Cerebral Monitoring Using Near-Infrared Time-Resolved Spectroscopy and Postoperative Cognitive Dysfunction
Recently, near-infrared time-resolved spectroscopy (TRS), which is an effective means of quantitatively monitoring tissue oxygenation, has been developed. We examined whether postoperative cognitive dysfunction (POCD) can be predicted by cerebral monitoring using TRS during cardiac surgery.
With institutional approval and informed consent, we studied ten patients (68.7 ± 6.1 years) undergoing cardiac surgery requiring a cardiopulmonary bypass (CPB). The source and detector probes for TRS were fixed on the forehead at a distance of 4 cm apart, and the cerebral oxygen saturation (T-SO2) in parts of the brain was continuously monitored using a TRS-10 (Hamamatsu Photonics K. K., Hamamatsu, Japan). To measure the jugular venous oxygen saturation (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 at several time points (1) before CPB, (2) at 5 min after the onset of CPB, (3) before aorta clamping, (4) after aorta clamping, (5) during rewarming, (6) after aorta declamping, (7) at the end of rewarming, and (8) at the end of CPB. Cognitive dysfunction was evaluated using the Mini Mental State Examination before and 7 days after the operation. A statistical analysis was performed using a repeated measure ANOVA followed by Fisher’s protected least significant difference test. A P-value less than 0.05 was considered statistically significant.
Four of the ten cases exhibited POCD. In patients without POCD (n = 6), the mean SjvO2 and T-SO2 values during surgery were 60.5 ± 9.7% and 63.9 ± 4.6%, respectively, and no significant differences between the values at any two time points were observed. However, in patients with POCD (n = 4), significant differences between the mean SjvO2 and T-SO2 values were observed during surgery (70.4 ± 14.9% [SjvO2] vs. 62.8 ± 5.6% [T-SO2], P = 0.0024), and the SjvO2 value was significantly higher than the T-SO2 value during the rewarming period (87.9 ± 6.3% vs. 65.0 ± 5.3%, P = 0.0014).
Our results demonstrate a lack of agreement between SjvO2 (global cerebral oxygenation) and T-SO2 (local regional oxygenation at the monitoring site) during cardiac surgery in cases who develop POCD. Therefore, we conclude that these two methods are not interchangeable, and the monitoring of both SjvO2 and T-SO2 during cardiac surgery might be useful not only for observing the dynamic changes in cerebral oxygenation but also for predicting the occurrence of POCD.
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