The application of retinal fluorescein angiography to brain circulation monitoring.

本研究旨在探讨视网膜荧光血管造影（RFA）对体外循环相关脑空气栓塞的诊断价值，以及对脑死亡患者脑循环障碍的诊断价值。经颈总动脉注射异硫氰酸荧光素葡聚糖可进行序贯RFA，无荧光素蓄积染料，并经颈总动脉注入一定量的空气，诱导视网膜空气栓塞。在该模型中，当注入超过0.1 ml的空气时，检测到视网膜空气栓塞。我们发现，虽然空气栓塞动脉阻塞后1分钟内在正常血压的动物注射空气缓解，闭塞持续超过3分钟时，平均动脉压降低到50毫米汞柱。这些结果表明，空气栓塞可导致严重的脑缺血条件下，如从体外循环复苏。此外，我们利用手持式视网膜摄像机在心脏直视手术期间进行RFA。我们尝试了7例患者，未发现任何不良反应，发现该方法适用于麻醉患者，但需要改进，如术中使用更大的放大倍率和联合视频系统进行同步诊断。所有病例的RFA均检测到视网膜循环，提示颈内动脉颅内第一分支眼动脉的血流在脑循环停止后仍得以保留，或脑死亡时视网膜循环由颈外动脉侧支循环维持。在任何一种情况下，RFA似乎都不能用于鉴别诊断脑死亡患者是否存在脑循环。

We studied on usefulness of retinal fluorescein angiography (RFA) for intraoperative diagnosis of brain air embolism associated with cardiopulmonary bypass and for diagnosis of absence of cerebral circulation in brain death patients.For the first purpose, we developed a canine model of brain air embolism, in which sequential RFA could be performed by the injection of fluorescein isothiocyanate dextran through common carotid artery without accumulation of fluorescein dye, and a certain amount of air was injected through common carotid artery to induce retinal air embolism. In this model, retinal air emboli were detected when more than 0.1 ml of air was injected. We found that while arterial obstruction by air emboli was relieved within 1 min after air injection in normotensive animals, the occlusion persisted more than 3 min when mean arterial pressure was reduced to 50 mmHg. These results indicated that air embolism could cause significant brain ischemia under hypotensive conditions like emergence from cardiopulmonary bypass. In addition, we utilized a hand-held retinal camera to perform RFA during open heart surgery. We tried seven patients without any adverse reactions and found that this method is applicable to anesthetized patients but needs some improvements such as larger magnification and combined video system for simultaneous diagnosis in intraoperative use.For the second purpose, we also used the hand-held retinal camera for RFA in four patients diagnosed with brain death. Retinal circulation was detected by RFA in all cases, suggesting that blood flow in ophthalmic artery, the first intracranial branch of internal carotid artery, is preserved even after cerebral circulation ceases, or retinal circulation is maintained by collateral circulation from external carotid artery in the condition of brain death. In either case, RFA does not seem to be useful for differential diagnosis of presence or absence of cerebral circulation in brain death.