Hemodynamic Profiles and Macro-Microcirculatory Coherence in Liver Transplantation: an Integrative Approach in the Immediate Postoperative Period

Overview

Hemodynamic instability is a common and serious condition in patients undergoing liver transplantation and is associated with increased morbidity and mortality if not promptly recognized and treated. It results from multiple interacting factors, including blood loss, changes in vascular tone, cardiac dysfunction, and complications related to the surgical procedure. Traditional monitoring strategies focus on global hemodynamic variables such as blood pressure and cardiac output. However, these parameters may not accurately reflect tissue perfusion or oxygen delivery at the microcirculatory level. As a result, patients may appear hemodynamically stable while still experiencing inadequate tissue oxygenation. This study aims to evaluate hemodynamic instability using an integrative physiological approach based on the interaction between different components of the cardiovascular system. Specifically, the study will assess four key interfaces: the relationship between the heart and the arterial system, the coherence between macrocirculation and microcirculation, the interaction between venous return and the right atrium, and the coupling between the right ventricle and the pulmonary circulation. The main objective is to identify distinct hemodynamic profiles in patients during the immediate postoperative period following liver transplantation. In addition, the study will evaluate the incidence of tissue hypoxia within the first 24 hours and its association with clinical outcomes, including 30-day evolution. This is a prospective observational study conducted in adult patients admitted to the intensive care unit after liver transplantation who develop hemodynamic instability requiring vasoactive support. During the first 24 hours, multimodal hemodynamic monitoring will be performed, including assessment of cardiac function, vascular tone, venous congestion, pulmonary circulation, and markers of tissue perfusion such as lactate levels and capillary refill time. By integrating these variables, patients will be classified into different hemodynamic profiles according to the predominant underlying mechanism. This approach aims to improve the understanding of cardiovascular dysfunction in this setting and to support more individualized and physiologically guided management strategies.

Hemodynamic instability during liver transplantation is a complex and multifactorial condition resulting from the interaction between the pathophysiological alterations of advanced cirrhosis, the hemodynamic impact of the surgical procedure, and perioperative complications. Patients with end-stage liver disease typically exhibit a hyperdynamic circulatory state characterized by reduced systemic vascular resistance, increased cardiac output, and impaired vascular responsiveness. These baseline alterations are further challenged during transplantation by factors such as hemorrhage, fluid shifts, vena cava clamping, reperfusion syndrome, myocardial dysfunction, vasoplegia, graft-related factors, and infectious complications. From a physiological perspective, the cardiovascular system can be understood as a network responsible for the generation, transmission, and utilization of energy to ensure adequate tissue perfusion. Hemodynamic instability may therefore be interpreted as a disruption in one or more of these components. However, conventional hemodynamic monitoring strategies are primarily based on macrocirculatory variables, such as mean arterial pressure and cardiac output, which may not adequately reflect microcirculatory perfusion or cellular oxygen utilization. This dissociation between global hemodynamic variables and tissue perfusion has been described as a loss of hemodynamic coherence. In this context, patients may present with apparently adequate systemic hemodynamic parameters while still developing tissue hypoxia and organ dysfunction. This limitation highlights the need for a more integrative approach to hemodynamic assessment. The present study is based on the evaluation of four key hemodynamic interfaces that represent fundamental components of cardiovascular function: (1) left ventricle-arterial system coupling, which reflects the efficiency of energy transfer from the heart to the arterial system; (2) macro-microcirculatory coherence, which describes the relationship between systemic hemodynamics and tissue-level perfusion; (3) venous return-right atrial interaction, which determines the capacity of the system to sustain cardiac output; and (4) right ventricle-pulmonary circulation coupling, which reflects the interaction between the right heart and pulmonary vascular load. The disruption or decoupling of these interfaces may lead to different patterns of hemodynamic inefficiency, contributing to the heterogeneity observed in critically ill patients undergoing liver transplantation. Identifying these patterns may provide a more precise understanding of the underlying mechanisms of instability and allow for a more individualized therapeutic approach. The primary objective of this study is to characterize and categorize hemodynamic profiles in adult patients during the immediate postoperative period following liver transplantation. The study also aims to determine the incidence of tissue hypoxia within the first 24 hours after surgery and to evaluate its association with clinical outcomes, including 30-day mortality and organ dysfunction. This is a prospective, observational study conducted in the intensive care unit of a high-complexity hospital. Adult patients admitted after liver transplantation who develop hemodynamic instability, defined as the requirement for vasoactive agents to maintain a mean arterial pressure of at least 65 mmHg, will be included. Patients with conditions that significantly interfere with hemodynamic assessment or limit short-term prognosis will be excluded. During the first 24 hours after ICU admission, patients will undergo multimodal hemodynamic monitoring. Data collection will include macrocirculatory variables (such as arterial pressure and cardiac output), echocardiographic assessment of ventricular function, indicators of venous congestion, variables related to pulmonary circulation, and markers of tissue perfusion. Tissue hypoxia will be defined using a combination of clinical and biochemical criteria, including elevated lactate levels, prolonged capillary refill time, reduced urine output, and alterations in oxygenation parameters. Based on these measurements, the degree of coupling between the different cardiovascular interfaces will be assessed, and patients will be classified into hemodynamic profiles according to the predominant pathophysiological mechanism. These profiles will be analyzed in relation to the occurrence of tissue hypoxia and clinical outcomes. Statistical analysis will be performed to evaluate differences between hemodynamic profiles, temporal trends during the first 24 hours, and their association with outcomes at 30 days. Continuous variables will be described using appropriate measures of central tendency and dispersion, while categorical variables will be expressed as proportions. Comparative and exploratory analyses will be conducted as appropriate. This study aims to provide a comprehensive physiological framework for understanding hemodynamic instability in liver transplantation. By integrating macrocirculatory and microcirculatory perspectives, this approach may contribute to the development of more precise monitoring strategies and individualized therapeutic interventions in critically ill patients.