MD & DO Fluid management question

[Maxilla54]

So I read that the default is to prescribe IV fluids in viral encephalitis (insensible losses from fever, decreased intake from confusion, risk of ARF).
Does encephalitis (viral or otherwise) tend to cause increased ICP and would this be a (relative) contraindication to fluid prescription?

Pardon me if this is a silly q, but is raised ICP ever a contraindication to fluid prescription? Mannitol or hypertonic saline are used to lower ICP, so would hypotonic or physiological solutions raise ICP?

edit:spelling

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[CliveStaples]

You would certainly not want to administer hypotonic fluid, but recognize that even in cases of cerebral edema (which viral encephalitis can certainly cause, but doesn't necessarily always cause), you will likely have a mildly elevated sodium goal that could even be achieved with normal saline. This is a rare case where I would probably reach for NS over LR but it still probably doesn't matter.

Regardless, people with cerebral edema are not fluid restricted in order to prevent edema. This is not a disease treated with lasix. Just don't use hypotonic fluids (which you should be avoiding anyways except in very specific cases).

 

[Chemist0157]

Goal would be normal physiology - euvolemic and normo-osmolar. Perhaps favoring mild hyperosmolar state. I would certainly want to avoid hypo-osmolar serum. I would not withhold volume resuscitation from someone who is volume depleted.

 

[longhaul3]

Encephalitis can cause increased ICP in a few ways—cerebral edema, hydrocephalus, hemorrhage, abscess, thrombosis, empyema, etc. You're not going to fluid overload the brain the way you would the heart. It's not the volume but the tonicity that's the issue—since the brain is extravascular, the volume of brain tissue depends on the osmotic gradient, not the total blood volume. Patients with increased ICP actually need to be adequately fluid resuscitated, and sometimes even pressed, to maintain their MAP and thus cerebral perfusion pressure.

1/2 NS is to be avoided in case of increased ICP because it will decrease plasma osmolality. NS is hypertonic to plasma. In hypo- to eunatremia, NS will tend to increase the serum Na, albeit slowly. We use it occasionally for mildly hyponatremic or low-eunatremic patients who we want to get to 140-145 but don't want to use 2% or 3%.

 

[AlteredScale]

Encephalitis can cause increased ICP in a few ways—cerebral edema, hydrocephalus, hemorrhage, abscess, thrombosis, empyema, etc. You're not going to fluid overload the brain the way you would the heart. It's not the volume but the tonicity that's the issue—since the brain is extravascular, the volume of brain tissue depends on the osmotic gradient, not the total blood volume. Patients with increased ICP actually need to be adequately fluid resuscitated, and sometimes even pressed, to maintain their MAP and thus cerebral perfusion pressure.

1/2 NS is to be avoided in case of increased ICP because it will decrease plasma osmolality. NS is hypertonic to plasma. In hypo- to eunatremia, NS will tend to increase the serum Na, albeit slowly. We use it occasionally for mildly hyponatremic or low-eunatremic patients who we want to get to 140-145 but don't want to use 2% or 3%.

So I always get this statement of "LR is good for everything but the brain" and I am assuming it's because LR is more osmotically similar to that of plasma, so in the setting of ICP it wouldn't do as much as NS?

 

[CliveStaples]

So I always get this statement of "LR is good for everything but the brain" and I am assuming it's because LR is more osmotically similar to that of plasma, so in the setting of ICP it wouldn't do as much as NS?

It’s just that LR is hyponatremic relative to plasma and generally you want to raise the sodium in increased ICP settings.

 

[Maxilla54]

Thanks to everyone for your replies. Very interesting points to consider! I love medicine

 

[Chemist0157]

So I always get this statement of "LR is good for everything but the brain" and I am assuming it's because LR is more osmotically similar to that of plasma, so in the setting of ICP it wouldn't do as much as NS?

LR is a balanced solution so yes, it would not change much unless the serum osm / sodium were already lower than what the LR has to offer.

 

[longhaul3]

So I always get this statement of "LR is good for everything but the brain" and I am assuming it's because LR is more osmotically similar to that of plasma, so in the setting of ICP it wouldn't do as much as NS?

The posts above answer this well. LR has 130 meq/L of Na, which is not only below the typical Na goal for patients with ICP issues, but below even the bottom of the eunatremic range, which is unacceptable in intracranial hypertension. There was a study (PMID 26914721) that demonstrated increased mortality in TBI patients resuscitated with LR vs. NS. Although LR and NS are similar in tonicity, sodium is most important.

We are usually less concerned about the other medical and electrolyte issues NS can cause like hyperchloremic acidosis, hyperkalemia, etc. and are therefore not really interested in the overall LR vs. NS debate. There is almost no pathology in medicine that trumps an ICP crisis (obviously hyperkalemia can cause cardiac arrest but I've never heard of saline infusion causing a K high enough to do that, even in ESRD patients, and you can treat hyperkalemia). In our average patient the only labs we really care about are Na, Hgb, plt, and coags.