Transcutaneous oxygen measurement during thoracic anaesthesia.

The value of transcutaneous oxygen tension (tcPO2) as an oxygen parameter during uncomplicated thoracic anaesthesia was examined in ten patients anaesthetized with oxygen-nitrous oxide and enflurane or flunitrazepam/fentanyl. tcPO2 was measured with the Radiometer TCM-I monitor at 45 degrees C. Measuring interference due to the anaesthetic agents was not observed. tcPO2 was found to be lower than the arterial tension (PaO2) at any inspiratory oxygen fraction (FIO2). When the peroperative readings were related to the preoperative values, no statistically significant difference was found between PaO2 and tcPO2 at FIO2 - 0.5, 0.4 and 0.3 (P greater than 0.3). Linear regression between PaO2 and tcPO2 shows disparity in pre- and peroperative regression. tcPO2 (preoperative) = -2.2 + 1.03 X PaO2 (4 = 0.89) tcPO2 (preoperative) = +3.1 + 0.56 X PaO2 (r = 0.87). This disparity indicates a decrease in the tcPO2/PaO2 ratio with increasing PaO2. It is concluded that tcPO2 cannot substitute for PaO2, but tcPO2 and PaO2 proved to be equally useful as oxygen parameters in the examined patients. Interpretation of tcPO2 during anaesthesia, however, necessitates a preoperative measurement as reference.