Clinical Validation of a Novel Ultrasound Probe (RescueDoppler) During Physiological Perturbations and Initiation Of- and Weaning from Cardiopulmonary Bypass 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.