[Detection of cerebral microembolisms during extracorporeal circulation with pulsatile flow using transcranial Doppler monitoring].

The incidence of focal neurological deficits and diffuse neuropsychiatric disorders in patients undergoing open-heart surgery still remains unacceptably high. The consensus is increasing that diffuse microembolism is the most important cause. Changes in blood flow velocity in the middle cerebral artery were investigated by transcranial Doppler sonography in 26 patients regarding the effect of continuous and pulsatile perfusion during extracorporeal circulation. The quotient of systolic and diastolic flow velocity was significantly increased in patients with pulsatile perfusion. Abnormal high-frequent Doppler-signals were registered in 8 patients using pulsatile perfusion without diastolic basic flow. All the other patients in whom continuous pump flow was applied (13) did not reveal any signs of hemodynamic disturbances. In the group treated with pulsatile perfusion the systolic pressures before and behind the oxygenator were significantly increased in patients with high-frequent Doppler-signals which are likely to be caused by gaseous microemboli. Investigating one type of four different oxygenators no cerebral hemodynamic alterations were recorded even during pulsatile perfusion. The use of membrane oxygenators and arterial filters during pulsatile perfusion cannot completely prevent the occurrence of gaseous microemboli; their principle causes are supposed to be the level of perfusion pressure, the flow velocity and the design of oxygenator.