Hyponatremia

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Background

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

Hypovolemic

Renal Causes

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

Extra-renal Causes

Hypervolemic

Euvolemic

Pseudohyponatremia

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

Evaluation

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

Work-Up

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

Symptomatic

  • 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

Asymptomatic

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

Disposition

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

See Also

External Links

References

  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
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