In Vivo Calibration of a Transcutaneous Oxygen Electrode in Adult Patients

Summary

Transcutaneous oxygen tension (tcPO₂) has been compared with arterial oxygen tension (PaO₂ in 14 haemodynamically stable patients in an intensive care unit. Two calibration methods have been compared: (1) “In vitro” calibration, a two point calibration procedure carried out before attachment to the skin. (2) “In vivo” calibration, calibration using a single arterial sample, to recalibrate the upper point after attachment of the electrode to the skin and stabilisation of the electrical output. After “in vitro” calibration the regression equation was given by tcPO₂ (mmHg) =0.58 PaO₂ +13.4 (95% confidence limits + 19.6). After “in vivo” calibration, the regression equation for 55 comparisons over the range 50 to 120mmHg was given by: tcPO₂ (mmHg) = 0.98 PaO₂ + 1.6 (95% confidence limits + 6.6). The “in vivo” calibration method therefore allows a close estimate of PaO₂ to be made from tcPO₂ values in adult patients providing strict operating criteria observed.