Hyponatraemia CCC

Cause of HYPOnatraemia

  • Definition: Serum sodium <130mEq/l
  • Cause: Excess of Water relative to Sodium
  • Affects: 1% of hospital population
  • Hypovolemic (Na deficit in xs of water deficit) (test urine sodium)
    • RENAL (urinary Na >20mmol)
      • Addison’s
      • Renal failure (Diuretic stage)
      • Salt losing nephropathy (RTA)
      • Diuretic- Thiazides and osmotic diuretics
      • Cerebral salt wasting
    • PRE-RENAL (Urinary Na <20mmol)
      • Third space losses (Burns, pancreatitis, bowel obstruction, cirrhosis)
      • Sweating/vomiting/diarrhoea with continued water intake
        • Alkalosis with upper GI and skin loss
        • Acidosis with lower GI loss
  • Normovolemic (Test urine osmolality)
    • Urine osmolality
    • Tea and toast diet, Beer potomania
    • Psychogenic polydipsia (>15 L/Day if normal kidneys)
    • Iatrogenic water overload in ED
    • Amphetamines
    • Exercise-Associated Hyponatraemia
  • Urine osmolality > serum osmolality
    • SIADH (urine Na >20mmol)
      • Malignancy (lung, pancreas, prostate, lymphoma, others)
      • CNS, Lung infection and granulomatous disease, Porphyria, positive pressure ventilation
      • Drugs: Psychoactive- MAOI, SSRI, TCA, NSAID, chlorpromazine, Chemotherapeutic (induce SIADH)
  • Hypervolemic (increased TBW relative to Na) (oedematous states)
    • Urinary sodium <20mmol/l
      • Increased interstitial salt
      • Low albumin and secondary hyperaldosteronism
      • CCF, cirrhosis, nephrotic syndrome, hepato-renal syndrome
    • Urinary sodium >20mmol/l
      • Renal failure
      • Hypertonic saline, early diuretics
      • Hypothyroidism
  • Fictitious (Pseudohyponatraemia)
    • Hyperglycaemia (draws water to ECF)
      • Corrected sodium…Measured Na + [glucose – 5]/4
    • Hyperproteinemia, hyperlipidemia
    • Mannitol
    • Glyceine washout for TURP and hysteroscopy
  • Click to enlarge


    Severity of symptoms associated with rapidity of loss and extent of fall

    • >125      Asymptomatic
    • 115-125 Lethargy, confusion, anorexia, nausea, vomiting
    • <115      Muscle cramps and weakness, convulsions, coma


    • Cerebral oedema
      • Secondary to abrupt sodium losses and free water shift from vascular to interstitial space
    • ECG changes
      • Cause of non-ischaemic ST elevation on ECG
    • Pontine demyelinosis (no clear evidence that associated with rapid correction)
      • Develops 3-5 days after treatment
        • Demyelination of central pons, corticobulbar and corticospinal tracts
        • Altered mental state, pseudobulbar palsies
        • Dysphasia and spastic quadriparesis
      • More likely in chronic hyponatraemia


    Depends on rapidity of onset and clinical symptoms

    • Asymptomatic hyponatremia
      • Slow at 0.5mEq/hr (max 12mmol/24 hours)
      • Rapid correction may lead to pontine myelinolysis
        • Water restriction is usually used (especially in SIADH)
        • Salt tablets and diuretics
        • Demeclocycline
      • Induces nephrogenic diabetes insipidus
      • Use with caution, potentially nephrotoxic
    • Symptomatic with neurological symptoms
      • Initial rate 1-2mmol/hr for first few hours
      • Monitor CNS symptoms regularly
      • Revert to 0.5mEq/hr after stable


    • Calculate Na deficit

    Na deficit= (desired Na-current Na) x (0.6 x body weight)


    • In acute severe hyponatraemia, aim for 1-2mEq/hour correction
    • In chronic severe hyponatraemia aim for 0.5-1mEq/hour correction.
    • Hypertonic saline replacement
      • 3% saline (513mEq/L) by giving (deficit/513) to the patient at the rate of 1mEq/hour over 4 hours
    • New AVP receptor antagonists are currently undergoing phase III clinical trials and show promise for the treatment of hyponatraemia.  The increase serum sodium by stimulating free water excretion.

    CCC 700 6

    Critical Care


    BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

    One comment

    1. Hi,

      I appreciate the help this page has provided for me. Just a correction, please let me know if I am wrong. But cerebral salt wasting presents as hypovolaemic which is what you have stated in the text. But in the picture summary at the in it is in the hypervolaemic section.

      Thank you!

      Best wishes

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