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 cardioth oracic procedures, we have developed a chronic porcine model to study retrograde cerebral perfusion, We have previously demonstrated that re trograde perfusion results in a small amount of nutritive flow and pro vides cerebral protection that appears to be superior to simple prolon ged hypothermic circulatory arrest; The current study was designed to evaluate the efficacy of retrograde cerebral perfusion in mitigating t he effects of particulate cerebral embolism occurring during cardiac s urgery, Four groups of pigs (19 to 28 kg) underwent cardiopulmonary by pass with deep hypothermia at an esophageal temperature of 20 degrees C: an antegrade control group (AC, n = 5), an antegrade embolism group (RE, n = 10), a retrograde control group (RC, n = 5), and a retrograd e embolism group (RE, n = 10), In addition, because of extreme heterog eneity in outcome in the initial RE group, an additional group of 10 a nimals underwent embolism and retrograde perfusion at a later time, Em bolization was accomplished by injection of 200 mg of polystyrene micr ospheres (250 to 750 mu g 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 t otal of 30 minutes in the antegrade groups; in the retrograde groups, retrograde Bow 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 3 0 mm Hg in the retrograde groups, and blood returning to the isolated aortic arch was collected and measured, All animals were allowed to re cover and were evaluated daily according to a quantitative behavioral score in which 9 indicates apparently complete normalcy, with lower nu mbers indicating various degrees of cerebral injury, At the time of pl anned death on day 6, half of the brain was used for recovery of embol ized 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, a lthough mild evidence of histologic damage was present in some animals in the retrograde control group. After embolization, unequivocal neur ologic injury occurred in both- groups, accompanied by significant cer ebral histopathologic abnormalities. Although neurologic outcome was n ot significantly better in the initial RE group as a whole than in the AE group, it ,vas noted that several of the RE animals recovered almo st completely after retrograde cerebral perfusion (behavioral scores > 7). The animals with good behavioral recovery were noted to have been perfused with markedly lower superior vena caval pressures than those used in animals that sustained severe neurologic injury. An additional 10 animals were therefore subjected to embolization and retrograde pe rfusion to clarify the impact on outcome of different superior vena ca val pressures during retrograde perfusion. When these additional anima ls are included in the analysis, the behavioral and neuropathologic ev idence suggests that use of retrograde cerebral perfusion may attenuat e the severity of cerebral injury resulting from particulate emboli wh en adequate retrograde perfusion can be maintained at low superior ven a caval pressures (<40 mm Hg). This observation merits further study.