Characterization of tissue oxygen saturation and the vascular occlusion test: influence of measurement sites, probe sizes and deflation thresholds

INTRODUCTION: Tissue oxygen saturation (StO(2)) and the vascular occlusion test (VOT) can identify tissue hypoperfusion in trauma and sepsis. However, the technique is neither standardized nor uses the same monitoring site. We hypothesized that baseline and VOT StO(2 )would be different in the forearm (F) and thenar eminence (TH) and that different minimal StO(2 )values during the VOT would result in different reoxygenation rates (ReO(2)). METHODS: StO(2 )and its change during the VOT were simultaneously measured in the F and TH, with 15 mm and 25 mm probes, using the 325 InSpectra monitor in 18 healthy, adult volunteers. Two VOTs were done to a threshold thenar StO(2 )of 40% interchanging the 15 mm and 25 mm probes between sites. Two additional VOTs were done to thresholds of 50% and 30%. Baseline StO(2 )(BaseO(2)), the deoxygenation rate (DeO(2)) and ReO(2 )were compared between sites, probes and (%O(2)/minute) thresholds. Results are presented as the median (interquartile range), P-value. RESULTS: BaseO(2), DeO(2), ReO(2), area under the curve and hyperemia duration values were different when comparing TH vs. F and 15 mm vs. 25 mm probes. ReO(2 )was different between different thresholds for the TH and 15 mm probes. TH(15 mm )vs. F(15 mm): BaseO(2), 90.4 (85.2, 93.5) vs. 85.2 (80.7, 90.2), P = 0.031; DO(2), -12.1 (-16.2, -11.3) vs. -8.5 (-10.3, -7.8), P = 0.011; ReO(2), 297.2 (213.7, 328.6), P < 0.0001; 15 mm vs. 25 mm probe: BaseO(2), 97.2 (89.4, 94.7) vs. 87.3 (81.7, 90.9), P = 0.016; DeO(2), -18.0 (-24.1, -14.8) vs. -9.9 (-15.3, -6.5), P < 0.0001; and ReO(2), 401.6 (331.7, 543.2) vs. 160.5 (132.3, 366.9), P = 0.012, respectively. TH(15 mm )vs. TH(25 mm): BaseO(2), P = 0.020; DeO(2), P < 0.0001; and ReO(2), P < 0.0001. Threshold StO(2 )values (15 mm probe only): ReO(2), P = 0.003; DeO(2), P = 0.60. ReO(2 )at 40% and 50% StO(2 )thresholds, P = 0.01. CONCLUSIONS: BaseO(2), DeO(2 )and ReO(2 )were different when measured in different anatomical sites (F and TH) and with different probe sizes, and ReO(2 )was different with differing VOT release StO(2 )threshold values. Thus, standardization of the site, probe and VOT challenge need to be stipulated when reporting data.