Dynamic evaluation of near-infrared peripheral oximetry in healthy volunteers: a comparison between INVOS and EQUANOX

Purpose: The present study aimed to compare peripheral regional tissue oxygen saturation (rSO2) values and desaturation/resaturation rates given by INVOS and EQUANOX devices.

Materials and methods: Twenty healthy volunteers were investigated during 4 experimental steps: baseline, hyperoxia, ischemia, and reperfusion. For each volunteer, 2 sensors INVOS and 2 sensors EQUANOX were placed on both left and right calves. Blood pressure, heart rate, and peripheral pulse oximetry were monitored.

Results: Peripheral rSO2 ranged from 40% to 95% (INVOS) and from 47% to 100% (EQUANOX): 81±12 vs 82±9 (P=.469). A significant relationship was found at baseline between absolute values of INVOS and EQUANOX (n=40; R2=0.159; P=.011). Bias was -0.4%, and limits of agreement were ±15.1%. The percent maximum differences vs baseline values during dynamic maneuvers were 33%±19% (95% confidence interval, 24-42) and 21%±14% (95% confidence interval, 15-28) for INVOS and EQUANOX, respectively. No significant relationship was observed between percent maximum differences in INVOS and EQUANOX (n=20; R2=0.128; P=.122). Rates of desaturation/resaturation during occlusive vascular tests were 3.65% per minute vs 2.36% per minute (P=.027) and 30.42% per minute vs 16.28% per minute (P=.004) for INVOS and EQUANOX, respectively.

Conclusions: INVOS and EQUANOX are not comparable in measuring both absolute values and dynamic changes of peripheral rSO2 and near-infrared spectroscopy-derived parameters during occlusion vascular tests.