Exercise Associated Hyponatremia
- 1 Other Names
- 2 Background
- 3 Pathophysiology
- 4 Risk Factors
- 5 Differential Diagnosis
- 6 Clinical Features
- 7 Evaluation
- 8 Classification
- 9 Management
- 10 Prevention
- 11 Rehab and Return to Play
- 12 Complications
- 13 See Also
- 14 References
- Exercise-Associated Hyponatremia
- Exercise-associated Hyponatremic Encephalopathy
- Defined as hyponatremia which occurs during or up to 24 hours following physical activity
- <1% of individuals have a pre-race sodium below 135 mmol/L
- This is in the expected range for the general population
- Asymptomatic EAH
- Symptomatic EAH
- Rare and occurs with less frequency than asymptomatic EAH
- Incidence estimated to be 0.06% - 1% in endurance events
- Incidence estimates range from 2 - 4 per 1000,000 person years in hikers, 4 - 13 cases per 100,000 person years in active duty military
- At least 14 documented deaths since 1981
- Hyponatremia: serum, plasma or blood sodium concentration below the normal reference range
- In most labs, this is typically less than 135 mmol/L
- Determinants of serum sodium
- Total body content of sodium
- total body content of potassium
- Total body water
- Can occur due to relative loss of sodium, potassium, total body water or some combination of both
- Symptoms are directly proportional to magnitude of decrease from baseline and the rate at which the decrease occurs
- Patients can become symptomatic at declines as low as 7-10% from baseline
- The role of thirst
- Thirst should provide adequate stimulus for preventing excess dehydration, markedly reduces the risk of developing EAH
- Defined as a “generalized, deep seated feeling of desire for water”
- Evolutionarily refined, finely tuned, regulatory mechanism serving to protect both plasma osmolality and circulating plasma volume
- Euvolemic (Euvolemic Hyponatremia)/ Hypervolemic (Hypervolemic Hyponatremia)
- In most cases, hyponatremia is dilutional, occurring due to relative excess of total body water intake.
- This occurs in excess of total body fluid losses which includes the sum of insensible (cutaneous, respiratory, and gastrointestinal), sweat and renal (urine) fluid losses
- Excessive water intake increases release of vasopressin, overwhelming renal water clearance, subsequently leading to water retention
- This cause is believed to be associated with all causes of morbidity and mortality associated with EAH
- Hypovolemic (Hypovolemic Hyponatremia)
- Defined by electrolyte depletion without expansion of total body water
- Well described in medical literature in non-exercising individuals
- More poorly defined in sports medicine literature, less commonly encountered
- Seen in extreme events such as ultra-marathons and ironman distance triathlons
- Male = Female
- Extrinsic risk factors
- Overdrinking (water, sports drinks, hypotonic beverages)
- Weight gain while exercising
- Duration of activity >4 hours
- Inexperienced athlete
- Inadequately trained athlete
- Slow running or performance pace
- High or low BMI
- Readily available fluids (on athlete)
- NSAID use: controversial
- Intrinsic risk factors
- Sports and Activities
- Exertional Heat Stroke
- Heat Exhaustion
- Acute Mountain Sickness
- High Altitude Cerebral Edema
- High Altitude Pulmonary Edema
- Exercise Associated Postural Hypotension
- Occurs when serum sodium is less than < 135 mmol/L
- Typically incidental when athlete participating in research protocol or blood work for other unrelated purpose
- Mild EAH
- Mild: Non-specific symptoms including lightheadedness, dizziness, nausea, puffiness, weight gain
- Severe EAH/ EAHE
- Typically present with headache, vomiting
- Altered mental status (confusion, seizure, disorientation, obtundation, seizure, coma)
- May due to cerebral edema (exercise-associated hyponatremic encephalopathy or EAHE)
- Signs of impending herniation (decorticate posturing, mydriasis)
- Frothly sputum, SOB, cough due to non-cardiogenic pulmonary edema
- Primarily a clinical diagnosis supported by laboratory findings
- Important to check sodium if clinical suspicion of EAH
- Mild (>130 mmol/L)
- Moderate (125 - 130 mmol/L)
- Severe (<125 mmol/L)
- Treatment should be directed primarily at the level of neurological impairment
- Not simply just the sodium
- Typically subclinical and found incidentally
- No treatment required if not symptomatic
- Post event, the athlete may be encouraged to avoid hypotonic fluid intake
- Goal is to achieve urine production
- Suggests vasopressin levels have fallen and urine is dilute
- Could consider administering oral hypertonic fluids to prevent progression to symptomatic EAH
- Less clear guidelines on patients with mild symptoms
- Can observe and restrict hypotonic and isotonic fluids until urinating
- Can administer oral Hypertonic Saline (HTS)
- Concentrated bouillon (4 cubes in 125 mL or 1/2 cup of water
- 3% Normal Saline 100 mL, preferably with flavoring
- Oral sodium tablets thought to be less effective than oral HTS
- More research is needed to better delineate this
- Disposition: Can be discharged once symptoms have resolved and micturitionhas ocurred
- Rapidly progressing, life threatening emergency
- Administer IV Hypertonic Saline (HTS)
- Typically, 3% Sodium Chloride
- Dose is 100 mL bolus of 3%
- Can use 8.4% NaHCO3 50 mL as an alternative
- Because this is an acute process, there is no risk of osmotic demyelination syndrome
- Repeated doses (every 10 minutes, up to 3 doses) should be administered until there is clinical improvement
- In certain clinical contexts, seizure, coma, etc, larger or more frequent doses should be considered
- The safety of this approach is well documented with one runner receiving 950 mL of 3% over a 7 hour period without complications
- If symptoms are severe, it is reasonable to HTS bolus prior to measuring the sodium
- Disposition: Goal is stabilize patient for transfer to advanced medical facility for further workup, monitoring and treatment
- The diagnosis should be communicated to the accepting physician to avoid administration of hypotonic or isotonic fluids
- Suspected diagnosis without the ability to measure sodium presents a common clinical conundrum
- If history and exam is suspicious, treatment with HTS is justified
- Can be a lifesaving therapy and unlikely to do harm
- Expand intravascular volume, low risk for osmotic demyelination syndrome
- Should receive immediate electrolyte evaluation
- If severe, should be treated as above
- Admission to critical care
- Fluid and electrolyte therapy should be considered ex-ante rather than ex-post facto
- Individuals should be discouraged from drinking prior to feeling a thirst sensation as this can lead to EAH
- Case series cites overdrinking water as a cause or contribution to the development of EAH
- Body can tolerate loss of 3% body mass or 5% total body water without reduction in performance
- Body weight is a reasonable surrogate for hydration status when measured daily after sleep
- It is imprecise during athletic events where EAH is most likely to develop
- Safest hydration strategy is to drink fluids when thirsty before, during and immediately following exercise
- This persists in both hotand coldenvironments
- Thus, drinking to thirst will, in most cases, prevent both dilutional EAH and performance decrements due to excessive dehydration
- Sodium Supplementation
Education & Event Management
- Safe hydration practices should be instituted and educational strategies disseminated
- This includes reducing the emphasis on high fluid intakes
- Example at one ironman competition
- Education program advised athletes of the risks incurred by overdrinking
- Additionally decreased the number of fluid stations to limit the fluid availability reduced the incidence of EAH
- In one 90 km footrace, education of safe drinking habits was shown to reduce the incidence of EAH
- Placing cycling stations 20 km apart in an ironman triathalon, 5 km apart in a standard marathon reduced EAH
- Need more studies to optimize spacing strategies
- Some athletes will seek more quantitative measurements by measuring pre- and post-race weights
Rehab and Return to Play
- Needs to be updated
Return to Play
- No clear guidelines
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