Aortic surgery, which includes replacing or reconstructing the ascending aorta, aortic arch, and proximal descending aorta, represents one of the most complex areas in cardiac surgery. Despite significant advancements in surgical techniques, perfusion management strategies, and neuroprotective measures, aortic arch surgery remains associated with a high perioperative risk, particularly concerning neurological complications. The earliest publications highlighting the role of transcranial Doppler (TCD) in aortic arch surgery emerged in the 1990s.1 However, its importance was overshadowed by the development of more advanced brain protection techniques.

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In Georgia, aortic arch surgery performed under deep hypothermia presents specific challenges. This approach is linked with complications such as consumptive coagulopathy, severe bleeding, the need for massive transfusion of blood components and clotting factors, kidney failure, and increased infection risk. Additionally, the absence of clotting factors and thrombus masses adds to the complexity of this procedure. These factors contributed to a notably high mortality rate for aortic arch surgeries performed under deep hypothermia in our clinic. Consequently, a decision was made to transition from deep hypothermia to the upper limits of mild hypothermia for aortic arch surgery. This necessitated the implementation of rigorous cerebral perfusion monitoring using transcranial Doppler (TCD), near-infrared spectroscopy (NIRS), and assessments of oxygen saturation in the jugular vein.

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The initial monitoring stage involved transcranial Doppler (TCD), which provides real-time data on cerebral blood flow changes. A decreased cerebral blood flow was associated with reduced oxygen concentration in venous blood, so TCD was the primary monitoring tool during aortic arch surgery.

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There are three main approaches to transcranial Doppler: orbital (via the ophthalmic artery), transtemporal (through the middle cerebral artery, ACM), and transoccipital (via the vertebral arteries). 

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Establishing TCD monitoring presented specific challenges, particularly related to the variability in the thickness of the cranial bone, which affects the quality of the transcranial window.2 Despite this, our experience showed that a trained researcher could obtain an adequate Doppler signal in nearly all patients. A unique holder was used to secure the transducer on both sides to eliminate variability in the signal caused by transducer movement and ensure continuous blood flow monitoring in real time. Blood flow profiles were examined in the ACM on both sides and in both common carotid arteries at several critical stages of the procedure: before switching to artificial circulation, after switching, at the start and during the progress of unilateral perfusion, and after the return to full circulation.

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Statistically, 15% of the population has an incomplete Circle of Willis, underscoring the importance of early diagnosis of reduced perfusion in the left hemisphere during unilateral perfusion, a standard practice in aortic arch surgery.3

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Decreased cerebral blood flow to various brain regions cannot be attributed solely to anatomical factors. Other potential causes include embolism, vasospasm, and reduced perfusion pressure. Transcranial Doppler allows for the early detection of these changes, enabling prompt intervention. These interventions involve transitioning to bilateral perfusion or employing strategies such as hypercapnia or the administration of vasoactive drugs, ultimately improving cerebral perfusion and patient outcomes.

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Hyperperfusion of the brain, accompanied by elevated intracranial pressure and fluid accumulation within the interstitial space (edema), results in significant changes that can be detected through alterations in the blood flow profile. These changes provide valuable information that may help prevent complications. Near-infrared spectroscopy (NIRS) is another monitoring technique with limitations and considerations. While there is no universal consensus on the normal values, a 20% decrease from the baseline is typically considered pathological, and it is generally accepted that values should remain above 50%.4 However, NIRS does not measure oxygen saturation across the entire brain; it only captures data from the surface of the frontal cortex at an average depth of 2.5 centimeters. In elderly patients, cortical atrophy causes the brain tissue to recede from the skull bones, reducing the sensitivity of NIRS and making it less reliable for assessing cerebral perfusion.4 Moreover, the application of ice packs for brain hypothermia has been shown to impair the accuracy of NIRS readings significantly.4 Severe hyperhidrosis can also lead to false changes in NIRS values, further limiting its reliability in such cases.4

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Transcranial Doppler (TCD), on the other hand, offers a broader and more detailed assessment of cerebral perfusion. Normative values for TCD readings in different cerebral arteries during unilateral or bilateral perfusion have not been definitively established. However, TCD enables the measurement of cerebral blood flow velocity in the anterior, middle, and posterior cerebral basins, providing a comprehensive overview of brain perfusion compared to NIRS.4 While skull bone thickness can affect the transcranial Doppler signal, our experience indicates that contraindications for its use are rare, and no adverse effects arising from extracranial factors were observed in our practice. Using a transducer holder further ensured the stability of the transducer position throughout the procedure, enhancing the reliability and objectivity of the acquired data.4

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It is important to emphasize that transcranial Doppler should not be viewed as an alternative to NIRS or the measurement of oxygen saturation in the jugular vein. Instead, these methods complement each other, enabling comprehensive brain perfusion and function monitoring.

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Cerebral ischemia and stroke are significant complications associated with aortic arch surgery, posing substantial risks to patient quality of life and contributing to increased mortality rates. These complications often arise from disruptions in cerebral perfusion, such as those caused by unilateral perfusion in the presence of atherosclerotic vascular lesions, incomplete formation of the Circle of Willis, or vasospasm. Additionally, perfusion cessation during hypothermic circulatory arrest further exacerbates the risk.

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To mitigate these complications, it is crucial to implement robust strategies for monitoring and optimizing cerebral perfusion alongside continual advancements in surgical techniques and adopting innovative approaches. Historically, cerebral perfusion monitoring relied on invasive techniques, such as arterial pressure measurement and cerebral oximetry, which assessed brain oxygen saturation. However, these methods provided limited insights into the regional distribution of cerebral blood flow and were often insufficient for dynamic intraoperative management.5

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Transcranial Doppler ultrasonography (TCD) has emerged as a non-invasive, safe, and effective alternative. TCD enables real-time monitoring of cerebral blood flow, offering a dynamic tool for assessing and optimizing cerebral perfusion during surgery. This approach allows surgeons to continuously track cerebral blood supply and swiftly address any emergent threats to neurological integrity.

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This study aims to evaluate the role of transcranial Doppler ultrasonography (TCD) in monitoring and optimizing cerebral perfusion during aortic arch surgery. The hypothesis posits that using TCD for cerebral perfusion optimization will improve postoperative neurological outcomes in patients undergoing this high-risk surgical procedure.