[Scanning electron microscopic examination of intra-arterial PO2 electrodes (author's transl)]

Continuous blood gas measurement by means of indwelling intraarterial electrodes facilitates and contributes to considerably improve the monitoring of pulmonary gas exchange in intensive care and anaesthesiology. Knowledge of the behaviour of the electrode surface in the blood stream is necessary to assess the characteristics of the measuring and the possible risks or complications. Scanning electron microscopic examinations were performed in a commercial-type polarographic PO2 electrode after in vitro and in vivo application. 14 electrodes were examined after continuous intra-arterial measurements in patients with chronic obstructive pulmonary disease and in intensive care patients. Duration of intra-arterial measurements was 2-109 h. Already after a measuring period of 2 h in nearly all cases a protein film was discovered on the electrode surface. Microthrombotic deposits were seen in 2 cases, in one of these despite of treatment with heparin. The electrode membrane showed a network ofmicro-cracks, small bubbles and dents. The membrane changes were probably the result of the drying process during the electron microscopic preparation, because the membrane material (Hydron) is hydrophil and swells during the measurement. Yet it cannot be excluded that these changes occur, in part, during the measurements. From these and other studies we conclude that the intra-arterial application of this electrode has a low risk of thromboembolic complications. The deposits on the electrode surface and the membrane changes may probably affect the response time and possibly also the stability of the electrode.