Abstract

Objectives: To evaluate the clinical utility of near-infrared spectroscopic (NIRS) monitoring of cerebral (Sco₂) and splanchnic (Sso₂) oxygen saturations for estimation of systemic oxygen transport after the Norwood procedure.

Methods: Sco₂ and Sso₂ were measured with NIRS cerebral and thoracolumbar probes (in humans). Respiratory mass spectrometry was used to measure systemic oxygen consumption (V̇o₂). Arterial (Sao₂), superior vena caval (Svo2) 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 (Do₂) 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. Sco₂ moderately correlated with Svo₂, mean arterial pressure, Qs, Do₂ and ERo₂ (slope 0.30, 0.64. 2.30, 0.017 and −32.5, p < 0.0001) but not with Sao₂, arterial oxygen pressure (Pao₂), haemoglobin and V̇o₂. Study 2. Sco₂ correlated well with Svo₂, Sao₂, Pao₂ 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). Sco₂ correlated weakly with V̇o₂ (slope −0.07, p  =  0.05) and moderately with Qs, Do₂ and ERo₂ (slope 3.2, 0.03, −33.2, p < 0.0001). Sso₂ showed similar but weaker correlations.

Conclusions: Sco₂ and Sso₂ 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.