Bedside Monitoring of Cerebral Energy State During Cardiac Surgery-A Novel Approach Utilizing Intravenous Microdialysis

Abstract

Objectives: This study investigated whether the lactate-to-pyruvate (LP) ratio obtained by microdialysis (MD) of the cerebral venous outflow reflected a derangement of global cerebral energy state during cardiopulmonary bypass (CPB).

Design: Interventional, prospective, randomized study.

Setting: Single-center, university teaching hospital.

Participants: The study included 10 patients undergoing primary, elective coronary artery bypass grafting.

Interventions: Patients were randomized blindly to low mean arterial pressure (MAP) (40-60 mmHg; n = 5) or high MAP (60-80 mmHg; n = 5) during CPB. The MD catheters were positioned in a retrograde direction into the jugular bulb, and a reference catheter was inserted into the brachial artery. The correlations among LP ratio, MAP, data obtained from bifrontal near-infrared spectroscopy (NIRS), and postoperative neurologic outcome measures were assessed.

Measurements and main results: The correlated difference between pooled LP ratio (low and high MAP) of the jugular venous and the arterial blood was significant (LP_arterial 17 [15-20] v LP_venous 26 [23-27]; p = 0.0001). No cerebral desaturations (decrease in rSO₂>20% from baseline) were observed in either group during CPB. In each group, 50% of the patients showed significant cognitive decline (mini-mental state examination, 3 points) 2 days after surgery.

Conclusion: The LP ratio of cerebral venous blood increased significantly during CPB, indicating compromised cerebral oxidative metabolism. Conventional monitoring of rSO₂ by NIRS did not show a corresponding decrease in cerebral oxygenation. As the patients exhibited decreased cognitive functions after CPB, increases in jugular venous LP ratio may be a sensitive indicator of impending cerebral damage.

Keywords: cardiac surgery; cardiopulmonary bypass; cerebral oxidative metabolism; microdialysis; neurologic outcome; regional cerebral oxygen saturation.