Take a balanced approach to sodium imbalances

Tips for treating patients on both ends of the sodium spectrum, from hyponatremia to hypernatremia.

Patients hospitalized with abnormal sodium levels can run the gamut, from elderly patients who can't get to a glass of water to athletes who exercise so hard they sweat out needed sodium.

At the annual meeting of the American Academy of Family Physicians, held in San Diego in September, Eddie Needham, MD, gave advice on treating patients at both ends of the sodium spectrum, from hypernatremia to hyponatremia. Dr. Needham, who is the program director of the family medicine residency program at Florida Hospital in Winter Park, Fla., has seen his share of sodium abnormalities.

“I joke with my residents…[if there's] a patient getting admitted from a nursing home who has a sodium greater than 135, there must be something wrong,” he said. “I don't see normal sodium on a regular basis.”

The prevalence of hyponatremia, especially among elderly patients, is an issue to consider when deciding on treatment, he noted. “If the patient's presenting for something totally different, and their sodium is in the high 120s, low 130s, that might be OK,” Dr. Needham said. “We see 126 and we want to fluid restrict them and correct it up to 135, then we send them home and they come back at 126.” Illnesses such as pneumonia can also cause fluctuations in sodium that correct themselves when the patient is well again, he added.

By definition, hyponatremia is any sodium level below 135 mEq/L, with a level between 120 and 130 considered moderate hyponatremia, and anything under 120 severe. Patients with mild or moderate cases often don't show symptoms, and even if they do, the most common symptoms—headache, lethargy/fatigue and nausea—have a wide differential, Dr. Needham noted. “The specificity is probably like 1% or 2%,” he said.

However, some hyponatremic patients present with severe neurologic and/or gastrointestinal symptoms. “Where we see symptoms is when there's an acute change in a patient's sodium level,” he said. “That gives you the massive alterations in your mental status.”

Such patients require urgent treatment, although the rush to treat low sodium shouldn't distract you from the need to collect useful data. “The first thing you want to do, anytime you want to cure a lab that's not normal, is to repeat the lab,” said Dr. Needham. In addition to blood, he said, you want to collect patients' urine, as soon as possible.

“Pardon the pun, but that first urine is golden,” said Dr. Needham. Analysis of urine sodium can help establish the role of the kidneys in the patient's hyponatremia. “If the urine sodium is less than 20 [mEq/L], the kidneys are attempting to absorb as much sodium as they can. If it's higher than 30, they're letting the sodium bleed through and you want to look at the kidneys,” he said. Serum osmolality can also be useful, he added. “It's 320, 330 [mOsm/kg]—it's more concentrated. If it's perhaps 250, 270—that's fluid overload with free water.”

Dilutional hyponatremia is often associated with failure of the heart, liver or kidneys. “You have an increase in your total body water that exceeds the increase you might have in sodium. This results in edema,” said Dr. Needham. He also told an anecdote of a psychiatric patient who developed dilutional hyponatremia after drinking vast quantities of water from a hospital showerhead, due to psychogenic polydipsia.

Depletional hyponatremia, on the other hand, could happen to that athlete who worked out too hard and drank only water. “Athletes should be replacing not just with free water, but at least every other drink with a hypotonic solution,” said Dr. Needham.

The depletional variety can also result from fluid loss from the gastrointestinal system (vomiting, diarrhea) or the third space (severe burns, sepsis). There are also several renal causes: Addison's disease, salt-losing renal diseases (polycystic kidney disease, pyelonephritis), and diuretic medications. “We have to remember when we give those to our patients, we should follow up and see how they are doing,” Dr. Needham said of the final category.

Regular follow-up is key to successful treatment of hyponatremia, too. “Whatever you do, whether the sodium is really, really low or really, really high, you only want to do it for a brief interval and then you want to come back to look to see what happened,” said Dr. Needham.

There are dire consequences to both under- and overtreatment of hyponatremia. Patients whose sodium drop is not corrected can suffer hyponatremic encephalopathy. “If you put more fluid in the cells in your brain, that can cause edema, and if it gets too severe, that can cause things like respiratory depression, tentorial herniation and death,” Dr. Needham said. “That's why if you have an acute change in mental status and someone's got really, really low sodium, those are people you should look at correcting acutely.”

On the other end, excessively rapid correction of hyponatremia can cause osmotic demyelination syndrome (formerly known as central pontine myelinolysis). The happy medium is to correct hyponatremia by 10 mEq/L per day.

“Your goal is no more than a 10-mEq/L rise in 24 hours,” said Dr. Needham. There are a number of ways to achieve this goal. In less acute dilutional cases, simple fluid restriction, or loop diuretics combined with salt tablets, may be sufficient.

Intravenous saline is often the best solution, however. When calculating how much saline a patient needs, remember that 0.9% normal saline has 154 mEq/L of sodium, Dr. Needham said. In patients with severe deficiencies, it may be tempting to use 3% saline, but be very cautious with such rapid corrections, he advised. “Hot salts—I've done it once,” he said.

Whichever saline you choose, check back soon to assess its effects. “I repeat the electrolytes in another couple of hours,” Dr. Needham said. Keep in mind that a patient who is hyperglycemic will have very different osmolality, he advised.

If none of these strategies fix the problem, the antidiuretic hormone (ADH) antagonists conivaptan and tolvaptan are both approved for treatment of hyponatremia, although Dr. Needham has never used them for this indication. “There are people who are repetitively symptomatic and that's where use of the drugs can be useful,” he said. The treatment of last resort is renal replacement therapy.

Finally, Dr. Needham offered some formulas useful in hyponatremia treatment (see box, above), and also suggested that physicians check the Internet for more resources. “There are excellent Web calculators,” he said.

Those calculators could also be helpful in treating patients with hypernatremia. High sodium levels can be caused by too little access to water and too much access to salt. It could also be a complication of gastrointestinal illness or a symptom of a hypothalamic lesion or diabetes insipidus, he said.

As with hyponatremia, a patient's free water deficit should be corrected at no more than 10 mEq/L per day, Dr. Needham noted. “When you're correcting these things, always guess low,” he said. Obviously, he noted, the correction should be made using 5% dextrose in water (D5W) rather than saline. “It's also important to allow access to water,” Dr. Needham said.

To determine whether diabetes insipidus is the cause of hypernatremia, he recommends collecting the patient's first urine of the day. “If you can concentrate that first urine, you probably don't have diabetes insipidus,” he said.

If it is diabetes insipidus, you'll need to distinguish whether the problem is central or nephrogenic. That can be accomplished with a trial of desmopressin. If the patient responds, that's central; if not, it's nephrogenic. That result will then guide further treatment, Dr. Needham said.