Exercise Associated Hyponatremia – stop the NS

Unable to put a finger on, or differentiate your young healthy patients first time seizure activity? The absence of trauma, infection, stroke, any pertinent historical findings,thCAIST0VW heat/altitude illness or other pharmacological based explanation leading you toward a primary diagnosis of neoplasm or some other insidious intracranial nasty?

As the summer and warmer months are upon us, the consideration of Exercise Associated Hyponatremia (EAH) is warranted in these individuals.

Wilderness Medical Society Practice Guidelines for the Ttreatment of Exercise Associated Hyponatremia are representative of “…the great strides that are taking place in an effort to prevent what is now recognized as a leading cause of preventable mobidity and mortality in endurance activities throughout the world“.

How does this affect me as a pre hospital practioner you ask? We here at rightseatmedicine have encountered a small cohort of patients in the Lower Mainland region of BC presenting with exercise associated hyponatremia.

All being young healthy males, not athletes but tradesman/roofers, who had been working for extended periods in heat stressed environments and with innappropriate/excessive hydration regimes. All of whom presented with first time seizures, a resistance to Midazolam in cessating the seizure activity and all with subsequent plasma sodium concentrations of <135mEq/L.

The two major mechanisms behind EAH include:PIIS108060321300063X_gr1_lrg

1) excessive fluid intake, and 2) impaired urinary water excretion, largely a result of persistent ADH secretion (Figure 1).

Minor factors include sweat sodium loss, an inability to mobilize sodium stores, ANP/BNP elevations and rapid water absorption from the GI tract.

Risk factors for EAH include excessive water intake beyond the capacity of renal excretion, continuous edurance work lating >4hrs, low or high BMI, inappropraite aclimitization, SSRI use along with some data suggesting NSAID useage as a contrinuting factor.

Prevention measures involve avoiding overhydration and by the individual simply using the sensation of thirst as the real-time guide to fluid ingestion during activity. Along with concurrently avoiding excessive sodium supplimentation and (less applicaable to the prehospital environment) the regular monitoring of body weight.

Thereapuetic options for field treatment of involves the recognition of EAH like symptomology and the subsequent restriction of hypo/iso tonic fluids in those patients.  Whilst provision of fluids to dehydrated patietns is warranted, the adminstration to the EAH patient can be disasterous (hydrocephalus).
Whereas the ideal treatment being the recognition for the potential for EAH, rapid transport to point of care blood analysis and advocacy of EAH throughotu the handover to the higher level of care.

As for the WMS suggested treamtent algorythm for EAH, see Figure 2. below.PIIS108060321300063X_gr2_sml

Further understanding of EAH amongst the prehospital community will hopefully bring an end to the paradigm of saline bolusing & innappropriate fluid challenges delivered not only to the backcountry athlete/adventurer, but those patients encountered with an exercise associated hyponatremic presentation.


1. Bennet, B.L. et al (2013) Wilderness Medical Practice Guyidelines for Treatment of Exercise-Associated Hyponatremia. Wilderness & Environmental Medicine. Vol 24, pp. 228-240.