Lactate monitoring with subcutaneous microdialysis in patients with shock: a pilot study

We describe the use of subcutaneous microdialysis for continuous sampling of lactate to monitor the plasma lactate concentration in eight patients with shock. The dialysate lactate concentrations were significantly correlated with the plasma lactate concentrations (r = 0.8229), but the linear regression lines varied between patients. Therefore, we used the individual regression line of each patient for calibration to calculate estimated plasma values from the dialysate concentrations. While the estimated values were linearly correlated to the plasma lactate values (r = 0.912), the 95% confidence interval of the estimated values was +/- 2.8 mmol/L. Thus, subcutaneous microdialysis does not allow accurate estimation of the plasma lactate concentration. In 3 of the 8 patients, there was a significant negative correlation between the dialysate/plasma lactate ratio and the plasma lactate concentration. This suggests that besides plasma lactate, other factors such as subcutaneous adipose tissue metabolism and blood flow, may influence subcutaneous sampling and dialysate lactate concentration as well. While microdialysis can be used for on-line sampling and continuous monitoring of the concentration of extracellular substances, for the purpose of plasma lactate monitoring, sampling probes should be designed that permit intravascular placement.