hyponatremia and 3% NaCl

[tambarino]

As a treatment for hyponatremia, my medical-surgical book mentions using an infusion pump to administer 3% NaCl, a hypertonic solution. This makes sense to me, but then it adds, hypertonic solutions can increase the risk of pulmonary and cerebral edema due to water retention. Careful monitoring is vital to prevent these complications and possible permanent damage.

Everything else I read suggests that a hypertonic IV will pull fluids out of the intercelluar space with the risk of sudden brain shrinkage. What would be the rationale for my book to suggest that fluids are being pulled into the intercellular spaces and causing cerebral and pulmonary edema. Any ideas? My instructor referred me back to the same page in the book that offers no rationale. I really want to understand this.

Thanks for any help!

[KelRN215, BSN, RN]

Yes a hypertonic solution can pull fluid from the cells and cause brain shrinkage. But if a patient is hyponatremic, the first line of treatment is oral fluids and possible IV NS. 3%NaCl would only be given in a severe case of low sodium or when the cause is hypervolemia. Also, in low serum sodium, their blood is hypotonic and already pushing fluid into the cells. The risk of cerebral edema comes from giving them too much sodium to where yes, the cells can have fluid pulled from them, but the fluid would also be retained due the sodium. So now they can get edema fluid retention. At least that's how I understand it (I am also still a student so I could have this all wrong lol)

Oral fluids as a treatment for hyponatremia? No. Fluid RESTRICTION is the first line of treatment for hyponatremia. Hyponatremia has many causes, the most common of which in the general population is drinking too much water. In neuro, we're often looking at either SIADH or Cerebral Salt Wasting. In SIADH, total body sodium is normal but the patient has an excess of water. Therefore, we restrict their oral intake of fluids. In Cerebral Salt Wasting, the patient is wasting salt into their urine so water restriction will not correct this issue. In this case, oral sodium supplements are necessary. 3% normal saline would only be used in severe cases. I've had patients kept on the floor with sodiums as low as 124 mEq/L. Also, there are some drugs (like Trileptal and some chemotherapies) that can cause hyponatremia.

Cerebral edema is a consequence of hypOnatremia, not hypernatremia. Water leaves the intravascular spaces because of osmosis and then the cells swell. Here's a story of a teenager who died from that: High school football player, 17, dies from water intoxication after drinking four gallons of fluids to stop cramps during practice | Daily Mail Online

And another of a runner in 2002's Boston Marathon: Marathon runner's death linked to excessive fluid intake

[icuRNmaggie, BSN, RN]

Good information tambarino! You are a thinker. Reverse osmosis from a disrupted blood brain barrier. Thanks!

[Here.I.Stand, BSN, RN]

You're right ilovegusgus...that should have said >20 for five minutes. I shouldn't type while distracted I guess. lol

I'm interested that you both do chem's more often than q 6 hrs though. We've done ours q 6 hrs as long as I've worked in that setting. I'll have to check into the evidence behind it. Checking more often seems to make more sense

[Underthemoonicp6]

Can anyone speak to why sometimes in a TBI they want the sodium 145-155 and other times they want it less than 145? To me it seems if the sodium is less than 145 then you're not really creating the gradient needed to decrease cerebral edema. And if that's the case then why are you administering a dangerous infusion when you could just give NS and probably achieve similar sodium levels

[Here.I.Stand, BSN, RN]

Goal Na++ levels can vary based on the pt's needs. If they're hyponatremic at baseline, a goal around 140 could achieve the purpose of decreasing cerebral edema w/o the risks of hypernatremia. Hypernatremia can increase the risk of renal failure, complications of fluid overload such as pulmonary edema, etc. so for some the risk of Na++ near 155 would outweigh the benefit.

Also, the risk of cerebral edema increases in the days following the initial injury; think if you've ever sprained your ankle or had your wisdom teeth out. Initially the swelling is minimal (if visible at all), but days later it will be very apparent. My bridal shower was a week after having my wisdom teeth out; I looked like a chipmunk storing acorns for winter, and that image is preserved in the pictures!! Same is true with brain trauma. So maybe initially they'll set a goal of 140-145, but days later they might try to get the levels into the 145-155 range.

There are probably other considerations too, but that's what I can think of off the top of my head.

It's a few years old, but this is a pretty good article on nursing considerations for hypertonic saline administration-- Medscape: Medscape Access

[KelRN215, BSN, RN]

Can anyone speak to why sometimes in a TBI they want the sodium 145-155 and other times they want it less than 145? To me it seems if the sodium is less than 145 then you're not really creating the gradient needed to decrease cerebral edema. And if that's the case then why are you administering a dangerous infusion when you could just give NS and probably achieve similar sodium levels

Do any of these patients have DI?