Alterations in urinary strong ion difference in critically ill patients with metabolic acidosis: a prospective observational study.

Background And Objective: The correct renal response to metabolic acidosis should be a negative shift in the urinary strong ion difference ([SID](urinary) = [Na(+)](urinary) + [K(+)](urinary) - [Cl(-)](urinary)). Our hypothesis was that the failure to decrease the [SID](urinary) is frequently present and leads to a more severe metabolic acidosis.

Design, Setting And Participants: Prospective observational study conducted in the medical/surgical intensive care unit of a teaching hospital between 1 January 2006 and 30 April 2007.

Comparison of three different methods of evaluation of metabolic acid-base disorders.

Objectives: The Stewart approach states that pH is primarily determined by Pco2, strong ion difference (SID), and nonvolatile weak acids. This method might identify severe metabolic disturbances that go undetected by traditional analysis. Our goal was to compare diagnostic and prognostic performances of the Stewart approach with a) the traditional analysis based on bicarbonate (HCO3) and base excess (BE); and b) an approach relying on HCO3, BE, and albumin-corrected anion gap (AGcorrected).