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

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 l 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.