Urinary strong ion difference is a major determinant of plasma chloride concentration changes in postoperative patients - Critical Care Science (CCS)

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±3mmol/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±3mmol/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±18mmol/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 salineinduced hyperchloremia.