Continuous intra-arterial Po₂ in normal man using a flexible microelectrode

¹ Departments of Bacteriology and Medicine, University of Sydney, New South Wales, Australia

A flexible microelectrode, for continuous recording of blood oxygen tension, has been developed for direct insertion into small blood vessels or passage through a cardiac catheter. The design overcomes difficulties arising from pressure of the oxygen-permeable membrane against the vessel wall and greatly increases the robustness and effective life of the electrode. For routine intra-arterial use a satisfactory compromise has been achieved between speed of response (95% in 15 sec), cathode current (3 x 10^–11 amp/mm Hg Po₂), and freedom from "stirring" artefact (less than 3%). Serial in vitro readings of Po₂ over periods of 4 hr have been reproducible (2 sd ± 3% pro rata) without recalibration. In vivo accuracy and stability have been established by continuous recording of Po₂ within the brachial artery of six nonheparinized humans for periods up to 1 hr. The maximum difference observed between initial in vivo and in vitro readings was 2.5%. The reproducibility of serial washout and washin curves has been analyzed to provide an indication of in vivo stability. The technique is safe provided that the precautions outlined to prevent thromboemboli are carefully followed.

Submitted on December 26, 1962