Association of serum chloride concentration with outcomes in postoperative critically ill patients: a retrospective observational study

BACKGROUND Although chloride is one of the major electrolytes measured routinely in dairy practice, the amount of attention chloride receives in critically ill patients is limited. There are still a few studies reporting the incidence of derangements of chloride and its association with patients' outcomes. Accordingly, we conducted a retrospective study to assess the prevalence of abnormality of serum chloride level in postoperative patients in the intensive care unit on the early phase of surgery and its association with outcome. METHODS We conducted a single-center retrospective observational study. All adult patients who underwent elective thoracic or abdominal surgery and required postoperative intensive care for more than 48 h between 2007 and 2011 were included. Chloride levels were measured on each morning of postoperative day 1 and day 2 in the intensive care unit. We defined all-cause hospital death as the primary outcome and compared serum chloride levels on postoperative day 1 and day 2 between hospital survivors and non-survivors. Comparisons among groups were conducted using the chi-square test for equal proportion, Mann-Whitney U tests, or Kruskal-Wallis test. RESULTS Among 98 patients included in this study, hypochloremia (less than 98 mmol/L) during the first 48 h occurred in 14 patients (14.3%). The mortality in hypochloremia patients was 28.6%, which is significantly higher than 6.0% in patients with normal chloride concentration (p = 0.007). Even after being adjusted for severity of illness, the incidence of hypochloremia was independently associated with the risk of hospital death (adjusted odds ratio 5.8 (1.1, 30.2), p = 0.04). Hyperchloremia (more than 112 mmol/L) occurred in one patient (1.0%), who was discharged from the hospital at day 9. There was no significant difference in the total volume of infused fluid (p = 0.30), sum of chloride administration (p = 0.33), and use of furosemide (p = 0.75) from intensive care unit admission to the morning of postoperative day 2 between survivors and non-survivors. CONCLUSIONS Hypochloremia observed within 48 h after surgery was not rare and was independently associated with the increased risk of hospital death. Hypochloremia might be a useful indicator of prognosis for patients in the postoperative intensive care unit.