0.45% NS is Hypernatremia?

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So, I am trying to wrap my head around why we would use 1/2 NS in hypernatremia patients.

Here's what I have worked out so far...

1/2 NS is a hypotonic solution which would cause cells in the blood to swell with water.

The only thing that I could think of would be that this would change osmolarity in the blood thus pulling in water from the interstitial fluid to replace blood volume, which would then dilute the serum sodium level. Am I on the right track?

I've googled and can't seem to find an answer on the cellular level, just that we do use 1/2 NS to correct hypernatremia.

Thanks in advance.

Specializes in Trauma ICU.

I'm glad you brought up about the slow correction of hypernatremia. We had a couple residents decide to correct a particularly high Na with D5 one day and the next day they dropped the persons Na by a significant amount (greater than 6 I think but I don't remember for sure). When the attending saw this, he was somewhat cross.

If a patient's blood were hypernatremic due to rapid water loss (vomiting/diarrhea, except doesn't diarrhea tend to dump sodium too?) adding a hypotonic solution (NA .45%) would dilute the hypernatremia by adding more water than sodium without just dumping straight water (D5W or similar) into the blood which would be too rapid of a dilution.

I decided to look for more information in one of the many books I accumulated in nursing school.... Any italicization or underlining is my emphasizing a point like i would if I were reading it aloud.

The following is an exceprt from Phillips manual of IV THeraputics 4th edition page 119-120

Serum sodium excess: Hypernatremia

The serum level of sodium is elevated to above 145 mEq/L in patients with hypernatremia. This elevation can be caused by a gain of sodium without water or a loss of water without loss of sodium.

Pathophysiology and Etiology

Increased levels of serum sodium can occur with deprivation of water, occurring when a person cannot respond to thirst; during hypertonic tube feeding wit hinadequate water supplements; with excessive parenteral administration of sodium-containing solutions; and when a person is drowning in seawater. Sodium is lost with watery diarrhea (a particular problem in infants), increased insensible loss, ingestion of sodium in unusual amounts, profuse sweating, heat stroke, and diabetes insipidus when water intake is inadequate. Cerebral cells adapt to high sodium levels by shrinking as the osmotic pressure drives fluid out of the cells, leading to decreased brain volume (Hogan & Wane, 2003).

Age Related Considerations

In aging adults, there is a diminished thirst response that may lead to inadequate fluid intake. Infants are unable to obtain fluid independently and may be at risk of inadequate fluid intake, especially in warmer weather.

-excluded s/s & diagnostics-

Treatment & Management

The goal of treatment of patients with hypernatremia is to gradually lower the serum sodium level, infusing a hypotonic electrolyte solution such as 0.45 percent normal saline or 5 percent dextrose in water. Gradual reduction is necessary to reduce the risk of cerebral edema. The sodium level should not be lowered more than 15 mEq/L in an 8 hour period of time for adults.

Generally, treatment guidelines for hypernatremia are:

1. Infusion of an isotonic solution (0.9 percent NaCl) or hypotonic electrolyte solution (0.45 percent NaCl or 5 percent dextrose in water)

2. Sodium levels can also be decreased by use of diuretics, which induce excretion of water and sodium

Nursing Points of Care: Hypernatremia

Nursing assessment includes:

1. Obtain a patient history of high-risk factors for hypernatremia (e.g., increased sodium intake, water deprivation, increased adrenocortical hormone production, use of sodium-retaining drugs).

2. Assess for signs of hypernatremia.

3. Obtain baseline values of laboratory tests, especially serum sodium.

Key nursing interventions include:

1. Monitoring laboratory test results with emphasis on serum sodium and serum osmolarity

2. Keeping accurate fluid intake and output records

3. Monitoring for signs of pulmonary edema when the patient is receiving large amounts of parenteral sodium chloride.

I had a similar situation yesterday. We have an elderly woman, hasn't been eating or drinking well the past couple days. Doctor concerned about dehydration. Started on hypodermoclysis at 75ml/hr - 0.9 NS. Labs came back and showed a critical sodium level. He gave an order for 200ml/hr IV of 0.9 NS and also wanted to keep the hypoderm. running at 75ml/hr. That's 275ml of 0.9 NS n hour. Is he trying to dilute her sodium level?

No. NS will not "dilute" her (presumably high) serum sodium. However, its always possible to have more than one thing wrong with you. She may need her intravascular volume improved for renal and other perfusion purposes before he goes screwing around with her serum sodium. She probably got hypernatremic slowly, so she should have it fixed slowly.

Try this post for a good explanation.

https://allnurses.com/general-nursing-student/fluids-and-electrolytes-662145.html

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