Abstract
Venous oxygen saturation (SvO2) poorly reflects regional oxygen supply-demand imbalance which suggests its limitations as an indicator of adequate perfusion during cardiopulmonary bypass (CPB). Recently, the role of oxygen delivery (DO2) in CPB has gained attention since studies have shown that maintaining sufficient DO2 is associated with reduced incidence of postoperative acute kidney injury (AKI). In this study, we investigated the relationship between AKI onset, SvO2 and DO2, and examined whether the limitations of SvO2 could be compensated by monitoring DO2.
We enrolled adult patients (estimated glomerular filtration rate >60mL/min/1.73m2) who underwent open heart surgery using CPB at Juntendo University Hospital and Tokyo Bay Urayasu Ichikawa Medical Center between March 2017 and December 2018. Postoperative AKI was used as an index of optimal perfusion. The area under the curve (AUC<SvO2 75, AUC<DO2 i300)and cumulative time(Time<SvO2 75, Time<DO2 i300)below the cutoff threshold were calculated. Wilcoxon test, Chi-square test, and receiver operating characteristic (ROC) analysis were used to evaluate the relationship between intraoperative variables and postoperative AKI.
Patients were stratified into AKI (n=191) and non-AKI groups (n=49). The AKI group had a larger AUC <DO2 i300 (450 vs 1103;p=0.025) and a longer Time<DO2 i300 (7.3 vs 16.3min;p=0.016), but AUC<SvO2 75 (42 vs 30;p=0.620) and Time<SvO2 75 (2.7 vs 3.7min;p=0.771) were not significantly different between the groups. The ROC analysis for AKI incidence showed significant difference between AUC values for Time<SvO2 75 and Time<DO2 i300 (0.098, p=0.028).
In both groups, SvO2 was generally maintained at the usual safe range of 75% or more. However, DO2 i was significantly lower in the AKI group, suggesting that maintaining SvO2 above 75% does not prevent postoperative AKI. Maintaining DO2 i levels >300mL/min/m2, in addition to the standard SvO2 monitoring, as target for blood flow management can help ensure optimal perfusion during CPB.
