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Cerebral monitoring with transcranial Doppler ultrasonography improves neurologic outcome during repairs of acute type A aortic dissection.Estrera AL, Garami Z, Miller CC, Sheinbaum R, Huynh TTT, Porat EE, Allen BS, Safi HJ. J Thorac Cardiovasc Surg 129:277-285, 2005.Reviewer: Mark A. Chaney, MD
Abstract: Neurologic complications following repair of acute type A aortic dissection remain substantial. The use of M-mode transcranial Doppler monitoring to verify cerebral blood flow during repair may help decrease cerebral ischemia by detecting malperfusion. These investigators analyzed the use of M-mode transcranial Doppler monitoring during repair of acute type A dissection with regard to neurologic outcome. They prospectively studied 56 patients (nonrandomized) undergoing repair of acute type A dissection. Repairs included profound hypothermic circulatory arrest and retrograde cerebral perfusion. Half of the patients were subjected to M-mode transcranial Doppler monitoring, which altered operative cannulation and guided retrograde cerebral perfusion flow in 28.5% (8/28) and 78.6% (22/28) of cases, respectively. The other half received no monitoring or modification and served as controls. Two patients presented with preoperative stroke, one in each group. One operative death occurred in each group. In-hospital mortality and the occurrence of new stroke were not significantly different between the two groups. However, temporary neurologic dysfunction occurred significantly less often in patients subjected to monitoring (14.8% [4/27] versus 51.8% [14/27], p = 0.008). The investigators conclude that by helping ensure cerebral blood flow by using M-mode transcranial Doppler monitoring and correcting potential cerebral malperfusion by modifying operative technique, neurologic outcome can be improved during repair of acute type A aortic dissection. Comments: The incidence of stroke during repair of acute type A aortic dissection may be as high as 10% and is associated with increased early and late mortality. Temporary neurologic dysfunction (confusion, agitation, delirium) varies in incidence from 10% to 30%. Like stroke, temporary neurologic dysfunction has been linked to detrimental long-term consequences. Thus, more reliable methods of cerebral protection are needed during these complex aortic repairs. Stroke is likely caused by cerebral macroembili and/or malperfusion while temporary neurologic dysfunction is likely caused by cerebral microemboli and/or malperfusion. Both stroke and temporary neurologic deficits may be worsened by suboptimal cerebral protection. Many methods of cerebral monitoring during complex aortic repair have been investigated, including transcranial Doppler, near-infrared spectroscopy, electroencephalography, and jugular venous oxygenation monitoring. While retrograde cerebral perfusion was used by these clinical investigators, recent evidence suggests that antegrade cerebral perfusion might be more effective in protecting the brain during periods of hypothermic circulatory arrest than either retrograde cerebral perfusion or no perfusion at all. These investigators found significant cerebral malperfusion (defined as any reduction in middle cerebral artery blood flow velocity to less than 50% of baseline) in almost 30% of monitored patients (8/28). In these eight patients, the operative procedure was modified to improve cerebral blood flow (as assessed via Doppler) and all did well (no strokes, one patient with temporary neurologic dysfunction). Furthermore, almost 80% of monitored patients required modification of retrograde cerebral perfusion to optimize potential cerebral protection (goal was reversal of flow in middle cerebral artery). However, this monitoring technique and clinical investigation have substantial limitations. M-mode transcranial Doppler monitoring requires an experienced ultrasonographer dedicated to monitoring, may be limited by patient variables, and does not quantify actual blood flow (velocities are assessed). Furthermore, this clinical investigation was nonrandomized (subject to selection bias) and did not enroll a true control group (patients with monitoring but with no maneuvers performed). The use or non-use of M-mode transcranial Doppler monitoring was determined on the basis of the availability of the device and ultrasonographer. Thus, generated conclusions are limited. In summary, cerebral malperfusion remains a substantial clinical problem during complex aortic surgery. Whether cannulation of the femoral artery, axillary artery, or ascending aorta is performed, some sort of assessment needs to be done verifying blood flow to the brain. Thus, identification of cerebral malperfusion requires some sort of cerebral monitoring. Numerous monitoring techniques have been clinically tested and, at the present time, none stand out. M-mode transcranial Doppler monitoring, as used by these clinical investigators, has the potential to detect cerebral malperfusion and direct modification of the operative technique to increase cerebral blood flow and enhance neurologic outcome following these challenging surgeries. Well-designed studies (prospective, randomized) will be required in order to determine the true benefits of this monitoring modality during complex aortic repair. Table of Contents:
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