Background: In critically ill patients, arterial blood lactate concentration (Lact(a)) and Lact(a) clearance are used for the diagnosis of shock, for prognosis assessment, and to guide therapy. In recent years, central venous oxygen saturation (ScvO(2)), a surrogate for mixed venous blood saturation, either measured by fiberoptic catheters or from central venous blood samples, was used in shock to estimate the global balance between oxygen delivery and consumption. When central venous blood is drawn for ScvO(2) measurement, it also could be used to measure central venous lactate concentration (Lact(cv)). In this study, we evaluated the utility of Lact(cv) and Lact(cv) clearance as predictors of Lact(a) and Lact(a) clearance, respectively, in critically ill patients.
Methods: This retrospective study was performed in an intensive care unit of a regional and teaching hospital. Using the electronic registry of our blood gas analyzer from March 2007 to December 2009, we identified patients with circulatory or respiratory failure who had pairs of Lact(cv) and Lact(a) obtained within a 30-minute interval. To assess the utility of Lact(cv) as a predictor of Lact(a) above 2 and 4 mmol/L, we calculated the area under receiver operating characteristic curves (AUCs) for these thresholds. We also calculated AUC of Lact(cv) clearance to detect a Lact(a) clearance <10% or >10%.
Results: Six hundred seventy-three Lact(cv)/Lact(a) pairs in 188 patients were analyzed. AUC of Lact(cv) to predict a Lact(a) above 2 and 4 mmol/L was 0.98 (95% confidence interval: 0.97-0.99) and 0.98 (95% confidence interval: 0.96-0.99), respectively. Lact(cv) with the cutoff value of 2 mmol/L can predict a Lact(a) above 2 mmol/L with sensitivity >92% and specificity >90%. AUC for Lact(cv) clearance to detect a Lact(a) clearance <10% or >10% was 0.93 or 0.94, respectively.
Conclusion: Lact(cv) and Lact(a) collected within a 30-minute range are interchangeable for clinical practice.