Slow ultrafiltration for continuous in vivo sampling: application for glucose and lactate in man Original Research Article

Background: An ultrafiltration (UF) technique was developed for continuous subcutaneous (s.c.) sampling and on-line analysis of absolute glucose and lactate concentrations in tissue. The relation between subcutaneous and blood concentrations was studied in men, because a subcutaneous monitoring device would put patients on less risks than an intravascular device. Methods: Ultrafiltrates were withdrawn continuously at a flow rate of 50–100 nl/min from a hollow fibre probe to measure glucose in the abdominal subcutis. Six healthy volunteers underwent an oral glucose tolerance test. In order to detect glucose and lactate in the same sample, a splitter was placed between the on-line flow injection valve and the parallel enzymatic conversion and electrochemical detection cells. Findings: Subcutaneous glucose concentrations were in steady state on the average 1.06 mM lower. They rose delayed and blunted as compared to blood levels. We demonstrated the ability of simultaneous lactate and glucose measurements in vivo (n=2). Interpretation: UF makes continuous monitoring of absolute extracellular concentrations in tissue possible. We interpret the deviations of subcutaneous measurements from intravascular levels in this way that the subcutis is a kinetic compartment not directly and exclusively linked to blood. The observed differences with blood suggest that diabetes management may demand intravascular monitoring. UF combined with analysis of glucose and lactate in the same sample offers the opportunity to study pathophysiology inside tissues.