Changes in blood lactate predict outcome better than absolute values in severe SIRS

Introduction: Serum lactate is considered to be a marker of tissue hypoxia (1) Cut-off values >4 mM predict poor outcome, yet many patients after resuscitation according Surviving Sepsis Campaign guidelines (SSCG) (2) have high mortality despite decreases in blood lactate. Our hypothesis was that dynamic, rather than absolute blood lactate concentrations predict survival. Further we tested the ability of microdialysis lactate (MD-lac) to follow dynamic changes in blood levels, and whether this was also predictive of survival. Methods: Prospective, observational, single-centre cohort study in a mixed-bed university hospital ICU. About 53 consecutive patients with SIRS and circulatory failure despite adequate fluid resuscitation according to the SSCG were included. Arterial blood lactate (B-lac) was measured 6- hourly and MD-lac in subcutaneous tissue measured 4- hourly. Changes in B- and MD-lac from baseline were also calculated. Results: There were no differences in absolute values of B- lac or MD-lac between survivors and non-survivors during the first 24 h, nor were there differences in the change in MD-lac. In contrast changes in B-lac were greater in survivors. Among patients who reached P-lac > 4 mM during the study period of 7 days, the mortality rate was 37% as compared to 21% in the others, although this did not reach statistical significance. Conclusions: Survivors of severe SIRS were characterized by greater changes in B-lac compared to baseline. This supports the concept of lactate clearance, rather than absolute values, as a useful end point for fluid resuscitation, as opposed to the traditional endpoints used in the SSCG. In contrast MD- lac was not a useful predictor of mortality in this population.