Noninvasive Optical Quantification of Cerebral Venous Oxygen Saturation in Humans

Rationale and Objectives: Cerebral oxygen extraction, defined as the difference between arterial and venous oxygen saturations (SaO₂ and SvO₂), is a critical parameter for managing intensive care patients at risk for neurological collapse. Although quantification of SaO₂ is easily performed with pulse oximetry or moderately invasive arterial blood draws in peripheral vessels, cerebral SvO₂ is frequently not monitored because of the invasiveness and risk associated with obtaining jugular bulb or super vena cava (SVC) blood samples. Materials and Methods: In this study, near-infrared spectroscopy (NIRS) was used to noninvasively measure cerebral SvO₂ in anesthetized and mechanically ventilated pediatric patients (n = 10). To quantify SvO₂, the NIRS signal component that fluctuates at the respiration frequency is isolated. This respiratory component is dominated by the venous portion of the interrogated vasculature. The NIRS measurements of SvO₂ were validated against the clinical gold standard: invasively measured oxygen saturations from SVC blood samples. This technique was also applied in healthy volunteers (n = 5) without mechanical ventilation to illustrate its potential for use in healthy populations with natural airways. Results: Ten pediatric patients with pulmonary hypertension were studied. In these patients, SvO₂ in the SVC exhibited good agreement with NIRS-measured SvO₂ (R² = 0.80, P =.001, slope = 1.16 ± 0.48). Furthermore, in the healthy adult volunteers, mean (standard deviation) NIRS-measured SvO₂ was 79.4 (6.8)%. This value is in good agreement with the expected average central venous saturation reported in literature. Conclusion: Respiration frequency-selected NIRS can noninvasively quantify cerebral SvO₂. This bedside technique can be used to help assess brain health in neurologically unstable patients.