|
The old motto for marathon runners was to "drink as much fluids as one can tolerate" during races.
This belief is still held today by many marathon runners, who consume large amounts of fluids thinking they are preventing dehydration.
Contrary to this belief, the majority of runners are putting themselves at risk for the consequences of hyponatremia from excessive fluid intake.
Symptoms
 |
| STARTING GUN: Julie Heidrich, BSN, RN, was inspired to warn others about hyponatremia in marathoners after her father experienced it during a race. |
Hyponatremia is defined as a serum sodium less than 135 mEq/L (normal range 135-145 mEq/L). Mild hyponatremia, defined as a serum sodium level of 130-135 mEq/L, is typically not associated with any symptoms. The development of nausea, vomiting and malaise occur when the serum sodium level falls below 130 mEq/L.
Severe hyponatremia, with a serum sodium level below 120 mEg/L, results in headache, confusion and lethargy. Severely low serum sodium, especially with rapid development, can result in cerebral edema, seizure, coma, permanent brain damage and death.
Causes
Hyponatremia is commonly a result of water imbalance instead of sodium imbalance. Serum osmolality (normal range 280-295 mOsm/kg) measurement is essential in determining extracellular fluid volume and the cause of hyponatremia.
Hyponatremia can be isotonic, hypertonic (serum osmolality greater than 295 mOsm/kg), or hypotonic (serum osmolality less than 280 mOsm/kg). The causes of isotonic hyponatremia include hyperproteinemia and hyperlipidemia. Hyperglycemia and radiocontrast agents can cause hypertonic hyponatremia.
There are multiple causes of hypotonic hyponatremia, which include diarrhea, syndrome of inappropriate antidiuretic hormone (SIADH), psychogenic polydipsia, hypothyroidism and congestive heart failure.
In athletes, hyponatremia is usually hypotonic and a consequence of excess fluid intake with hemodiluation, not inadequate salt replacement.1
Runners who develop severe hyponatremia commonly have the SIADH. Treatment for hyponatremia is determined by the patient's volume status.
Risks
A large study of runners in the 2002 Boston Marathon reported participants who gained weight secondary to excessive fluid intake during the race were at increased risk for developing hyponatremia.2
The risk of developing a serum sodium less than 130 mEq/L was correlated with a body weight gain of greater than 2 kg. The risk was unchanged even when electrolyte solutions were consumed versus pure water.2 Sports drinks do not provide adequate sodium replacement and are hypotonic compared to blood, which does not protect runners from hyponatremia.1
Other risk factors identified in the Boston Marathon study included slower runners (finishing time greater than 4 hours), low body mass index and inexperienced runners.2 It is especially important to note slower marathon runners often consume larger amounts of fluids over a longer time period and should be monitored closely at the finish line and 24 hours post-race for signs of hyponatremia.
Prevention
The guidelines for fluid intake during marathon races were updated in 2006 by the International Marathon Medical Directors Association.3
These guidelines address elite and non-elite athletes, i.e., those who've trained for years to compete at the highest level versus those who just want to finish a race, for example, heat stroke, postural hypotension, and fluid intake recommendations. The association no longer makes a broad recommendation for fluid intake.3
The general recommendation is for runners to drink fluids when they feel thirsty. The exact recommendations is: "runners should aim to drink ad libitum 400-800 mL/hr, with the higher rates for the faster, heavier runners competing in warm environmental conditions and the lower rates for slower runners/walkers completing marathon races in cooler environmental conditions."3
Runners should not be encouraged to drink as much as tolerated by staff and bystanders.
Along with fluid intake guidelines, pre- and post-race weight measurements are one way to screen runners who are at greatest risk for hyponatremia.4 Although this is not a routine practice at marathons, it should be recommended to all marathon participants to monitor weight changes and follow-up in the first aid tent (or an emergency department) if they gain more than 2 kg. This prevention strategy of monitoring weight should also be recommended to runners during long-distance training runs.2
Education
Marathon runners should be educated about correct fluid intake depending on thirst, body size, running experience and estimated finish time. The elite marathon runners are at greatest risk for dehydration and heat stroke, while slower marathon runners are at greatest risk for developing hyponatremia.
Participants, observers and marathon staff should understand the signs and symptoms of hyponatremia. Participants suspected of having hyponatremia should be taken for medical attention. The correct treatment for mild hyponatremia, without signs of cerebral edema, is fluid restriction until urination occurs.
If signs of severe hyponatremia develop, the patient should be transferred to a hospital where serum sodium can be measured. The treatment for severe hyponatremia is hypertonic saline solution administered at a slow rate to prevent osmotic demyelination from rapid sodium repletion.1
Healthcare Connection
Education is one of the most critical aspects to prevention of disease processes.
As professionals in the healthcare field, we find ourselves amazed at the devotion and endurance marathon runners have. We often do not think severe and fatal consequences can develop in these healthy participants.
It is important we advocate for marathon runners to follow current guidelines and adequately address the risk of hyponatremia. This includes adjusting fluid intake according to thirst and measuring pre- and post-weights.
References for this article can be accessed here.
Julie Heidrich is a University of Pennsylvania MSN candidate from Jeffersonville, PA.
|