Lactate in cardiogenic shock: pathophysiology, prognostic value, and clinical interpretation.

In cardiogenic shock (CS), blood lactate concentration is routinely used to assess shock severity and guide clinical decisions. However, lactate interpretation is often oversimplified, leading to confusion between disease severity, shock reversibility, and treatment failure. A clinically grounded understanding of lactate behavior throughout the course of CS is therefore required. In CS, lactate elevation primarily reflects the magnitude and duration of systemic hypoperfusion caused by reduced cardiac output, often compounded by regional ischemia, particularly in the splanchnic territory. In addition to anaerobic mechanisms, lactate production is influenced by adrenergic stimulation, post-cardiac arrest syndrome, ischemia-reperfusion injury, systemic inflammation, and mitochondrial dysfunction. Impaired hepatic and renal clearance further contributes to sustained hyperlactatemia, explaining why lactate may remain elevated despite apparent restoration of macrocirculatory variables. Clinically, admission lactate is a robust marker of initial shock severity and is consistently associated with early mortality. However, once resuscitation has started, isolated lactate values provide limited information. Serial measurements and lactate trajectories over time more accurately reflect metabolic recovery and response to therapy. Early lactate clearance identifies patients with reversible shock physiology, whereas persistent or rising lactate levels indicate refractory shock, ongoing microcirculatory dysfunction, or impaired clearance. In CS patients requiring mechanical circulatory support, particularly veno-arterial extracorporeal membrane oxygenation (VA-ECMO), lactate plays a central role in clinical assessment. Pre-implantation lactate reflects disease severity but should not be interpreted as a stand-alone criterion for futility. Following VA-ECMO initiation, early lactate clearance is one of the strongest predictors of survival, while persistent hyperlactatemia despite adequate device flow is associated with multiorgan failure and poor outcome. In CS, lactate should be interpreted as an integrative and dynamic biomarker reflecting the balance between hypoperfusion, metabolic stress, and clearance rather than tissue hypoxia alone. Trajectory-based lactate assessment, closely aligned with clinical context and circulatory support strategies, provides critical information for risk stratification, therapeutic guidance, and evaluation of shock reversibility.