Background
Exercise Associated Hyponatraemia (EAH) is a serum sodium level < 135 mmol/l in an individual engaged in prolonged physical activity (generally >4 hours), or within 24 hours of it ending.
Risk factors
- low body weight
- slow speed of running (ease of drinking)
- NSAID use
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Causes
- Excessive intake of hypotonic fluid during prolonged exercise, resulting in dilutional hyponatremia with an increase in total body water
- Inadequate antidiuretic hormone (ADH) suppression (due to factors such as over exertion, nausea, vomiting, exertional hypovolemia, pain and thermal stress)
- failure to mobilize osmotically inactive extracellular sodium stores (e.g. in bone)
Clinical
EAH has an exceptionally high mortality rate and presents:
No symptoms
Mild symptoms
- Bloating, weakness, dizziness, headache, nausea and/or vomiting
Severe symptoms
- Pulmonary oedema and/or encephalopathy (confusion, seizures, coma)
- Cardiac Arrest: Ensure all Cardiac Arrests in Marathon Runners have U&E done before terminating resuscitation
Management
- Resuscitation — attend to ABCDEFG (don’t ever forget glucose)
- Secondary survey to check for injury (fall/ seizure
- Supportive treatment and monitoring
- Fluid restriction to correct dilutional hyponatremia, but ensure adequate urine output to avoid renal failure secondary to rhabdomyolysis
- Be aware that unabsorbed hypotonic fluids in the GI tract can lead to further dilutional hyponatremia
- Consider hypertonic saline (see below)
- Referral to HDU/ ICU for ongoing monitoring in severe cases
Indications Hypertonic NaCl in EAH?
- Severe hyponatremia (Na <120 mmol/L)
- Significantly symptomatic (e.g. encephalopathy or acute pulmonary oedema)
When confirmed, in severe cases with epileptic seizures or severe mental changes suggesting worsening cerebral oedema, exercise associated hyponatraemia should be treated with hypertonic saline (to correct sodium to a level of 125 mmol/l over 1-2 hours, and to normal level over the following 2-4 hours.)
There are no reports of cerebral pontine myelinoysis resulting from over-vigorous treatment of exercise-associated hyponatremia (an acute process) with hypertonic saline.
5% saline
- Bolus 60 ml of 5% saline to raise the sodium quickly and prevent cerebral oedema (more on 5% NaCl)
- Up to 2 further boluses of 60 ml 5% saline may be administered at 10 min intervals if there is no clinical improvement
- Thereafter, 5% hypertonic saline should be infused at 1 ml/kg/h
- This may be increased to 2 ml/kg/h if urine output is inadequate
- The infusion rate can be decreased following significant water diuresis
- Infusion should be stopped when the patient is asymptomatic with a normal level of consciousness
- Serum electrolytes need to be closely monitored (e.g. hourly initially).There are no reports of cerebral pontine myelinoysis resulting from over-vigorous treatment of exercise-associated hyponatremia (an acute process) with hypertonic saline
- Aim to correct sodium to a level of 125 mmol/l over 1-2 hours, and to normal level over the following 2-4 hours
- 5% Hypertonic saline should be delivered by well secured large bore peripheral (> 18 gauge) cannula over 10 min
Prevention
Don’t drink too much!
Athletes should drink only according to thirst: (generally no more than 400 to 800 ml/h).