Chloride alterations in hospitalized patients: Prevalence and outcome significance.

Serum Cl (sCl) alterations in hospitalized patients have not been comprehensively studied in recent years. The aim of this study is to investigate the prevalence and outcome significance of (1) sCl alterations on hospital admission, and (2) sCl evolution within the first 48 hr of hospital admission. We conducted a retrospective study of all hospital admissions in the years 2011-2013 at Mayo Clinic Rochester, a 2000-bed tertiary medical center. Outcome measures included hospital mortality, length of hospital stay and discharge disposition. 76,719 unique admissions (≥18 years old) were studied. Based on hospital mortality, sCl in the range of 105-108 mmol/L was found to be optimal. sCl <100 (n = 13,611) and >108 (n = 11,395) mmol/L independently predicted a higher risk of hospital mortality, longer hospital stay and being discharged to a care facility. 13,089 patients (17.1%) had serum anion gap >12 mmol/L; their hospital mortality, when compared to 63,630 patients (82.9%) with anion gap ≤12 mmol/L, was worse. Notably, patients with elevated anion gap displayed a progressively worsening mortality with rising sCl. sCl elevation within 48 hr of admission was associated with a higher proportion of 0.9% saline administration and was an independent predictor for hospital mortality. Moreover, the magnitude of sCl rise was inversely correlated to the days of patient survival. In conclusion, serum Cl alterations on admission predict poor clinical outcomes. Post-admission sCl increase, due to Cl-rich fluid infusion, independently predicts hospital mortality. These results raise a critical question of whether iatrogenic cause of hyperchloremia should be avoided, a question to be addressed by future prospective studies.