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Hyponatremia: The Most Common Electrolyte Abnormality…Ever

When learning anything, we should always ask ourselves two  important questions:

1) Does this make sense to me?

2) Is this relevant to me?

Obviously you won’t be able to retain any of the information you learn if you don’t even understand it. And you’re even less likely to retain it if it has no relevance to your life.

I realized I needed to post something on Hyponatremia when I had to go back to my Mass Gen hyponatremia algorithm flow chart for the hundreth time that day all the while knowing that in 5 minutes I’d forget it again. So I sat down and decided to break it down so it made sense to me.

That having been said, I present to you a simplified understanding of the management of hyponatremia, the most common electrolyte abnormality…ever.

So why is this important to you? In other words what is the relevance?

1) It’s common. In fact it is the most common electrolyte abnormality with up to 30% of hospitalized patients developing it, mostly in elderly.

2) Its deadly dangerous. (Anytime you have death as a potential outcome there is something to look out for.) The risk of morbidity and mortality increases with the severity of hyponatremia in almost every known disease state.

3) Possible treatments vary greatly from each other. They vary so greatly that they are in fact opposites (i.e. giving fluids vs. restricting fluids) Choosing the wrong treatment option can lead to above mentioned “death” scenario.

Please make sure he never suffers at the hands of hyponatremia:

The Basics:
Definition: <135 mEq/L, severe if < 125 mEq/L
Normal range: 135-145 mEq/L

One key point to remember here: The extracellular sodium concentration is more indicative of water balance than it is of total body sodium content. Essentially, the serum sodium value says more about how much water is in blood vessels than it does about the actual sodium content. Think dilution.

Signs/Symptoms: It begins very nonspecific and mild with headaches and irritability and progresses to nausea and vomiting, some mental slowing, unstable gait/falls, confusion/delirium, and disorientation. Then to the more severe, what you don’t want to see in your patients: stupor/coma, convulsions, respiratory arrest and…I would put death here but at that point its not a very helpful symptom in terms of management. In general, the more severe the symptom the more quickly and aggressive you need to treat.

Here is what most med students, and very likely most interns think of when going through Hyponatremia (sorry for the blurred font)

Just so you’re not that intern. Here are the Big Picture Steps for understanding Hyponatremia:

Hyponatremia Management: The BIG Picture

OVUM (for those of you mnemonic freaks out there, I’m one too.)
Osmolality + Volume status + Urine = Management!

1) Check Serum Osmolality: Why? To rule out causes of “false” hyponatremia such as an increase in protein, lipids, glucose, mannitol, or glycine (secondary to urolgic or gynecologic procedures). Essentially we are asking, is this “true” or not?

Question: Why do lipids, glucose, protein, mannitol affect serum sodium values?
Non sodium solutes such as glucose cause fluid to shift into the vasculature essentially causing a dilution of serum sodium concentration. Osmotic pressure baby. What this does is give the appearance of a drop in sodium. Remember this formula?  Corrected Serum Osmolality = 2Na + Glucose/18 + BUN/2.8. Well, now you know why BUN and Glucose are in there. There are strong solutes.

2) Check Volume status: Why? Whether fluid is retained or not helps us tentatively approach the etiology (Is is due to cirrhosis, heart failure, nephrotic syndrome? Or is it due to diarrhea, vomiting,  diuretic use?) Then we can decide which treatment options to consider: To give water or not to give water, that is the question…

Whether ’tis nobler in the mind to suffer
The slings and arrows of outrageous fortune,
Or to take arms against a sea of troubles
And by opposing end them.

Take arms I say, take arms! Arms filled with bags of saline…unless of course the patient has SIADH.

Question: How do we determine volume status? This is done clinically. (ie. check for postural hypotension, JVP, tachycardia, skin turgor, signs of swelling/edema.)

3) Check Urine Osmolality and Urine Na: Why? To find out if the kidneys are the culprit. If Urine Na >20 → most likely yes.

4)Management/Treatment: Ultimately you either replace fluids or restrict them. The correct decision needs to be made to avoid unwanted outcomes. Additional info along the way can lead you to discovering the underlying pathology. An example would be finding out that the Urine Osmolality is >100 mOsm/kg suggesting an SIADH picture (ADH causes you to retain water by activating aquaporin channels in the collecting ducts so naturally the Urine Osmolality would be higher). Might there be a pulmonary or CNS lesion we are unaware of? This can lead to a crucial discovery for the patient’s care.

Question: Why are patients often euvolemic in SIADH while also excreting so much sodium?
In Syndrome of Inappropriate Antidiuretic hormone Hypersecretion, you have just that – hypersecretion of ADH, causing retention of water at the level of the collecting ducts. The thing is, the body’s Osmoregulatory systems are still working fine. It senses and increase in fluid and tries to get rid of the excess as best as it knows how: by getting rid of sodium, hoping that water will follow. Which of course it doesn’t. Hence patients tend to either be euvolemic or slightly hypervolemic and hyponatremic. Voila!

One last major point to consider during the initial workup is if this acute or chronic. An acute episode of hyponatremia is defined as being <48 hours and evidenced by neurological sequelae, since the brain has much less time to adapt to the osmotic differential.

The long and the short of it (The Review)

When being presented with a patient that is hyponatremic I realize that I first need to know whether this hyponatremia is “true” or not which is where serum osmolality comes in. Second, I need to know whether I should be preparing to give this guy fluids or restrict fluids. This is where knowing the volume status comes in. And finally, checking his Urine tells me whether I am dealing with something kidney related or not. Instead of relying on a blurred mental image of the hyponatremia algorithm I can actually think it through in a way that makes sense. Which is why it’ll stick this time around.

Train yourself to review

Did that make sense? Was it relevant to you? I hope you can answer yes to both questions. Try to get into the habit of reviewing material you’ve just read especially when studying for the boards or for exams. The review will help you to realize if there was something you didn’t really understand as well as help your brain file it away appropriately, having made the important connections and associations. It literally can take only 5 seconds for a big picture review.

Dive back into those physio and biochem books if you have to and make sure you get the basics. As a resident, these concepts are foundational and inform your decision making.

Enjoy your sodium!

Drinking too much water

One interesting phenomenon that I think we as clinicians will be seeing more of is hyponatremia secondary to drinking too much water. You’ll see this mainly in athletes training for a marathon, a triathlon, or just exercising really. The excess water intake essentially dilutes serum sodium before the body has time to excrete the excess. The treatment for water intoxication is just fluid restriction in mild cases, and in severe cases the use of diuretics and/or vasopressin receptor antagonists such as the Vaptans.

Helpful Algorithms
(Click on the images to make them bigger)

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Two, Seven, Nine, Ten, C, S, and Z

Today while rounding, our attending asked a seemingly innocuous question, “What are the vitamin K dependent clotting factors?” Among the barrage of knee jerk responses the intern had clearly gotten his words out first, “Two, Seven, Nine and Ten.” The attending’s response, “No.” The look on that intern’s face was priceless. It had a mix of utter disbelief, shock, and even some anger in there. “What do you mean, No?” The intern asked. “I mean, No.” The attending was thoroughly enjoying this. After a palpable pause, a friend of mine (the other med student) ended up saving the day with two more syllables, “C, S.” The attending was pleased.


We ended up spending the next few minutes discussing why it is so important to consider these other two proteins in our knee jerk response. If a patient needs to be anti-coagulated for any acute venous thromboemboli you should treat with heparin AND warfarin. Warfarin inhibits vitamin K dependent carboxylation of the factors mentioned above, and because Proteins C and S have anticoagulating properties and have relatively shorter half lives, they get affected by Warfarin first and create a temporary PROTHROMBOTIC state. The heparin given for the first 5-6 days of the treatment is to cover that brief window where Proteins C and S are out of commission, at least until the INR is therapeutic (2.0-3.0).

Interestingly enough, I found out that there is another anticoagulant that is Vitamin K dependent, Protein Z. It seems it works on inhibiting Xa…good to know. If this was all boring repetition for you then great, thats kind of the point. I thought I’d put this up here because I was surprised at how many had forgotten exactly the roles of Proteins C and S.

And here’s our lovely cascade for your reviewing pleasure:

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Feeling Safe?

Its been awhile since I’ve posted. Recap: I passed Step 1 and I’m very happy. I’ve just begun my studying for Step 2 and came back to this blog wanting to share more tools and tricks up for improving the studying process.


David Sousa talks about several barriers we have when learning. Two major barriers mentioned can be summed up in the following two questions: 1) Do you understand the material? and 2) Is it meaningful?  Asking ourselves these two questions can revolutionize how we study and help us retain information better. Once you become more aware of these two points you’ll be amazed at how often you just continue reading without having fully understood what was just read. The same goes for whether the passage is meaningful.

Our brain is an incredible triage nurse constantly asking whats more pressing? whats more important? what needs to be done NOW? Therefore if you dont even get what you are reading, the brain throws it out. If its not meaningful in any way, if it doesn’t hold your attention, then your brain right clicks and ’empties trash contents’. Done.

My suggestion: At the end of every section or subsection you read stop and ask yourself: Did I understand that material? Really? Was it meaningful? How so?


Those two barriers of comprehension and meaning are dwarfed however by another more massive barrier. That of safety. Basically –

Do you feel safe?

This single insight has rocked my cognitive world. Essentially Sousa is saying that due to evolutionary reasons we homo sapiens place safety far far above anything else in regards to the brain’s time and energy investments. Naturally this makes sense. We would rather be alive first, an expert at tracing our hands on cave walls second.

Heres the rub though, the brain makes no distinction between externally perceived threats and internal ones. So your worrying about getting into a residency program could be as threatening as a pack of wolves might have been to our fore fore fore fathers (for some of us more so). In both instances the brain senses a threat (real or imaginary) and responds with a massive and often continuous flood of hormones, neurotransmitters, and electromagnetic changes that all but shut down our ability to learn, process, and retain any information not directly related to the threat.

For me, this meant I study better and infinitely more effectively when I’m safe and at peace, obviously externally but more importantly internally as well.

Why do you think children who go to schools with metal detectors or who live in generally more dangerous neighborhoods don’t do as well as their safer counterparts? Factoring out socioeconomic status and other similar reasons, its been shown that students who feel safer perform better. Period.

My question to you: DO YOU FEEL SAFE?

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First Step

I want to welcome you to this site on this first post. My hope is provide a place that offers guidelines and tools you might want to use as you take the USMLE Step 1 exam. My plan is continue this site for future Step exams for those doing Steps 2/3.

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