Hyponatremia is a medical condition termed for a low concentration of sodium in the blood (serum). By definition, hyponatremia occurs when serum sodium levels in the plasma fall below <135mEq/L. This has been shown to occur in up to 30% of ultra-endurance participants. Hyponatremia is mainly caused by overhydration, but can also be caused by intake of hypotonic fluid in excess of sweat and urine output, excessive sodium losses, or other hormonal dysfunctions that affect the maintenance of sodium stores in the body. The table below shows the risk factors associated with hyponatremia.


How do you prevent hyponatremia?

  • Have a hydration plan in place
    • Supplement water with electrolyte beverages, especially if exercise is lasting longer than 1 hour
  • Universal guidelines are not realistic due to the following factors
    • Variation in individual sweat rate
    • Variation in individual sweat sodium concentration
    • Environmental conditions
  • Record body weight before and after exercise to monitor fluid consumption
  • Know the sweat rate to determine fluid consumption during exercise
    • This also helps establish individual hydration plans
  • Know the signs and symptoms of hyponatremia
  • Have an emergency plan in place for dealing with hyponatremia
  • Monitor the duration and intensity of exercise for determining risk of hyponatremia
  • Educate athletes of risks from fluid overload and encourage moderate hydration.
  • Establish individualized hydration protocol based on personal sweat rate and sports dynamic.
  • Consume adequate dietary sodium.
  • Allow 8-14 days of training in the heat for acclimatization.
  • Identify pre-exercise hyponatremia by recording body weight each day


What puts an individual at risk for hyponatremia?

Risk Factors
Exercise duration greater than 4 hours or slow pace
Female sex
Low body weight
Excessive drinking (>1.5 L/hour) during the event
Pre-exercise overhydration
Abundant availability of drinking fluids at event
Nonsteroidal anti-inflammatory drugs
Other drugs associated with SIADH (SSRI’s)
Extreme hot or cold environment

Look for these symptoms in athletes when hyponatremia is suspected:

  • Signs and Symptoms vary depending on severity and are related to cerebral edema caused by the osmotic flow of fluid into the brain cells
  • Patients that are asymptomatic or mildly symptomatic can present with any of the following:
    • Weakness, dizziness, headache, nausea, and/or vomiting and the resulting serum sodium levels range from 129-134mEq/L
  • Patients with more severe hyponatremia can present with any of the following:
    • Serum sodium levels less than 129mEq/L, presents with signs and symptoms of seizures, coma and death

How do you know if this is hyponatremia?

  • Indication of hyponatremia based on onset of symptoms
    • Type, duration, and intensity of exercise
    • Amount of fluid consumed
    • Post exercise body weight is greater than pre exercise body weight
  • Measurement of blood sodium levels
    • A measure <130mEq/L would indicate moderate-severe hyponatremia and coincide with observation of symptoms
  • Measurement of vitals


What else could this be?

  • Exertional Heat Stroke
  • Heat Exhaustion
  • Heat Cramps
  • Rhabdomyolysis
  • Cardiac Condition
  • Exertional Sickling
  • Respiratory Condition


How do you treat an individual with hyponatremia?

  • Treatment varies depending on severity of hyponatremia
  • DO NOT provide normal saline solution or fluids
  • Asymptomatic or mildly symptomatic
    • Treated with fluid restriction and observed until either serum sodium levels return to within normal limits or there is a resolution of symptoms and spontaneous diuresis
    • Consume oral hypertonic saline (e.g. bouillon) or salty foods such as potato chips, pickles, jerky
    • Hypertonic saline IV should be considered if a blood sodium level can be measured
  • Severe Hyponatremia
    • 3% hypertonic saline should be administered immediately due to the risk of cerebral edema that can ensue if treatment is delayed
    • It is also recommended that patients presenting with hyponatremia receive supplemental oxygen in case cerebral edema leads to hypoxia·      The following flow chart represents when an athlete should be transported to the nearest hospital


Hyponatremia Algorithm

When can the individual return to activity?

  • Athlete will need to follow up with his/her primary care physician
  • Blood sodium levels will need to measure within normal limits (>135mEq/L)
  • Return to full activity should follow a graded exercise protocol similar what would be done during a period of exercise/heat acclimatization
  • Athlete will need to be educated on proper hydration before, during and post exercise to avoid the risk of suffering from hyponatremia again.


Recommended Equipment List

  • Hypertonic saline
  • IV equipment
  • Portable blood Na+ analyzer kit (e.g. i-stat)
  • AED
  • Salty foods (e.g. bouillon cubes, pretzels, canned soup, and potato chips, pickles)
  • Rectal thermometer (used to rule out exertional heat stroke)
  • Blood pressure cuff
  • Stethoscope
  • Stretcher



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