Association between fluctuations in serum chloride levels and 30-day mortality among critically ill patients: a retrospective analysis

BACKGROUND: This study investigated the associations of fluctuations in serum chloride (Cl(−)) levels with 30-day mortality after intensive care unit (ICU) admission among critically ill patients. METHODS: We retrospectively analyzed the medical records of adult patients (≥18 years old) admitted to the ICU between January 2012 and December 2017. Positive and negative fluctuations in Cl(−) were defined as the differences between the Cl(−) upon ICU admission (baseline Cl(−)) and the maximum and minimum Cl(−) levels, respectively, measured within 72 h after ICU admission. RESULTS: The final analysis included 18,825 adult patients. In multivariable Cox regression analyses, the risk of 30-day mortality increased by 8% per 1-mmol L(− 1) positive fluctuation in Cl(−) within 72 h (hazard ratio = 1.08, 95% confidence interval: 1.04–1.11, P < 0.001). In subgroup analyses, a positive fluctuation in Cl(−) was associated with increased 30-day mortality among patients with a severe positive cumulative fluid balance (FB, > 10%), normochloremia (97–110 mmol L(− 1)) or hyperchloremia (> 110 mmol L(− 1)) upon ICU admission. Furthermore, a negative fluctuation in the Cl(−) level during the first 72 h of an ICU stay was associated with a negative cumulative FB (< 0%) or hypochloremia (< 97 mmol L(− 1)) upon ICU admission. CONCLUSIONS: A fluctuation in the Cl(−) level during the first 72 h of an ICU stay was found to associate independently with increased 30-day mortality among critically ill adult patients. However, the nature of this association differed according to the cumulative FB status or dyschloremia status upon ICU admission. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12871-019-0753-3) contains supplementary material, which is available to authorized users.