Transcutaneous pO2 imaging during tourniquet-induced forearm ischemia using planar optical oxygen sensors

Background: Oxygen-dependent quenching of luminescence using transparent planar sensor foils was shown to overcome the limitations of the polarographic electrode technique in an animal model. This method was then transferred to a clinical setting to measure the transcutaneous pO(2) (p(tc)O(2)). Methods: In six healthy subjects, a cuff on the upper arm was occluded up to 20 mmHg above systolic pressure and released after 8 min. P(tc)O(2) was measured at the lower arm every 30 s before, during, and up to 20 min after cuff occlusion (40 degrees C applied skin temperature) using luminescence lifetime imaging (LLI) of platinum(II)-octaethyl-porphyrin immobilized in a polystyrene matrix. For validation, the polarographic Clark electrode technique was applied in close proximity, and measurements were conducted simultaneously. Results: P(tc)O(2) measurements before (70.8 +/- 19.1 vs. 66.2 +/- 7.7 mmHg) and at the end of ischemic (2.7 +/- 1.2 vs. 3.6 +/- 1.7 mmHg) and reperfusion phases (72.2 +/- 3.6 vs. 68.4 +/- 8.9 mmHg) did not differ significantly using the Clark electrode vs. LLI. At both the initial ischemic and the reperfusion phases, the Clark electrode measured a faster decrease or increase, respectively, in p(tc)O(2) because of the oxygen consumption occurring in this method. Conclusion: The presented method provides accurate and reproducible p(tc)O(2) values under changing microcirculatory conditions. The lack of oxygen consumption during measurement allows both a more realistic estimation of p(tc)O(2) than compared with the gold standard and permanent use in regions with critical oxygen supply.