- Author: Eric E Simon, MD; Chief Editor: Vecihi Batuman, MD, FACP, FASN more...
Further Inpatient Care
Patients with hyponatremia from any cause require close attention to their electrolyte and fluid status.
Patients with symptomatic hyponatremia who are being actively treated often require several daily measurements of serum sodium to avoid a rate of correction that is too rapid.
After acute treatment, follow-up generally is dictated by the underlying etiology of the hyponatremia.
Clinical manifestations include clouding of consciousness, confusion, stupor, or coma. Seizures commonly occur with rapid reductions in serum sodium or with serum sodium concentrations of less than 115-120 mEq/L.
For unknown reasons, premenopausal women seem to have a less efficient osmotic adaptation. This increases their susceptibility to severe hyponatremia and rapid progression from minimal symptoms (eg, headache, nausea) to respiratory arrest. Cerebral edema and herniation have been found at autopsy.
Correction of hyponatremia that is too rapid may cause permanent neurologic impairment. Central pontine myelinolysis (CPM) and extrapontine myelinolysis (EPM), complications of excessive correction of chronic hyponatremia, are now diagnosed by diffusion-weighted magnetic resonance imaging (MRI). Of note is that conventional CT and MRI scan findings typically lag behind the clinical manifestations of myelinosis by 2-4 weeks.
The clinical course of these patients features initial encephalopathy secondary to hyponatremia, then improvement as the plasma Na concentration increases, and finally deterioration several days later. The disorder can resolve completely or result in permanent disability or death. This typical clinical course has been called the osmotic demyelination syndrome (ODS). The clinical neurologic picture may be confusing, as it may include a variety of findings from psychiatric, behavioral, and movement disorders, such as dysphagia and flaccid or spastic quadriparesis, depending on the involvement of extrapontine or central pontine myelinolysis. Disruption of the blood-brain barrier is presumed to play an important role in the pathogenesis of osmotic demyelination.
An increased susceptibility to osmotic demyelination is also observed in cirrhotic patients. In this setting, myoinositol, the most abundant organic osmolyte, is depleted because of glutamine- and hyponatremia-induced brain cell swelling. CPM is a common and often fatal complication of orthotopic liver transplantation, affecting up to 10% of patients who were hyponatremic prior to transplant.
The prognosis for patients with hyponatremia is predicated upon the underlying etiology. A study by Doshi et al found that hyponatremia among patients with cancer is associated with extended hospital stays and higher mortality rates; however, whether long-term correction of hyponatremia would improve these outcomes is unclear.
A meta-analysis of 15 studies encompassing 13,816 patients found that any improvement in hyponatremia was associated with a reduced risk of overall mortality (odds ratio [OR]=0.57). With the eight studies that reported a threshold for serum sodium improvement to >130 mmol/L, the association was even stronger (OR=0.51). The reduction in mortality risk persisted at 12-month follow-up (OR=0.55). Reduced mortality was more evident in older patients and in patients with lower serum sodium levels at enrollment.
Patients to be treated with a fluid restriction often require education regarding the free water content of foods and an explanation of the need to limit the intake of liquids to a predetermined level.
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