Maintenance Intravenous Fluids in Acutely Ill Patients

Hyponatremia is the most common electrolyte abnormality encountered in clinical practice. The reported frequency of the disorder is determined by a number of factors, including the definition of hyponatremia, the frequency of testing, the healthcare setting, and the patient population. This review focuses on the incidence and prevalence of hyponatremia. In acute hospital care, particular attention is given to admission versus hospital-acquired hyponatremia. Although less well studied, the epidemiology of hyponatremia in the ambulatory-based setting and the geriatric/nursing home population is also summarized. Finally, the frequency of hyponatremia occurring in special clinical conditions--including congestive heart failure, cirrhosis, pneumonia, and acquired immunodeficiency syndrome--as well as in marathon runners will be reviewed. Substantial additional work is still required to determine the true occurrence of hyponatremia in the various clinical settings. Beyond the phenomenologic value, advances in the epidemiology of hyponatremia should also provide insights in the prognostic implications as well as the preventive and management strategies of the disorder in various clinical settings.

The study objective was to determine the eventual consequences (falls, unsteadiness, and cognitive impairment) of mild chronic hyponatremia, which is generally considered as asymptomatic. In a case-control study, we focused on the incidence of falls among 122 patients (mean age 72+/-13 years) with asymptomatic chronic hyponatremia (mean serum sodium concentration [SNa] 126+/-5 mEq/L), who were admitted to the medical emergency department, compared with 244 matched controls. To explore the mechanisms of the excess of falls, we prospectively asked 16 comparable patients (mean age 63+/-15 years; SNa+/-2 mEq/L) to perform 8 attention tests and a gait test consisting of 3 steps "in tandem," in which we measured the "total traveled way" by the center of pressure or total traveled way. Thereafter, the patients were treated and tested again (50% of the patients were tested first with normal SNa to avoid learning biases). Epidemiology of falls: Twenty-six patients (21.3%) of 122 were admitted for falls, compared with only 5.3% of the control patients (adjusted odds ratio: 67; 95% confidence: 7.5-607; P <.001). The frequency of falls was the same regardless of the level of hyponatremia. Gait: The total traveled way by the center of pressure significantly increased in hyponatremia (1336+/-320 mm vs 1047+/-172 mm with normal SNa; P=.003). Attention tests: The mean response time was 673+/-182 milliseconds in hyponatremia and 615+/-184 milliseconds in patients with normal SNa (difference: 58 milliseconds, P <.001). The total error number in hyponatremia increased 1.2-fold (P=.001). These modifications were comparable to those observed after alcohol intake in 10 volunteers. Mild chronic hyponatremia induces a high incidence of falls possibly as the result of marked gait and attention impairments. Treating these patients might prevent a considerable number of hospitalizations.

We prospectively evaluated the frequency, cause, and outcome of hyponatremia (plasma sodium concentration, less than 130 meq/L), as well as the hormonal response to this condition, in hospitalized patients. Daily incidence and prevalence of hyponatremia averaged 0.97% and 2.48%, respectively. Two thirds of all hyponatremia was hospital acquired. Normovolemic states (so-called syndrome of inappropriate secretion of antidiuretic hormone) were the most commonly seen clinical setting of hyponatremia. The fatality rate for hyponatremic patients was 60-fold that for patients without documented hyponatremia. Nonosmotic secretion of vasopressin was present in 97% of hyponatremic patients in whom it was sought. In edematous and hypovolemic patients, plasma hormonal responses (increases in plasma renin activity and aldosterone and norepinephrine levels) were compatible with baroreceptor-mediated release of vasopressin. Hyponatremia is a common hospital-acquired electrolyte disturbance that is an indicator of poor prognosis. Nonosmotic secretion of arginine vasopressin is a major pathogenetic factor in this electrolyte disturbance.