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Emergency And Acute Medicine: Hypernatremia
Basics
Description Hypernatremia is defined as a serum sodium concentration >145 mEq/L. Mild hypernatremia is 146–155 mEq/L, while severe hypernatremia is >155 mEq/L and is associated with high morbidity and mortality.
Etiology Hypernatremia is categorized by volume status. Hypovolemic hypernatremia is the most common and results from loss of water and sodium with proportionally greater water loss. Causes include renal failure, diuretics, lactulose, osmotic diuresis (mannitol, glucosuria, high-protein feeds), insensible losses (burns, sweating), respiratory losses, impaired thirst, lack of access to water, diarrhea, vomiting, and intubation. Isovolemic hypernatremia results from free water loss without sodium loss, commonly due to fever or diabetes insipidus. Central diabetes insipidus may follow head trauma, tumors, congenital disease, infection, granulomatous disease, stroke, or aneurysm. Nephrogenic diabetes insipidus may be congenital or drug-induced (lithium, amphotericin B, foscarnet, demeclocycline) or associated with obstructive uropathy, chronic tubulointerstitial disease, or electrolyte disturbances. Hypervolemic hypernatremia results from excess sodium gain exceeding water gain, most commonly iatrogenic from sodium bicarbonate, hypertonic IV fluids, parenteral nutrition, hypertonic dialysis, or sodium-containing medications; less common causes include endocrine disorders and seawater drowning.
Pediatric considerations Children are more susceptible to iatrogenic hypernatremia and have higher risk of death or permanent neurologic injury, with morbidity up to 50%. Neonates may present with irritability, lethargy, high-pitched cry, or muscle weakness; poor breastfeeding or improper formula preparation are common causes.
Geriatric considerations Older adults are at highest risk due to impaired thirst and renal concentrating ability; neglect should be considered when dehydration is unexplained.
Pregnancy considerations Transient diabetes insipidus of pregnancy may occur. Vasopressin and desmopressin are pregnancy category B. Physical examination is less reliable for assessing hydration.
Diagnosis
Signs and symptoms Clinical features often reflect the underlying cause and are more pronounced with acute elevations. Sodium ≥185 mEq/L is frequently fatal. Neurologic manifestations, typically seen at levels ≥160 mEq/L, include headache, irritability, tremor, ataxia, confusion, delirium, seizures, coma, hyperreflexia, asterixis, chorea, intracranial hemorrhage, and dural sinus thrombosis. Musculoskeletal findings include spasticity, weakness, and muscle twitching. Other features include anorexia, tachypnea, poor skin turgor, nausea, and vomiting. Hypovolemic hypernatremia presents with tachycardia, orthostasis, dry mucous membranes, oliguria, and azotemia. Hypervolemic hypernatremia may cause pulmonary and peripheral edema.
Physical exam Assess hydration using mucous membranes, skin turgor, neck veins, and orthostatic vitals. Perform and repeatedly reassess a full neurologic examination.
Essential workup Confirm with serum sodium measurement.
Diagnosis tests and interpretation
Laboratory Obtain electrolytes, BUN/creatinine, glucose, CBC, urinalysis with specific gravity, urine and serum osmolality, and urine sodium.
Imaging Chest radiograph for infection, aspiration, or pulmonary edema. CT brain for altered mental status, venous sinus thrombosis, or intracranial hemorrhage.
Diagnostic procedures Consider Foley catheter placement for accurate intake and output monitoring.
Differential diagnosis Diabetic ketoacidosis, hyperosmolar hyperglycemic state, and primary CNS pathology.
Treatment
Prehospital Begin volume resuscitation if hypovolemia or hemodynamic instability is present.
Initial stabilization/therapy Ensure airway, breathing, and circulation. Administer 0.9% normal saline bolus for hypotension. Treat altered mental status with glucose assessment and supportive measures.
Emergency department management Calculate free water deficit: Water deficit = 0.6 × weight (kg) × (1 − desired Na/actual Na). Avoid rapid correction; decrease serum sodium by no more than 0.5–0.7 mEq/L per hour to prevent seizures and cerebral edema. Hypovolemic hypernatremia requires initial volume resuscitation with normal saline, then transition to hypotonic fluids (D5W or 0.45% saline) once stable. Isovolemic hypernatremia is treated by replacing free water with D5W or hypotonic saline, correcting half the deficit in the first 24 hours and the remainder over 1–2 days. Hypervolemic hypernatremia requires removal of excess sodium and water with diuretics or dialysis, followed by cautious free water replacement once euvolemic. Diabetes insipidus management includes sodium restriction, desmopressin for central DI, adjunctive agents such as chlorpropamide or carbamazepine when appropriate, thiazide diuretics for nephrogenic DI, and discontinuation of offending drugs.
Medication Desmopressin 1–2 μg IV/SC q12h or 5–20 μg intranasally; chlorpropamide 100–500 mg/day. First line initial volume correction with normal saline if hypovolemic. Second line treat the underlying cause and correct free water deficit.
Follow-up and disposition
Admission criteria Newly diagnosed sodium >150 mEq/L, sodium >160 mEq/L, symptomatic patients, or those requiring close monitoring; ICU admission for severe or symptomatic cases.
Discharge criteria Sodium <150 mEq/L and asymptomatic, or chronically hypernatremic patients at baseline with no symptoms.
Follow-up recommendations Repeat serum sodium within one week or sooner based on clinical course.
Key points Acute hypernatremia carries a high risk of permanent neurologic injury; meticulous neurologic documentation is essential. Extremes of age and chronic illness increase vulnerability. Ongoing fluid losses require frequent reassessment and recalculation of water needs, with serial laboratory monitoring to ensure safe correction.
Basics
Description Hypernatremia is defined as a serum sodium concentration >145 mEq/L. Mild hypernatremia is 146–155 mEq/L, while severe hypernatremia is >155 mEq/L and is associated with high morbidity and mortality.
Etiology Hypernatremia is categorized by volume status. Hypovolemic hypernatremia is the most common and results from loss of water and sodium with proportionally greater water loss. Causes include renal failure, diuretics, lactulose, osmotic diuresis (mannitol, glucosuria, high-protein feeds), insensible losses (burns, sweating), respiratory losses, impaired thirst, lack of access to water, diarrhea, vomiting, and intubation. Isovolemic hypernatremia results from free water loss without sodium loss, commonly due to fever or diabetes insipidus. Central diabetes insipidus may follow head trauma, tumors, congenital disease, infection, granulomatous disease, stroke, or aneurysm. Nephrogenic diabetes insipidus may be congenital or drug-induced (lithium, amphotericin B, foscarnet, demeclocycline) or associated with obstructive uropathy, chronic tubulointerstitial disease, or electrolyte disturbances. Hypervolemic hypernatremia results from excess sodium gain exceeding water gain, most commonly iatrogenic from sodium bicarbonate, hypertonic IV fluids, parenteral nutrition, hypertonic dialysis, or sodium-containing medications; less common causes include endocrine disorders and seawater drowning.
Pediatric considerations Children are more susceptible to iatrogenic hypernatremia and have higher risk of death or permanent neurologic injury, with morbidity up to 50%. Neonates may present with irritability, lethargy, high-pitched cry, or muscle weakness; poor breastfeeding or improper formula preparation are common causes.
Geriatric considerations Older adults are at highest risk due to impaired thirst and renal concentrating ability; neglect should be considered when dehydration is unexplained.
Pregnancy considerations Transient diabetes insipidus of pregnancy may occur. Vasopressin and desmopressin are pregnancy category B. Physical examination is less reliable for assessing hydration.
Diagnosis
Signs and symptoms Clinical features often reflect the underlying cause and are more pronounced with acute elevations. Sodium ≥185 mEq/L is frequently fatal. Neurologic manifestations, typically seen at levels ≥160 mEq/L, include headache, irritability, tremor, ataxia, confusion, delirium, seizures, coma, hyperreflexia, asterixis, chorea, intracranial hemorrhage, and dural sinus thrombosis. Musculoskeletal findings include spasticity, weakness, and muscle twitching. Other features include anorexia, tachypnea, poor skin turgor, nausea, and vomiting. Hypovolemic hypernatremia presents with tachycardia, orthostasis, dry mucous membranes, oliguria, and azotemia. Hypervolemic hypernatremia may cause pulmonary and peripheral edema.
Physical exam Assess hydration using mucous membranes, skin turgor, neck veins, and orthostatic vitals. Perform and repeatedly reassess a full neurologic examination.
Essential workup Confirm with serum sodium measurement.
Diagnosis tests and interpretation
Laboratory Obtain electrolytes, BUN/creatinine, glucose, CBC, urinalysis with specific gravity, urine and serum osmolality, and urine sodium.
Imaging Chest radiograph for infection, aspiration, or pulmonary edema. CT brain for altered mental status, venous sinus thrombosis, or intracranial hemorrhage.
Diagnostic procedures Consider Foley catheter placement for accurate intake and output monitoring.
Differential diagnosis Diabetic ketoacidosis, hyperosmolar hyperglycemic state, and primary CNS pathology.
Treatment
Prehospital Begin volume resuscitation if hypovolemia or hemodynamic instability is present.
Initial stabilization/therapy Ensure airway, breathing, and circulation. Administer 0.9% normal saline bolus for hypotension. Treat altered mental status with glucose assessment and supportive measures.
Emergency department management Calculate free water deficit: Water deficit = 0.6 × weight (kg) × (1 − desired Na/actual Na). Avoid rapid correction; decrease serum sodium by no more than 0.5–0.7 mEq/L per hour to prevent seizures and cerebral edema. Hypovolemic hypernatremia requires initial volume resuscitation with normal saline, then transition to hypotonic fluids (D5W or 0.45% saline) once stable. Isovolemic hypernatremia is treated by replacing free water with D5W or hypotonic saline, correcting half the deficit in the first 24 hours and the remainder over 1–2 days. Hypervolemic hypernatremia requires removal of excess sodium and water with diuretics or dialysis, followed by cautious free water replacement once euvolemic. Diabetes insipidus management includes sodium restriction, desmopressin for central DI, adjunctive agents such as chlorpropamide or carbamazepine when appropriate, thiazide diuretics for nephrogenic DI, and discontinuation of offending drugs.
Medication Desmopressin 1–2 μg IV/SC q12h or 5–20 μg intranasally; chlorpropamide 100–500 mg/day. First line initial volume correction with normal saline if hypovolemic. Second line treat the underlying cause and correct free water deficit.
Follow-up and disposition
Admission criteria Newly diagnosed sodium >150 mEq/L, sodium >160 mEq/L, symptomatic patients, or those requiring close monitoring; ICU admission for severe or symptomatic cases.
Discharge criteria Sodium <150 mEq/L and asymptomatic, or chronically hypernatremic patients at baseline with no symptoms.
Follow-up recommendations Repeat serum sodium within one week or sooner based on clinical course.
Key points Acute hypernatremia carries a high risk of permanent neurologic injury; meticulous neurologic documentation is essential. Extremes of age and chronic illness increase vulnerability. Ongoing fluid losses require frequent reassessment and recalculation of water needs, with serial laboratory monitoring to ensure safe correction.
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