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AMAA experts examine hyponatremia's challenging characteristics at Boston.

The AMAA 32nd Annual Sports Medicine Symposium at Boston addressed hyponatremia in distance runners and other athletes over the course of two comprehensive lectures on Saturday, April 19.

"Hyponatremia: Scope, Causes, Features, and Prevention," with Randy Eichner, M.D., and Bob Murray, Ph.D., provided a highly useful overview to this rare but serious condition that occurs when plasma sodium levels fall dangerously below normal.

Eichner is the team internist for the Oklahoma Sooners at the University of Oklahoma Medical Center. He specializes in hematology and electrolyte imbalance. Murray is the director of the Gatorade Sports Science Institute in Barrington, IL.

The second lecture was co-hosted by John Cianca, M.D., and Joe Chorley, M.D., both from the Baylor College of Medicine in Houston, TX. As the physicians of the Houston Marathon, they have carefully analyzed incidents of hyponatremia over the past five years, including their causes and development. The doctors reported their findings in a lecture entitled "Hyponatremia in Marathon Runners: A Five Year Review," which revealed that hyponatremia is a far more prevalent problem than they had originally anticipated.

These informative presentations were immediately followed by a panel discussion with the doctors, and additionally, Mary Adner, M.D., medical director of the Boston Marathon.

A Useful Way of Thinking About Cause

Hyponatremia, also known as water intoxication, is diagnosed in patients with less than 135 millimoles of sodium per liter of plasma (mEq/L). Normal values range from 142 to 138. Symptoms usually begin at values below 130. When a patient's sodium level dips below 120, the condition results in massive brain swelling and is considered a medical emergency. The causes of hyponatremia can be boiled down into two categories: consumption of too much fluid over too short a time span, or inordinate sodium loss through bodily sweat. It is possible for these two factors to be in play at once, which exacerbates the risk and can also make the general public's understanding of the condition somewhat difficult. Hyponatremia at times appears contradictory.

The Gatorade Sports Science Exchange states that salty sweaters who also sweat excessively are at a higher risk; however, excessive fluid intake for a normal sweat rate will lead to inadequate fluid loss and therefore hyponatremia as well. It is useful, then, to think of the two factors as largely independent. If you are an excessive, salty sweater, your sodium loss will be greater than that of a moderate sweater. This is what makes it possible for hyponatremia to occur even in athletes who are simultaneously dehydrated. At the same time, if a person is overdrinking--that is, not using the amount of water they are consuming for their level of exertion--they will dilute their plasma sodium concentration and therefore be more prone to the condition. This is what makes it possible for a person to become hyponatremic without exercising at all.

In this way, an excessively hot and humid day can contribute to cases of hyponatremia (through inadequate replenishment of the large amounts of sodium lost in sweat), as well as can an unexpectedly cold day (on which it's more likely a marathoner will have overdrank for the amount of fluid the body will use). And it's important to remember that overdrinking can accumulate in the days leading up to a marathon. As Murray points out, "One danger is water-loading in the days before an event in an effort to stay hydrated. A marathoner's daily fluid intake remains high even though [through tapering] their training load has decreased."

Profiling Those Most at Risk

In 2000, of the 21 cases Cianca and Chorley treated at the Houston Marathon, two were severe. Although it turned into a very hot and humid day as the race progressed, one of the most severe cases was a woman who had drank 2.5 gallons of fluid prior to running. "It turned out she was a friend of mine," Cianca explained, but the patient was so bloated by the time he saw her that "she was absolutely unrecognizable." The more fluid a person consumes per kilogram of weight, the higher the likelihood of overdrinking. Therefore, smaller runners are more at risk. Women should take care to avoid consuming fluid like men.

However, Chorley's research showed that even women who drank the same amount of fluid per kg--and at the same rate--consistently lost less weight during the marathon than their male counterparts, regardless of whether they became hyponatremic. They also dropped more sodium. "We can't account for this by drinking behavior," Chorley said. It is thought that this phenomenon is partly due to the greater amount of lean body mass men possess, and the fact that women start out with about 10 percent less body water.

Water absorption rates are different between the genders, and this leads to one recurring theme of the discussions in Boston: know the facts, know your own body, and don't look at what your neighbors are doing--don't always follow the generally accepted rule of thumb. "You need to be relatively sophisticated about this," insists Chorley. "Everybody looks to the big blanket statements like, 'What did this organization say to drink?' But it's an individual thing, and it's going to change from even one time of year to another."

In addition to lightweight marathoners, there are several reasons why the Houston data shows that four- and five-hour marathoners are at increased risk too. Eichner points out that these often first-time runners tend to be hypervigilant. They may not be exerting themselves enough to justify all the drinking they are doing before, during and after the marathon. "When we were delivering a lecture at the Expo this morning, everybody in the audience was just sipping themselves silly. Everybody had a water bottle. This is two days before the race. Some of those people are going to come to the start line with sodiums of 130," he warned.

Another reason is that five-hour finishers simply have more time to consider stopping for water as they slowly pass each aid station. And at more moderate speeds, these same people are likely to get that much more fluid into their mouths, as opposed to down the fronts of their shirts, like the elite athletes who blaze by in an effort to shave every possible second off their finish times.

Triathietes and those completing Ironman events represent a different group at increased risk. These athletes are out there so long that they are more likely to lose too much sodium through sweat than they are to overdrink. Eichner points out that rates of fluid consumption and sweating have a lot to do with hyponatremia risk as well. The most dangerous cases are those with the most rapid changes in blood sodium levels.

Symptoms and Medical Dangers

Early signs that you are hyponatremic include feeling bloated, followed by nausea and vomiting. Patients claim that they "just don't feel right." This is usually followed by visible bloating, including an inability to rotate one's wedding band or an uncharacteristic lack of "play" in the wristwatch. High blood pressure and headache often come next. It is at this stage that Eichner and Murray recommend everyone seek medical attention. What follows in more severe cases begins with feelings of restlessness, lethargy and/or confusion. Respiratory distress and seizures are not unheard of at this level of severity. The most advanced stages of the condition are then indicated by coma, and finally brainstem herniation and death.

Educating Colleagues

On April 21, 2003, Tim Schmal, a 46-year-old 13-time marathoner from San Jose, CA, completed the Boston Marathon in 4:51 (partly due to pre-race injury and illness), though his time in Chicago was 3:26. He proceeded to walk back to his hotel, but an hour after he finished, he was taken by ambulance to Tuft's New England Medical Center and--eventually--treated for hyponatremia. He was hospitalized Monday night and Tuesday, with a plasma sodium level of 124. He had been given fluids in both the ambulance and the emergency room, where he was initially treated for myocardial infarction.

The Boston Athletic Association would have no knowledge of Schmal's case if he had not written to AMAA member Arthur Siegel, M.D., at the Department of Internal Medicine at McLean Hospital. Schmal asserts, "The Tuft's people were wonderful. They took a sodium test, and I certainly have no criticism of them or the BAA, though I do have a concern that the EMTs and ER personnel should have been attuned to the hyponatremia issue, especially in light of last year's death." Schmal estimates that he consumed about 65 cups of fluid during the race, in part due to "a failure to realize that there were more aid stations than I'm normally used to and I stopped at all of them."

The primary goal for the medical community now is to become educated about hyponatremia, and to pass that education along to medical personnel across the country and to the general public. Siegel says, "We can't have EMTs pick up runners who cob lapse on the course and put an IV in and start to run normal saline. The runner who died in Boston last year received normal saline on the way to the hospital, and she received it after she got there." While tent workers at marathons are arguably now among the best educated about hyponatremia, there is a long way to go spreading the word to every level of health care employee everywhere, or cases like Schmal's will continue to present themselves.

Once a marathon is determined to be the cause of illness, it is essential that medical workers obtain a sodium level. Questionnaires about patient's diets like those used in Houston are a good way to determine sodium intake on the day, as well. These may also be useful in determining how fast sodium concentration has plummeted. And weighing people is perhaps the simplest way to help determine if hyponatremia is the cause of a marathoner's illness.

The symptoms of hyponatremia can certainly be similar to those of heat illness and dehydration. Dr. Susan Briggs, supervising medical officer of the Boston Disaster Team, which volunteers its services each year for the marathon, pointed out the Medical Operations Manual kept in Athletes Village, at the finish and at each aid station along the course. It contained detailed information about how to differentiate between marathon illnesses, and what to do. This would undoubtedly be a useful document to dispense to local emergency room and ambulance staff on the day of a city's event.

Typically, after intubation with a concentrated sodium solution, and often times a diuretic to accelerate water loss, medical stations will employ a wait-and-see attitude regarding sodium level. If it's rising, the patient will likely recover shortly. If it continues to fall, hospital admittance might be necessary. Anti-convulsive medications are administered in severe cases where seizure is a concern.

Saving People from Themselves?

Education is the cornerstone of ensuring the proper handling of hyponatremia cases in the medical community, as well as the key to prevention with a public that has been taught only to avoid dehydration. As Cianca cautions, "If you don't take it upon yourself to learn how your body reacts, there's not a lot anybody else can do about it, until you present yourself with a problem."

While reducing fluid stations along the course is one oft-mentioned solution, it would seem that if marathoners don't understand the true risks of overdrinking they will find other ways to get the water they think they need. Water-carrying back packs are one way; another is in the days prior, to simply partake of the excessive water-loading that leads to reduced sodium levels long before the gun goes off.

The argument that if "cutting the number of fluid stations saves even one life, it will have been worth it," is a compelling one indeed. Health care professionals quite reasonably consider reducing risk of death their number one priority. However, the adverse effects on performance many runners would feel if fluid stations were reduced is not the only concern. Even sub-clinical dehydration increases the risk of heat exhaustion and potentially deadly heat stroke. Adner is reluctant to cut them in Boston because of overcrowding concerns, and favors teaching people to simply avoid stopping at every fluid station.

Above all else, participation in a 26.2-mile running event should not be undertaken lightly. As Cianca wisely noted, "There are too many people out there making the broad assumption that they can participate in a marathon just because somebody said they could. I will remind everybody that the very first marathoner died."

Charity runners are a cause of concern for some because they are often inexperienced and possess an "I must finish" mentality. But Adner is worried not about charity runners so much as the legions of bandits. While many, if not most, charities have their own trainers who guide the participants through every phase of safely completing a marathon, runners who jump in the race last-minute tend to know little or nothing about completing it, much less how their own bodies will react on a given day under a certain set of weather conditions.

It is essential to point out through both the media and in marathon medical pamphlets that, while rare, overdrinking is a concern and more is not necessarily better when it comes to fluid intake. As Chorley puts it, "The problem is if the runner feels wonky and thinks, 'I must be dehydrated."'

Long-term Solutions

Simply put, fluid intake during a marathon should never exceed fluid loss. Therefore, a runner's change in weight is a great indicator of whether they are drinking the right amount. "Rarely do we find something that correlates that well," says Chorley. Encouraging and even mandating that runners weigh in prior to the race gives them an easy way to monitor themselves.

The body expels excess water through urine, usually at a maximal rate of about one liter per hour. During a race, urine production decreases 20 to 60 percent due to a decrease in blood flow to the kidneys. if you're especially nervous or running in hot weather, the decrease will be on the higher end of this estimate. So a good starting point is to expect to lose perhaps two percent of your premarathon body weight; any more and you are likely dehydrated, any less and you are likely hyponatremic. Gaining weight is a sign you are dangerously overdrinking.

The logistics of weighing everyone at the start of a marathon like Boston or, worse, New York make it unlikely However, suggestions from panelists and audience members alike included placing scales in the Port-a-johns, or perhaps even better, forcing people to weigh in as they pick up their bibs at the Expo. This could alleviate crowding because it would be held over the course of several days, yet it's adequately dose to the race to at least get a decent picture of normal weight loss post-race. Ideally, runners would weigh themselves at home and record their pre-race weight on their bibs the morning of the marathon.

Marathoners should favor sports drinks over water, not only to replace lost calories, electrolytes and carbohydrates, but to gain back some of the sodium lost in sweat. This in itself, however, may be insufficient. It's a good idea to carry a salty snack like pretzels along the course, particularly if you are competing in a triathion or the like; you're not in danger of getting too much sodium this way

Why isn't there a Gatorade Marathon concoction then, with enough sodium to make hyponatremia a non-issue? As Murray points out, "We've tested this kind of beverage, but it becomes very salty-tasting very quickly, much sooner than the level [of sodium] we consider to be most effective." The body's reaction to such a drink is to involuntarily diminish its own drive for drinking it.

There is a similar palatability issue with salt tablets, which many people cannot keep down. "But if your body can tolerate them and you can use them wisely by balancing them with adequate fluid intake, then they're probably a good thing," Murray adds. Cianca has found that the ideal fluid may be salty chicken broth, though he is quick to point out it's something of an uphill battle getting anyone in Houston to drink this on marathon day

Maybe an appropriate message for the non-medical community of marathoners is: The hotter the weather, the more salt you should consume. The cooler it is, the less you should drink. (This doesn't mean avoid taking any fluids, of course. Runners should remember that fluid loss occurs through exhaled water vapor, even on cold days.) Houston uses a weather advisory system that provides runners with updates at miles 0,7, 13 and 20. This helps give runners an idea of how much they'll be sweating.

Runners should also be made aware that they retain up to two pounds of water weight at night when carbo-loading. This should factor into their pre-race weight, and they'll need extra sodium to compensate for the water retention. And the myth that "you should aim for totally clear urine" needs debunking. "If it's dark and concentrated, with little output, you're dehydrated," says Murray "But it should be free-flowing and tainted yellow, not completely dear."

Finally, after a marathon, Randy Eichner asks, "What's the rush? I would downplay all this urgent post-hydration. You're not going to be running a marathon the next day That's for multi-event sports." Perhaps you should instead choose a salty snack and nice hot bowl of chicken broth.

Jeff Venables is the editor of Running & FitNews, the publication of the American Running Association.
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Author:Venables, Jeff
Publication:AMAA Journal
Date:Mar 22, 2003
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