Effect of Cardiopulmonary Bypass on Cortical Cerebral Oxygenation During Coronary Artery Bypass Grafting

Objective: To investigate the changes in cerebral oxygenation during coronary artery bypass grafting (CABG) with normothermic cardiopulmonary bypass (CPB) using near infrared spectroscopy.

Methods: Measurement of cerebral cortical oxygenation changes included concentration of deoxygenated haemoglobin [HHb], oxygenated haemoglobin [O₂Hb], changes in the redox status of the cytochrome c oxidase [Cyt-Ox], cerebral saturation as expressed by the tissue oxygenation index (TOI), and cerebral blood volume (CBV) as expressed by tissue haemoglobin index (THI). Measurements were performed in 19 consecutive patients undergoing normothermic (34–36 °C) CPB. Data were recorded at 0.5s intervals and averaged into 30 s epochs. Data analysis was carried at baseline, 1, 20, and 40 min after start of CPB, at rewarming, on weaning from CPB, and at closing of chest.

Results: There were no in-hospital death, neurological deficits, or myocardial infarcts. Compared to baseline, during the entire CPB duration, there was a marked reduction in [O₂Hb] and CBV which reached their worst level 40 min after initiation of CPB (from –3.03±5.1 to –9.25±7.20 µmol/l for [O₂Hb], and a 24% reduction for CBV (both P<0.0001)). The deterioration in [O₂Hb] was recovered by the end of surgery, while the changes in CBV persisted. No significant changes occurred with respect to [HHb], [Cyt-Ox], and TOI.

Conclusions: Conventional CABG is responsible for deterioration in [O₂Hb], and CBV, which peak at 40–60 min following initiation of CPB. The changes in [O₂Hb] are reversible whereas the reduction of CBV persists to the end of the surgery. This suggests a transient impairment in the autoregulatory mechanisms controlling cerebral blood flow following discontinuation of cardiopulmonary bypass.