Assessment of the relationship between cerebral and splanchnic oxygen saturations measured by near-infrared spectroscopy and direct measurements of systemic haemodynamic variables and oxygen transport after the Norwood procedure

Objectives: To evaluate the clinical utility of near-infrared spectroscopic (NIRS) monitoring of cerebral (Sc-O2) and splanchnic (Ss(O2)) oxygen saturations for estimation of systemic oxygen transport after the Norwood procedure. Methods: Sc-O2 and Ss(O2) were measured with NIRS cerebral and thoracolumbar probes ( in humans). Respiratory mass spectrometry was used to measure systemic oxygen consumption (V-O2). Arterial (Sa(O2)), superior vena caval (Sv(O2)) and pulmonary venous oxygen saturations were measured at 2 to 4 h intervals to derive pulmonary (Qp) and systemic blood flow (Qs), systemic oxygen delivery (D-O2) and oxygen extraction ratio (ERO2). Mixed linear regression was used to test correlations. A study of 7 pigs after cardiopulmonary bypass ( study 1) was followed by a study of 11 children after the Norwood procedure ( study 2). Results: Study 1. Sc-O2 moderately correlated with Sv(O2), mean arterial pressure, Qs, D-O2 and ERO2 ( slope 0.30, 0.64. 2.30, 0.017 and 232.5, p < 0.0001) but not with Sa(O2), arterial oxygen pressure (Pa-O2), haemoglobin and V-O2. Study 2. Sc-O2 correlated well with Sv(O2), Sa(O2), Pa-O2 and mean arterial pressure ( slope 0.43, 0.61, 0.99 and 0.52, p < 0.0001) but not with haemoglobin (slope 0.24, p > 0.05). Sc-O2 correlated weakly with V-O2 ( slope 20.07, p = 0.05) and moderately with Qs, D-O2 and ERO2 (slope 3.2, 0.03, -33.2, p < 0.0001). Ss(O2) showed similar but weaker correlations. Conclusions: Sc-O2 and Ss(O2) may reflect the influence of haemodynamic variables and oxygen transport after the Norwood procedure. However, the interpretation of NIRS data, in terms of both absolute values and trends, is difficult to rely on clinically.