High oxygen treatment during preparation of children for open-heart surgery leads to a decrease in total antioxidant capacity

Introduction

Children who undergo cardiac surgery with cardiopulmonary bypass (CPB) often suffer myocardial damage after the operation. It has been hypothesized that this damage is enhanced by mechanisms that involve increased oxidative stress. This oxidative stress damage could be caused by ischaemia-reperfusion injury, which could be intensified by the high oxygen treatment that is used during CPB and by inflammatory activity. To verify this, we assessed the antioxidant capacity in plasma samples collected at a number of time points before, during and after CPB, from children undergoing open-heart surgery.

Method

Total trolox equivalents in antioxidant capacity (TEAC) were calculated from the reactivity toward the artificially generated 2,2'-azinobis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) radical. To exclude the possibility that TEAC values decrease as a result of haemodilution, we measured the triglyc-eride content using the GPO-trinder (Sigma) reagent in a microtitre-plate spectrophotometric analysis.

Results

Total antioxidant capacity was decreased shortly after the onset of surgery in plasma of children (aged 8-14 months) treated for ventricular septal defect (VSD; n = 17) and tetralogy of Fallot (TOF; n = 15). Figure 1 shows a significant (Friedman test; P < 0.05) decrease in both VSD and TOF from time point 1.1 (induction of anaesthesia) to time point 2 (heparin administration before CPB). Decrease in TEAC values can therefore not be a result of haemodilution during CPB. This was confirmed by the fact that total plasma triglyceride values did not decrease between these time points. Shortly after CPB (time point 4) the TEAC values were already significantly (P < 0.05) higher than at time point 3 (10 min after the onset of CPB), and they returned to normal during the 4 h after the operation and remained normal thereafter.

Figure 1

Average TEAC and triglyceride values in infants with VSD or TOF. Shown are changes in TEAC and triglyceride values before, during (grey area) and after CPB.

Conclusion

We showed a decrease in antioxidant capacity early during the operation, which could not have been caused by haemodilution. The most likely cause appears to be the high oxygen that was given during preparation for CPB. The methodology described here will be useful for study of the influences of different approaches in, for example, oxygen treatment, clamping techniques, temperature treatment and antioxidant supply on the oxidative stress that occurs during open-heart surgery.