) or by no more than 20 mEq/L/d (20 mmol/L/d). Allows idiogenic osmoles to resolve (mostly taurine in brain cell water)
- Hypocalcemia may occur during correction of hypernatremia. Add calcium (50 mg/kg 10% calcium gluconate) to IV fluids.
- Acidosis often is present in severely dehydrated patients. Add sodium bicarbonate, 50 mEq/L, to IV fluids. If both acidosis and hypocalcemia are present simultaneously, correct the calcium deficit 1st.
- Potassium and phosphate, if needed
• Neurogenic diabetes insipidus (DI)
- Desmopressin (DDAVP) acetate: Adults 10-40 ug intranasally in 1-3 divided doses; children 5-30 ug in a single evening dose or in 2 divided doses. Oral DDAVP now available, dosage varies
- May use 2.5% dextrose in water if giving large volumes of water in diabetes insipidus or neurogenic diabetes insipidus to avoid glycosuria
• Nephrogenic diabetes insipidus (NDI)
- Chlorothiazide: 10 mg/kg per dose given b.i.d.
- Chlorpropamide: 100-250 mg each morning
• Contraindications: Refer to manufacturer's literature.
• Precautions
- Rapid correction of hypernatremia can cause cerebral or pulmonary edema, seizures, or death. Hypocalcemia often occurs during correction.
- Diabetes insipidus: High rates of dextrose 5% in water can cause hyperglycemia and glucose-induced diuresis.
• Significant possible interactions: Refer to manufacturer's literature.
Second Line
Consider NSAIDs in nephrogenic diabetes insipidus.
FOLLOW-UP
DISPOSITION
Admission Criteria
Symptomatic patient with serum Na >155 mEq/L requires IV fluid therapy.
Discharge Criteria
Stabilization of serum Na level and symptoms are minimal.
Issues for Referral
• Children should be referred to a pediatrician.
• Underlying renal involvement associated with hypernatremia should be seen by a nephrologist.
• Follow-up with primary care physician is essential.
PROGNOSIS
Most recover, but rate of neurologic impairment is high.
COMPLICATIONS
• Central nervous system (CNS) thrombosis or hemorrhage
• Seizures
• Mental retardation
• Hyperactivity
• Chronic hypernatremia: >2 days' duration has higher mortality.
• Serum Na >180 mEq/L (>180 mmol/L): Often results in residual CNS damage
PATIENT MONITORING
• Frequent re-examinations in an acute setting
• Frequent electrolytes
• Urine osmolality and urine output in diabetes insipidus
• Ensure adequate ingestion of calories, because patients may ingest so much water that they feel full and do not eat.
• Daily weights
REFERENCES
1. Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342:1493-99.
2. Barratt T, Avner E, Harmon W, eds. Pediatric Nephrology, 4th ed. Baltimore: Williams  Wilkins; 2000.
3. Kokko J, Tannen R, eds. Fluid and Electrolytes, 3rd ed. Philadelphia: WB Saunders; 1996.
4. Kraft MD, Btaiche IF, Sachs GS, et al. Treatment of electrolyte disorders in adult patients in the intensive care unit. Am J Health-System Pharm., 2005;62:166382.
5. Kugler JP, Hustead T. Hyponatremia and hypernatremia in the elderly. Am Fam Physician. 2000;61:3623-3630.