This study explored how inspiratory effort affects the accuracy of the distensibility index of inferior vena cava (dIVC) in assessing fluid responsiveness (FR).This prospective observational study was conducted in an intensive care unit of a university hospital and included shock patients receiving ventilation with spontaneous breathing activity. Hemodynamic parameters were collected before and after fluid challenge by the pulse indicator continuous cardiac output. dIVC was calculated by ultrasound, and respiratory effort was assessed using airway occlusion pressure (P0.1) and end-expiratory occlusion pressure (Pocc) before fluid administration. Responders were defined by a ≥10% increase in cardiac output (CO) after 250 mL saline infused in 10 minutes. The dIVC \> 18% was considered indicative of FR. Predictive performance was evaluated using area under receiver operating characteristic curves (AUROC), stratified by P0.1 and Pocc.