Regional tissue blood flow and pH in the brain during deep hypothermic retrograde brain perfusion

Deep hypothermic retrograde brain perfusion is used to protect the brain during aortic arch operations. However, all experiments have failed to demonstrate retrograde blood flow in the brain tissue. We developed an experimental model of sagittal sinus and simultaneous superior vena cava perfusion. Brain tissue blood flow was mapped with colored microspheres during deep hypothermic retrograde brain perfusion in 9 dogs. Regional brain pH was mapped photometrically using neutral red as a pH-indicating dye after 90 min of retrograde brain perfusion in 28 dogs and after 60 min of circulatory arrest in 8 dogs. Cerebral surface blood flow was also measured during retrograde brain perfusion. They were analyzed as functions of driving pressure between sagittal sinus and aorta. Total brain blood flow (ml/min/100 g) was 1.4 +/- 1.3, 3.8 +/- 2.6, and 4.6 +/- 2.6 when the driving pressure was 15, 25, and 35 mmHg, respectively (P < 0.05, 15 mmHg vs 25 mmHg). Regional cerebral blood flow (ml/min/100 g) with a driving pressure of 25 mmHg was 12.1 +/- 9.4, 7.0 +/- 5.6, 4.4 +/- 2.8, and 2.2 +/- 1.4 in the frontal cortex, anterior, mid, and posterior cerebrum, respectively. Cerebral cortex pH was 6.86 +/- 0.23, 7.15 +/- 0.18, and 6.46 +/- 0.13 after 90 min of retrograde brain perfusion with driving pressure of less than 20 mmHg, after that of above 20 mmHg, and after 60 min of circulatory arrest, respectively. Brain tissue pH, blood flows measured with microspheres, and laser flowmetry were highest when driving pressure was between 25 and 35 mmHg. We conclude that retrograde brain perfusion may provide maximum brain protection with driving pressure of 25 to 35 mmHg.