Sepsis is a highly heterogeneous syndrome with persistently high incidence and mortality. Patients with underlying chronic diseases have worse outcomes due to reduced organ reserve capacity. Fluid resuscitation, a key component of sepsis bundle therapy, has shown efficacy in certain populations; however, standardized resuscitation strategies are often limited in patients with chronic heart failure, chronic lung disease, or chronic kidney disease, and may even exacerbate organ injury. Organ reserve capacity, reflecting the body's compensatory ability under stress, is an important reference for individualized resuscitation strategies. For patients with heart failure, fluid resuscitation should be guided by precise assessment of fluid responsiveness; for those with chronic lung disease, treatment should balance respiratory support and lung protection to avoid fluid overload and ventilator-related injury; for patients with chronic kidney disease, early initiation of renal replacement therapy and careful fluid management are essential. Individualized resuscitation based on organ reserve capacity has the potential to improve outcomes in septic patients with chronic comorbidities. Therefore, this study aims to investigate the clinical value of organ reserve capacity in fluid resuscitation decision-making among patients with sepsis and underlying chronic diseases, in order to inform the development of more precise and safer individualized resuscitation strategies across different chronic disease populations.