Sodium (Na) Gumbo & Sports Drinks!

https://tomschexnaildremd.com

Book an Appointment (Men in AL & AL)

Key points: 

Sodium is the primary determinant of plasma osmolality (saltiness).

The kidneys are very precise when dialing in your plasma sodium.

When Na is abnormal on routine labs, medication lists MUST be investigated, as medications are often the culprit.

Low sodium and high sodium cause fluctuations in intracellular water, which can be dangerous, especially if Na is <120 mmol/L.

What should you drink when you get gastroenteritis? (vomiting & diarrhea)

Water + Salt - this can be obtained in Pedialyte, adding salt to water, eating salty foods with water, or drinking sports drinks (I don't recommend because they have too much sugar and not enough salt). You can also use these: LMNT

Let's connect! YouTube | Instagram | LinkedIn |X

This is not medical advice and is for information purposes only. Listeners should not delay in seeking medical advice for any medical concern. No physician patient relationship is formed by listening to this podcast.

Transcript

To understand sodium, you have to understand water. They can be separated and discussed theoretically just like you can pull the cornbread off of the hotdog, but in reality, they are one in the same. They’re friends. Where sodium goes, water goes. After we get through some technical stuff, we’ll hear about how Kid Boudreaux makes gumbo, and wrap it up with the most common sodium abnormalities.

First, let’s talk about water, specifically where it is in the body and how intake is balanced by output. Water makes up 55% of body weight in women and 60% in men. ⅔ of that 55-60% is inside of cells, aka intracellular, and about 1/3 is outside of cells, aka extracellular.  The extracellular water is either in the plasma, which is inside of blood vessels, or the interstitium, which is the space outside of cells and outside of blood vessels. The interstitium is what bathes the cells, and interstitial fluid gets there by leaking out of capillaries and returns to the circulation by way of the lymphatic system. Another way to think of water compartments is as spaces. The first space is inside cells. The 2nd space is in the blood vessels, and the 3rd space is in the interstitium. To summarize this concept, most body water is inside of cells. Water that is NOT inside of cells is in transit - either going toward them or going away from them. It’s in constant flux. The body maintains water balance by matching water intake from what we eat and drink with what we excrete. Most water leaves the body as urine, but smaller amounts  leave the body via stool (about 200cc), and breath and sweat (insensible, but about 500cc). Intake is about 2-2.5L daily. Water freely flows in and out of cells to achieve osmotic equilibrium. As we will see shortly, the osmolality, or solute concentration is the same in all water compartments, but the solute composition is different. Ok let’s talk about electrolytes.

In contrast to water, electrolytes do not move freely. The intracellular and extracellular environments of the body have different purposes. The extracellular environment is a transport system that exists to deliver nutrients, oxygen, hormones, and other molecules to cells and carry away waste products, CO2, etc. The cells perform metabolism and their cell specific functions. As a result, the electrolyte compositions of these compartments are different from one another.  Na and Cl are the main extracellular electrolytes. K and Phos are the main intracellular electrolytes. The differences in electrolyte compositions are intentionally maintained by the body. The most important way is by the Na K ATPase, which is on all animal cell membranes. It uses ATP energy to pump 3 Na out of the cell and pump 2K into the cell. This creates a cross membrane electrolyte and charge imbalance called an electrochemical gradient that is used in many ways. This is why 90% of total body sodium is extracellular and 98% of body potassium is intracellular. The most important point of the episode is that sodium is the primary determinant of plasma osmolality. The body seeks to maintain the plasma osmolality, or solute concentration very precisely, and it does that by manipulating the retention and excretion of water and sodium, mainly at the level of the kidneys. 

Now it's time for a story. In a wooden shack down the bayou in Louisiana, Kid Boudreaux is standing over the big black boiling pot holding his wooden paddle. The seafood gumbo is coming along great. Never mind the fact that he is 60, still goes by the name kid, and has a huge fire lit in the middle of his wooden house. This is cajun country baby. Anyway, he breathes in the peppery, rich steam rising off the pot. He’s cooked this gumbo so many times, one smell is all he needs to dial in the recipe. The okra, shrimp, and alligator bob in the roux. The 2 goals of making the gumbo, of course, are to feed the whole family, and make sure it tastes perfect. You wouldn’t think it by looking at him, but kid is actually very mathematical. First, he fills the pot with the perfect amount of water and ingredients. Next, he adds the salt. When the fire gets going, that’s when the magic happens. If it’s not salty enough, kid has 2 options: add more salt, or boil off more water. If it’s too salty, he adds more water or gets rid of some salt that’s already in the recipe, which is a secret cajun superpower. If there’s not enough volume in the pot, he adds both salt and water. 

Kid Boudreaux represents the kidneys. The kidneys are responsible for making the perfect blood plasma gumbo. This comes down to 2 things: plasma gumbo volume - is there enough gumbo to feed the entire family of body organs, tissues, and cells, and plasma gumbo saltiness - does it taste perfect, which is mainly determined by sodium? The kidneys get recipe recommendations from all sorts of people: pressure receptors in the carotid arteries, sodium concentration receptors in the brain, hormonal influences from the renin-angiotensin aldosterone system, sympathetic fight or flight instructions from the nervous system, and their good buddy antidiuretic hormone from the brain hypothalamus.

Antidiuretic hormone is worth a little more detail, because malfunctions involving him cause the majority of sodium abnormalities. When the body senses sodium concentration being too high, antidiuretic hormone, or anti dehydration hormone, as I think it should be called, is released from the brain and allows more water to be reabsorbed into the blood from the kidney tubules. This dilutes the sodium concentration and lowers plasma osmolality to normal. Sometimes ADH takes it too far and retains too much water, causing low sodium.

ADH works together with thirst, which is activated or inhibited based on plasma sodium concentration. When plasma sodium is high, you get thirsty. When it is low, you’re not. Think about times when you’ve been thirsty: after exercise, eating pizza, vomiting, etc. Those are times when your Na was too high.

Now let’s talk about high and low sodium.

Low plasma sodium, or hyponatremia, is much more common than high plasma sodium, or hypernatremia. 2 reasons for this, which I just briefly touched on:

1. ADH often overdoes it. He causes the kidney to reabsorb too much water, dropping the plasma sodium level below normal. This is called the “syndrome of inappropriate ADH secretion” and is a secondary consequence of something else, which we will further discuss in a minute. 
2. Hypernatremia is rare, and here’s why” Our thirst mechanism is strong and drinks are abundant. Bedbound nursing home patients are one of the few groups to get severe hypernatremia. They don’t have a normal thirst mechanism and are also unable to get out of bed to get water even if they are thirsty. 

As far as levels of severity go, mild hyponatremia is 130-135 mmol / L, moderate is 120-130, and severe is less than 120. The number isn’t the only thing that matters though. It is important how FAST the sodium changes. Here’s why: Sodium fluxes cause water to move in and out of cells. Cells swell when water moves in and shrink when water moves out. The brain is 85% water and is encased in the inflexible bony skull. Sodium changes, even small ones, can cause brain cell swelling and shrinkage, which causes brain symptoms like headaches, confusion, lethargy, weakness, and even seizures or death. If the plasma sodium lowers fast and water rushes into the brain cells, a person could develop life threatening symptoms even with a sodium in the moderate range. If I was looking at my labs and the sodium was less than 120, I’d go straight to the ER, and if I had any symptoms even with a level 125-130, I’d call my doctor right away. Let’s talk about a few more common scenarios for someone who just got routine labs done:

Medications will probably be the biggest culprit. They have different ways of causing low sodium: diuretics like chlorthalidone, hydrochlorothiazide, and furosemide limit the kidney’s ability to reabsorb salt and water. They take out the chef, and without the chef, the gumbo recipe is wrong. Antidepressants (like prozac and zoloft), antiseizure, and antipsychotic drugs cause increased production of ADH, making the gumbo recipe too dilute. Rare causes would be nicotine patches, blood pressure medications like lisinopril or amlodipine, some antibiotics like bactrim or cipro, and others. Medication lists always deserve very close scrutiny when there is a lab problem!

Volume depletion. I said volume depletion very intentionally, not dehydration. You now know that sodium and water roll together. While we use the word dehydration for convenience, there is really only 1 scenario where our bodies lose free water: water loss from breathing, which amounts to about 500cc per day. Lost body fluids always contain some amount of salt, from low amounts, as in sweat, all the way to the exact composition of plasma in cases of bleeding. It's important to note that when body fluids are lost, all electrolytes are affected, not just sodium. Let’s take vomiting, for example. Gastric juices are acidic because of hydrochloric acid (HCl). When that is lost in large amounts, there will be a metabolic alkalosis (higher than normal pH) because of lost acid, low chloride, and low potassium for reasons we’ll discuss in a later episode. Secretions from diarrhea are high in bicarbonate. So when diarrhea is the culprit, the loss of bases leaves a more acidic blood pH with low bicarbonate. An interesting question arises while we’re talking about it: what should you drink if you have gastroenteritis? Well as much as I hate sports drinks, I would recommend them (personally, I would replace about ⅓ of the bottle with water and add a pinch of salt), pedialyte, salty broth, or water and salty dry foods. The reason why sugar is part of the WHO rehydration solutions for cholera is that the intestines have sodium glucose cotransporters, so in order to reabsorb the sodium you drink, there needs to be a small amount of glucose as well. Not as much as is contained in sports drinks though.

Exercise. This is a great example of good advice gone bad. Exercise without drinking anything will cause hypernatremia from mostly hypotonic sweat loss. But the more dangerous hyponatremia happens when athletes over consume water or sports drinks thinking that will improve their performance. Sports drinks, while they are technically hyperosmolar compared to plasma, most of that solute is actually sugar, not electrolytes, so when that sugar is metabolized, the remaining solution is hypotonic relative to plasma. So it is essentially like drinking water. The best advice for athletes: drink to thirst!

High blood sugar. This is actually an example of “pseudohyponatremia,” meaning sodium is normal, but the presence of high blood sugar draws water into the plasma, diluting out the sodium level, making it read low. To correct, add 2 to the sodium level for every 100 points the blood sugar is above the upper limit of normal. 

Lastly for low sodium, I want to mention the group with advanced heart failure, cirrhosis, and kidney failure. This group will retain water but have decreased intravascular volume. So the receptors that influence the gumbo recipe will tell the kidneys to retain water, causing hyponatremia. Do you have one of these diagnoses? If so, this is likely heavily influencing your low sodium, and the prescribed diuretics may also be contributing.

Okay, in summary: Where sodium goes, water goes. When sodium is low, that means water is relatively high and vice versa. The body needs enough volume to give all the cells what they need and it has to have the perfect salty flavor! Next episode, we’ll cover potassium, chloride, and bicarbonate!

Send me your questions, comments, and of course, your favorite gumbo recipe!