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Hyponatremia Approach: Definition, Classification, Symptoms, Diagnostic strategy, Treatment and Management


    Hyponatremia is one of the most electrolytes disturbances in clinical practice, its enormous differential diagnosis makes it a complex problem in the praxis.

    Definition and classification

    Hyponatremia exists when natrium amount in serum < 135 mmol/l

    It can be classified in:
    • Simple hyponatremia: Natrium 130-134 mmol/l
    • Middle hyponatremia: Natrium 125-129 mmol/l
    • Severe hyponatremia: Natrium < 125 mmol/l

    According to the speed, in which hyponatremia occurs, results another classification:
    • Acute hyponatremia: occurs in less than 48 hours
    • Chronic hyponatremia: occurs in more than 48 hours
    • When the timing is unknown, then consider it as chronic

    Symptoms of hyponatremia

    Another classification of hyponatremia can be thought, according to the intensity of the symptoms:

    1- Hyponatremia with severe symptoms:
    • Coma
    • Somnolence
    • Convulsion
    • Vomiting
    • Cardiopulmonary instability
    2- Hyponatremia with moderate symptoms:
    • Headache
    • Confusion
    • Nausea
    3- Hyponatremia without symptoms

    Diagnostic strategy

    Source: accessmedicine.mhmedical.com

    You need whatever the case may be a bundle of tests when hyponatremia exists:

    1- Sonography of the abdomen:
    • You need to check the kidneys and the bladder
    • Is there any urinary retention or congestion?
    • Is Vena cava dilated > 2.4 cm and its diameter not breathing-related> es exists intravascular hypervolemia
    • Is Vena cava collapsed < 1.8 cm, es exists intravascular hypovolemia
    2- You need to determine the amount of Natrium in Serum and urine
    3- You need to determine serum and urine osmolality

    How to interpreter the results:

    Step one: Serum natrium < 135 mmol/l


    Step two: Serum osmolality

    here we have 3 cases:

    1- Osmolality > 290 mosmol/kg: hyperosmolar hyponatremia

    That could occur by:
    • hyperglycemia
    • hyperlipidemia
    • infusion of mannitol  
    • hyperproteinemia
    • hypothyroid

    2- Osmolality 275-290 mosmol/kg: normoosmolar hyponatremia with the same causes as above
    3- Osmolality < 275 mosmol/kg: hypoosmolar hyponatremia (real hyponatremia: see step three

    Step three: Urine osmolality

    here we have two cases:

    1- Urine osmolality < 200 mosmol/kg: 
    causes could be:
    • Psychogenic polydipsia
    • Low salt intake
    Treatment here is causal

    2- Urine osmolality > 200 mosmol/kg: see step 4

    Step four: Natrium in urine

    here we have two cases:

    1- Urine natrium < 30 mmol/l 
    (note: this means that the patient doesn’t lose his natrium throw the kidneys, thus the renal excretion of natrium is low: the kidneys are trying to keep natrium in the body)

    Here we have again two cases:

    a.      Hypervolemia case: hypervolemic hypoosmolar hyponatremia:
    • Heart insufficiency
    • Liver cirrhosis
    • Nephrotic syndrome
    • Angioedema
    b.      Hypovolemia case: hypovolemic hypoosmolar hyponatremia:
    • Water loss either gastrointestinal: diarrhea, vomiting
    • Or cutaneous: fever with sweating
    • Or in third space: ascites, pleural effusion

    2- Urine natrium > 30 mmol/l 
    (note, although natrium in blood is low, the kidneys are wasting natrium and not trying to keep it!), causes:
    • Renal insufficiency
    • Diuretics? Henle loop diuretics, thiazide
    • Renal tubular acidosis
    • Cerebral salt lose syndrome
    • Adrenal insufficiency
    • Neither of the above + euvolemia: SIADH
    That’S it: very easy !!

    source: www.aafp.org


    The art of treatment to be chosen depends on the intensity of symptoms:

    First case: Patient with severe symptoms

    Make sure that there is no hypovolemia, when yes: give NaCl 0.09% solution

    Other way:
    150 ml of NaCl 3% solution as a slow infusion over 20 minutes: control natrium
    You can repeat until natrium be elevated about 5 mmol/l

    Here you have 2 cases:

    1- Symptoms have improved:
    Don’t give NaCl 3% anymore
    Give NaCl 0.09% as a slow infusion and make sure:
    • Natrium elevation at first day NOT exceed 10 mmol/l
    • Natrium elevation at following days NOT exceed 8 mmol/l
    • Keep giving NaCl  0.09% until natrium has reached 130 mmol/l

    2- Symptoms haven’t improved: 
    you have to Repeat NaCl 3% but make sure:
    a. Natrium elevation not to exceed 1 mmol/hour
    b. Stop when:
    • Natrium elevation in total has reached 10 mmol/l
    • Natrium amount in serum has reached 130 mmol/l
    • Symptoms have improved otherwise: consider another disease!

    BUT HOW to calculate the Natrium change ratio in one hour??
    Natrium change = (natrium infusion – natrium serum)/ (total body water +1)

    WHAT !!! don’t panic:
    • Natrium infusion in NACH  3% = 165 mmol/l
    • Total body water = 0.6 x body weight in men, 0.5 x body weight in women

    Second case: Patient with moderate symptoms

    1- Give NaCl 3% once, the goal is Natrium elevation of 5mmol/l
    2- Like above, limits are NOT to be exceeded:
    • Natrium elevation at first day NOT exceed 10 mmol/l
    • Natrium elevation at following days NOT exceed 8 mmol/l
    • Natrium level of 130 mmol/l is acceptable

    Third case: acute hyponatremia without symptoms

    1- Just in case natrium fall > 10 mmol/l: 150 ml NaCl 3% solution over 20 minute
    2- Try to stop all medications or solution that could have caused this fall in natrium

    Fourth case: chronic asymptomatic hyponatremia

    1- Simple hyponatremia: don’t give any NaCl solution
    2- Moderate to severe hyponatremia: give NaCl 0.09% solution and make sure:
    • Max. elevation pro day 10 mmol/l then 8 mmol/l
    • Treat the cause

    Fifth case: hypervolemic hypoosmolar hyponatremia

    • Don’t give NaCl
    • Water restriction
    • Don’t give Tolvaptan (vasopressin antagonist)
    • Diuretics?

    Sixth case: hypovolemic hypoosmolar hyponatremia

    • Give NaCl 0.09% or Ringer lactate 0.5-1 ml/kg/ hour
    • By unstable patients give volume regardless of how fast increase the natrium is

    Seventh case: SIDAH (syndrome of inappropriate antidiuretic hormone secretion)

    • Volume restriction
    • NaCl intake per os in combination low dose loop diuretics (2D)
    • In moderate/severe hyponatremia is Tolvaptan not recommended (1C recommendation

    Note: What are SIADH criteria:
    • Hyponatremia < 135 mmol/l
    • Hypoosmolality
    • Urine osmolality > 200 mosmol/ kg
    • Natrium in Urine > 30 mmol/l
    • Euvolemia
    • Another causes are excluded: renal insufficiency, adrenal insufficiency, no diuretics

    What if natrium corrector overcome 10 mmol/l pro day?
    • Stop any active therapy of hyponatremia
    • Give 10 ml /kg Glucose solution 5%
    • Give 2 µg desmopressin x3 pro day

    Resource: Clinical practice guideline on diagnosis and treatment of hyponatraemia, European Journal of Endocrinology (2014) 170, G1–G47

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