Cerebral near-infrared spectroscopy insensitively detects low cerebral venous oxygen saturations after stage 1 palliation

Background: Measurement of cerebral venous oxyhemoglobin saturation (ScvO(2)) is considered a gold standard in assessing the adequacy of tissue oxygen delivery (DO2) after the stage 1 palliation (S1P), with SvO(2) < 30% often representing severely compromised DO2. Regional oxygenation index (rSO(2)) based on near-infrared resonance spectroscopy (NIRS) frequently is used to screen for compromised DO2, although its sensitivity to detect severe abnormalities in SvO(2) is uncertain. Methods: ScvO(2) was measured by co-oximetry from the internal jugular vein as clinically indicated in 73 neonates after S1P. These values were compared with cerebral rSO(2) (FORE-SIGHT; CASMED) via mixed effects model linear regression, Bland-Altman analysis, and sensitivity analysis. Because NIRS devices measure a composite of arterial and venous blood, we calculated an rSO(2)-based ScvO(2) designed to remove arterial contamination from the rSO(2) signal: rSO(2)-based ScvO(2) = (rSO(2) - arterial oxygen saturation x 0.3)/0.7. Results: Among 520 time-matched pairs of ScvO(2) and cerebral rSO(2), the slope of the relationship between rSO(2) and ScvO(2) (after we adjusted for effects of hemoglobin) was 0.37 +/- 0.04 with only modest correlation (r(2) = 0.39), and mean bias of +8.26. When ScvO(2) was < 30%, cerebral rSO(2) was < 30 in less than 1%, < 40 less than 1%, and < 50 in 45.7% of data points; specificity of rSO(2) in the same range is > 99%. Correction of rSO(2) for arterial contamination significantly decreased mean bias (+3.03) and improved the sensitivity of rSO(2) to detect ScvO(2) < 30 to 6.5% for rSO(2) < 30, 29% for rSO(2) < 40, and 77.4% for rSO(2) < 50. Conclusions: Cerebral rSO(2) in isolation should not be used to detect low ScvO(2), because its sensitivity is low, although correction of rSO(2) for arterial contamination may improve sensitivity. Cerebral rSO(2) of 50 or greater should not be considered reassuring, though values below 30 are specific for low ScvO(2).