Hyponatremia—a serum sodium level of < 135 mEq/L—is the most common electrolyte disturbance, affecting 1% of hospitalized patients. While it is equally frequent in men and women, children and menstruating women are most vulnerable to the brain damage it can cause.
In an exclusive interview with MDLinx, Isabel Maples, MEd, RDN, a spokesperson for the Academy of Nutrition and Dietetics, explained the various clinical concerns surrounding hyponatremia.
“Hyponatremia is usually a problem of getting too much fluid—not too little sodium,” said Maples. “Overdrinking, even something as ‘safe’ as water or sports drinks, can dilute the amount of sodium in the blood. The kidneys can’t remove the water fast enough before the fluid moves into tissues including the brain. The extra pressure from too much water affects the function of vital organs.”
Maples stressed the universal nature of hyponatremia.
“Anyone can fall victim. Recreational athletes are at risk; they know they need to drink but overestimate the amount they need versus the amount they’re working out and sweating. Women are at greater risk since they tend to have a smaller body size and therefore, a lower sweat rate,” she said.
“Medical conditions can affect one’s risk of hyponatremia, as can medications and some illegal drugs,” she continued. “It can be caused by heavy sodium loss, like with sweating, diarrhea or vomiting (especially when combined with drinking a lot of fluid). Some people have very heavy salt losses in their sweat. Those people will have salt visible on their skin as their sweat dries.”
In a healthy person, excess water load—either from excess intake or retention—will result in rapid excretion. The fall in plasma osmolality secondary to dilution suppresses the release of antidiuretic hormone (ADH), which leads to the release of diluted urine.
Here are some major pathological causes of hyponatremia in which antidiuretic hormone levels are higher:
- Depletion of effective circulating volume
- True volume depletion (eg, vomiting, diarrhea, bleeding, and urinary loss)
- Thiazide diuretics
- Hormonal changes: adrenal insufficiency, hypothyroidism, and pregnancy
- Congestive heart failure and cirrhosis
- Syndrome of inappropriate ADH secretion
Here are some of the signs and symptoms of early hyponatremia, a condition that warrants immediate medical attention.
- Stomach bloating
- Swelling in the ankles, toes, wrists, and fingers
- Difficulty breathing
- Loss of consciousness
Treatment of hyponatremia
Four issues must be considered when treating the hyponatremic patient:
- The risk of osmotic demyelination
- The appropriate rate of correction to minimize the risk of osmotic demyelination
- The best method for raising the plasma sodium concentration; and
- The estimation of sodium deficit to determine the proper amount of sodium to be administered
Every medical student learns that correcting sodium levels too quickly can lead to a very scary condition called central pontine myelinolysis, or “locked-in” syndrome. According to one study, neurologic complications tend to happen if the rate of sodium correction is greater than 0.6 mmol/L/hr.
According to Maples, there are two easy ways to determine how much water you need to prevent hyponatremia. First, heed your thirst. Second, monitor the color of your urine. It should be pale yellow—resembling the color of lemonade—not darker in color, like apple juice.
You can also weigh yourself to gauge hydration status.
“Athletes can weigh themselves before and after a workout to determine if they are drinking enough while working out. People who work outside, especially in hot, humid weather, can use this technique as well, to help estimate water lost in sweat, so they can determine how well they’re replacing that fluid,” said Maples.
Finally, you may be wondering about sports drinks. Here’s what Maples has to say about the subject:
“Sports drinks do contain a small amount of sodium (100-110 mg/8 oz). That sodium is not really there to replace sodium. (It’s easier to replace sodium at the next meal.) Instead, for hard exercise longer than 60 minutes or exercise in high heat or humidity, the salt in a sports drink helps the body hold on to and use the fluid in the drink. The salt makes the kidneys save more fluid, rather than urinate more of it out.”