FLOW VELOCITY OF CENTRAL RETINAL ARTERY AND RETROBULBAR VESSELS DURING CARDIOVASCULAR OPERATIONS

Objective: Both blood how monitoring and pressure monitoring are neces sary to avoid inadequate cerebral perfusion during cardiovascular oper ations. Inasmuch as transcranial Doppler ultrasonography does not prov ide a consistently good signal, especially during cardiopulmonary bypa ss, we examined the blood flow through the central retinal artery, whi ch has proved to reflect an obstruction of the carotid artery. Method: Twenty-eight consecutive cases were examined with a 5 or 7.5 MHz conv entional echocardiographic probe. Correlation between the maximal velo city at the central retinal artery and systolic blood pressure was exa mined. The blood flow of the central retinal artery and retrobulbar ve ssels was examined during selective or retrograde cerebral perfusion o r intraaortic balloon pumping. Results: Blood flow could be clearly vi sualized but disappeared below a certain pressure in every case. With data from 478 measuring points, systolic blood pressure correlated wit h maximal velocity (r = 0.6902, p < 0.0001). The blood pressure-axis i ntercept, known as ''critical closing pressure,'' was 35.8 +/- 14.8 mm Hg, varying among individuals and bilateral eyes. Pulsatility index i ncreased 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 how during anastomosis of the ipsilateral artery. During retrog rade cerebral perfusion, blood flow was detectable at the retrobulbar vessels. During intraaortic balloon pumping, the central retinal arter y flow was augmented on inflation of the balloon. Conclusion: Orbital vessel monitoring provides the critical closing pressure of the centra l retinal artery and confirms patency of the circle of Willis. The eye can be ''an acoustic window'' into intracranial blood flow during car diovascular surgery.