Association Between ICU-Acquired Hypernatremia and In-Hospital Mortality: Data From the Medical Information Mart for Intensive Care III and the Electronic ICU Collaborative Research Database

Abstract

Objectives: Describe the relationship between ICU-acquired hypernatremia and in-hospital mortality and investigate the optimal hypernatremia correction rate.

Design setting participants and measurements: Observational study including two individual ICU cohorts. We used the Medical Information Mart for Intensive Care III v. 1.4 database consists of all ICU patients admitted to the Beth Israel Deaconess Medical Center in Boston from 2001 to 2012 (n = 46,476). The electronic ICU v. 2.0 database consists of all ICU patients admitted to 208 distinct hospitals across the United States from 2014 to 2015 (n = 200,859). We included all adult patients admitted to an ICU with two consecutive sodium samples within normal range (135-145 mmol/L) and without two consecutive hyponatremic samples (< 135 mmol/L) during the ICU stay.

Results: Of 23,445 patients identified in Medical Information Mart for Intensive Care III, 9% (n = 2,172) developed hypernatremia during their ICU stay. In electronic ICU, 88,160 patients were identified and 7% (n = 5,790) developed hypernatremia. In both cohorts, patients with hypernatremia had a higher mortality (Medical Information Mart for Intensive Care III: 20% vs 42%; p < 0.01 and electronic ICU: 6% vs 22%; p < 0.01), with hypernatremia increasing the risk of in-hospital mortality (Medical Information Mart for Intensive Care III: odds ratio, 1.15; 95% CI, 1.13-1.17 and electronic ICU: odds ratio, 1.11; 95% CI, 1.10-1.12) and over time using a Cox regression. Rapid sodium correction rate (> 0.5 mmol/L/hr) was associated with an increased in-hospital mortality in both cohorts (Medical Information Mart for Intensive Care III: odds ratio, 1.08; 95% CI, 1.03-1.13 and electronic ICU: odds ratio, 1.10; 95% CI, 1.06-1.13). In the electronic ICU cohort, rapid correction rates were associated with a significant difference in in-hospital mortality, but there was no statistically significant association in the Medical Information Mart for Intensive Care III cohort.

Conclusions: ICU-acquired hypernatremia is associated with increased in-hospital mortality. Furthermore, a rapid sodium correction rates may be harmful. This suggests it is important to both prevent ICU-acquired hypernatremia and to avoid rapid correction rates if a patient becomes hypernatremic.

Keywords: Medical Information Mart for Intensive Care III; correction rates; electronic ICU Collaborative Research Database; hypernatremia; mortality.

Figure 1.

A, Consolidated Standards of Reporting Trial flow diagram. B, An example of variable extraction. The graph shows a patient with three hypernatremic periods (filled gray area) and correction rates (blue lines), where the periods are added together to calculate hypernatremic duration (red lines) and hypernatremic burden. The highest peak sodium and sodium correction rate are extracted. eICU = electronic ICU, MIMIC-III = Medical Information Mart for Intensive Care III, P-Na = plasma sodium.

Figure 2.

Variables from the Medical Information Mart for Intensive Care III (MIMIC-III) (left column) and electronic ICU (eICU) (right column) database associated with in-hospital mortality. Top row presents the mortality rate based on maximum sodium value (peak sodium). Patients with peak sodium within normal range but below 140 mmol/L were combined in one group, and patients with maximum values above 156 mmol/L were combined another group. Middle row presents the accumulated hypernatremic duration and the association with in-hospital mortality, and the bottom row shows the association between hypernatremic burden and mortality. The line (blue) shows the univariable regression line. The groups for duration and burden are stratified based on group size, which are presented in dark red.

Figure 3.

Correction rates of hypernatremic patients. Left column is Medical Information Mart for Intensive Care III (MIMIC-III), while the right column is electronic ICU (eICU). Upper row presents mortality rate based on maximum correction rate with aggregated values greater than 15 to 15 mmol/L, with numbers in each group presented with dark red. Lower row presents the mortality rate based on three groups. p value shown is the Fisher exact test, with Bonferroni correction.