Hypernatremia, Liquids and electrolites Manual (Constain, Alfred)

Hypernatremia means serum Na >145 mmol /ml. Severe hypernatremia >160 mmol/ml has a mortality rate of 75%.

Comprehense three categories:

1. Normovolemic hypernatremia

2. Hypervolemic Hypernatremia

3. Hypovolemic Hypernatremia

1. Normovolemic hypernatremia: It can occur in a wide spectrum of entities that cross since the insipid diabetes to overhydration.

2. Hypervolemic Hypernatremia: Occur principally in the hyperosmolar saline solutions context.

3. Hypovolemic Hypernatremia: Is the most comun, can occur in insipid diabetes, chronic renal failure, deshydration, shock.

Like general rule the sodium reposition can't be >10mmol/L in 24 hours and can't be superior to 0.5mEq/h.

So there are two formules to correct the sodium in hypernatremia:

1. Na plasma variation= ([Na] in the solution available - [serum Na]) / (Percentage of body water +1)

2. Na plasma variation= ([Na + K] in the solution available - [serum Na] / (Percentage of body water)

[Na] in the solution available= For example, the normal saline solution has 154mEq/L. 0.2% saline solution has 34 mEq/L. Normally, the reposition of water in hypernatremia is performed with 0.2% and 0.45% saline solution.

Percentage of body water= Men: 0.6*weight in Kg , Women: 0.5*weight in Kg

Example

A 65 yo man arrives to emergency department with HR:122bpm, AP: 120/75 mmhg, RR: 18 bpm, weight: 72Kg. [Na]= 162. Oral mucose was dry. The final diagnose is Pulmonary tromboembolism. ¿How do you correct this severe hypernatremia?

Percentage of body water= 43.2L

If we use a 5% dextrose solution, the [Na]= 0 mEq/L

Na plasma variation= ( [0] - 162) / (43.2 + 1) = 3.67 mEq

The value that we are going to replace is 3.67mEq/L, but we got to replace it till 10mEq/24h, hence 10/3.67= 2.62 L 5% of dextrose, wich is 113,5ml /h. After the first date of replacement we can perform it at 1mEq/h (i.e second day)