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

Background: An ultrafiltration (UF) technique was developed for continuous subcutaneous (s.c.) sampling and on-line analysis of absolute glucose and l actate concentrations in tissue. The relation between subcutaneous and bloo d concentrations was studied in men, because a subcutaneous monitoring devi ce would put patients on less risks than an intravascular device. Methods: Ultrafiltrates were withdrawn continuously at a flow rate of 50-10 0 nl/min from a hollow fibre probe to measure glucose in the abdominal subc utis. Six healthy volunteers underwent an oral glucose tolerance test. In o rder to detect glucose and lactate in the same sample, a splitter was place d between the on-line flow injection valve and the parallel enzymatic conve rsion and electrochemical detection cells. Findings: Subcutaneous glucose concentrations were in steady state on the a verage 1.06 mM lower. They rose delayed and blunted as compared to blood le vels. We demonstrated the ability of simultaneous lactate and glucose measu rements in vivo (n=2). Interpretation: UF makes continuous monitoring of absolute extracellular co ncentrations in tissue possible. We interpret the deviations of subcutaneou s measurements from intravascular levels in this way that the subcutis is a kinetic compartment not directly and exclusively linked to blood. The obse rved differences with blood suggest that diabetes management may demand int ravascular monitoring. UF combined with analysis of glucose and lactate in the same sample offers the opportunity to study pathophysiology inside tiss ues. (C) 1999 Elsevier Science B.V. All rights reserved.