Sports Medicine Review – Ankle
November 15, 2018
Sports Medicine Review – Cardiac Emergencies in Sport
January 8, 2019

Journal Club – Hyponatremia

Exercise-Associated Hyponatremia (EAH) in Endurance Sports
Presenter: SuFei Yue, PGY3 Sport and Exercise Medicine, University of Toronto
October 9th, 2018



• Hyponatremia occurring during or up to 24 hours after physical activity
• Defined by serum, plasma, or blood [Na+] below the normal reference range of 135 mmol/L
• Asymptomatic EAH: ranges from 0% to 13% in standard marathons, up to 51% post-161 km ultramarathons
• Symptomatic EAH: much less frequent, from 0.06% to 1% in endurance events
Risk factors
• Single most important risk factor is excessive fluid intake with positive fluid balance
• Other risk factors include weight gain, exercise duration >4h, event inexperience, extremes of BMI, readily available fluids
• Dilutional hyponatremia from excessive fluid intake and ADH-mediated water retention
• Fluid overconsumption with increased ADH secretion in hypervolemic hyponatremia, typically presenting with weight gain
• High sweat rate leading to sodium depletion coupled with non-osmotic ADH secretion in hypovolemic hyponatremia, typically presenting with weight loss
Clinical Presentation
• Symptoms are generally non-specific
• Mild EAH: lightheadedness, dizziness, nausea, weight gain
• Severe EAH or EAH encephalopathy: vomiting, headache, altered mental status, seizure coma, decorticate posturing, mydriasis, respiratory distress
• Clinical symptoms and signs of EAH, with serum, plasma, or blood [Na+] below 135 mmol/L
Differential Diagnosis
• Exertional heat illness, altitude sickness, hypernatremia, hypoglycemia, ACS, anaphylaxis, bronchospasm, exercise-associated postural hypotension
General Approach to Triage
• Primary survey including ABC’s, mental status, ability to communicate
• Immediate interventions required for any positive findings identified on primary survey
• If primary survey does not identify any causes AND collapse occurs immediately post-exercise, exercise-associated postural hypotension is likely the cause -> place athlete in supine position with legs elevated (i.e. Trendelenburg position)
• Consider tests if readily available (BP, rectal temperature, blood Na and glucose) -> initiate treatment accordingly for any identifiable or presumed medical condition
• If no medical condition has been identified or been presumed likely AND the athlete is unable to communicate -> initiate emergency unresponsive protocol (empiric IV hypertonic saline and glucose, cooling if hot), emergency evacuation
• Large endurance events are now recommended to have on-site [Na+] testing
• Documented hyponatremia with mild symptoms without encephalopathy
o Observation and fluid restriction until urinating freely, or
o Oral hypertonic solutions
♣ Concentrated chicken broth (4 bouillon cubes in 125 mL of water)
♣ 100 mL of 3% saline flavoured with Crystal Light, Kool Aid
• Symptoms of encephalopathy, with documented or suspected hyponatremia
o IV hypertonic saline bolus until clinical improvement
♣ Minimum 100 mL of 3% saline, repeated twice at 10 min intervals as needed
♣ Larger boluses may be necessary for severe symptoms, per clinical discretion

Article 1 – Almond C, Shin A, Fortescue E, Mannix R, Wypij D, Binstadt B et al. Hyponatremia among Runners in the Boston Marathon. New England Journal of Medicine. 2005;352(15):1550-1556.

This prospective study aimed to estimate the incidence of hyponatremia and to identify its major risk factors in marathon runners. The authors concluded that 13% of enrolled participants had hyponatremia. Hyponatremia was associated with weight gain, longer race time > 4 hours, and low BMI < 20.

Strengths Limitations
– Prospective design

– Demonstrated that hyponatremia occurred in a considerable number of marathon runners

– Showed that the strongest predictor was significant weight gain during the race from overconsumption of fluids

– Low follow-up rate of 67%

– True incidence of hyponatremia may be underestimated as those who did not follow up tended to have less marathon experience and were slower

– Did not stratify the amount of NSAID used to see if higher dose may be associated with risk

Article 2 – Owen B, Rogers I, Hoffman M, Stuempfle K, Lewis D, Fogard K et al. Efficacy of oral versus intravenous hypertonic saline in runners with hyponatremia. Journal of Science and Medicine in Sport. 2014;17(5):457-462.

This randomized controlled trial set out to determine whether the IV route was more effective than the oral administration of 3% saline in raising blood [Na+] in a group of ultramarathon runners with hyponatremia. The authors concluded that there was no difference between the IV and the oral route in its effect on blood [Na+]. Both increased blood [Na+] by 2 mmol/L at 60 minutes following a 100 mL 3% saline bolus.

Strengths Limitations
– Showed that both oral and IV 3% saline boluses were effective in hyponatremia

– Supported the use of oral 3% saline in mild cases

– Hyponatremia in ultramarathon runners was associated with reduced effective circulating volume

– No placebo control group

– Did not show baseline characteristics of the subjects to ensure success of randomization

– Difficulty applying the results to the more symptomatic, hypervolemic patients as the subjects had average weight loss in this study

– Study was done in asymptomatic subjects

Other Resources
1. Hew-Butler T, Rosner M, Fowkes-Godek S, Dugas J, Hoffman M, Lewis D et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. British Journal of Sports Medicine. 2015;49(22):1432-1446.
2. Hew-Butler T, Loi V, Pani A, Rosner M. Exercise-Associated Hyponatremia: 2017 Update. Frontiers in Medicine. 2017;4.
3. Hoffman M, Rogers I, Joslin J, Asplund C, Roberts W, Levine B. Managing Collapsed or Seriously Ill Participants of Ultra-Endurance Events in Remote Environments. Sports Medicine. 2014;45(2):201-212.