Understanding Exercise Associated Hyponatremia (EAH)
Exercise-associated hyponatremia (EAH) is a serious condition characterized by abnormally low blood sodium levels ($<135$ mmol/L) that develops during or after prolonged physical exertion. It is primarily caused by overconsuming hypotonic fluids (like water) beyond the body's ability to excrete them, often combined with high levels of vasopressin (ADH), a hormone that retains water. This leads to excess fluid retention and dilution of the body's sodium.
Symptoms range from mild, such as nausea, headache, and dizziness, to severe, including confusion, seizures, and coma resulting from cerebral edema. Differentiating EAH from dehydration or heat-related illness is crucial, as the wrong treatment can be life-threatening. The key differentiator is that symptomatic EAH often involves weight gain or no weight loss, distinguishing it from dehydration where weight is typically lost.
The Correct Approach to Treating EAH
Treatment for EAH is not one-size-fits-all and depends entirely on the athlete's symptoms and the severity of their condition. The guiding principle is to correct the sodium imbalance without causing harm from over-correction.
Treatment for Mild, Asymptomatic EAH
For athletes with a serum sodium level below 135 mmol/L but showing no symptoms, the intervention is conservative. Fluid restriction is the primary strategy. This allows the kidneys to naturally excrete excess water as vasopressin levels normalize after exercise. Simply instructing the athlete to cease fluid intake until they urinate is often sufficient for full recovery.
Treatment for Mildly Symptomatic EAH
If an athlete presents with mild symptoms like nausea, headache, or dizziness but is alert and oriented, oral sodium replacement is the recommended course of action.
Oral Sodium Repletion Options:
- Oral Hypertonic Saline: Pre-packaged oral hypertonic saline solutions are as effective as IV options for mild cases. Studies have even shown faster recovery times for athletes receiving oral treatment.
- Salted Pretzels: A simple and accessible option for sodium intake.
- Concentrated Broth: Broth can be used as oral hypertonic saline.
Treatment for Severe EAH or Hyponatremic Encephalopathy
Severe EAH, or exercise-associated hyponatremic encephalopathy (EAHE), is a medical emergency marked by altered mental status, seizures, or coma. This requires immediate and aggressive intervention with intravenous hypertonic saline (3% NaCl).
Steps for Severe EAH Treatment:
- Immediate Action: Do not delay treatment awaiting blood sodium test results if severe neurological symptoms are present.
- Bolus Administration: Intravenous hypertonic saline may be administered.
- Repeat if Necessary: This may be repeated at intervals if the patient shows no clinical improvement.
- Transport: The athlete should be transferred to a hospital for further monitoring and treatment.
- Caution with Fluid: The treatment of EAH encephalopathy is prompt correction with hypertonic saline, not isotonic fluids. IV isotonic fluids can worsen EAH by retaining more water.
Differential Diagnosis: EAH vs. Heat-Related Illness
Misdiagnosis between EAH and heat illness is a common and dangerous pitfall. Both can cause confusion and nausea, but their underlying pathology and treatment are opposite. A key distinguishing sign is body weight change.
| Feature | Exercise Associated Hyponatremia (EAH) | Heat-Related Illness (Dehydration) |
|---|---|---|
| Body Weight | Weight gain or minimal weight loss | Significant weight loss |
| Primary Cause | Overhydration with hypotonic fluids | Excessive fluid and sodium loss via sweat |
| Fluid Strategy | Fluid restriction, sodium replacement | Fluid replacement (and electrolytes) |
| Urine Output | Often reduced (oliguria) due to high AVP | Typically reduced or dark from dehydration |
Prevention is the Best Medicine
The best way to manage EAH is to prevent it from occurring in the first place. Proper hydration habits based on individual needs are paramount.
Key Prevention Strategies:
- Drink to Thirst: Overwhelming evidence supports drinking according to the sensation of thirst as a safe and effective strategy for preventing both over- and under-hydration.
- Monitor Body Weight: Weighing yourself before and after exercise can help gauge fluid balance. Weight gain indicates overhydration, and further fluid intake should be limited.
- Avoid Excessive Pre-loading: The practice of "hyper-hydrating" with large volumes of water before a race can be dangerous and increase the risk of EAH.
- Understand Fluid Type: During prolonged exertion, simply drinking water is not enough. Sports beverages or salty foods help replenish lost sodium, but over-reliance on hypotonic sports drinks still risks EAH if overconsumed.
- Athlete Education: Athletes, coaches, and medical staff should all be educated on the risks, symptoms, and appropriate management of EAH.
Practical Advice for Athletes and Staff
To ensure athlete safety, race directors and medical staff should be equipped to handle EAH effectively. This includes having point-of-care sodium testing available at events and stocking hypertonic saline. Athletes should be aware of the early, non-specific symptoms and seek medical attention if they persist. Avoiding non-steroidal anti-inflammatory drugs (NSAIDs) during prolonged exercise is also advised, as they may increase the risk of EAH by affecting kidney function.
By prioritizing education and adopting a "drink to thirst" hydration strategy, the incidence of EAH can be significantly reduced. For event organizers, equipping medical tents with the necessary supplies and protocols for both mild and severe cases is a vital component of athlete safety. Ultimately, recognizing the signs and applying the correct, severity-dependent treatment are the most important steps in managing exercise associated hyponatremia.
Conclusion
Effectively treating exercise associated hyponatremia (EAH) is a graduated process that depends on the severity of the condition. For mild, asymptomatic cases, fluid restriction is key to allowing the body to correct itself naturally. Mildly symptomatic individuals can be treated with oral sodium, such as hypertonic saline or broth. In severe, life-threatening scenarios involving neurological symptoms like seizures, immediate medical intervention with intravenous hypertonic saline is critical and potentially life-saving. In all cases, correctly diagnosing EAH—distinguishing it from dehydration—is the most crucial first step, as incorrect treatment can have fatal consequences. Education and prevention, centered on the simple principle of drinking to thirst, remain the most effective long-term strategy for safeguarding athlete health.
