CEREBROVASCULAR ASSESSMENT OF THE HIGH-RISK PATIENT - THE ROLE OF TRANSCRANIAL DOPPLER ULTRASOUND

With increased attention to the causes and effects of neurologic injur y related to cardiopulmonary bypass anesthesia and surgery, multiple m odality examination and monitoring of cerebral function and perfusion in the perioperative period may prove to be advantageous. Transcranial Doppler examination and monitoring is inexpensive, noninvasive, safe, provides unique information about the functional status of the intrac ranial circulation, and complements the duplex Doppler study of the ex tracranial carotid vessels of the neck for preoperative evaluation of the surgical patient. The transcranial Doppler examination permits qua ntitation of blood flow velocity of the intracranial vessels, evaluati on of autoregulatory capacity and vasomotor reserve, determination of symmetry of flow velocity in the circle of Willis, assessment of colla teral circulatory capacity, examination of vessels not accessible to t he duplex Doppler and serves as a baseline for intraoperative monitori ng and the postoperative examination. Noninvasive, unilateral or bilat eral, continuous monitoring of brain blood flow velocity intraoperativ ely or postoperatively with trending, storage, and correlation with ot her physiologic variables provides evidence of cerebral perfusion, occ urrence and rate of cerebral embolism, and continuous monitoring of th erapeutic interventions. A review of the incidence of stroke and neuro psychologic deficit after bypass surgery is focused on parameters amen able to diagnosis using transcranial Doppler. Patient-specific risk fa ctors for neurologic injury derived from previous studies are discusse d as well as risk factors that are related to anesthetic and surgical management and equipment. A description of Doppler technology and the correlation of transcranial Doppler findings with angiography and radi onucleotide scans establishes the accuracy of the Doppler examination. The preoperative examination, provocative tests of vasomotor reserve, the evaluation of cerebral collateral circulation, and examples of Do ppler applications are discussed. Copyright (C) 1996 by W.B. Saunders Company.