Hyponatremia ( < 135 )


Etiology Chart

Serum osmolarity
Increased: Normal: Decreased: (Evaluate volume status)
- glycemia
-Hypertonic infusions (mannitol, contrast agent, post TURP, etc.)
Pseudo hyponatremia:
-Severe lipids,
Hypovolemia: Euvolemic: Hypervolemia:
GI losses
Diuretics (thiazides)
3rd space
Burns, etc.
"water intoxication": hypotonic IV fluids, etc.
Adrenal insuff.
Renal failure,
Nephrotic syndrome.

Serum osmolarity





Physical Exam/Signs


Differential Diagnosis

Condition Diagnosis Treatment
Hyperglycemia (e.g., in diabetic ketoacidosis) Elevated glucose levels (> 400 mg per dL [22.2 mmol per L]), elevated anion gap Insulin, intravenous fluids, isotonic saline
Hyperlipidemia Elevated total and low-density lipoprotein cholesterol levels Statin therapy
Hyperproteinemia (e.g., in multiple myeloma) Serum and urinary monoclonal protein, bone marrow biopsy, lytic bone lesions detected on radiography Chemotherapy
Laboratory errors Repeat sodium levels  
Hypovolemic hyponatremia
Cerebral salt wasting Diagnosis of exclusion (e.g., head injuries, intracranial hemorrhage); urinary sodium > 20 mEq per L Isotonic or hypertonic saline
Diuretic use Clinical; urinary sodium > 20 mEq per L Stop diuretic therapy
Gastrointestinal loss (e.g., diarrhea, vomiting) Clinical; urinary sodium < 20 mEq per L Intravenous fluids
Mineralocorticoid deficiency (e.g., Addison disease [primary],
pituitary failure [secondary],
hypothalamic failure [tertiary])
Low aldosterone and morning cortisol levels
Hyperkalemia, increased plasma renin level
Low or increased adrenocorticotropic hormone level (cause-dependent),
Urinary sodium > 20 mEq per L,
Positive results on cosyntropin stimulation test,
21-hydroxylase autoantibodies (Addison disease),
CT of adrenal glands to rule out infarction
Steroid replacement therapy
Osmotic diuresis Elevated glucose level, mannitol use Correct glucose level, stop mannitol use
Renal tubular acidosis Urinary osmolar gap, increased urinary pH, urinary sodium > 25 mEq per L, fractional excretion of bicarbonate > 15% to 20%,
Hyperchloremic acidosis,
Decreased serum bicarbonate level, potassium abnormalities (type dependent)
Correct acidosis, sodium bicarbonate
Salt-wasting nephropathies Urinary sodium > 20 mEq per L Correct underlying cause
Third spacing (e.g., bowel obstruction, burns) Clinical; computed tomography Intravenous fluids, relieve obstruction
Euvolemic hyponatremia
3,4-methylenedioxymeth-amphetamine (“Ecstasy”) use Urine drug screen  --
Beer potomania syndrome Excessive alcohol consumption, low serum osmolality Therapy to decrease alcohol use and nutritional counseling to increase protein intake
Exercise-associated hyponatremia Clinical Isotonic or hypertonic saline, depending on symptoms
Glucocorticoid deficiency Low aldosterone, morning cortisol, and adrenocorticotropic hormone levels, hyperkalemia, increased plasma renin level Steroid replacement therapy
Hypothyroidism Elevated thyroid-stimulating hormone level, low free thyroxine level Thyroid replacement therapy
Low solute intake Clinical Increase sodium intake
Nephrogenic SIADH Same as SIADH, with low vasopressin levels Fluid restriction, loop diuretics
Psychogenic polydipsia History of schizophrenia with excessive water intake Psychiatric therapy
Reset osmostat Free water challenge test, normal fractional excretion of uric acid (urate) Treat underlying disease
SIADH Decreased osmolality, urinary osmolality > 100 mOsm per kg, euvolemia, urinary sodium > 20 mEq per L, absence of thyroid disorders or hypocortisolism, normal renal function, no diuretic use Fluid restriction, consider vaptans
SIADH secondary to medication use (e.g., barbiturates, carbamazepine [Tegretol], chlorpropamide, diuretics, opioids, selective serotonin reuptake inhibitors, tolbutamide, vincristine) SIADH with use of causative agent Stop causative medication
Water intoxication Clinical; excessive water intake Diuresis
Hypervolemic hyponatremia
Heart failure Clinical (e.g., jugular venous distention, edema), elevated B-type natriuretic peptide level, echocardiography, urinary sodium < 20 mEq per L Diuretics, angiotensin-converting enzyme inhibitors, beta blockers
Hepatic failure/cirrhosis Elevated liver function tests, ascites, elevated ammonia level, biopsy, urinary sodium < 20 mEq per L Furosemide (Lasix), spironolactone (Aldactone), transplant
Nephrotic syndrome Urinary protein, urinary sodium < 20 mEq per L Treat underlying cause
Renal failure (acute or chronic) Blood urea nitrogen–to-creatinine ratio, glomerular filtration rate, proteinuria, urinary sodium > 20 mEq per L Correct underlying disease with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers



  1. Initial
  2. Medical/Pharmaceutical
  3. Surgical/Procedural


Osmotic demyelination syndrome, or Central Pontine Myelinolysis:
  • Overly rapid correction of hyponatremia may cause osmotic demyelination syndrome, or central pontine myelinolysis, sometimes resulting in permanent neurologic deficits after a brief improvement in neurologic status.
  • Signs and symptoms may include dysarthria, dysphagia, paresis, coma, and seizures.
  • It is believed that brain volume shrinks because it cannot assimilate the new electrolytes fast enough and water is lost from the cells.




  1. Admit all pts w/ Na+ < 130 mEq/L [130 mmol/L]
  2. Admit to ICU if Na+ <120 mEq/L [120 mmol/L] or seizure, or altered mental status
  3. May discharge mild decr Na+ w/ clear etiology (such as vol depletion)



1. Admit to:
2. Diagnosis: Hyponatremia
3. Condition:
4. Vital Signs: q4h. Call physician if BP >160/90, <70/50; P >140, <50; R>25, <10; T >38.5 C.
5. Activity: Up in chair as tolerated.
6. Nursing: Inputs and outputs, daily weights.
7. Diet: Regular diet.
8. Special Medications:

Hyponatremia with Hypervolemia and Edema
(low osmolality <280 mOsm/L, UNa <10 mmol/L: nephrosis, heart failure, cirrhosis):
-Water restrict to 0.5-1.0 L/d.
-Furosemide 40-80 mg IV or PO qd-bid.

Hyponatremia with Normal Volume Status
(low osmolality <280 mOsm/L,
UNa <10: water intoxication;
UNa >20: SIADH, diuretic-induced):

-Water restrict to 0.5-1.5 L/d.
-Conivaptan (Vaprisol) 20 mg IV over 30 minutes once, followed by a continuous infusion of 20 mg over 24 hours. If the response i
s insufficient, increase dose to 40 mg/24 hours; max 4 days. ADH inhibitor.

Hyponatremia with Hypovolemia 
(low osmolality <280 mOsm/L)
UNa <10 : vomiting, diarrhea, third space/respiratory/skin loss;
UNa >20 : diuretics, renal injury, RTA, adrenal insufficiency, partial obstruction, salt wasting:
-If volume depleted, give 0.5-2 L of 0.9% saline over 1-2 hours until no longer hypotensive, then 0.9% saline at 125 mL/h; or 100-500 mL 3% hypertonic saline over 4h.

Severe Symptomatic Hyponatremia:
If volume depleted, give 1-2 L of 0.9% saline (154 mEq/L) over 1-2 hours until no longer orthostatic.
Determine volume of 3% hypertonic saline (513 mEq/L) to be infused:

Na (mEq) deficit = 0.6 x (wt kg)x(desired [Na] - actual [Na])

Volume of solution (L)

Number of hrs


Sodium to be infused (mEq)

(mEq/L in solution) x Number of hrs

-Correct half of sodium deficit intravenously over 24 hours until serum sodium is 120 mEq/L; increase sodium by 12-20 mEq/L over 24 hours (1 mEq/L/h).
-Alternative Method: 3% saline 100-300 mL over 4-6h, repeated as needed.

9. Extras: CXR, ECG, head/chest CT scan.
10. Labs: CMP, osmolality, triglyceride, liver panel, A1c, TSH, Serum Osmolarity. UA, urine specific gravity. Urine osmolality, Urine sodium.