The application of retinal fluorescein angiography to brain circulation monitoring.

为探讨视网膜荧光素血管造影术(RFA)在体外循环相关脑空气栓塞术中的诊断和脑死亡患者无脑循环的诊断中的应用价值。首先，我们建立了犬脑空气栓塞模型，通过颈总动脉注射异硫氰酸荧光素葡聚糖而不积聚荧光素染料，并通过颈总动脉注入一定量的空气诱导视网膜空气栓塞。在这个模型中，当注入超过0.1ml的空气时，可以检测到视网膜空气栓子。我们发现，在正常血压动物中，空气栓子造成的动脉阻塞在注射空气后1分钟内解除，而当平均动脉压降低到50毫米汞柱时，动脉阻塞持续3分钟以上。这些结果表明，在低血压条件下，如从体外循环中苏醒，空气栓塞会导致明显的脑缺血。此外，在心脏直视手术期间，我们使用手持视网膜摄像机进行RFA。我们尝试了7例患者，没有任何不良反应，发现这种方法适用于麻醉患者，但需要改进，如放大倍数更大，术中使用联合视频系统进行同步诊断。对于第二个目的，我们还使用手持视网膜相机对4例脑死亡患者进行了RFA。所有病例RFA均检测到视网膜循环，提示在脑循环停止后，眼动脉--颈内动脉的第一个颅内分支--的血流仍得以保留，或在脑死亡的情况下，通过颈外动脉的侧支循环维持视网膜循环。无论在哪种情况下，RFA似乎都不能用于鉴别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.