Abstract
Critical care medicine is at a pivotal stage of transformation from symptom-based approaches toward systems science. Building on a first-principles understanding of the mechanisms underlying critical illness, we propose the entropic critical illness theory (ECIT). Grounded in the second law of thermodynamics, ECIT posits that critical illness arises when the body’s capacity to regulate entropy production is impaired, leading to systemic disorder. This process is manifested by the concurrent escalation of host response entropy and hemodynamic entropy, resulting in disruptions in blood flow and oxygen delivery, ischemia, and hypoxia at the level of the critical unit, which is defined as the terminal microcirculatory–mitochondrial functional unit, ultimately culminating in multi-organ dysfunction. This study delineates the theoretical foundations of ECIT and outlines an entropy-based critical care framework that may inform future multimodal entropy-informed monitoring, risk stratification, and AI-assisted precision intervention in critical care medicine.