Inclusion of oxygen consumption improves the accuracy of arterial and venous oxygen saturation interpretation after the Norwood procedure

Objective: Management strategy for the postoperative Norwood neonate has been formulated from models that have estimated oxygen consumption (VO2) Superior vena caval oxygen saturation (SVO2), systemic arterial and superior vena caval oxygen saturation difference (Sa-VO2), and oxygen excess factor (Omega=arterial oxygen saturation/Sa-VO2) have been used as indirect indicators to estimate systemic blood flow (Qs) and oxygen delivery (DO2). We sought to examine the correlation of the indirect indicators to VO2-derived measures of oxygen transport. Methods: Respiratory mass spectrometry was used to continuously measure VO2 after the Norwood procedure (n=13). Measured saturations and the direct Fick equation were used to obtain pulmonary blood flow, Qs, DO2, and oxygen extraction ratio (ERO2) values. Correlations to SVO2, Sa-VO2, and Omega were sought. Results: There was a close correlation of SVO2, Sa-VO2, and Omega to ERO2 (r=0.92, 0.96, and 0.97, respectively; P<.0001). Correlation to Qs and DO2 was variable (r=0.39 to 0.78, respectively; P<.0001). Correlation to VO2 was poor but significant (r=0.24 to 0.40, P<.0001). Inclusion of VO2 improved the correlation to Qs and DO2 (r=0.66 to 0.97, P<.0001). Conclusions: The close correlation of SVO2, Sa-VO2, and Omega to ERO2 indicates that each is a measure of the balance of DO2 and extraction. The significant but less reliable correlation to DO2 and VO2 indicates the values for SVO2, Sa-VO2, and Omega do not discriminate between the contribution of DO2 and VO2. Measured VO2 and hemodynamics may improve the optimization of postoperative management strategy in the individual neonate.