Abstract
<title>Abstract</title> <p>Background Fluid responsiveness, defined as a ≥ 15% increase in cardiac output (CO) following fluid administration, is a critical determinant in guiding resuscitation strategies in patients with shock. While pulmonary artery catheterization remains the gold standard for hemodynamic monitoring, it is invasive and associated with procedural risks. Non-invasive modalities, such as the internal jugular vein distensibility index (IJVDi) and changes in end-tidal CO₂ (ΔETCO₂), have been proposed as alternatives for predicting fluid responsiveness. Methods Trial was registered at Thai Clinical Trials Registry on 29 November 2025 (TCTR20251129004). This prospective diagnostic study enrolled 80 mechanically ventilated patients with shock at King Chulalongkorn Memorial Hospital. Baseline hemodynamic parameters—including IJVDi, ΔETCO₂, pulse pressure variation (PPV), and CO (via FloTrac™)—were recorded. A standardized fluid challenge (4 mL/kg crystalloid over 5 minutes) was administered, and reassessment was performed at 1–2 minutes post-infusion. Results Fluid responsiveness was identified in 43.75% of patients. The mean pre-challenge resuscitation volume was 1,588 mL (27.2 mL/kg), with mean lactate 3.9 mmol/L and mean APACHE II score 25.8. IJVDi ≥ 18.5%, ΔETCO₂ ≥2 mmHg, and ΔETCO₂ ≥5.8% demonstrated sensitivities of 97.1%, 88.6%, and 88.6% and specificities of 82.2%, 86.7%, and 88.9%, respectively. The combined use of IJVDi and ΔETCO₂ further enhanced diagnostic accuracy, yielding a sensitivity of 85.7%, specificity of 93.3%, and an area under the receiver operating characteristic curve (AUC) of 0.895 (95% CI, 0.826–0.965). Conclusion These findings support IJVDi and ΔETCO₂ as reliable, non-invasive predictors of fluid responsiveness in mechanically ventilated shock patients. The combined assessment offers superior diagnostic performance, representing a practical alternative to invasive monitoring techniques.</p>