Hemodynamic Evaluation and Assessment of DIRECT myocaRdial and Sublingual Capillary Perfusion in Thoracic Surgery Patients on Cardiopulmonary Bypass

Microcirculatory Perfusion

cardiac surgery, microcirculation, capillary perfusion

After cardiac surgery, some people may experience problems with their circulation or how well the heart pumps. This can occur because the smallest blood vessels in the heart do not function properly. When these vessels don't work correctly, organs and tissues don't receive enough oxygen and nutrients, which can lead to circulatory problems and organ damage. Typically, treatments focus on improving the larger blood vessels, such as blood pressure and heart function, but the investigators don't yet know enough about the smallest blood vessels. In this study, the investigators measure blood flow using a special camera (a microscope) at two locations: under the tongue and directly on the heart. Measurements under the tongue are already performed more frequently, but measurements directly on the heart are still new. If the investigators can demonstrate that differences in cardiac blood flow can also be observed under the tongue, it will become easier to conduct research on microcirculation. The use of the device is safe, and measurements are performed under strict supervision and control by experienced physicians and researchers. Ultimately, the investigators hope to use this knowledge to better prevent or treat complications after cardiac surgery. The aim of this research is to investigate whether measurements of blood flow in the smallest blood vessels (microcirculation) on the heart provide the same information as measurements of microcirculation under the tongue. This appears to be describing a clinical study comparing sublingual and epicardial microcirculation monitoring techniques to potentially establish a less invasive method for assessing cardiac microvascular function in post-surgical patients.

Congruence of micro- and macrocirculation is essential in participants during the postcardiotomy period to maintain hemodynamic stability \[1,2\]. At the capillary (i.e. microcirculatory) level, gas and nutrient exchange occurs, while macrocirculation facilitates these exchanges by ensuring that blood flows with appropriate pressure and velocity. A mismatch in this relationship, where the capillary perfusion does not correlate with the macrocirculatory parameters, is frequently observed in patients with shock or heart failure \[3,4\]. This discrepancy is often caused by capillary leak or hemodilution. To date, treatment has primarily focused on correcting macroscopically observed variables or values derived from them and resulting in pressure- or flow-dependent therapies. While sublingual capillary perfusion measurements provide systemic insights, direct myocardial capillary perfusion assessment offers a direct and regional perspective. Unlike systemic capillary beds, myocardial perfusion is directly influenced by filling pressures, such as left ventricular end-diastolic pressure (LVEDP) \[5\]. Impaired myocardial capillary perfusion can lead to a cascade of cardiac dysfunction, including reduced oxygen delivery, inadequate nutrient exchange and making it vulnerable to ischemia or hibernation \[1\]. Current literature has examined intra- and postoperative sublingual (i.e., systemic) capillary perfusion following cardiac surgery \[5\]. Cardiopulmonary bypass (CPB), commonly used in many types of heart surgeries, inherently disrupts capillary perfusion due to its extracorporeal nature. The use of CPB alone triggers systemic inflammation, reperfusion injury and hemodilution, leading to the accumulation of metabolic waste products, formation of free oxygen radicals and perfusion alternations \[7\]. Additionally, the participants undergo an invasive cardiac procedure, accompanied by anesthesia and other contributing factors that negatively impact the capillary perfusion \[8\]. These alterations manifest in differences in microcirculatory parameters, including total vessel density (TVD), perfused vessel density (PVD), proportion of perfused vessels (PPV), microvascular flow index (MFI), and heterogeneity index (HI) \[9\]. Additionally, unloading the left ventricle (LV) unloading is posited to be critical for improving myocardial circulation. LV unloading is a promising concept that theoretically could improve capillary perfusion by reducing LVEDP and hence myocardial work. LV unloading could be particularly important for heart failure patients in acute cardiogenic shock. It may help promote myocardial circulation and prevent pulmonary edema. However, there is currently no robust scientific evidence to support these benefits and remains a subject of debate and philosophical discourse within the medical community \[11-13\]. To address this, the investigators aim to investigate whether capillary perfusion changes induced by CPB flow alterations, measured at sublingual and myocardial sites, provide consistent results. Additionally, the investigators will assess the effect of LV unloading on the capillary perfusion. The investigators will employ a handheld IDF-microcamera to perform real-time measurements of capillary perfusion. The investigators hypothesize that during hemodynamic alternations via CPB-flow sublingual and myocardial capillary perfusion measurements will show minimal differences and correlate with each other. This would supporting the validity of sublingual capillary perfusion measurements as a reliable, non-invasive proxy for the myocardial capillary perfusion status. Furthermore, the investigators anticipate an improvement in solely myocardial of both sublingual and myocardial capillary perfusion with LV unloading. These findings will significantly advance our understanding of the interaction between macro- and microcirculatory systems, providing a foundation for the use of sublingual measurements in both clinical and research settings. Ultimately, this could simplify monitoring techniques, enhance perioperative management, and help elucidate the mechanisms underlying persistent hemodynamic instability, guiding the development of more effective strategies to optimize postoperative outcomes

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