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Autonomous robotic transcranial Doppler: A new standard of care in open aortic arch surgery?

Liverpool Heart and Chest Hospital (LHCH) has become the first European heart centre to purchase NovaSignal’s NovaGuide—a new, autonomous robotic transcranial Doppler (TCD) system for perioperative monitoring.

The device was purchased by the Liverpool team as part of a strategy to reduce stroke and delirium in patients undergoing open aortic arch surgery.

Mark L Field, honorary clinical professor and clinical lead for Thoracic Aortic Surgery at LHCH, shares a case in which a patient underwent total aortic arch replacement with frozen elephant trunk (FET), demonstrating how the management of cerebral protection during deep hypothermic circulatory arrest may be improved with autonomous TCD.

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eurological impairment during open aortic arch surgery, whether that be stroke, transient ischaemic attack, or injury to the recurrent laryngeal nerve, is a major issue undermining meaningful outcomes. Longterm cognitive dysfunction has long been a concern in aortic surgery, however, more recently, acute confusional state and delirium have been recognised as a significant challenge for patients, family, and healthcare resources. Data from Liverpool, UK, suggest an average stroke risk of 9% and a delirium rate of 30% in patients undergoing total aortic arch replacement. Typical adjunctive neuroprotective strategies during such cases, apart from pharmacoprotective measures,

include core cooling, scalp cooling and anterograde cerebral perfusion (ACP)/retrograde cerebral perfusion (RCP). Contemporary neuromonitoring for these cases include bispectral index (BIS) and near infrared spectroscopy (NIRS) monitoring. TCD has been explored in the past during such operations, but devices were cumbersome, high maintenance and unreliable. However, assuming these challenges could be solved, TCD has the potential to inject a level of sophistication and nuance to neuromonitoring, resulting in patient-specific neuroprotective strategies.

NovaSignal’s NovaGuide has the potential to deliver this promise.

Neurological injury following open aortic arch surgery is the Achilles’ Heel of aortic arch surgery with stroke rates of around 10% and acute delirium rates of around 30%. These complications have a significant impact on patients, families, and healthcare resources.

It is hoped that minimising instrumentation of the cerebral vasculature, whilst ensuring minimum effective cerebral blood flow with TCD, will reduce the risk of stroke and cerebral oedema that contributes to delirium.”

Autonomous robotic TCD: A new standard of care?

Autonomous TCD is being explored in the setting of open aortic arch surgery and early experience in Liverpool, UK, suggest a number of benefits: The device was easy to set up and required minimal maintenance, allowing a non-specialist to automatically find the acoustic window and optimise the signal.

Normal neuromonitoring devices could be used concurrently including BIS and NIRS as well as a cooling cap.

We were able to determine “minimal therapeutic target” flows as the middle cerebral flow at target core temperature for DHCA. We were able to measure reverse bilateral MCA flow with retrograde cerebral perfusion.

We were able to measure bilateral MCA flow with unilateral anterograde cerebral perfusion.

MTT flow was lower than we would generally flow in adjunctive ACP and RCP. The entire Circle of Willis could be interrogated.

The NovaGuide allows a patientspecific approach to neuroprotection.

Ultimately, more data are required to understand the impact on stroke and delirium.

Autonomous TCD has the potential to inject a level of sophistication and nuance to neuromonitoring, resulting in patient-specific neuroprotective strategies.”

Mark L Field Mark L Field (second from the left) and team at the Liverpool Heart and Chest Hospital

Case report: Use of autonomous robotic TCD in open total aortic arch surgery Patient profile: A patient presented with acute type B aortic dissection with evolving acute type A intramural haematoma requiring repair of her aortic root, total aortic arch and placement of a FET. Procedure: The autonomous TCD system was positioned along with BIS and NIRS monitoring (Figure 1a: typical arrangement). Signal from the middle cerebral artery (MCA) was autonomously acquired and maintained throughout the case (Figure 1b: typical displays). Routine adjunctive cerebral protection strategies

used include core cooling, scalp cooling, as well as a mix of RCP and ACP. Following sternotomy, the patient was centrally cannulated for cardiopulmonary bypass and cooling commenced with a target core body temperature of 22oC. A noticeable and incremental decrease in MCA flow was noted during cooling, around 50%, just prior to deep hypothermic circulatory arrest (DHCA). The MCA flow prior to DHCA was adopted as our minimum therapeutic target (MTT) flow for RCP/ACP. Following circulatory arrest, retrograde cerebral perfusion was commenced via the superior

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vena cava, starting at 100ml/min and incrementally increased, while observing reverse flow in the MCA bilaterally. A flow of 300ml/min achieved negative MTT, several fold less than we would normally flow retrogradely (500–800ml/min directed by central venous pressure 25–50mmHg).

Having dissected out the aortic arch for reconstruction, ACP was commenced up the right common carotid artery with a 13Fr cannula and flow incrementally increased from 100ml/min. MTT was achieved bilaterally at 300mls/min without requiring two or three vessel cannulation again significantly lower than we would normally flow (10ml/kg/min). NIRS was maintained at these flows. A valve sparing root was completed as well as total arch and FET. The patient was returned to the intensive care unit and extubated the following day free of stroke or delirium.

Conclusion: The autonomous TCD helped us avoid two and three vessel instrumentation for ACP whilst giving us the assurance of bilateral MCA flow to the MTT. Pictured: Arrangement of autonomous robotic transcranial Doppler monitoring during an operation.

A) TCD in place allowing additional monitoring with BIS and NIRS, as well as placement of cooling cap, endotracheal tube, transoesophageal echocardiography, nasopharyngeal temperature, and central venous access.

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B) Visual displays showing autonomous bilateral signal acquisition and MCA flow.