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
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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
hyponatremia
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 !!
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source: www.aafp.org |
Treatment
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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