Hyponatremia

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. Although previously considered to be more prevalent in endurance activities, hyponatremia cases are also now being reported in non-endurance sports and activities. Hyponatremia is mainly caused by hyperhydration, but can also be caused by intake of hypotonic fluids (including sport drinks) that exceed 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.

What Puts an Individual at Greater 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
  • Abundant availability of drinking fluids at event
  • Nonsteroidal anti-inflammatory drugs, antidepressants, or diuretics use
  • Other drugs associated with SIADH (SSRI’s)
  • Not heat acclimatized
  • Low sodium diet
  • Extreme hot or cold environment

How Do You Prevent Hyponatremia?

      • Understand that universal guidelines are not realistic due to the following factors
        • Variation in individual sweat rate
        • Variation in individual sweat sodium concentration
        • Environmental conditions
      • Be familiar with the signs and symptoms of hyponatremia
      • Have an emergency plan in place for dealing with hyponatremia
      • Have appropriate personnel to educate athletes and staff on fluid balance
        • Educate athletes that hyperhydration does not improve performance and both hyponatremia and hypohydration is associated with performance decrements
      • 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

          Pre-Exercise

          • Establish an individualized hydration plan to determine proper fluid intake
            • Individualize based on personal sweat rate, acclimatization state, body size, fluid preferences and tolerances
            • Consider sports dynamic and environment
          • Record body weight before exercise for baseline measurement

          During Exercise

          • Monitor the duration and intensity of exercise for determining risk of hyponatremia
          • Supplement water with electrolyte beverages, especially if exercise is lasting longer than 1 hour

          Post-Exercise

          • Record body weight after exercise to monitor fluid losses/consumption
            • Physically active individuals should not consume fluid amounts that exceed the amount of exercise-related body mass lost
            • Body mass should not increase during exercise unless they begin exercise with an unavoidable fluid deficit
          • Refuel within 2 hours of exercise to replace electrolytes, carbohydrates, and protein.
            • Opt for foods that contain sodium and other electrolytes

          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:
            • Muscular weakness and/or twitching, dizziness, lightheadedness, headache, nausea and/or vomiting, body weight gain from baseline, and swelling of hands and/or feet.
            • Serum sodium levels ranging from 129-134mEq/L
          • Patients with more severe hyponatremia can present with any of the following:
            • Signs and symptoms of altered mental status, signs of herniation, signs of noncardiogenic edema, seizures, coma and death
            • Serum sodium levels less than 129mEq/L

          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
          • A patient can be both hypohydrated (decreased total body water) and hyponatremic at the same time.
            • Blood sodium assessment can distinguish between the two conditions

          What Else Could This Be?

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

          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

          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 to 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

            References

            1. Almond CS, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the boston marathon. N Engl J Med. 2005;352(15):1550-1556.
            2. Armstrong LE, McDermott BP. Exertional hyponatremia. In: Casa DJ, eds. Preventing Sudden Death in Sport and Physical Activity. Sudbury, MA: Jones & Bartlett Learning. 2012:185-199.
            3. Binkley HM, Beckett J, Casa DJ, Kleiner DM, Plummer PE. National Athletic Trainers’ Association position statement: exertional heat illnesses. J Athl Train. 2002;37(3):329-343.
            4. Casa DJ, Clarkson PM, Roberts WO. American College of Sports Medicine roundtable on hydration and physical activity: consensus statements. Curr Sports Med Rep. 2005;4:115-127.
            5. Casa DJ, Armstrong LE, Hillman SK, Montain SJ, Reiff RV, Rich B, Roberts WO, Stone JA. National Athletic Trainers’ Association position statement: fluid replacement for athletes. J Athl Train. 2000;35(2):212-224.
            6. Convertino VA, Armstrong LE, Coyle EF, et al. American college of sports medicine position stand. exercise and fluid replacement. Med Sci Sports Exerc. 1996;28(1):i-vii.
            7. Hew-Butler T, Ayus JC, Kipps C, Maughan RJ, Mettler S, Meeuwisse WH, Page AJ, Peid SA, Rehrer NJ, Roberts WO, Rogers IR, Rosner MH, Siegel AJ, Speedy DB, Stuempfle KJ, Verbalis JG, Weschler LB, Wharam PM. Statement of the second international exercise-associated hyponatremia consensus development conference, New Zealand. Clin J Sport Med. 2008;18(2):111-121.
            8. Montain SJ, Sawka MN, Wenger CB. Hyponatremia associated with exercise: risk factors and pathogenesis. Exer Sport Sci Rev. 2001;29(3):113-117.
            9. Noakes TD, Sharwood K, Speedy D, et al. Three independent biological mechanisms cause exercise-associated hyponatremia: Evidence from 2,135 weighed competitive athletic performances. Proc Natl Acad Sci U S A. 2005;102(51):18550-18555.
            10. Rosner MH. Exercise-associated hyponatremia. Semin Nephrol. 2009;29(3):271-281.
            11. Rosner MH, Kirven J. Exercise-associated hyponatremia. Clin J Am Soc Nephrol. 2007;2(1):151-161.
            12. Siegel AJ, Verbalis JG, Clement S, et al. Hyponatremia in marathon runners due to inappropriate arginine vasopressin secretion. Am J Med. 2007;120(5):461.e11-461.e17.
            13. Speedy DB, Noakes TD, Rogers IR, et al. Hyponatremia in ultradistance triathletes. Med Sci Sports Exerc. 1999;31(6):809-815.
            14. Toy BJ. The incidence of hyponatremia in prolonged exercise activity. J Athl Train. 1992;27(2):116-118.