Chapter 6 Abstract Coronary artery bypass graft (CABG) surgery is associated with significant morbidity and mortality. Worsened control of cerebral blood flow, due to hyper- tension, diabetes or other conditions impose patients peri-operatively to increa- sed risk of neurological complications. However, evaluation of cerebral hemody- namics is not common practice. We present a technique to evaluate dynamic cerebral autoregulation (dCA) and cerebral carbon dioxide reactivity (CO2R) during normothermic nonpulsatile cardiopulmonary bypass (CPB). The techni- que uses continuous recording of invasive arterial blood pressure, middle cere- bral artery blood flow velocity through transcranial Doppler sonography, absolu- te cerebral tissue saturation via near-infrared spectroscopy, in-line arterial carbon dioxide and pump flow measurement. dCA during CPB is estimated by transfer function analysis based on the response to blood pressure variation induced by cyclic 6/min changes of indexed pump flow from 2.0 to 2.4 up to 2.8 l/min/m2. CO2R is calculated from recordings of both cerebral blood flow veloci- ty and cerebral tissue oxygenation. In 37 patients during CPB we tested the feasibility of our technique to estimate dCA and CO2R at hypocapnia (paCO2 = 30 mmHg), normocapnia (paCO2 = 40 mmHg), and hypercapnia (paCO2 = 50 mmHg). dCA phase decreased significantly (p<0.01) with increasing paCO2 from hypocapnia (0.58 ± 0.3 rad) to normocapnia (0.31 ± 0.2 rad) and hypercapnia (0.1 ± 0.1 rad). Also gain decreased (p<0.01) with increasing paCO2 from hypocapnia (3.4 ± 2 %/mmHg) to normocapnia (2.2 ± 0.9 %/mmHg) and hypercapnia (1.4 ± 0.4 %/mmHg). CO2R is preserved during CPB, but significantly lower (p<0.01) for hypocapnia (2.5 ± 1 %/mmHg) compared to hypercapnia (5.0 ± 2 %/mmHg). Studying dynamic cerebral autoregulation and cerebrovascular reactivity during cardiopulmonary bypass is feasible by changing pump flow in a 6/min rate. Hypercapnia results in impaired dCA. Ongoing and future studies are expected to clarify optimal perfusion strategies for various patient populations scheduled for operations involving cardiopulmonary bypass. 100
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