Acid–base effects of continuous infusion furosemide in clinically stable surgical ICU patients: an analysis based on the Stewart model

Objectives We sought to test the strength of correlation between predicted and observed systemic acid–base status based on the Stewart model equations during continuous infusion (CI) furosemide therapy. Design, setting and participants This was a prospective, single-center, observational study conducted in the Surgical ICU of a large academic medical center. Ten critically ill patients who received CI furosemide were included. Main outcomes and measures The primary purpose was to characterize the relationship between changes in serum electrolyte and acid–base status and the excretion of electrolytes in the urine during infusion of CI furosemide in critically ill patients. As a secondary endpoint, we sought to evaluate the predictive application of the Stewart model. Over 72-h, intake and output volumes, electrolyte content of fluids administered, plasma and urine electrolytes, urine pH, and venous blood gases were collected. Predicted and observed changes in acid-based status were compared for each day of diuretic therapy using Spearman’s correlation coefficient. Results The mean (SD) strong ion difference (SID) increased from 45.2 (3.2) at baseline to 49.6 (4.0) after 72 h of continuous infusion furosemide. At Day 1, the mean SID (observed) (SD) was 47.5 (3.5) and the predicted SID was 49.5 (5.8). Day 1 observed plasma SID was positively correlated with the predicted SID ( r s = 0.80, p = 0.01). By Days 2 and 3, the correlations of observed and predicted SID were no longer statistically significant. Conclusions and relevance Using the Stewart model, increases in SID as an indicator of metabolic alkalosis due to the chloruretic effects of furosemide were observed. Predicted and observed SID correlated well over the first 24 h of treatment.