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

Abstract

Background

Measurement of cerebral venous oxyhemoglobin saturation (ScvO₂) is considered a gold standard in assessing the adequacy of tissue oxygen delivery (DO₂) after the stage 1 palliation (S1P), with SvO₂ <30% often representing severely compromised DO₂. Regional oxygenation index (rSO₂) based on near-infrared resonance spectroscopy (NIRS) frequently is used to screen for compromised DO₂, although its sensitivity to detect severe abnormalities in SvO₂ is uncertain.

Methods

ScvO₂ was measured by co-oximetry from the internal jugular vein as clinically indicated in 73 neonates after S1P. These values were compared with cerebral rSO₂ (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 rSO₂-based ScvO₂ designed to remove arterial contamination from the rSO₂ signal: rSO₂-based ScvO₂ = (rSO₂ − arterial oxygen saturation × 0.3)/0.7.

Results

Among 520 time-matched pairs of ScvO₂ and cerebral rSO₂, the slope of the relationship between rSO₂ and ScvO₂ (after we adjusted for effects of hemoglobin) was 0.37 ± 0.04 with only modest correlation (r² = 0.39), and mean bias of +8.26. When ScvO₂ was <30%, cerebral rSO₂ was <30 in less than 1%, <40 less than 1%, and <50 in 45.7% of data points; specificity of rSO₂ in the same range is >99%. Correction of rSO₂ for arterial contamination significantly decreased mean bias (+3.03) and improved the sensitivity of rSO₂ to detect ScvO₂ <30 to 6.5% for rSO₂ <30, 29% for rSO₂ <40, and 77.4% for rSO₂ <50.

Conclusions

Cerebral rSO₂ in isolation should not be used to detect low ScvO₂, because its sensitivity is low, although correction of rSO₂ for arterial contamination may improve sensitivity. Cerebral rSO₂ of 50 or greater should not be considered reassuring, though values below 30 are specific for low ScvO₂.