Understanding Hyponatremia

What is hyponatremia and what are its physical effects?

Hyponatremia means a reduced blood sodium (salt) concentration. When the sodium level falls below 130 mmol per liter, it creates, in mild cases, a general clouding of consciousness not unlike the slowing of brain function that occurs in drunkenness. Nausea and vomiting as well as lightheadedness and dizziness are frequently observed with mild cases. The brain swells as the sodium level gets lower which results from the general state of fluid overload. In the most severe cases, the athlete lapses into unconsciousness, develops epileptic-like seizures and may stop breathing or suffer cardiac arrest. Fluid overload of the lungs may produce pulmonary edema that leads to shortness of breath and coughing up blood-stained sputum. In marathon and half-marathon athletes suffering from hyponatremia, I have observed gross swelling of the hands and forearms in runners with serum sodiums of 130. If you can’t get your rings off at the end of the run, your serum sodium may be low.

How and why do distance runners get hyponatremia?

When you run or walk long distance, blood is shunted to the legs; less blood flow goes to the kidneys. Therefore salt regulatory hormones ADH and AVF inappropriately increase causing the kidney to make the athlete concentrate their urine with salt and retain the free water. Even Gatorade, Poweraide and all Sports Drinks or IV NS will therefore increase free water and lower serum sodium. Giving salt during the run may in fact be protective and it reminds runners about hyponatremia so that they will not overdrink!

By drinking too much fluid during prolonged exercise, athletes therefore develop this dangerous condition.. We usually find that athletes who develop the condition drink over 1 cup (8oz) every 20 minutes. If a participant stops at every fluid station and drinks just 1 cup sports drink or water , they will be hyponatremic by mile 17! As a result of overdrinking, they develop the progressive fluid overload.

Who gets it most commonly?

First time marathoners and charity participants (who are usually first-timers) tend to be at risk. They fear they will become dehydrated in heat and wrongly drink too much not understanding the danger. Women are at much greater risk than men for reasons that we don’t yet understand. It is clear that a big part of the problem is the inability of the athlete to excrete the excess fluid because of high levels of fluid-retaining hormones ADH and AVF.

Those taking NSAIDs (non-steroidal anti-inflammatory meds like Advil, Aleve, Motrin, Naproxen, Ibuprofen, Aspirin, Celebrex, Vioxx, etc) are also at increased risk. These drugs work by blocking prostaglandins in the body. By blocking prostaglandins, blood flow is decreased to the kidney thereby setting up the cascade that increases ADH and AVF.

How can marathoners make sure they are getting enough fluids but not so much as to be at risk for hyponatremia?

Recent scientific research has shown that drinking only when you are thirsty is the best prevention. If participants are drinking no more that 1 cup (8oz) every 20 minutes while on the course they will have enough fluids. The risk of dehydration, even in the heat, is far less than developing hyponatremia. Not drinking at every water station will prevent hyponatremia.

How can marathoners (or medical personnel) spot hyponatremia in another athlete?

Aside from some medical conditions that are usually well recognized, there are really few conditions specific to sport that cause an altered level of consciousness, nausea, vomiting, lightheadness and dizziness during or after prolonged exercise: exercise associated collapse, dehydration, heat stroke and hyponatremia.

Measuring body temperature is the first step in the differential diagnosis. If the body temperature (measured by rectal thermometer) is above 104, the diagnosis is heatstroke, and the athlete must be placed in/on ice to lower his or her body temperature. If the temperature is normal then one must strongly consider the diagnosis of hyponatremia. The diagnosis can be confirmed by measuring the blood sodium content, and obtaining a result below 130 mmol per liter. Medical doctors on scene are trained in evaluating these conditions and, if they suspect hyponatremia, will call for a transport as well as give oral salt.

What should be done for a stricken runner?

The best treatment of the hyponatremia of exercise is prevention. After suspected, if mild, doing nothing and stopping drinking for a while is best.. Given time, the body will start to get rid of the fluid excess by increasing urine production. Full correction of hyponatremia requires that the athlete gradually ingest some salt over the next 6 hours. Given the participant 1 salt packet under the tongue is a good start toward their treatment.
All patients suspected of having hyponatremia are transported to the hospital with an IV lock or NS at KVO (keep vein open) only so as to have access for meds if seizures develop. Oxygen should be given to provide maximum 02 saturation to a brain that may be undergoing swelling. IV Fluids are not to be given since the kidney will take the salt out, retain the free water and thereby worsen the hyponatremia.

Hospital personnel will take a STAT serum sodium and determine treatment based on that level. The physicians may choose to manage the condition by replacing the lost salt with a very concentrated [3 percent] salt solution given intravenously at a very slow rate [less than 50 ml of fluid per hour; they may start with a 100cc bolus]. This hypertonic saline is usually given in a hospital setting with proper monitoring.

What should not be done to a runner with hyponatremia?

Athletes with an altered level of consciousness should never be given intravenous fluids until it has been determined that the individual is not suffering from hyponatremia. We need more people to understand that the mild levels of dehydration experienced by modern marathoners does not cause loss of consciousness. Giving fluid to hyponatremic athletes will, at best, worsen the condition and delay recovery. At worst, it may produce respiratory and or cardiac arrest as a result of a sudden worsening of the brain swelling.

Pain Relievers

Recent medical research has shown that non-steroidal anti-inflammatories (NSAIDs) like Advil, Motrin, Aleve, ibuprofen, naproxen, etc. may be harmful to runners’ kidney function if taken within 24 hours of running; acetaminophen (Tylenol®) has been shown to be safe. These NSAIDs are thought to increase the possibility of hyponatremia while running long distances due to their decreasing blood flow to the kidneys and interfering with a hormone that helps the body retain salt. Therefore it is recommended that on race day (specifically beginning midnight before you run) you do not use anything but acetaminophen (Tylenol®) if needed until 6 hours after you have finished the race, are able to drink without any nausea or vomiting, have urinated once, and feel physically and mentally back to normal. Then, an NSAID would be of benefit in preventing post-event muscle soreness.

To avoid hyponatremia I recommend you follow these easy guidelines:

  • Follow the fluid recommendations….drink only when thirsty.
  • Include pretzels or a salted bagel in your pre-race meal.
  • Favor a sports drink that has some sodium in it over water, which has none.
  • In the days before the race, add salt to your foods (provided that you don’t have high blood pressure or your doctor has restricted your salt intake).
  • Eat salted pretzels during the last half of the race.
  • Do the salt! Carry 2 (two) small salt packets with you (steal from your favorite fast food restaurant), and before the race and again during the last half of the race (marathon or half marathon) consume a single packet under your tongue.
  • After the race, drink a sports drink that has sodium in it and eat some pretzels or a salted bagel.
  • Stop taking non-steroidal anti-inflammatories 24 hours before your race and do not start again until a minimum of 6 hours after finishing the race.

If you understand the above, unfortunately you may know more than medical personnel at a local race or an Emergency Room. Carry this blog with you (to show a doctor if you have to), follow the advice, do the salt, and you will have happy marathons and half marathons without worrying about hyponatremia.

Enjoy the ride!