Observations of retinal vessels during intermittent pressure-augmented retrograde cerebral perfusion in clinical cases

Retrograde cerebral perfusion (RCP) has been used as a cerebroprotective method under hypothermic circulatory arrest (HCA) during aortic surgery. As reported in an animal model in 2005, intermittent pressure-augmented-RCP (IPA-RCP) provides more effective cerebral perfusion than RCP. In 2013, the clinical efficacy of IPA-RCP was described in terms of clinical outcomes and regional cerebral oxygen saturation using infrared spectroscopy. However, the state of cerebral microcirculation during IPA-RCP has not been investigated in humans. The aim of the present study was to investigate cerebral microcirculation during IPA-RCP in humans by assessing the retinal vessels.Between 2013 and 2014, 8 consecutive patients underwent elective total replacement of the aortic arch for true thoracic aortic aneurysms. The IPA-RCP protocol consisted of a continuous venous pressure that was intermittently augmented at 45 mmHg for 30 s and then decreased to 20 mmHg for 120 s after isolated HCA for 300 s. The retinal vessels were assessed via non-invasive direct visualization of the cerebral microcirculation using a fundus camera. Assessments were done before cardiopulmonary bypass, during isolated HCA, and during IPA-RCP at 20 and 45 mmHg. Ratio of the diameter of retinal vessels to that of the optic disc was calculated from the diameters of the retinal arteries, veins and optic disc at each time point and was statistically examined.There were no neurological deficits and mortality. When compared with the control group and both IPA-RCP groups, the retinal vessels in the isolated HCA group were collapsed and the peripheral retinal vessels could not be clearly observed. The RVR was significantly larger in the control group and in both IPA-RCP groups when compared with the isolated HCA group. The RVR of the control group was similar to that of both IPA-RCP groups with regard to the retinal arteries and veins. The RVR of IPA-RCP at 45 mmHg was significantly larger than that at 20 mmHg with regard to the retinal veins.Our study suggested that intermittently augmented venous pressure at 45 mmHg opened the cerebrovenous vessels and enabled adequate cerebral perfusion. IPA-RCP may provide more effective cerebral perfusion under HCA in humans.