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Algorithm for Hyponatremia
  • Defined as sodium concentration <135meq/L[1]
  • Patients often not symptomatic until <120meq/L although this level varies by patients and may be higher if the change occurred abruptly[2]
  • Generally accepted recommendations are to avoid correction of more than 12 mmol/L/day (0.5mmol/L/hr) to avoid central pontine myelinolysis. Faster correction (1-2mmol/L/hr) is acceptable with 3% hypertonic saline if the patient is seizing.[3]
  • Often described in terms of tonicity and volume status of the patient with the main types by tonicity being: [4]
    • Hypertonic Hyponatremia
    • Isotonic (pseudo) hyponatremia
    • Hypotonic Hyponatremia

Clinical Features

Hyponatremia Types by Tonicity

Hypertonic Hyponatremia

  • Defined as osmolarity > 295mmol/L with the following causes:
  1. Hyperglycemia
    • Traditional teaching: [Na+] decreases by 1.6-1.8mEq/L for each 100mg/dL increase in glucose over 100mg/dL
    • 2.4mEq/L may be a more accurate correction factor (Hillier 1999)
  2. Mannitol excess

Isotonic (pseudo) hyponatremia

  • Defined as osmolarity > 275-295mmol/L. Often referred to as pseudo hyponatremia because the elevated lipids or proteins interfere with the laboratory sodium reading. The following are common causes:
  1. Hyperlipidemia
  2. Hyperproteinemia

Hypotonic Hyponatremia

Hypotonic Types by Volume Status


Renal Causes

  • Thiazide diuretic use
  • Na-wasting nephroathy (RTA, CRF)
  • Osmotic diuresis (glucose, urea)
  • Aldosterone deficiency

Extra-renal Causes




  • Hyperglycemia
    • Na+ drops 1.6 mEq/L for every 100mg/dL increase in glucose over 100
  • Displaced sodium in lab specimen
    • Hyperlipidemia
    • Hyperproteinemia


  • Must determine volume status and calculated osm
    • In true hyponatremia the osm is reduced


Prior to giving treatment

  • Urine
    • Urinalysis
    • Urine electrolytes
    • Urine urea
    • urine uric acid
    • urine osmolality
    • urine creatinine
  • Serum
    • Chemistry
    • Serum osmolality
    • Uric acid
    • TSH
    • Cortisol

Treatment by Patient Status


  • Adults: 3% NS 100cc bolus over 10min; repeat after 10min x1 if no improvement[6]
    • Each 100 ml will raise sodium by ~2 mmol/l
    • In general, 200-400 mL of 3% NaCl is reasonable dose in most adult patients with severe symptomatic hyponatremia, which may be given IV over 1-2 hr until resolution of seizures.
  • Pediatrics: 2 cc/kg of 3% over 10-60 minutes can be infused with a repeat of up to 3 times.[7]
  • Fluid restrict


Step 1

Calculate total body water[8]

  • TBW(kg) = Wt(kg) x 0.6 = [Wt(lb) x 0.45] x 0.6 = Wt(lb) x 0.27

Step 2

Calculate mEq deficit

  • (Desired Na - Measured Na) ~ must be ≤ 10

Step 3

Calculate NS rate to be given over 24hr

  • NS rate (cc/hr) = TBW x mEq deficit x 0.27
  • If using 3% sodium chloride (to avoid volume overload) divide above rate by 3.33

Treatment by Type of Hyponatremia

Hypertonic hyponatremia

  • Correct underlying disorder which is often hyperglycemia[9]
  • Often volume depleted due to osmotic diuresis and normal saline provides adequate volume repletion

Isotonic (pseudo) hyponatremia

  • No treatment needed [9]

Hypotonic hyponatremia

  1. Hypovolemic
    • Give NS but be cautious of raising the serum sodium more than 12 mmol/L/day (0.5mmol/L/hr) and causing central pontine demylinosis[3]
  2. Euvolemic[9]
    • Water restrict
    • Treat underlying cause
  3. Hypervolemic
    • Water restriction
    • Diuresis
    • Treat underlying cause

Na Therapy

Max correction 10mEq/L in first 24hr and 18mEq/L in first 48hr (lowers risk of central pontine demylinosis) [10]

Sodium Containing fluid Concentrations
Fluid type Sodium Concentration
1/2 Normal Saline 77 mEq/L
Normal Saline 154 mEq/L
Lactated Ringers 130 mEq/L
3% Saline 513 mEq/L


  • Admit if symptomatic or if Na <125mEq/L

See Also

External Links


  1. Upadhyay A, Jaber BL, Madias NE. Epidemiology of hyponatremia. Seminars in Nephrology 2009 29 227–238
  2. Spasovski G. et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transplant. 2014
  3. 3.0 3.1 Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med. 2000 May 25;342(21):1581-9.
  4. Understanding Lab Testing for Hyponatremia. Clin J Am Soc Nephrol 2008;3:1175
  5. Review of Drug-Induced Hyponatremia. Am J Kidney Dis 2008;52:144
  6. Spasovski et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transplant (2014) 0: 1–39. fulltext
  7. Moritz ML, Ayus JC. 100cc 3% sodium chloride bolus: a novel treatment for hyponatremic encephalopathy. Metab Brain Dis. 2010 Mar; 25(1): 91-6.
  8. The hyponatremia formulas do not work so well (Clin J Am Soc Nephrol 2007;2:1110 and Nephrol Dial Transplant 2006;21:1564)
  9. 9.0 9.1 9.2 Schrier RW, Bansal S. Diagnosis and management of hyponatremia in acute illness. Curr Opin Crit Care 2008;14:627-34
  10. Nagler EV1, Vanmassenhove J, van der Veer SN et al. Diagnosis and treatment of hyponatremia: a systematic review of clinical practice guidelines and consensus statements. BMC Med. 2014 Dec 11;12:1