Hyponatremia

1. WEEKLY DISPATCH

Hot enough for you? Most of the northern hemisphere is baking right now and the heat is putting extra demands on daily rides.

Hydration is a key concern in high temperatures. A roadie can easily sweat off several pounds of water weight on a three-hour ride, making it imperative to keep chugging down liquids.

Right? Maybe not. When it comes to hydration there can definitely be too much of a good thing.

That caution comes from Lulu Weschler, a physical therapist and long-distance cyclist. In 2005 she authored the summary of the first International Exercise-Associated Hyponatremia Consensus Development Conference in Cape Town, South Africa. In October she'll fly to New Zealand for the next session.

The key word: . It describes a dangerous condition caused by over-hydration -- drinking to the point where sodium levels in the blood become so low a medical crisis is at hand (see below).

Dehydration is bad, but hydrating to the point of hyponatremia can be deadly.

Here's the scary thing: Hyponatremia can occur even when drinking seemingly reasonable amounts. To explain, we're turning this over to Ms. Weschler, who has written extensively about the malady. At the end we'll provide the link to a more detailed article she wrote for the UltraMarathon Cycling Association website.

LESSONS FROM LULU

Every serious case (including deaths) of hyponatremia thus far reported during or after exercise has involved over-hydration. Sodium is lost during exercise and that's a concern, but by far the dominant factor in exercise-related hyponatremia is excessive fluid intake.

Some cyclists assume they're safe because they're drinking sports drinks with electrolytes. However, a sports drink has a much lower concentration of sodium than blood. Thus, drinking too much sports drink can dilute blood sodium to a dangerous level, just like drinking too much water.

Salty snacks and/or salt capsules do not necessarily protect you from hyponatremia if you are overdrinking.

Hyponatremia means that when you divide the amount of sodium by the volume of blood plasma, the number you get is too small. This number is called plasma sodium concentration. (Hypo means too small; natremia means sodium status.)

Theoretically, there are two ways to make the number too small: (a) by decreasing the amount of sodium, or (b) by increasing the volume of fluid. Thus far, in exercise-related hyponatremia cases studied, there has always been increased volume of water. (We do not know to what extent sodium loss was a contributor to the illness.)

Fatal Brain Swelling

Over-hydration all by itself (regardless of whether or not sodium is "washed out") can cause hyponatremia simply by diluting sodium. When the dilute blood gets to the brain, water seeps into brain cells and causes swelling. In hyponatremia deaths, brain swelling is the killer.

Over-hydration during exercise can happen not only when you grossly over-drink, but also when you are moderately over-drinking and retaining the overload that you would urinate at rest.

Take seriously any sign that you are putting on water weight during a ride.

Weighing yourself before and after a ride is a good way to sort out hydration needs. You should never finish with a weight higher than when you started.

Other signs of over-hydration include bloating -- puffiness in the hands or feet (at the sock line, watch, rings) or at the shorts line; "boggy" feeling flesh; headache (especially noticeable when you ride on a bumpy road); and looking like or feeling like the Michelin Man.

Early Signs

Nausea and vomiting are often seen early in the development of hyponatremia.

Since it's the brain swelling that kills, signs of weight gain plus any change in mental status (confusion, memory loss, disorientation) or any neurological symptom (uncoordination, slurred speech) are a clear indication of hyponatremia and represent a dire medical emergency.

What to do? Stop drinking.

You want urination to dump the fluid overload. A strong dose of salt could help get urination started. The medical staff at the Boston Marathon uses concentrated bouillon, one bouillon cube per ounce of water. This is the one exception to the no-drinking rule -- you need a delivery vehicle for salt. Other remedies include V-8 or tomato juice to which salt is added. Find a way to get salt in. Then wait eagerly to start urinating.

Do not drink sports drink (unless a significant amount of salt is added). The concentration of sodium is way too low and the additional fluid will make the situation worse. Do not resume drinking until you are certain that you have gotten rid of the fluid overload.

Not What It Seems

Sometimes over-hydration is counterintuitive. For example:

---"I'm drinking a reasonable amount, not a huge amount. Why am I going bloaty?" (You can retain a water overload during exercise that you would normally urinate at rest.)

---"I haven't urinated for a long time. Doesn't that mean I am dehydrated and need to drink more?" (No! not if you are retaining water.)

---"Isn't this just an issue of sodium intake? Won't I be okay if make sure to keep up my salt intake?" (No! not if you over-drink.)

To prevent hyponatremia, think first about not drinking too much. A distant second is increasing salt intake.

These are two misconceptions I often hear:

---"I'm hot and sweaty and I feel crappy. It must be because I'm not drinking enough."

Not necessarily. You can be perfectly well hydrated and be generating more heat than your body can dump, so it warns you by making you feel bad. In other words, when it's hot and you feel poorly, it may well be because it is hot.

---"Hydration is the most important thing, so I'll continue drinking. But to prevent hyponatremia I'll take in more salt."

We have seen people who are way over-salted and have, as a result, stored fluid. Secondly, some people think that if they chug a sports drink instead of water they will be fine. But again, if you over-drink a sports drink you will go hyponatremic almost as fast as if you over-drink water.

The best hydration strategy: "Drink to thirst, salt to taste."

In other words, don't force anything. Listen to your body.

(For more information on hyponatremia, sodium and hydration, see Lulu Weschler's article at http://tinyurl.com/ensuc)

 

Wow, that is a great article. There have been many times that when riding I just can't bring myself to drink...I am not thirsty. So I will lightly sip occasionally. I try to do most of my drink a few days ahead of time so that I won't drink a lot while riding. I do like V-8...and plain tomato juice is pretty good too. It really works.

 

Excellent advice! Consider your over all health too. My health has been crappy for a few years now. I know when it is this hot I am going to be affected. So no triking for me right now. Guess I will have to start all over. {sigh} I was having so much fun too..........

Mattvon

 

Be careful of the opposite effect. Dehydration results in Hypernatremia (too high a concentration of sodium).

I'd be interested in knowing the percentage of people who suffer hyponatermia with overhydration of sports drinks vs water and how much it takes. I know it's not hard if you are out for 4 hours or more in hot humid weather and only drink plain water.
The article reads like its easy to get into overhydration problems, even with sports drinks. I highly doubt it's as easy as it sounds to get into this kind of trouble.

As for the urinating part, as long as your kidneys are working properly the excess fluid is stored in your bladder, not your circulatory system.

Dehydration is more likely. Most people need to consume about one large water bottle (24oz) of fluid per hour to prevent dehydration. If you are going to be out less than an hour, plain water is fine. If you are going to be riding an hour and a half or more, a sports drink is a good idea. It provides both carbohydrate for energy and electrolytes.

The general rule of thumb in exercise physiology and sports nutrition is to drink before you're thirsty and eat before you're hungry. But don't force yourself. You don't want to be drinking so much you feel it sloshing in your belly.

So can overhydration (and water poisioning) happen? Absolutely. But don't go overboard trying to prevent it and end up dehydrating yourself. Balance and common sense is the key.

Mike

 

HA! I have had numerous times when I had to stop drinking because of belly slosh. I learned really quick to SIP and GO.

Worst case of dehydration I EVER had was on my last florida Tour (AD can vouch for me...he had to give me lots of aspirin) I had massive leg cramps in my quads...hamstrings...and calves. I couldn't stand or sit...I had to stand with my legs in a half leg squat position until I got to the grass and had to force my legs straight...LOTS of pain. I was barely able to ride the rest of the day. Whew! don't ever want to experience that again.

 

Living here in Columbus with the heat a constant issue I have wrestled with the fluid reploacement issue. I came accross a fluid and electrolyte replacement calculator a year or so ago and now I can't find the exact one. A great formula that included Body weight, level of activity, outside temp, even included amount of climbing per mile.

After boiling it down and relating it for me to the local centuries I ride where it is almost always hot I came up with this

2 liters of Gatorade Endurance
24 oz of Spiz meal replacement with about 500 calories

this is what I carry for each 50 miles. Meaning I have to replace my stock around the 50 mile mark. Most rides seem to have a SAG around there and it works pretty well for me.

When I can't get the Endurance Gatorade I will carry 2 -12 bottles of V8 juice along with me or make sure the ride goes by stores where I can by them. I discovered last summer that a v8 or two can really pick you up.

Now these figures were for my body style riding pretty high intensity in my area with only moderate hill climbing.

I have included one link about fluid replacement calculation, maybe someone else will find the one I can't seem to right now

http://www.aims-association.org/guidelines_fluid_replacement.htm

Ward

 

The V8 juice is new to me. Several of you have said how good it is for riding. I have in the past used Cytomax only. I may take a V8 to drink first then Cytomax for the duration.

I will use this strategy on the upcoming Clarksville ride. I am planning on riding 62 miles (my first METRIC CENTURY). I won't break any speed records, but I am planning to have fun.

Hopefully we will have a group of recumbents who can pace each other throughout the ride and enjoy each others company. Sign up if you are planning to attend!

 

Jon, I find the V8 works better if I drink it at a rest stop 1/2 or 2/3rds of the way thru the ride. Also, I know that T Marsh who is very very fast and a few other Bacchetta riders are going to be at the ride.

Good luck and have fun
Ward

 

I learned about the V-8 juice a couple of years ago while doing the MS-150 tour. Works great, and I really like the Gatorade Endurance too. The only problem there is that you can't get it in Maryville anywhere except at Target. I don't know if they continue to stock it or not, haven't been in there in a while.

 

Last week they had the endurance gatorade powder on sale 1/2 price. I jumped on it

Ward

 

Oh man! I need to see if the Target here has it on sale. I will probably buy a couple of cases.

 

That would be at www.performancebike.com