Hyponatremia in Athletes

HYPONATREMIA: The most serious cause of exercise associated collapse

 A potentially fatal condition that can be seen in endurance athletes when their sodium levels drop too low either from hyper-hydration or from dehydration.

Dehydration = a low blood level resulting in low sodium content

Hyper-hydration = diluting the level of sodium

NORMAL 135-145

MILD   131-134

MODERATE  126-130

SEVERE  Less than 126

Too much H2O (water intoxication) can cause a lethal physiologic reaction where water rushes into cells including brain cells. 

Doctors can misdiagnose it as dehydration and mistakenly treat with IV fluids

How it happens:

During high intensity exercise, sodium is lost along with sweat. Athletes can lose up to 2 grams of salt per liter of sweat.  An athlete who only replaces the lost fluid with water will have a decreased blood-sodium concentration. Sodium balance is necessary for transmitting nerve impulses and proper muscle function.   

Consider a full glass of salt-water. If you dump out half of the contents of the glass (as is lost in sweat), and replace that with water only, the sodium concentration of in the glass is far less and the water is more dilute. This can occur in the bloodstream of an athlete who only hydrates with water during excessive sweating. The result is …… HYPONATREMIA

RUNNER’S PROFILE: Mark Robinson

Completed Boston Marathon at age 27

Drank gallon H2O before race

A cup at every drink station

Drank H20 after finishing race despite vomiting

Collapsed in parents home

Air-lifted to a Boston Hospital

Misdiagnosed with Dehydration, Given fluids

Was in a Coma for 4 days before recovering.

SIGNS OF HYPONATREMIA

Headache

Confusion

Nausea/Vomiting

Cramping

Bloated Stomach

Altered Consciousness

Swelling in extremities (fingers and ankles)

Seizures

Lethargy

FOR ATHLETES: HOW TO AVOID HYPONATREMIA

Use a sodium containing sports drinks during long distance (more than 60-90 minutes long)

Increase salt intake per day several days prior to competition (except for those with hypertension)

Try not to drink more then you sweat

During a marathon a good rule of thumb is to drink about 1 cup of fluid every 20 minutes

Avoid use of NSAIDS (like ibuprofen) medicines that contain sodium during event.

FOR PHYSICIANS: HOW TO AVOID PITFALLS IN THE TREATMENT OF HYPONATREMIA

Do not misdiagnose Acute Hyponatremia as Dehydration and give fluids and cause CEREBRAL EDEMA

Do not use Hypertonic saline in patients that do not have signs of CNS involvement

Do not correct Na greater than 4-6 meq/L and cause central pontine myelinolysis.

ACUTE

When serum sodium concentration falls rapidly

Over 24-48 hours

The compensatory mechanism is overwhelmed which can lead to cerebral edema and brainstem herniation

CHRONIC

Develops over more than 48hrs

Experience milder degrees of cerebral edema for a given serum sodium level

Brainstem herniation has not been observed

The causes of morbidity and death are status epilepticus (when chronic hyponatremia reaches levels of 110 mEq/L or less) and central pontine myelinolysis when corrected improperly.

The distinction between ACUTE hyponatremia and CHRONIC hyponatremia has critical differences in proper corrective therapy.

Acute evolution of hyponatremia (as in marathon runners and high endurance athletes) leaves little opportunity for compensatory extrusion of CNS intracellular solutes.

Hypertonic saline (3%) on a rare occasion may be used to rapidly increase serum sodium level in patients with severe acute or chronic hyponatremia if manifested by severe confusion, coma, seizures, or evidence of brainstem herniation

An increase of 4-6 mEq/L over a few hours is sufficient. Further correction is dangerous and must be avoided unless necessary to correct continued seizures or other severe CNS abnormality

Equation for use of Hypertonic Saline.

Required volume = (Na desired - Na current)(TBW) / (Na Fluid- Na Current)