Can central-venous oxygen saturation be estimated from tissue oxygen saturation during a venous occlusion test?

OBJECTIVE: To test whether tissue oxygen saturation (StO(2)) after a venous occlusion test estimates central venous oxygen saturation (ScvO(2)). METHODS: Observational study in intensive care unit patients. Tissue oxygen saturation was monitored (InSpectra Tissue Spectrometer Model 650, Hutchinson Technology Inc., MN, USA) with a multiprobe (15/25mm) in the thenar position. A venous occlusion test in volunteers was applied in the upper arm to test the tolerability and pattern of StO(2) changes during the venous occlusion test. A sphygmomanometer cuff was inflated to a pressure 30mmHg above diastolic pressure until StO(2) reached a plateau and deflated to 0mmHg. Tissue oxygen saturation parameters were divided into resting StO(2) (r-StO(2)) and minimal StO(2) (m-StO(2)) at the end of the venous occlusion test. In patients, the cuff was inflated to a pressure 30mmHg above diastolic pressure for 5 min (volunteers’ time derived) or until a StO(2) plateau was reached. Tissue oxygen saturation parameters were divided into r-StO(2), m-StO(2), and the mean time that StO(2) reached ScvO(2). The StO(2) value at the mean time was compared to ScvO(2). RESULTS: All 9 volunteers tolerated the venous occlusion test. The time for tolerability or the StO(2) plateau was 7 ± 1 minutes. We studied 22 patients. The mean time for StO(2) equalized ScvO(2) was 100 sec and 95 sec (15/25mm probes). The StO(2) value at 100 sec ([100-StO(2)] 15mm: 74 ± 7%; 25mm: 74 ± 6%) was then compared with ScvO(2) (75 ± 6%). The StO(2) value at 100 sec correlated with ScvO(2) (15 mm: R(2) = 0.63, 25mm: R(2) = 0.67, p < 0.01) without discrepancy (Bland Altman). CONCLUSION: Central venous oxygen saturation can be estimated from StO(2) during a venous occlusion test.