Hyponatremia resident survival guide
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.D. [2]
Definition
Hyponatremia is defined as a serum sodium concentration < 135 meq/L.
Causes
Hyponatremia causes can be classified into 3 types based on calculating serum osmolality, which is calculated as follows:
Sosm(mmol/kg) = (2 x serum Na+ conc.) + (serum glucose conc./18) + (blood urea nitrogen/2.8) Where Ssom is Serum osmolality.
- Hyponatremia with
- REDIRECT Management#===Life Threatening Causes===
Conditions that may cause death or permanent disability within the next 24 hours
Common Causes
Management
| Serum sodium < 135 mEq/L | |||||||||||||||||||||||||||||||||||||||||||||
| Plasma osmolality | |||||||||||||||||||||||||||||||||||||||||||||
| Hypotonic < 280 | Isotonic/Hypertonic (Pseudohyponatremia) > 280 | ||||||||||||||||||||||||||||||||||||||||||||
| Assess volume status | Increase in osmotically active compounds; glucose, protein, lipid, mannitol, sorbitol | ||||||||||||||||||||||||||||||||||||||||||||
| Hypovolemia | Hypervolemia | Euvolemia | Treat etiology | ||||||||||||||||||||||||||||||||||||||||||
| Spot urine Na < 10, BUN/Creatinine > 20:1, Urine osmolality > 450 | Same as hypovolemia, Spot urine Na < 10, BUN/Creatinine > 20:1, Urine osmolality > 450 | Spot urine Na > 20, BUN/Creatinine < 20:1, Urine osmolality > 300 | |||||||||||||||||||||||||||||||||||||||||||
| GI, renal losses, dehydration, diuretics, adrenal insufficiency, cerebral salt wasting syndrome | heart failure cirrhosis renal failure | Urine osmolality > 300 | Urine osmolality 50-100 | ||||||||||||||||||||||||||||||||||||||||||
| (a) Normal saline; (b) If neurological sign/symptoms 3% hypertonic saline, and furosemide | Fluid restriction, Diuretics, Treat etiology | SIADH, Hypothyroidism | Compulsive water drinking | ||||||||||||||||||||||||||||||||||||||||||
| (a) Fluid restriction (b) Demeclocycline (if fluid restriction fails) (c) Vaptans; Conivaptan, Tolvaptan for resistant cases | Treat etiology | ||||||||||||||||||||||||||||||||||||||||||||
Do's
1) Cerebral salt wasting syndrome causes hypo-osmolar hyponatremia with lab parameters similar to that seen in SIADH. It is associated with conditions like hypovolemia, hypotension, neurosurgical procedure, and subarachnoid hemorrhage (within previous 10 days). It is treated as hypoosmolar hyponatremia.
2) While deciding the rate of normal saline for hypovolemia hyponatremia, consideration of the following factors are helpful: patient's BMI (faster rates for higher BMI), cardiac (slower rate for low ejection fraction) and renal function (slower rates for low GFRs).
3) Common causes of SIADH are, small cell lung cancer, intracranial pathology, increased intrathoracic pathology, medications (thiazides, SSRI, tricyclic antidepressant, narcotics, phenothiazine, carbamazepine)
4) Vaptans such as conivaptan (intravenous), and tolvaptans (oral preparations) can be used for resistant euvolemic, and hypervolemic hyponatremia. These are very expensive and should be initiated in hospital.
Don'ts
1) Serum sodium shouldn't be corrected faster than 0.5 meq/h, as faster correction increases the risk for central pontine myelinolysis.