Dynamic changes in cerebral oxygenation by two methods during cardiac surgery and postoperative cognitive decline

Introduction

Recently, near-infrared time-resolved spectroscopy (TRS), which is quite effective in quantitative monitoring tissue oxygenation, because it offers the actual measurement of photon migration in the tissues, and the photon mean path length is easily obtained from the center of gravity of the temporal profile, has been developed. In this study, we investigated whether the changes in the cerebral oxygen saturation (T-SO₂) obtained with the TRS and the jugular venous oxygen saturation (SjvO₂) predicted cognitive decline after cardiac surgery.

Methods

With institutional approval and informed consent, we studied 10 patients (68.7 ± 6.1 years) undergoing cardiac surgery under cardiopulmonary bypass (CPB). T-SO₂ was continuously monitored using a TRS-10 (Hamamatsu Photonics KK, Hamamatsu, Japan). For measurement of SjvO₂, a 5.5 Fr oximetry catheter was inserted by retrograde cannulation of the right internal jugular vein. The values of T-SO₂ and SjvO₂ were compared with each point: before CPB, 5 minutes after the onset of CPB, before aorta clamp, after aorta clamp, rewarming, aorta declamp, end of rewarming, and end of CPB. The cognitive decline was evaluated by Mini Mental State Examination before and 7 days after the operation. The statistical analysis was performed by repeated-measures ANOVA followed by Fisher's PLSD. P < 0.05 was considered statistically significant.

Results

Four of 10 cases showed postoperative cognitive decline. The mean values of T-SO₂ and SjvO₂ during operation in patients without postoperative cognitive decline (n = 6) were 63.9 ± 4.6% and 60.5 ± 9.7%, respectively, and there were no statistical significances between these values. However, the mean values of T-SO₂ and SjvO₂ during operation in patients with postoperative cognitive decline (n = 4) were 62.8 ± 5.6% (T-SO₂) and 70.4 ± 14.9% (SjvO₂), and showed significant differences between two values (P = 0.0024), and at the rewarming period, the values of SjvO₂ was significantly higher than those of T-SO₂ (87.9 ± 6.3% vs 65.0 ± 5.3%, P = 0.0014).

Conclusions

Our results demonstrate a lack of agreement between SjvO₂ and T-SO₂ for monitoring cerebral oxygenation at the occurrence of postoperative cognitive decline. Therefore, we conclude that the two methods are not interchangeable, and the TRS instrument may be useful for obtaining accurate values for cerebral oxygen saturation under CPB.