Background: Recent studies have challenged assumptions about slow correction of severe hyponatremia and have shown that rapid correction is associated with shorter hospital length of stay. However, the confounding effect of admission diagnosis has not been fully explored. The objective of this study was to determine whether rapid correction is still associated with shorter length of stay when controlling for admission diagnosis.
Methods: This retrospective cohort study is based on the Medical Information Mart for Intensive Care, including data from both MIMIC-III (2001-2012) and MIMIC-IV (2008-2019). Patients were identified who presented to the hospital with initial sodium <120 mEq/L and were categorized according to total sodium correction achieved in the first day (<6 mEq/L; 6-10 mEq/L; >10 mEq/L). Linear regression was used to assess for an association between correction rate and hospital length of stay, and to determine if this association was significant when controlling for admission diagnosis classifications based on diagnosis related groups (DRGs).
Results: There were 636 patients included in this study. Median [IQR] hospital length of stay was 7 [4, 11] days. Patients had a median [IQR] initial sodium value of 117 [114, 118] mEq/L and final sodium value of 124 [119, 128] mEq/L. In a univariate linear regression, the highest rate of correction (>10 mEq/L) was associated with a shorter length of stay than a moderate rate of correction (coef. -2.363, 95% CI [-4.710, -0.017], p=0.048), but the association was not significant when controlling for admission diagnosis group (coef. -1.685, 95% CI [-3.836, 0.467], p=0.125).
Conclusions: Faster sodium correction was not associated with shorter length of stay when controlling for admission diagnosis categories, suggesting that the disease state confounds this association. While some patients may be discharged earlier if sodium is corrected more rapidly, others may not benefit or may be harmed by this strategy.