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

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 !!

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