The effect of retrograde cerebral perfusion after particulate embolization to the brain

Neurologic injury as a consequence of cerebral embolism of either air or atherosclerotic debris during cardiac or aortic surgery is still a major cause of postoperative morbidity and mortality. While exploring various means of improving cerebral protection during complex cardiothoracic procedures, we have developed a chronic porcine model to study retrograde cerebral perfusion. We have previously demonstrated that retrograde perfusion results in a small amount of nutritive flow and provides cerebral protection that appears to be superior to simple prolonged hypothermic circulatory arrest. The current study was designed to evaluate the efficacy of retrograde cerebral perfusion in mitigating the effects of particulate cerebral embolism occurring during cardiac surgery. Four groups of pigs (19 to 28 kg) underwent cardiopulmonary bypass with deep hypothermia at an esophageal temperature of 20 degrees C: an antegrade control group (AC, n = 5), an antegrade embolism group (AE, n = 10), a retrograde control group (RC, n = 5), and a retrograde embolism group (RE, n = 10). In addition, because of extreme heterogeneity in outcome in the initial RE group, an additional group of 10 animals underwent embolism and retrograde perfusion at a later time. Embolization was accomplished by injection of 200 mg of polystyrene microspheres (250 to 750 micrograms in diameter) via the aortic cannula into an isolated aortic arch preparation in the AE and RE groups; the control groups received injections of 10 ml of saline solution. After infusion of the microspheres or saline solution, conventional perfusion, with the aortic arch pressure maintained at 50 mm Hg, was continued for a total of 30 minutes in the antegrade groups; in the retrograde groups, retrograde flow was initiated via a cannula positioned in the superior vena cava, and was continued for 25 minutes. Superior vena caval flow was regulated to maintain a sagittal sinus pressure of approximately 30 mm Hg in the retrograde groups, and blood returning to the isolated aortic arch was collected and measured. All animals were allowed to recover and were evaluated daily according to a quantitative behavioral score in which 9 indicates apparently complete normalcy, with lower numbers indicating various degrees of cerebral injury. At the time of planned death on day 6, half of the brain was used for recovery of embolized microspheres after digestion with 10N sodium hydroxide. The other half was submitted for histologic study. Neurologic recovery in both the antegrade and retrograde control groups appeared to be complete, although mild evidence of histologic damage was present in some animals in the retrograde control group.(ABSTRACT TRUNCATED AT 400 WORDS)