A triathlete who died at a recent Ironman Austria, two young American footballers who died in 2014, a comatose Ironman triathlete who spent more than two days in intensive care, a golfer treated in extremis just before sinking into a coma. What do all these people have in common? All were in perfect health and participated in sports activities in hot weather. All wanted to avoid dehydration or simple muscle cramps by drinking large amounts of fluids. All were found to have hyponatremia, which corresponds to a blood sodium level abnormally low and which contributed directly to their condition. Exercise-associated Hyponatremia (EAH) is a condition relatively unknown to the general public, but has become increasingly frequent these days, probably due to the proliferation of endurance sports events.
What’s more natural and essential than drinking water? With lots of advertising, bottled water and energy drink companies constantly remind us of the need to hydrate. All endurance sports coaches and trainers recommend drinking every 20 minutes during, before and after strenuous sports, under penalty of very serious consequences to our performance or our health. It is true that a state of dehydration can affect performance and contribute to an increase in body temperature but when does it becomes a factor? It is well documented that up to 2 to 3% of body weight loss by dehydration can be tolerated without too much effect on performance. Also, it is not uncommon to see a high-level athlete lose up to 5% of his or her weight during an endurance event and still achieve a good performance. The body is therefore able to tolerate a significant level of dehydration without too many consequences, as long as it is acclimatized to the environment and adequately trained.
The human body is indeed a marvel of adaptation to hostile environments. Endurance events take place in places as unlikely as Death Valley in California, the Sahara Desert or even Antarctica and we are not witnessing multiple casualties every time. How then can someone become intoxicated with water to the point where the body can no longer adapt?
Exercise-associated hyponatremia (EAH) is defined by a rate of blood sodium below 135 mmol/l up to 24 hrs after participating in a sporting event. A normal reading is between 135 and 145 mmol/l, a range that is fiercely maintained by various physiological mechanisms. The speed and the magnitude of the decline in sodium levels are directly related to the intensity of the symptoms.
What are the causes of hyponatremia associated with exercise? The most recent consensus among experts on the subject attributes the cause mainly to excessive an consumption of hypotonic fluids, ie. low in electrolytes when replacing sodium losses. Hyper-hydration creates an effect of dilution and a decrease in the rate of sodium. It also appears that an increase in the hormone Arginine-Vasopressin (AVP), promoting water retention, is involved in the process.
Who is at risk of developing an EAH? Most of the scientific literature comes from studies or case histories documented in tests of endurance such as ultra-marathons, Ironman triathlons and marathons. In these tests it was documented that up to 60% of participants were in a state of hyponatremia at one time or other during the event. Longer events appear to involve the highest risk.
More recently there have been recorded cases of EAH in activities as diverse as hiking, military training, football and even golf. The main risk factors identified include:
- A significant ingestion of water, sports drinks and other hypotonic beverages.
- Weight gain after a physical activity of more than 4 hours.
- A lack of physical preparation and a very slow pace of race.
- A high body mass index.
- Wide availability of fluids on the race course.
- There may be also a connection between the use of anti-inflammatories and EAH.
Fortunately, all of these athletes were not symptomatic of their hyponatremia. Often, when there is only a slight drop in sodium levels, the athlete will show no symptoms. With a larger and more rapid decline, however, clinical signs of a hyponatremic state will appear. Symptoms of mild impairment may be more subtle to detect: bloating, fatigue, headaches or nausea and sometimes a slight psychomotor impairment. More severe alterations generally occur with neurological manifestations such as: speech impairment, vision disorders, ataxia and balance disorders, vomiting, altered level of consciousness with involuntary movements imitating running and biking, convulsions and respiratory distress, all leading up to coma and eventually death by herniation secondary to cerebral edema.
It is therefore important to recognize the clinical presentation of this condition and to be very suspicious of any athlete matching this description. Frequently in endurance events, and especially in hot weather, the symptoms are generally attributed to dehydration, which prompts a hydration treatment, and only contributes to a deterioration in the athlete’s condition. When the diagnosis of hyponatremia is confirmed, either in a hospital or through a portable blood test device, fluid intake restriction and treatment to increase the sodium level should be promptly initiated.
For lightly symptomatic cases, simple measures like limiting fluid intake and waiting for diuresis to resume are generally sufficient. Supplementation in sodium with hyper-concentrated chicken broth (approximately 3-4 cubes in 125 ml of water) or a mixture of 100 ml of saline 3% NaCl with flavored crystals (Cool-aid or other) will be generally sufficient to rapidly increase osmolality even for moderate cases that can tolerate oral intake. When vomiting prevents oral intake or the symptomatology is too severe to try oral supplementation, it is necessary to administer a hypertonic saline solution (3% NaCl) intravenously.
In the field, when it is not possible to determine blood sodium levels, it is essential that all volunteers and first aid attendants know how to recognize the signs and symptoms of EAH. When in doubt, for example, with an athlete who has gained weight, is nauseous, bloated and has slowed down, there is no risk in giving sodium supplementation (either oral or IV). Conversely, additional hypotonic or isotonic intravenous or oral hydration could instead exacerbate hyponatremia. It is even more important to act quickly and provide supplementation with hypertonic saline IV in cases where an athlete shows neurological symptoms for which exercise-associated hyponatremia is strongly suspected.
It goes without saying that the main way to prevent the occurrence of EAH is through preventive measures. The first recommendation from the most recent international consensus of experts is to change the approach to hydration during endurance events. Instead of advocating hydration according to a precise timetable with the goal of completely replacing water losses, reasonable hydration based on thirst would be more appropriate and less likely to result in EAH. Similarly, aid stations planning should take account of this reality by promoting electrolyte-supplemented drinks and providing salty foods and snacks, especially at long-duration events. The most important measure remains the education of athletes and coaches about the risks of over-hydration, as well as with aid station volunteers, first responders and medical team staff so that they can be alert and quickly recognize signs and symptoms of EAH.
Dying from drinking too much water makes no sense, especially when this outcome is easily preventable with simple measures and education.
Marc Gosselin MD
Medical Director, Sirius Wilderness Medicine
Medical Director, Ironman Mont-Tremblant