Clinical Validation of a Novel Handsfree Doppler Ultrasound Device, RescueDoppler, in Adult Cardiac Surgery Patients

During high- risk surgery and critical illness, the main goal is to maintain an adequate cardiac output and oxygen delivery to vital organs. Accurate hemodynamic monitoring is essential in current critical care medicine and high-risk surgery. A systematic review and meta- analysis of non-invasive techniques compared to thermodilution as the reference standard, revealed only modest agreement and inadequate percentage error despite advances in medical technology over the last decades. This highlights the urgent need for reliable non-invasive method to monitor the perfusion of vulnerable organs during hemodynamically unstable situations.

During cardiac arrest (CA), the quality of cardiopulmonary resuscitation (CPR) relies on adequate chest-compressions and early shock when indicated. As such, the recommendations in international and European CPR guidelines consist of several methods to assess the quality of CPR. The pulse has been one of the most important diagnostic signs, first described in ancient medicine. Puls-check is still one of the recommended methods to guide CPR and evaluate possible return of spontaneous circulation (ROSC). However, the pulse-check is imprecise. In one study, 10% of healthcare workers detected pulse when the patient had cardiac arrest and only 45% were able to palpate pulse when the systolic blood pressure was higher than 80 mmHg. In addition, pulse check does not predict the magnitude of blood flow. In patients with out-of-hospital cardiac arrest (OHCA), a correlation has been shown between high end tidal carbondioxide (EtCO2) values during CPR and ROSC, as well as improved long-term survival. This method is recommended in international CPR guidelines as a decision-making tool to confirm the correct placement of the endotracheal tube in the trachea, serve as a quality indicator of CPR, and detect the return of a pulsatile heart rhythm. However, despite its utility, this method has known limitations in identifying ROSC and blood flow, and it has limited capacity to differentiate between various causes of cardiac arrest.

In cardiac surgery, particularly during cardiopulmonary bypass (CPB), patients experience various manipulations and circulatory changes that increase their vulnerability to complications in multiple organs. CPB is an extracorporeal technique that diverts the patient's blood away from the heart and lungs, rerouting it outside the body. This method replaces the normal physiological functions of the lungs and heart by managing oxygenation, ventilation, and maintaining adequate blood flow through several components of the CPB machine, including the pump, oxygenator (for gas exchange), tubing, and heat exchange units. The CPB pump functions like an artificial heart, generating continuous blood flow through a propeller mechanism. Blood is collected from the right heart or the vena cava (superior and/or inferior) and is then fully oxygenated before being returned via a cannula into the ascending aorta.

At St. Olavs Hospital, Trondheim University Hospital, the routine practice involves cross-clamping the ascending aorta and administering a cardioplegia solution-a cold fluid enriched with electrolytes and medication-to induce cardiac electromechanical silence during procedures. These physiological hemodynamic changes are of significant interest to the study group, as they involve transitions in blood flow from pulsatile (with a fully functioning heart) to non-pulsatile (due to cross-clamping and cardiac electromechanical silence) during the initiation of CPB, and back to pulsatile during weaning. While cerebral perfusion during CPB has been assessed in previous studies, to our knowledge, no prior research has specifically investigated cerebral blood flow during the initiation and weaning phases of CPB.

Protocols for hemodynamic management during CPB aim for a target flow of 2.2-2.8 liters/min/m², which approximates normal physiological values. It is recommended to monitor this flow based on oxygenation and metabolic parameters, including central venous oxygenation (SvO2), oxygen extraction (O2ER), Near-Infrared Spectroscopy (NIRS), venous carbon dioxide (VCO2), and lactate levels.

Critical illness and intensive care medicine involve a variety of medical conditions, making tailored monitoring challenging. Many available monitoring tools are invasive, require advanced equipment (such as PICCO and pulmonary artery catheters), or involve time-consuming interventions like passive leg raises, which may lead to the omission of hemodynamic guidance in busy clinical settings.

Ultrasound has emerged as a vital diagnostic and decision-making tool in critical care, particularly echocardiography, which can assess cardiac activity and function. However, it is user-dependent, requires specialized knowledge, and provides only a snapshot of the clinical situation.

The brain is particularly sensitive to hypoxia, and during cardiac arrest or surgery, hypoperfusion and vasoplegia can impair oxygen delivery, affecting treatment outcomes. Near-Infrared Spectroscopy (NIRS) is used to monitor oxygen delivery to the frontal brain during cardiac surgery, offering feedback to the treatment team on when to adjust hemodynamic support. Research indicates that a 20% decrease in regional hemoglobin oxygen saturation (rSO2) increases the risk of neurological complications.

Monitoring cerebral blood flow in the middle cerebral artery (MCA) with Transcranial Doppler (TCD) provides real-time data on blood flow during surgery. A significant reduction in MCA blood flow can signal complications, allowing for timely intervention to prevent brain ischemia. However, TCD requires ultrasound expertise and may present challenges in identifying the insonating window.

Carotid Doppler Ultrasound (CD) is an important method for monitoring blood flow and diagnosing carotid artery stenosis. Recently, it has been explored as a non-invasive hemodynamic monitoring tool. While some studies show promising results, the current literature presents mixed findings due to variations in patient populations and study designs. Like other ultrasound techniques, CD is user-dependent and offers only a snapshot of the situation.

In all the clinical situations mentioned, a precise, non-operator-dependent tool for continuous monitoring to guide and tailor treatment would be highly valuable. RescueDoppler is a novel Doppler ultrasound device designed to continuously measure blood flow in the common carotid artery. The concept originated from the need for improved methods to guide cardiopulmonary resuscitation (CPR) and monitor blood flow across various cardiac rhythms.

With the increasing body of research supporting carotid Doppler ultrasound as a non-invasive hemodynamic monitoring tool, the RescueDoppler technique becomes even more compelling. It is user-independent, featuring a self-adhesive patch that can be easily positioned using clear anatomical landmarks on the neck. While animal studies in cardiac arrest piglets show promising results, and unpublished data from a study of RD in in-hopsital and out-of-hospital cardiac arrest show that the RescuDoppler device is feasible. More human studies are still needed.

The overall aim of the study is to evaluate the RescueDoppler system's performance as a circulatory monitoring tool beyond feasability in patients going through different hemodynamic changes in a safe, clinical setting for better patient outcome. We will investigate subjects, aged 18-80, male and female, accepted for cardiac surgery either with coronary artery disease and/or valve or aortic disease at St. Olav´s Hospital, Trondheim, Norway. This is a single-center clinical study. We will include 42 patients. The enrollment periode will be Q1-Q4 2024. There will be no randomization or blinding in this study.

The two phases of the investigation will be conducted sequentially.

The primary investigation will compare and by that validate the RescueDoppler device against conventional Doppler ultrasound (CD). Blood flow velocities in the left common carotid artery will be measured first using CD, followed by the RD. The primary objective is to evaluate if the RescueDoppler device is noninferior to CD, by comparing the flow patterns and velocities recorded with the two methods. The primary endpoint is peak systolic velocity, secondary outcomes are diastolic velocity, time-averaged blood flow velocity (TAV) among others.

During cardiac surgery and CPB, the RescueDoppler patch will remain positioned over the left carotid artery. We will measure blood flow during key phases such as initiation of CPB, aortic cross-clamping, and weaning from CPB, and compare these measurements with hemodynamic and respiratory variables. The primary objective of this part is to evaluate the blood flow signals recorded continuously by the RescueDoppler device by assessing in subjects undergoing circulatory changes from pulsatile- to non-pulsatile blood flow when initiating- and back when weaning from CPB. The primary endpoint is time-averaged blood flow velocity (TAV).

Within the study, data about signal quality, fastening device functionality, data signal management and usefulness of blood flow information will be collected. Additionally, data will be collected to evaluate the initial clinical safety as per intended use.