Diagnostic performance of axillary-vein distensibility index (AXV-DI) versus inferior-vena-cava distensibility index (IVC-DI) for predicting fluid responsiveness in patients with septic shock

Background Septic shock relies on early goal-directed fluid resuscitation. Inferior vena cava (IVC) ultrasound is standard for volume evaluation, yet the IVC is frequently affected by abdominal distension, emphysema or high intra-abdominal pressure. This study aimed to compare the diagnostic performance of axillary vein distensibility index (AXV-DI) and inferior vena cava distensibility index (IVC-DI) for assessing fluid responsiveness in mechanically ventilated patients with septic shock in the intensive care unit. Materials and methods This was a single-center prospective observational study that enrolled 95 mechanically ventilated patients with septic shock in the ICU. A standardized fluid challenge with 500 mL of Lactated Ringer's solution infused intravenously over 15 min was performed. The primary outcome was the comparison of the diagnostic performance (area under the receiver operating characteristic curve) of AXV-DI vs. IVC-DI for predicting fluid responsiveness. The secondary outcome was the changes in hemodynamic and ultrasonic parameters before and after standardized fluid challenge in responder and non-responder groups. Results Eighty-six patients were analyzed (60 responders, 26 non-responders). For the primary outcome, the ROC AUC values for predicting fluid responsiveness were 0.93 for IVC-DI and 0.80 for AXV-DI. The DeLong test confirmed that IVC-DI exhibited significantly superior diagnostic performance compared with AXV-DI ( P = 0.009). For the secondary outcome, responders presented more significant changes in LVOT-VTI and venous distensibility indices after fluid resuscitation compared with non-responders. Baseline hemodynamic and ultrasonic parameters were significantly different between the two groups. Conclusions Both AXV-DI and IVC-DI can predict fluid responsiveness in patients with septic shock, although AXV-DI exhibits lower diagnostic performance than IVC-DI.