Sodium Deficit In Hyponatremia Calculator

Variables and formula

The above calculator determines the sodium deficit to be corrected in patients diagnosed with hyponatremia.

There are four variables required:

■ Patient gender: there is a gender differentiation in the formula. The gender factor is 0.6 for men and 0.5 for women;

■ Normal weight: can be input in either lbs or kg;

■ Serum Na: this is the current sodium level, determined via blood test;

■ Desired Na: target sodium value to be established by clinician, at least 120 mEq/L.

The formula used for hyponatremia correction is:

Na deficit = TBW x (Desired Na – Serum Na)

Where:

Total Body Water (TBW) = Gender factor x Normal Weight

Gender factor for men is 0.6 and for women is 0.5.

Na is measured in mEq/L.

Therefore, the Na deficit = 0.6 (for men) or 0.5 (for women) x Weight in kg x (Desired Na – Serum Na)

Hyponatremia and sodium deficit guidelines

When there is a relative excess of water in relation to body sodium and its serum levels fall under 136 mEq/L (when normal values are between 135 and 145 mEq/L), hyponatremia is likely.

Acute hyponatremia is a medical emergency and requires rapid correction with infusate or else there is a high risk of neurological symptoms and cerebral edema.

Moderate to severe hyponatremia usually requires correction with saline solutions.

Depending on the balance between sodium and water levels, there are three types of hyponatremia:

Increases in body water may be caused by primary polydipsia (excessive water intake), renal failure, ADH hormonal irregularities, adrenal insufficiency, or hypothyroidism.

Not all patients experience symptoms, however, acute episodes are usually accompanied by a marked decrease of serum sodium (with levels below 120 mEq/L suggesting risk of neurological complications), nausea, fatigue, dizziness and a state of lethargy.

Muscle cramps and confusion occur in moderate to severe cases and can lead up to impaired mental status, seizures and even coma.

Hyponatremia diagnosis is put based on blood tests, urine and plasma osmolality.

Differential diagnosis with hypothyroidism is put based on determination of serum thyroid-stimulating hormone and free thyroxine level whilst adrenocorticotropic hormone ACTG stimulation is checked to exclude adrenal suppression.

Original source

Adrogué HJ, Madias NE. Hyponatremia. N Engl J Med. 2000; 25;342(21):1581-9.

Other references

1. Mohmand HK, Issa D, Ahmad Z, Cappuccio JD, Kouides RW, Sterns RH. Hypertonic saline for hyponatremia: risk of inadvertent overcorrection. Clin J Am Soc Nephrol. 2007; 2(6):1110-7.

2. Oh MS, Uribarri J, Barrido D, Landman E, Choi KC, Carroll HJ. Danger of central pontine myelinolysis in hypotonic dehydration and recommendation for treatment. Am J Med Sci. 1989; 298(1):41-3.