Background <p>Inferior vena cava (IVC) respiratory variability is widely used to assess volume status and fluid responsiveness, but its interpretation depends on the physiological context. During rigid bronchoscopy, jet ventilation creates a distinct ventilatory environment, and its impact on IVC-derived indices remains unclear.</p> Methods <p>This prospective self-controlled observational study included 60 adult patients undergoing rigid bronchoscopy under general anesthesia. Measurements were obtained at three predefined time points: awake baseline (T0), mask-assisted positive-pressure ventilation during induction (T1), and stable intraoperative jet ventilation (T2). IVC parameters were assessed using M-mode ultrasonography. The primary outcome was the paired change in IVC distensibility index (dIVC) between T1 and T2.</p> Results <p>dIVC decreased significantly from T1 to T2 (86.29 ± 35.09% vs. 22.08 ± 12.86%, <i>P</i> &lt; 0.001). The mean paired change (ΔdIVC) was − 64.22 ± 35.84%, corresponding to a large effect size (Cohen’s d = 1.79). This change was accompanied by an increase in IVCmin and a reduction in absolute IVC diameter variation. In contrast, heart rate and mean arterial pressure remained stable.</p> Conclusions <p>IVC-derived respiratory variability changed markedly after transition from mask-assisted positive-pressure ventilation to open jet ventilation during rigid bronchoscopy. This observation suggests that IVC-derived indices are sensitive to ventilation mode and airway openness, and should not be interpreted as direct evidence of intravascular volume status or fluid responsiveness in this setting. Conventional IVC thresholds derived from spontaneous breathing or closed positive-pressure ventilation should therefore be applied with caution during open jet ventilation.</p> Trial registration <p>This study was registered in the Chinese Clinical Trial Registry on March 24, 2026 (ChiCTR2600121550).</p>