In vivo vs in vitro response time of trancutaneous PO2 electrodes. A comparison of four devices in newborn infants.

Four devices for transcutaneous PO2 (tcPO2) monitoring have been applied simultaneously in 16 infants. Both during a maximal change in PaO2 and during physiological PO2 variations, the in vivo response time of the electrodes did not show the differences observed in vitro. We compared A, a prototype of the electrode by Huck, Lübbers and Huch (25 micrometer Telfon membrane) ; B, the commercial version of A by Hellige--Draeger (25 micrometer Telfon); C, the Radiometer TCM I oxygen monitor (25 micrometer polypropylene); and D, the Roche macrocathode electrode (6 micrometer Mylar), at 44 degree C. In vitro the 50% response times were 2.9 (A), 4.4 (B), 3.7 (C), and 7.4 (D) sec. The rates of tcPO2 changes at the midpoint of the response curves were 3.8(A) 2.0 (B), 3.0 (C), and 1.7 (D) kPa/sec. In vivo during a sudden change from hyperoxemia (FIO2 1.0) to normoxaemia the respective rates were 0.6 (A), 0.8 (B), 1.1 (C), and 1.0(D) kPa/sec. The in vivo 50% response times were 53.3 (A), 51.1 (B), 46.2 (C) and 45.3 (d) kPa/sec. The in vivo 50% response time were 53.3 (A), 51.1 (B), 46.2 (C), and 45.3 (d) kPa/sec. The in vivo 50% resonse time were 53.3 (A), 51.1 (B), 46.2 (C), and 45.3 (D) sec. The lag time between PaO2 and tcPO2 was about one third of this overall response time. The response to more physiological variations of PaO2 (periodic breathing) was not different among the tested electrodes in terms of damping and of delay of the tcPO2 deflections. In a steady state the correlation of tcPO2 44 degree C vs PaO2 was close (r = 0.98) with all devices up to 6.1 kPa (456 torr).