Predicting Outcome In Hypernatremic Patients
ABSTRACT & COMMENTARY
Synopsis: Elderly patients with hypernatremia have a poor prognosis (66% mortality in this series), although this is probably determined more by their underlying medical condition than by the electrolyte disturbance. Hypernatremic patients with confusion, obtundation, or abnormal speech were more likely to die than those without these findings.
Source: Mandal AK, et al. Am J Emerg Med 1997;15: 130-132.
Hypernatremia is a relatively common electrolyte abnormality in hospitalized patients. From the clinical laboratory records of two large university-affiliated teaching hospitals, Mandal et al found 116 patients whose serum sodium levels exceeded 145 mEq/L during a one-year period. They reviewed the hospital records of these patients in order to determine the patients’ demographic characteristics, their diagnoses, and the outcomes of their hospitalization in relation to clinical findings.
Patients with hypernatremia were elderly (mean age, 68 years), and 66% of them died during the hospitalization. Age, gender, primary diagnosis, and initial heart rate could not be associated statistically with a fatal outcome. Patients who were hypernatremic on admission were not more likely to die than those who developed it during hospitalization. Hypernatremic patients who experienced hypotension during hospitalization (< 100 mmHg systolic and/or < 60 mmHg diastolic) were more likely to die (P < 0.001), although it is not clear whether this was a preterminal finding in some of them. More importantly, patients who died were more likely to have cognitive defects than those who survived: confusion (57% vs 36%), obtundation (61% vs 39%), and abnormal speech (58% vs 39%) (all, P < 0.05).
COMMENT BY DAVID J. PIERSON, MD
Hypernatremia can result either from an increase in sodium intake or a decrease in body water. (See table.) Except for its occurrence in individuals with diabetes insipidus or one of the other disorders listed in the table, this electrolyte disturbance is most likely to be encountered in debilitated elderly persons or in others who are unable to obtain water or communicate their thirst, such as those with severe developmental delay or other disability.
Table
Clinical conditions associated with hypernatremia
Excess sodium: Increased intake Salt ingestion Bicarbonate administration during CPR Administration of hypertonic saline
Excess sodium: Decreased elimination Renal tubular disease with Na+ retention Acute renal insufficiency Urinary diversion into colon/ileum
Water loss: Inadequate intake Decreased consciousness Loss of thirst sensation Water deprivation
Water loss: Excessive loss Diabetes insipidus (central; nephrogenic) Diabetes mellitus; polyuria Burns; severe generalized skin disorders Diarrhea; excessive nasogastric suctioning Osmotic agents (e.g., mannitol) Fever; heat stroke
Excessive solute load with insufficient water High-protein, high-carbohydrate tube feedings IV administration of concentrated glucose or fat emulsion
Hypernatremia is the major extracellular and intravascular ion, and its excess results in hyperosmolality (serum osmolality = [2´Na+] + [glucose/18] + [BUN/3]; normal 285-295 mOsm/L). An increase in serum osmolality attracts water from the intracellular and interstitial spaces to the intravascular extracellular space, causing the cells to shrink and producing neurologic sequelae such as confusion and obtundation. Although the level of serum sodium that produces clinical manifestations varies, an osmolarity exceeding 310 mOsm/L (as with an increase in serum sodium to 150 mEq/L or more) would be expected to cause problems. Both the survivors and nonsurvivors in this study had mean peak serum sodium values of 157 mEq/L, but the higher frequency of neurologic disturbances in those who died suggests a more pronounced osmotic effect on the brain cells of those individuals.
Additional useful clinical information about hypernatremia comes from a study by Palevsky et al (Ann Intern Med 1996;124:197-203) who described 18 patients admitted with hypernatremia and an additional 85 who developed this finding during hospitalization. The former group were elderly, but the latter did not differ in age from the general hospital population. Of patients whose hypernatremia developed in the hospital, 86% lacked free access to water, 74% had enteral water intake of less than 1 L/d, and 94% received less than 1 L/d of electrolyte-free intravenous fluid. In half of the patients, no increased free water was administered in the first 24 hrs after hypernatremia developed. Thus, hypernatremia is not uncommonly iatrogenic, and treatment is often delayed and inadequate.
In the Palevsky study, mortality among all patients was 41%. However, hypernatremia was judged to have contributed to death in only 16% of patients, emphasizing the importance of their underlying medical status rather than (presumably) the hypernatremia itself.
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