Orihashi K, Matsuura Y, Sueda T, Shikata H, Morita S, Hirai S, Sueshiro M, Okada K
First Department of Surgery, Hiroshima University School of Medicine, Japan.
J Thorac Cardiovasc Surg. 1997 Dec;114(6):1081-7. doi: 10.1016/S0022-5223(97)70023-0.
Both blood flow monitoring and pressure monitoring are necessary to avoid inadequate cerebral perfusion during cardiovascular operations. Inasmuch as transcranial Doppler ultrasonography does not provide a consistently good signal, especially during cardiopulmonary bypass, we examined the blood flow through the central retinal artery, which has proved to reflect an obstruction of the carotid artery.
Twenty-eight consecutive cases were examined with a 5 or 7.5 MHz conventional echocardiographic probe. Correlation between the maximal velocity at the central retinal artery and systolic blood pressure was examined. The blood flow of the central retinal artery and retrobulbar vessels was examined during selective or retrograde cerebral perfusion or intraaortic balloon pumping.
Blood flow could be clearly visualized but disappeared below a certain pressure in every case. With data from 478 measuring points, systolic blood pressure correlated with maximal velocity (r = 0.6902, p < 0.0001). The blood pressure-axis intercept, known as "critical closing pressure," was 35.8 +/- 14.8 mm Hg, varying among individuals and bilateral eyes. Pulsatility index increased after cardiopulmonary bypass (1.095 +/- 0.245 to 1.525 +/- 0.268, p < 0.0001). Patency of the circle of Willis was confirmed by the blood flow during anastomosis of the ipsilateral artery. During retrograde cerebral perfusion, blood flow was detectable at the retrobulbar vessels. During intraaortic balloon pumping, the central retinal artery flow was augmented on inflation of the balloon.
Orbital vessel monitoring provides the critical closing pressure of the central retinal artery and confirms patency of the circle of Willis. The eye can be "an acoustic window" into intracranial blood flow during cardiovascular surgery.
