Hyponatremia is a potentially life-threatening condition that occurs when there is too little sodium in the blood. Early signs may include fatigue, headaches, confusion and nausea. If not quickly resolved, hyponatremia can lead to seizures, coma and death.
Defined as a blood sodium level below 135 mmol/L, hyponatremia can occur when excessive amounts of sodium are lost through urination, perspiration, vomiting or diarrhea. Health conditions or medications that cause fluid retention can cause dilutional hyponatremia, as can overhydration. Medical conditions that may lead to hyponatremia include congestive heart failure, kidney disease and syndrome of inappropriate anti-diuretic hormone. Psychogenic polydipsia, which leads sufferers to drink excessive amounts of water, affects up to one-fifth of psychiatric patients and frequently leads to hyponatremia.
Overhydration leading to hyponatremia used to be more common among athletes, particularly women, who participated in long-duration sports, such as marathons. Nowadays, those who engage in endurance sports — as well as emergency personnel who treat athletes in distress — are far better equipped to prevent, recognize and manage hyponatremia, thanks to a concerted effort in the sports medicine community to raise awareness about risks and signs of overhydration.
But there are other at-risk populations who health professionals may encounter. Being alert to risk factors and early signs of hyponatremia enables nutrition professionals to work with the entire health-care team to avert acute problems. Diuretics may deplete the body of electrolytes, including sodium. SSRI antidepressants, such as paroxetine, which increase levels of antidiuretic hormone, have led to life-threatening cases of hyponatremia, especially in elderly patients.
Intravenous administration of hypotonic fluids, which contain a lower concentration of sodium than blood, in excessive quantities or speeds can cause dilutional hyponatremia. This occurs most commonly in children and the elderly. Patients receiving parental nutrition also need to be closely monitored, and their orders adjusted as needed, to maintain proper fluid and electrolyte balance.
Avoiding dietary sodium, on the other hand, is unlikely to cause hyponatremia. Even a very low-sodium diet (500 to 1,000 milligrams/day) should maintain adequate levels under normal circumstances.