Hyponatremia natural history, complications and prognosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Complications
Neurological (brain) symptoms typically occur with very low levels of plasma sodium (usually <115 mEq/L). When sodium levels in the blood become excessively low, excess water enters the brain cells and the cells swell. This is called hyponatremic encephalopathy. This is very dangerous because the soft brain is confined by the rigid skull. As the brain expands tentorial herniation can occur which is a squeezing of the brain across the internal structures of the skull.
This can lead to headache, nausea, vomiting and confusion, seizures, brain stem compression and respiratory arrest (stopping breathing), and non-cardiogenic pulmonary edema (fluid in the lungs). This can be fatal if not treated promptly.
The severity of symptoms depends on how fast and how severe the drop in blood salt level. A gradual drop, even to very low levels, may be tolerated well if it occurs over several days or weeks, because of neuronal adaptation. The presence of underlying neurological disease, like a seizure disorder, or non-neurological metabolic abnormalities, also affects the severity of neurologic symptoms.
Chronic hyponatremia can lead to such complications as neurological impairments. These neurological impairments most often affect gait and attention and can lead to falls, osteoporosis, and slowed reaction time.
Complications for chronic hyponatremia are most dangerous for geriatric patients. Falls are the leading cause of deaths related to injury among people 65 years or older. In a recent study[1] the incidence of hyponatremia in elderly patients with large-bone fractures was more than double that of non-fracture patients. Recent work by Verbalis et al.[2] suggests that hyponatremia induces osteoporosis and found the adjusted odds ratio for developing osteoporosis to be 2.87 times higher among adults with mild hyponatremia compared to those without.
Acute hyponatremia can lead to much more serious complications including brain disease, brain herniation, cardiopulmonary arrest, cerebral edema, seizures, coma, and death.
Prognosis
The outcome depends on the condition that is causing the problem. In general, acute hyponatremia, which occurs in less than 48 hours, is more dangerous than hyponatremia that develops slowly over time. When sodium levels fall slowly over a period of days or weeks (chronic hyponatremia), the brain cells have time to adjust and swelling is minimal.
References
- ↑ Harminder, S. Sandhu et al. "Hyponatremia associated with large-bone fracture in elderly patients." Int Urol Nephrol (2009) 41:733-737.
- ↑ Ayus, Juan Carlos and Michael L. Moritz. "Bone Disease as a New Complication of Hyponatremia: Moving Beyond Brain Injury". CJASN ePress. Jan 14, 2010. 10.2215/CJN.09281209.