Robotically assisted devices in medicine represent a promising field that has been only partially applied to clinical practice. Initial evidence regarding the application of ra-TCD for a single-shot examination has been reported for instance by a multicenter study comparing ra-TCD and transthoracic echocardiogram for right-to-left shunt detection in stroke patients suggesting ra-TCD to be more effective.22 However, our study is the first to show that this new ra-TCD system allows to easily monitor cerebral hemodynamics in different hospital settings.
Feasibility in our population was remarkably high overall. Intensive care patients could be monitored for a few hours despite the presence of different invasive equipment such as endotracheal tube, tracheostomy and ECMO. In patients with an ICP probe the examination could be completed in most cases, except for two with a posterior site of insertion of the intracranial probe. Our study is the largest to date testing ra-TCD in the intensive care setting, confirming preliminary data of a study on 12 patients with subarachnoid hemorrhage that showed safety and efficacy of the same device.23 Due to its numerous applications, TCD has also been described as the “stethoscope of the brain” for critically ill patients.15 In fact, it easily allows an early identification of cerebral hemodynamic alterations, such as vasospasm, altered cerebral autoregulation, pulsatility index rise thus guiding clinical management. Ra-TCD, being operator-independent, might further boost this technique allowing prolonged monitoring of cerebral hemodynamics, thus becoming an integral part of neuromonitoring.
The highest feasibility was demonstrated in the stroke unit and the general neurological ward, with only a minority of cases where the examination was impeded by uncommon anatomical characteristics of patients. This preliminary data opens the field to the potential application of continuous monitoring of cerebral hemodynamics in ischemic stroke patients, for example after thrombectomy, where flow parameters in the recanalized vessel have shown to correlate with prognosis.24–26 Another possible application of ra-TCD is the prolonged monitoring of MCA signal in patients with asymptomatic carotid artery stenosis, where the detection of MES in the ipsilateral MCA significantly increases the risk to develop ischemic stroke.27 Prolonged monitoring would raise the chances of MES detection and help identify atherosclerotic plaques at higher risk of distal embolization.27
Concerning the comparison of blood flow velocities among ra-TCD and manual TCD, our study did not find any statistical difference. No real-world studies are available in literature comparing ra-TCD and manual TCD. However, since the device we utilized employs an already validated and widely tested TCD we think these results reinforce the validity of ra-ultrasound devices and their potential to expand hemodynamics monitoring in neurovascular patients.
Regarding TCD-related complications, only one patient reported moderate transient unilateral subcutaneous edema in the temporal region due to the probe’s mechanical pressure. The edema regressed quickly and spontaneously right after the end of the examination, and it was not considered a matter of concern by the authors. Nonetheless, it would be advisable to reduce the probe pressure on the temple. No similar reports are available in the literature, although the experience is scant so far. A previous study performing non-monitoring TCD examinations in 129 patients proved the device to be safe. Specifically, no serious adverse events were reported, while only two non-serious events were documented both unrelated to the device.23
TCD is a unique tool in detecting microemboli entering the MCA during heart surgery and cardiologic procedures, although the clinical relevance of these findings is still debated.8,9 In our study, prolonged TCD monitoring was easily performed during cardiological interventional procedures, opening the field for exploration of cerebral hemodynamic parameters and MES detection in this very interesting setting. On the other hand, ra-TCD was not feasible during neurological interventional procedures such as acute mechanical thrombectomy and carotid stenting, because the probes were radiopaque, not allowing patients to undergo intraprocedural radiological checks. An updated version of the ra-TCD with radiotransparent probes has been recently released, but it needs to be re-evaluated in this setting. Ra-TCD was also not feasible during open carotid surgery, because the size of the device interfered with the surgical field. This is a drawback, as detection of MES during CEA showed a significant relationship with perioperative cerebral complications and new ischemic lesions in different studies.10,11 Ra-TCD has a great potential as it could be applied to study the risk of perioperative cerebral complications after different kinds of surgery (eg. orthopedic surgery), expanding the data of first explorative reports.29
Altogether, the results of the current study show the need for further technological advancement to perform operator-independent monitoring of cerebral hemodynamics and guide the improvement of cardiovascular or neurovascular procedures to reduce stroke burden.