e²FAST: Integrating Inferior Vena Cava Ultrasound Into the Extended Focused Assessment With Sonography for Trauma as a Rapid Diagnostic Tool of Hemorrhagic Shock in Trauma Patients

Hemorrhagic shock remains a leading cause of preventable trauma-related deaths, highlighting the need for rapid and accurate diagnosis. This study evaluates whether integrating inferior vena cava ultrasound (IVC-US) into the extended focused assessment with Sonography for trauma (eFAST), referred to as "e²FAST," improves early shock detection and guides fluid resuscitation in trauma patients. A comprehensive narrative review was conducted to assess the diagnostic and prognostic value of IVC-US as a rapid diagnostic tool for hemorrhagic shock in trauma patients. Studies published from 2000 to January 2025 were searched across PubMed, MEDLINE, EMBASE, Cochrane Library, and Scopus databases. Studies were included if they involved adult trauma patients and evaluated IVC diameter or the collapsibility index (IVC-CI) to determine volume status, shock, or fluid responsiveness. Two independent reviewers screened and selected studies based on predefined inclusion criteria. In total, 13 eligible studies, including randomized controlled trials, prospective and retrospective cohorts, and cross-sectional analyses, were reviewed qualitatively. Key outcomes extracted included diagnostic accuracy, fluid responsiveness, transfusion requirements, intensive care unit (ICU) admission, and mortality. IVC-US demonstrated a sensitivity of 71% and specificity of 75% in detecting hypovolemia. A smaller IVC diameter (<1.5 cm) was significantly associated with increased ICU admissions (51.3%), higher transfusion rates (12.2%), increased emergency surgery requirements (16.2%), and elevated mortality (13.5%). Additionally, an IVC-CI greater than 38.5% provided 80% sensitivity and 85.7% specificity for predicting fluid responsiveness in patients with major blunt trauma. Post-resuscitation assessments (IVC-CI ≤28.6%) were predictive of fluid unresponsiveness (80% sensitivity, 75% specificity). Moreover, IVC-US reliably predicted 24-hour fluid requirements, helping in real-time fluid management. Integrating IVC-US into the eFAST as the e²FAST protocol enhances diagnostic accuracy for identifying hemorrhagic shock and provides critical real-time guidance for fluid resuscitation. Given its non-invasive nature, reliability, and predictive value for patient outcomes, standardized inclusion of IVC measurements in trauma protocols is recommended. Future research should prioritize multicenter randomized trials and standardized operator training to minimize variability and support broad clinical implementation.