title: Hyperchloremia after noncardiac surgery is independently associated with increased morbidity and mortality: a propensity-matched cohort study.
abstract: BACKGROUND
  The use of normal saline is associated with hyperchloremic metabolic acidosis. In this study, we sought to determine the incidence of acute postoperative hyperchloremia (serum chloride >110 mEq/L) and whether this electrolyte disturbance is associated with an increase in length of hospital stay, morbidity, or 30-day postoperative mortality.
  
  
  METHODS
  Data were retrospectively collected on consecutive adult patients (>18 years of age) who underwent inpatient, noncardiac, nontransplant surgery between January 1, 2003 and December 31, 2008. The impact of postoperative hyperchloremia on patient morbidity and length of hospital stay was examined using propensity-matched and logistic multivariable analysis.
  
  
  RESULTS
  The dataset consisted of 22,851 surgical patients with normal preoperative serum chloride concentration and renal function. Acute postoperative hyperchloremia (serum chloride >110 mmol/L) is quite common, with an incidence of 22%. Patients were propensity-matched based on their likelihood to develop acute postoperative hyperchloremia. Of the 4955 patients with hyperchloremia after surgery, 4266 (85%) patients were matched to patients who had normal serum chloride levels after surgery. These 2 groups were well balanced with respect to all variables collected. The hyperchloremic group was at increased risk of mortality at 30 days postoperatively (3.0% vs 1.9%; odds ratio = 1.58; 95% confidence interval, 1.25-1.98) (relative risk 1.6 or risk increase of 1.1%) and had a longer hospital stay (7.0 days [interquartile range 4.1-12.3] compared with 6.3 [interquartile range 4.0-11.3]) than patients with normal postoperative serum chloride levels. Patients with postoperative hyperchloremia were more likely to have postoperative renal dysfunction. Using all preoperative variables and measured outcome variables in a logistic regression analysis, hyperchloremia remained an independent predictor of 30-day mortality with an odds ratio of 2.05 (95% confidence interval, 1.62-2.59).
  
  
  CONCLUSIONS
  This retrospective cohort trial demonstrates an association between hyperchloremia and poor postoperative outcome. Additional studies are required to demonstrate a causal relationship between these variables.
authors.affiliation: Department of Anesthesia and Pain Management, Toronto General Hospital, University Health Network, 200 Elizabeth St., EN 3-405, Toronto, Ontario M5G 2C4, Canada. stuart.mccluskey@uhn.on.ca
authors.forename: Stuart A
authors.initials: SA
authors.lastname: McCluskey
authors.forename: Keyvan
authors.initials: K
authors.lastname: Karkouti
authors.forename: Duminda
authors.initials: D
authors.lastname: Wijeysundera
authors.forename: Leonid
authors.initials: L
authors.lastname: Minkovich
authors.forename: Gordon
authors.initials: G
authors.lastname: Tait
authors.forename: W Scott
authors.initials: WS
authors.lastname: Beattie
mesh_terms: D000138:Acidosis / Q000097:blood / Q000401:mortality*; D000368:Aged; D015415:Biomarkers / Q000097:blood; D002712:Chlorides / Q000097:blood*; D005260:Female; D006801:Humans; D015994:Incidence; D007902:Length of Stay; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D009864:Ontario; D011183:Postoperative Complications / Q000097:blood / Q000401:mortality*; D057216:Propensity Score; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; D002712:Chlorides