Retrograde brain perfusion beyond the venous values. Hemodynamics and intracellular pH mapping.

Twenty-one dogs (group 1) had retrograde brain perfusion for 90 minutes through the sagittal sinus and superior vena cava with pressure-regulated cardiopulmonary bypass, and 10 dogs (group 2) had 60 minutes of circulatory arrest with an additional 30-minute evaluation of brain slices, both at 20 degrees C. In group 1, cerebral blood flow determined by laser flowmetry was 8.98 +/- 2.02 ml/100 gm/min with a driving pressure of 29.69 +/- 9.92 mm Hg during the retrograde perfusion, whereas it was 0.85 ml/100 gm/min during solitary perfusion through the superior vena cava. Retrograde cerebral vascular resistance was slightly higher than the antegrade resistance. Neutral red stain was given intraperitoneally as an intracellular pH indicator. Regional intracellular pH was calculated from photoabsorption at 440 and 535 nm with the use of color transparency photographs of the brain and spinal cord slices taken after retrograde cerebral perfusion in group 1 and after circulatory arrest in group 2. The pH mapping showed that the retrograde brain perfusion maintained the pH within 6.77 to 7.14, whereas the cerebral pH decreased to 6.24 to 6.43 at 60 minutes of circulatory arrest and further decreased to 5.81 to 6.22 at 90 minutes. The pH after the retrograde brain perfusion was significantly higher than the pH after circulatory arrest in the entire brain and the spinal cord. We conclude that the brain is protected when perfused retrogradely beyond the venous valves with a driving pressure above 20 mm Hg.