[Phenomenon of unstable tcpO2 level in transcutaneous oximetry in patients with diabetes mellitus].

The back of the foot is a standard region for measuring transcutaneous oxygen tension (tcpO2) with a reliably determined threshold of ischaemia, but such measurement reflects blood supply of only a portion of angiosomes of the foot. Determining the reference values of tcpO2 in other regions of the lower extremity is of current importance. However, measuring the tcpO2 level on the plantar surface and in some other regions not uncommonly reveal a phenomenon of its steady decrease instead of formation of a plateau. The purpose of the present study was to analyse the frequency of the phenomenon of a steady decrease in ptcO2 level while performing transcutaneous oximetry in various zones of the lower extremity. We retrospectively analysed the results of a total of 160 measurements of tcpO2 in 35 patients with diabetes mellitus. The patients' mean age amounted to 68 (47-87) years, with the duration of diabetes mellitus averaging 14 (1-24) years. The male-to-female ratio was 60:40. Seventy-seven percent of patients had foot ulcers/wounds, 34% of patients had a history of previously endured revascularization. The examination was carried out in the dorsal, plantar, medial plantar regions of the foot, on the medial surface of the crus and in the subclavian region, using the TCM 400 monitoring device (Radiometer, Denmark). The measurements were performed by an experienced operator in strict accordance with the manufacturer's recommendations. We evaluated the average value of tcpO2 between the 15th and 19th minutes of measurement and the peculiarities of the tpcO2 curve (plateau/increase/decrease of the value) within this time interval. The mean tcpO2 value in the medial plantar region was significantly higher than that on the back of the foot: 34 (3-70) versus 22 (1-59) mm Hg, p=0.003. A portion of measurements demonstrated a steady decrease in the tpcO2 during the measurement up to the 40th minute. Complying with the stable plateau phase criteria we had developed were 92% of measurements in the subclavian region, 100% - in the middle third of the crus, 76% - on the back of the foot, 77% - in the medial plantar region and 43% - on the plantar surface of the foot. CONCLUSIONS: 1) the revealed phenomenon of a steady decrease of tcpO2 in some patients needs to be taken into consideration in clinical practice and deserves further study; 2) the nature of this phenomenon is unclear, with a possible effect of skin creams on the results of the measurements; 3) it is advisable to include into the functions of the devices for transcutaneous oximetry an algorithm for confirmation of the true phase of the plateau and calculation of the mean tcpO2 value for a chosen period; 4) despite the need for measurement of tcpO2 in the 'alternative zones' it is necessary to thoroughly study the reliability of the data in these zones and to determine the normal values of the parameter separately for each of them.