NIRS Measurement of Peripheral Fractional Oxygen Extraction (FOE) after Cardiopulmonary Bypass

Abstract

Objectives: To compare peripheral fractional oxygen extraction (FOE), as measured by near infrared spectroscopy (NIRS), with conventional indicators of tissue perfusion in haemodynamically stable and unstable children after cardiopulmonary bypass. Design: Observational study. Setting: Paediatric Intensive Care Unit of a large teaching hospital. Patients: 17 children immediately after cardiopulmonary bypass. Male : female = 9 : 8, median age 7 months (range, newborn to 16 years). Methods: On admission, children were classified as “stable” or “unstable” based on the haemodynamic support they needed. Peripheral venous oxyhaemoglobin saturation (SvO₂) was measured non-invasively using NIRS with venous occlusion. FOE was calculated from SvO₂ and arterial saturation measured by pulse oximetry. Repeated measurements of peripheral SvO₂ were made for up to 8 hours. In 5 children who had pulmonary artery catheters, simultaneous mixed SvO₂ measurements were recorded. Results: Median FOE was 7.9% higher in the unstable group than in the stable group (p = 0.013). Peripheral SvO₂ and mixed SvO₂ were correlated (R² = 0.65, p < 0.0001). Conclusions: Peripheral FOE is higher in unstable children. Changes in peripheral SvO₂ are related to changes in mixed SvO₂. These measurements may provide useful information about haemodynamic status in critically ill children. Further evaluation of the technique is warranted.