Serial lactate measurements using microdialysis of interstitial fluid do not correlate with plasma lactate in children after cardiac surgery

Objectives: Serial postoperative blood lactate (BL) concentrations have been shown to predict outcome of children after congenital heart surgery (CHS), and interventions aimed at lowering lactate can improve the outcome of these children. The cumulative blood loss for diagnostic purposes, such as repetitive arterial blood sampling in the intensive care unit, contributes, especially in small children, to anemia. Techniques to limit blood loss can therefore be of use. Microdialysis is a technique to monitor tissue chemistry in various clinical settings, and we hypothesized that it may be a valuable alternative for frequent blood sampling to monitor lactate in children after CHS. Methods: Fifteen children with a mean age of 40 months (range, 4-118 months) were prospectively enrolled after CHS. A CMA double lumen microdialysis catheter was inserted into the subcutaneous adipose tissue of the abdominal wall and infused with an isotone mannitol 5% solution at 1 mu L/min via the inlet tubing. Microdialysate fluid was collected every hour for 48 hrs and stored at -80 degrees C for lactate determination (interstitial fluid lactate, IFL). Every hour arterial blood was taken for lactate determination. Individual profiles, correlation coefficient, and Bland-Altman analysis were used to compare BL and IFL results. Results: There were no complications with the microdialysis technique. All patients were discharged alive from hospital. Six hundred twenty paired samples were analyzed. Mean recovery of microdialysate fluid was 84%. Median (interquartile range) was 0.95 (0.70-1.15) mmol/L for BL and 1.13 (0.86-1.48) mmol/L for IFL (p < 0.0001). Individual profiles showed that IFL follows changes in BL in some, but not all children. With this study, we could not explain this discrepancy. The correlation between BL and IFL was poor (r =.77 (p < 0.0001) r(2) =.59). Bland-Altman analysis confirmed the insufficient performance of the current microdialysis-based procedure compared with BL. Conclusion: Serial lactate measurements in microdialysis fluid of subcutaneous adipose tissue are feasible, but cannot be used as a reliable interchangeable method for plasma lactate analysis in children after CHS at this time. Whether this technique has its own place in the assessment of the overall hemodynamic status and tissue perfusion in children after CHS needs to be addressed in future studies. (Pediatr Crit Care Med 2009; 10:66-70)