title: Urinary strong ion difference is a major determinant of plasma chloride concentration changes in postoperative patients.
abstract: OBJECTIVE
  To show that alterations in the plasma chloride concentration ([Cl-]plasma) during the postoperative period are largely dependent on the urinary strong ion difference ([SID]urine=[Na+]urine+[K+]urine-[Cl-]urine) and not on differences in fluid therapy.
  
  
  METHODS
  Measurements were performed at intensive care unit admission and 24 hours later in a total of 148 postoperative patients. Patients were assigned into one of three groups according to the change in [Cl-]plasma at the 24 hours time point: increased [Cl-]plasma (n=39), decreased [Cl-]plasma (n=56) or unchanged [Cl-]plasma (n=53).
  
  
  RESULTS
  On admission, the increased [Cl-]plasma group had a lower [Cl-]plasma (105 ± 5 versus 109 ± 4 and 106 ± 3 mmol/L, p<0.05), a higher plasma anion gap concentration ([AG]plasma) and a higher strong ion gap concentration ([SIG]). After 24 hours, the increased [Cl-]plasma group showed a higher [Cl-]plasma (111 ± 4 versus 104 ± 4 and 107 ± 3 mmol/L, p<0.05) and lower [AG]plasma and [SIG]. The volume and [SID] of administered fluids were similar between groups except that the [SID]urine was higher (38 ± 37 versus 18 ± 22 and 23 ± 18 mmol/L, p<0.05) in the increased [Cl-]plasma group at the 24 hours time point. A multiple linear regression analysis showed that the [Cl-]plasma on admission and [SID]urine were independent predictors of the variation in [Cl-]plasma 24 hours later.
  
  
  CONCLUSIONS
  Changes in [Cl-]plasma during the first postoperative day were largely related to [SID]urine and [Cl-]plasma on admission and not to the characteristics of the infused fluids. Therefore, decreasing [SID]urine could be a major mechanism for preventing the development of saline-induced hyperchloremia.
authors.affiliation: Unidade de Terapia Intensiva, Sanatorio Otamendi y Miroli, Buenos Aires, Argentina.
authors.forename: Fabio Daniel
authors.initials: FD
authors.lastname: Masevicius
authors.forename: Alejandro Risso
authors.initials: AR
authors.lastname: Vazquez
authors.forename: Carolina
authors.initials: C
authors.lastname: Enrico
authors.forename: Arnaldo
authors.initials: A
authors.lastname: Dubin
mesh_terms: D000368:Aged; D002712:Chlorides / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011188:Potassium / Q000652:urine*; D011446:Prospective Studies; D012964:Sodium / Q000652:urine*
chemical_list: D002712:Chlorides; D012964:Sodium; D011188:Potassium