Abstract
OBJECTIVE: This study aims to investigate the association between acquired blood chloride abnormalities and all-cause in-hospital mortality in adult patients who were critically ill with normal blood chloride at admission to the intensive care unit (ICU). DESIGN: A retrospective cohort study. SETTING: Serum chloride concentration was measured by an indirect potentiometric method. PARTICIPANTS: This study encompassed adult patients who were critically ill and admitted to the ICU, and who exhibited normal blood chloride levels (99-110 mmol/L) at Xiangyang Central Hospital between 1 April 2020 and 30 April 2022. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was in-hospital mortality, defined as death from any cause during hospitalisation. The secondary outcomes included 30-day mortality, the length of ICU stay and the total length of stay in the hospital. RESULTS: This study included 1131 patients. The baseline characteristics were comparable among the three groups of patients (all p>0.05). The all-cause in-hospital mortality rate was 11.4% (n=129). The incidence of acquired hyperchloraemia 48 hours after admission was 16.53% (n=187), with a mortality rate of 17.6% (n=33). The incidence of acquired hypochloraemia was 9.37% (n=106), with a mortality rate of 12.3% (n=13). The proportion of patients with persistently normal blood chloride was 74.09% (n=838), with a mortality rate of 9.9% (n=83). ICU-acquired hyperchloraemia was associated with a higher in-hospital mortality rate than patients with persistently normal blood chloride (OR 1.83, 95% CI 1.09 to 3.05, p=0.022). Furthermore, for every 1 mmol/L increase in blood chloride levels, there was an 11% increase in the risk of all-cause in-hospital mortality (OR 1.11, 95% CI 1.02 to 1.20, p=0.014). CONCLUSIONS: Acquired hyperchloraemia 48 hours after ICU admission is independently associated with a higher risk of all-cause in-hospital mortality in adult patients who were critically ill.