Association of Preoperative Serum Chloride Levels With Mortality and Morbidity After Noncardiac Surgery: A Retrospective Cohort Study

BACKGROUND: Postoperative hyperchloremia is known to be related to increases in mortality and morbidity after surgery. However, the relationship between preoperative hyperchloremia and hypochloremia and postoperative mortality and morbidity is not well established. Our aim was to evaluate the relationship between preoperative hyperchloremia or hypochloremia, as assessed using preoperative serum chloride tests, and 90-day mortality and morbidity after noncardiac surgery. METHODS: In this retrospective cohort study, we reviewed the medical records of patients >20 years of age who underwent noncardiac surgery between January 2010 and December 2016. Patients were categorized into one of the following groups on the basis of the results of serum chloride testing performed within 1 month before surgery: normochloremia, 97-110 mmol·L; hyperchloremia, >110 mmol·L; and hypochloremia, <97 mmol·L. The primary end point of this study was the difference in postoperative 90-day mortality among the preoperative serum chloride groups. The secondary end point was the difference in postoperative acute kidney injury incidence among the preoperative serum chloride groups. RESULTS: A total of 106,505 patients were included in the final analysis (2147 were allocated to the preoperative hypochloremia group and 617 to the hyperchloremia group). Multivariable Cox regression analysis revealed significantly increased 90-day mortality in the hypochloremia (hazard ratio, 1.46; 95% CI, 1.16-1.84; P = .001) and hyperchloremia (hazard ratio, 1.76; 95% CI, 1.13-2.73; P = .013) groups when compared with the normochloremia group. In addition, multivariable logistic regression analysis revealed a 1.83-fold increased odds of acute kidney injury in the preoperative hypochloremia group when compared with the normochloremia group (odds ratio, 1.83; 95% CI, 1.53-2.19; P < .001). CONCLUSIONS: Preoperative hypochloremia and hyperchloremia were related to increased 90-day mortality after noncardiac surgery. In addition, preoperative hypochloremia was related to an increased risk for postoperative acute kidney injury.