Central venous oxygen saturation and blood lactate levels during cardiopulmonary bypass are associated with outcome after pediatric cardiac surgery

Abstract

Introduction: Central venous oxygen saturation and blood lactate are different indices of the adequacy of oxygen delivery to the oxygen needs. In pediatric cardiac surgery, lactate level and kinetics during and after cardiopulmonary bypass are associated with outcome variables. The aim of this study was to explore the hypothesis that the lowest central venous oxygen saturation and the peak lactate value during cardiopulmonary bypass, used alone or in combination, may be predictive of major morbidity and mortality in pediatric cardiac surgery.

Methods: We conducted a retrospective analysis of 256 pediatric (younger than 6 years) patients who had undergone cardiac surgery with continuous monitoring of central venous oxygen saturation and serial measurement of blood lactate.

Results: Peak lactate was significantly increased when the nadir central venous oxygen saturation was < 68%. Both nadir central venous oxygen saturation and peak lactate during cardiopulmonary bypass were independently associated with major morbidity and mortality, with the same accuracy for major morbidity and a higher accuracy of peak lactate for mortality. A combined index (central venous oxygen saturation < 68% and peak lactate > 3 mmol/L) provided the highest sensitivity and specificity for major morbidity, with a positive predictive value of 89%.

Conclusions: The combination of a continuous monitoring of central venous oxygen saturation and serial measurements of blood lactate during cardiopulmonary bypass may offer a predictive index for major morbidity after cardiac operations in pediatric patients. This study generates the hypothesis that strategies aimed to preserve oxygen delivery during cardiopulmonary bypass may reduce the occurrence of low values of central venous oxygen saturation and elevated lactate levels. Further studies should consider this hypothesis and take into account other time-related factors, such as time of exposure to low values of central venous oxygen saturation and kinetics of lactate formation.

Figure 1

Peak whole blood lactate according to the nadir ScVO₂ value. Significance assessed with the Kruskal-Wallis test.

Figure 2

Predicted major morbidity and mortality rates (logistic regression analysis) according to the nadir ScVO₂ value, for a cardiopulmonary bypass (CPB) duration of 90 minutes.

Figure 3

Predicted major morbidity and mortality rates (logistic regression analysis) according to the peak whole blood lactate value, for a cardiopulmonary bypass (CPB) duration of 90 minutes.

Figure 4

Receiver operating characteristic curve for major morbidity. Different cut-off values for nadir ScVO₂, peak lactate, and a combined index are explored. PPV, positive predictive value; NPV, negative predictive value.

Figure 5

Patient distribution according to the cut-off values of 68% (nadir ScVO₂) and 3 mmol/L (peak lactate).

Figure 6

Receiver operating characteristic curve for mortality. Different cut-off values for nadir ScVO₂, peak lactate, and a combined index are explored. PPV, positive predictive value; NPV, negative predictive value.