Early detection and proper treatment of exercise-associated hyponatremia can reduce morbidity and mortality in these cases. Doctors must be able to distinguish exercise-associated hyponatremia from hyponatremia caused by other things (such as dehydration and heatstroke). Although they have similar symptoms, these cases require very different procedures.

Definition

What is Exercise-Associated Hyponatremia?

Exercise-associated hyponatremia is a condition in which decreased blood sodium concentration ([Na+]) is below 135 mmol / L and occurs during or up to 24 hours after physical activity.

Exercise-associated hyponatremia can be symptomatic or asymptomatic. In severe conditions, Exercise-associated hyponatremia can cause clinical manifestations in the form of changes in mental status such as delirium, seizures, and coma due to cerebral edema.


Etiology

What physical activities can cause Exercise-associated hyponatremia?

Physical activity that often causes Exercise-associated hyponatremia is moderate to severe intensity exercise. That tests endurance such as marathon (42.2 km), triathlon (3.8 km swimming, 180 km cycling, and 42.2 km running), and ultramarathon (100 km). However, sometimes EAH can also be found in individuals who are hiking, backpacking, or cycling for recreational needs.


Pathophysiology

How can exercise cause exercise-associated hyponatremia?

Important points that cause hyponatremia are reduced solutes (sodium), increased solvents (liquids), or both. 
Three things underlie the pathophysiology of EAH:
  1. overhydration with hypotonic fluid,
  2. arginine vasopressin (AVP) secretion, 
  3. and sodium loss through sweating.


Overhydration with Hypotonic Fluids
When exercising, a person usually drinks a lot of hypotonic fluids such as plenty of water or sports drinks. Hyponatremia can occur when the hypotonic fluid volume intake is more than the physiological fluid excreted through sweat, urine, and insensible water loss.

Arginine Vasopressin hormone secretion
The arginine vasopressin (AVP) hormone is an antidiuretic hormone. In the distal renal tubule, AVP induces water reabsorption. This process will increase the volume of water and eventually reduce the concentration of sodium in the serum. AVP secretion can increase when someone is exposed to heat or undergo physical activity.

Loss of Sodium Through Sweat
The relationship of sodium loss through sweat with Exercise-associated hyponatremia is still controversial because the amount of sodium lost through sweating varies greatly between individuals. This pathophysiology is mainly associated with several cases of Exercise-associated hyponatremia with hypovolemic conditions.


Diagnosis

How to make diagnose Exercise-associated hyponatremia?

The primary diagnostic method for EAH is to check the concentration of sodium in the serum. However, this examination facility is often not available in places where do exercise. Therefore, doctors need to know how to detect EAH even though serum sodium analysis is not available.


Clinical Manifestations

What are the symptoms and signs of Exercise-associated hyponatremia?

The clinical manifestations of Exercise-associated hyponatremia can vary from mild to severe, depending on sodium serum levels. In mild EAH cases, signs and symptoms that are common include:
  • Dizzy
  • Nausea and vomiting
  • Malaise
  • Bloated
  • Weight gain due to increased fluid intake


In severe EAH cases, osmotic water movement can occur from the intercellular space to the intracellular space, which causes cell edema. It can cause increased brain intracranial pressure and noncardiogenic pulmonary edema. Symptoms that can appear are:
  • Headache
  • Throw up
  • Lethargy
  • Disorientation
  • Convulsions
  • Loss of consciousness
  • Hard to breathe
  • Frothy Sputum


In patients with the above symptoms, the doctor needs to analyze the following further and consider the diagnosis of Exercise-associated hyponatremia if:
  • There is a history of hypotonic fluid consumption with a greater volume than the loss of body fluids volume.
  • The absence of typical dehydration symptoms (such as thirst, postural dizziness, dry mucous membranes, and orthostatic) causes hypotension or tachycardia when standing.
  • An increase in body weight after exercise due to increased fluid intake
  • Low urine output


Treatment of Exercise-associated hyponatremia

The treatment of EAH patients based on symptoms, whether mild symptoms and severe symptoms. This treatment should be performed when the diagnosis of Exercise-associated hyponatremia has been confirmed or is strongly suspected.

a. Exercise-associated mild hyponatremia

In patients with mild symptomatic EAH, the treatment procedures are oral fluids restriction, consuming foods or drinks containing sodium, and administering isotonic intravenous fluids only when necessary.

Peroral Fluid Restriction:
Patients with EAH due to overhydration and fluid retention need to undergo restriction of oral fluid consumption until urination occurs. This treatment is contrary to the treatment of EAH due to dehydration. Therefore, the differential diagnosis of dehydration must be completely ruled out.

Consumption of Foods or Drinks containing sodium:
Oral administration of sodium (both hypertonic fluid and sodium-rich foods) is recommended in patients with mild EAH symptoms (without nausea and vomiting). Examples of foods or drinks are 100 ml of hypertonic saline given flavorings or 3-4 blocks of broth (containing 880 mg of sodium per block) dissolved in 125 mL of water.

Administration of intravenous fluids:
One of the clinical manifestations of EAH is nausea and vomiting. Not infrequently, patients have difficulty receiving fluids or food orally. Giving intravenous isotonic fluid is not recommended for EAH with fluid overload. But this can be considered in hemodynamically unstable conditions or severe vomiting. Administration of intravenous hypotonic fluid is contraindicated in EAH patients.

b. Exercise-associated severe hyponatremia

Give 100 mL of hypertonic fluid (NaCl 3%) by intravenous bolus immediately. It can be repeated two times at intervals of 10 minutes. The target increase in serum sodium is 4-5 mmol / L or until the neurological symptoms improve.

Intravenous hypertonic fluid administration for severe EAH case with encephalopathy is beneficial in relieving brain edema and reducing intracranial pressure. The absence of an intravenous hypertonic solution poses a risk of developing pulmonary edema, progressive cerebral edema, brain stem herniation, and death.

After the patient arrives at the hospital, immediately analyze the concentration of sodium in the serum. The doctor also needs to examine further whether there are brain edema and pulmonary edema that may occur in all EAH patients. Provide isotonic and hypotonic fluid if only the sodium level has been corrected or the hypovolemic condition is confirmed.