Name:
RTL- Ep 93- Hypernatremia
Description:
RTL- Ep 93- Hypernatremia
Thumbnail URL:
/images/podcast-microphone-banner.jpg
Duration:
T00H17M06S
Embed URL:
https://stream.cadmore.media/player/b1cff022-7e62-4229-92d2-149acb3eb0b9
Content URL:
https://cadmoreoriginalmedia.blob.core.windows.net/b1cff022-7e62-4229-92d2-149acb3eb0b9/RTL- Ep 93- Hypernatremia.wav?sv=2019-02-02&sr=c&sig=0TQrWLFAfrjZBFWDmo9Nj3trHMJOwb6otBwlecf3FPg%3D&st=2024-05-06T08%3A09%3A53Z&se=2024-05-06T10%3A14%3A53Z&sp=r
Upload Date:
2023-03-21T00:00:00.0000000
Transcript:
Language: EN.
Segment:0 .
[Dr. Smith] Welcome back to Run the List, a medical education podcast in partnership with McGraw Hill Medical. Our hosts are Dr. Navin Kumar, Dr. Walker Redd, Dr. Emily Gutowski, Dr. Joyce Zhou, and myself, Blake Smith. As a quick disclaimer, this podcast is meant for informational and educational purposes only, and should not be understood as medical advice under any circumstances.
[intro music] [intro music] [intro music] [Dr. Zhou] Welcome back to Run the List. My name is Joyce Zhou, and I'm here with Dr. Alexis "AC" Gomez who is a second year renal fellow at the Mass General Brigham Boston Children's Nephrology program.
You guys might remember that two weeks ago, she shared wise words on how to think about hyponatremia, and today, we will continue to talk about sodium but this time focusing on hypernatremia. Dr. Gomez, a.k.a. the great defender of the kidneys, welcome back to Run the List. [Dr. Gomez] Thank you, Joyce. It's great to be back. [Dr. Zhou] The context of "the great defender of the kidneys" is that a few hours after we recorded our last episode on hyponatremia, I saw on Twitter a picture of Dr. Gomez in what I remembered was a Captain America T-shirt, and that was the T-shirt I saw during our recording, it turns out it's not actually a Captain America T-shirt but a renal one, and her caption on her tweet read something along the lines of, "I dress for the job I want so every day I dress as the late stay great stay sole defender of the kidneys," which I bet is exactly how she feels at times, so thank you, Dr. Gomez, for your service to the beans.
[Dr. Gomez] It's true. I often rep the renal gear when I'm at work or at home, and a lot of days it feels like the kidneys don't get enough love. So we got to show people how great it is. [Dr. Zhou] Definitely. So hopefully we'll be able to talk a little bit more about the beans today. We're excited for another kidney-centric conversation on hypernatremia, let's kick it off with a case. So we'll start with Ms. E.
Ms. E is a 38-year-old female. She has a history of developmental delay, arterial venous malformation status post-cavernous angioma resection, a seizure disorder on levetiracetam or Keppra, as well as a neurogenic bladder status post-ileocecal augmentation cystoplasty. She also has a history of recurrent UTIs, and she presents from a group home to the emergency department with two days of altered mental status.
She's found to have a UA with pyuria, and a white count of 14. Her admitting sodium level is 146, that baseline was 134 one week prior, and she has an AKI on admission with a creatinine of 2.1 from a baseline of 0.9. She received two liters of LR, she's kept NPO due to her altered mental status, and she was started on cefepime for a potential UTI.
12 hours later another BMP is checked with a sodium of now 159, up from 146, and on recheck six hours later, had uptrended up to 166. She was NPO again this whole time. In other words, this patient presented with a mild hypernatremia that got progressively worse after admission to the hospital. So let's dive in on this hypernatremia case, but before we get started, how do you define hypernatremia?
And like hyponatremia, are there initial safety concerns that worry you? Does chronicity matter? [Dr. Gomez] So first of all, hypernatremia is defined as a serum sodium concentration greater than 145 mEq/L. Similar to hyponatremia, here we can have acute or chronic, with chronic being greater than 48 hours. With hypernatremia though, almost all patients are going to fall into this chronic category, even if they're symptomatic, and that's for reasons that we'll discuss.
Similar to hyponatremia, we want to consider our target rate of correction here. And remember that as we discussed last time, the risk of overcorrection with hyponatremia is osmotic demyelination syndrome. Here, our risk with overcorrection of hypernatremia is cerebral edema, although this risk is much less well-defined. Interestingly, and this almost never happens, where this risk is much better defined is in pediatrics.
So in this case, remember that much of our data on safe correction rates comes from pediatrics. [Dr. Zhou] Excellent. So even though kids are not just little adults, sometimes we get our data from pediatrics, and we take what we can. So now, I would like to turn to your approach to the causes of hypernatremia.
How do you think about what causes hypernatremia? [Dr. Gomez] Yeah, so in general, when we think about hypernatremia, we want to think about water losses exceeding water intake. So we want to think about what it could be that's causing our water loss, and what it could be that's causing impaired intake. In terms of the losses, the things I think about are skin losses, GI tract losses, and renal losses.
So for skin losses, you want to think about factors that would increase water loss, so things like fever, exercise, or high temperatures. For GI losses, I think about things like vomiting or diarrhea, especially an osmotic diarrhea where water's being pulled into the GI tract by some osmotically active substance that results in significant electrolyte free water losses this way.
Lastly, I think about renal losses. So with renal losses, you can have things like a diabetes insipidus which can be central or nephrogenic. In this case, you are either not secreting or responding to ADH, which if you'll recall from last week's episode, is a hormone that increases water reabsorption. So if you're not secreting or not responding to it, you'll excrete a dilute urine and lose free water.
I also think about an osmotic diuresis. So similar to our example of an osmotic diarrhea, here, we're thinking about things like glucose, mannitol, or urea, which are substances that will increase the osmolality of the urine. But if the urine is relatively electrolyte-free, your serum sodium will increase. Again, going back to last week's episode, this is why with any case of sodium derangements, we want to know not only an urine osmolality but also an urine sodium and potassium so that we can figure out the electrolyte free water loss that's occurring.
But any of these causes independently, should stimulate thirst, so under normal circumstances, if you or I had one of these, we would not be expected to develop hypernatremia. So this is where we want to think about what could be causing impaired water intake. If you have a hypothalamic lesion or disease, you can develop hypodipsia or adipsia where your thirst mechanism is impaired or not intact, along with other more rare CNS issues that also result in impaired thirst.
The other thing I think about with respect to free water intake is your ability to respond appropriately. So here, I think about patients with altered mental status, or patients who for some reason can't access water. Lastly, while factors that result in increased water loss compared to water intake should always be at the top of your differential for hypernatremia, much less commonly, we do want to think about things that increase sodium itself.
So here, we think about salt poisoning or administration of hypertonic saline. For example, in peds, we always think about salt administration or inappropriately mixed formulas. In adults, we often think about hypertonic sodium bicarb administration or hypertonic saline, especially in patients in our neuro ICUs who have things like a traumatic brain injury where we may administer these intentionally to increase the serum sodium.
[Dr. Zhou] Great, so my understanding is that I hear there are two different things you should think about. One, there is a concern for something that leads to increased free water losses, such as GI losses, renal losses, et cetera, but there's also things that stimulate impaired water intake. So you need both of these in order to have hypernatremia. Let's turn back to this patient, Ms. E, now.
So you talk about some of these causes, can you apply those causes to this particular patient? [Dr. Gomez] Yeah, so I think in this patient, there's a couple of things that could apply here, and I'd probably go back to the ER to get a little bit more history on this patient to figure out what might be going on, but certainly, we can talk through some of the things that I'm thinking initially when I get this consult.
So one is that in any of our patients who have any type of intellectual disability, or who may have altered mental status, we want to think about their access to free water, so whether or not they're able to access that free water. And then you also want to think about along those lines in these patients, how do they typically get their intake? So are they eating and drinking on their own?
Are they able to do that because they're altered? Are they getting feeds through a G-tube? And so what exactly is all of that history? Then again, you want to think about the things that could be causing losses. So what has their urine output been like? And certainly, we want to get some urine studies that we'll discuss. Have they had any vomiting or diarrhea?
It doesn't necessarily sound like this is the case for this patient, and then in this patient who has a history of recurrent UTIs and altered mental status, who it sounds like probably has a UTI, has she been having fevers and things like that that can increase your insensible losses? So probably in this patient, my biggest thing would be if she's had a history of fevers, and then how she's able to get free water, and how she gets her feeds.
[Dr. Zhou] Wonderful. Now, can you talk me through how you think about labs or diagnostic testing in these particular cases? [Dr. Gomez] Absolutely. So as with most things, your most important tool here is going to be your history and your physical. So I've rarely had a case of hypernatremia where the answer as to why it occurred was not apparent after getting the history, which is why my first step would be to go back to the emergency room and kind of ask a few more questions.
But we also do want to get some studies to help reinforce this, as well as to guide our treatment. So in addition to knowing our serum sodium, we'll want an urine osmolality as well as an urine sodium and potassium to understand our electrolyte free water clearance. And as always, I want to know the urine output. So for example, one thing in this case that strikes me is the rapid rise in sodium in a very short amount of time.
I'm not sure of this patient's weight but if we knew it, we could actually calculate how much free water she would've had to have lost to cause that much of a rise in her sodium over that short of a time. If we knew her urine output and those labs, specifically the urine sodium and potassium, we could get an estimate of her urinary free water loss, and get a better sense for if this rise in sodium was real, or if we have a concern that some of the labs may have been in error.
[Dr. Zhou] I really appreciate that final point because in particular, we never really think about BMPs or sodiums to be inaccurate, but sometimes a repeat lab will be helpful in cases where I think the urine output doesn't correspond to what you would expect to cause a sodium change. So in particular, for this patient, we actually thought that the initial normal sodium per the renal team was actually a lab error, given the amount of urine she had put out.
So they thought she had put out less than what corresponded with how much free water you needed to cause that rapid degree of sodium rise in the first 24 hours, but after that first number, if you took that first number away, they explained the rest of her hypernatremia primarily with what they thought was a post-ATN diuresis, as well as some free water losses due to fevers. So let's turn now to treatment.
Do you have general approaches to how you treat hypernatremia? What guidelines you have in approaching chronic versus acute hypernatremia? And I'll just throw out the phrase, free water deficit, everyone talks about the free water deficit, how does one calculate that? [Dr. Gomez] So with hypernatremia, you'll want to calculate your free water deficit like you mentioned.
I promise you can always look up this equation, but basically, it's your current sodium divided by 140, then subtract 1, and then multiply this number by your total body water. Again, I promise you can look it up. Your total body water is estimated as roughly 50 to 60% of your lean body mass, but this number depends on your age, your gender, and how water depleted you are.
Still, it can help with a rough initial estimate. I also want to know their ongoing losses, and especially their urine output. This is really important because our patients are not a closed box of water and sodium, but instead they have ongoing losses, and we need to account for this in our correction. So similar to hyponatremia, if this is acute, which again, it rarely is in these cases, you can correct your serum sodium much more quickly as you have a lower concern for overcorrection.
However, you'll want to be a little bit more cautious if it's chronic. [Dr. Zhou] All right, so primarily, more or less, hypernatremia is typically more of a chronic problem than an acute problem, usually, but how do you think about the rate of corrections in these particular cases? What kinds of fluids would you like to administer? Particularly, this question of isotonic versus hypotonic fluids is always something that comes up.
[Dr. Gomez] Yeah, so I agree, this comes up pretty much every case of hypernatremia that we get. So again, with acute hypernatremia which is uncommon, we can aim to correct the serum sodium relatively quickly, but most of your cases are going to be chronic hypernatremia, and for this a reasonable goal that's extrapolated from pediatric data is roughly 10 to 12 mEq per day. But given the paucity of data, that there's significant risk of overcorrection in hypernatremia in adults, if we exceed this goal, we don't aim to raise the serum sodium back up if we exceed it. So as you may recall, this is a significant departure from our approach to hyponatremia, where if we exceed our goal, we do want to lower our serum sodium back down to that goal.
In terms of fluids I recommend what I always tell teams is if it's relevant to the case, separate out in your mind hypovolemia, meaning water and sodium losses, from dehydration. I often have teams ask if they can treat the hypovolemia as they worry that we won't achieve our target serum sodium goals if they're giving NS or LR for resuscitation. My answer to this is, yes, hypovolemia can certainly cause a patient to be clinically unstable, and this does need to be addressed.
And keep in mind, this will often also help to correct the hypernatremia, although at a slower rate than if you were giving free water. Next, I recommend addressing the free water deficit itself. So again, here I'll often get questions about if we can just do hypotonic fluids like half NS, to address both, but I typically find that the amount of volume you need to address the hypovolemia, and the amount of free water you'll need to address the hypernatremia are not the same.
So again, I would just separate these two out in your mind. In terms of treatment of hypernatremia, I most often choose D5 water or enteral free water. My goal rate is determined by calculating the free water deficit to get down to my goal sodium for the day, plus my ongoing free water losses. Then I divide this up over 24 hours, either as an hourly rate if I'm giving a D5 water infusion, or by the number of enteral water boluses I plan on giving.
Typically, the most significant ongoing free water loss that I want to account for are urinary free water losses. So here, specifically, we're looking at electrolyte free water clearance. To calculate this, you take your urine sodium plus your urine potassium, divide this number by your serum sodium, then subtract this from 1. Multiply it by your urine volume, and that will give you your electrolyte free water clearance.
So to give us some numbers to work with to help conceptualize this, if you have an urine sodium plus an urine potassium concentration that is half that of your serum sodium, this would be 0.5. 1 minus 0.5 is just 0.5, and then if you multiply that by your urine volume, let's say that you're making a liter of urine, half of it or 500 cc's would be free water.
[Dr. Zhou] Great, so I want to close out the case and share what happened with Ms. E. So she was started on free water at 200 cc's an hour of D5W with this goal to decrease her sodium up to 12 points to 154 after 24 hours. In reality, she went down to 157 in one day, and then normalized to 145 the day after that, and was discharged home with close follow-up for her sodium levels.
Hypernatremia shares some principles as you can tell, with hyponatremia, but it is one of those things that we see a little bit less in the hospital, and deal more with hyponatremia, sending some of these studies, but it is really helpful to hear how you think about how you correct these things, how we calculate some of these values.
So before we wrap up, Dr. Gomez, can you share a few pearls you want us to walk away with after this episode? [Dr. Gomez] Yeah, absolutely. So first of all, as with hyponatremia, remember that your history is your most important tool. Most commonly, you'll want to think about a combination of what caused free water loss, and the inability to keep up with those water losses, but very rarely, you may have a case of sodium loading.
Typically though, water is the key. Next, always remember, as with any other patient, stabilizing them is your first priority. So if you need to treat hypovolemia, don't be afraid to do it. And last, when you calculate your rate of water administration for correction, don't forget, it's not just replacing your free water deficit, but you'll also need to account for ongoing free water losses.
[Dr. Zhou] Great, so we can't just look at the sodium, calculate our number and go from there, we always have to keep reevaluating. Dr. Gomez, thank you so much for joining us today to talk about hypernatremia. We are lucky enough to have you again next episode on acid-base disorders, so I really look forward to chatting with you then. Thank you so much.
[Dr. Gomez] Thank you. [outro music] [outro music]