In this scenario, the patient has sustained a stab injury to the right lower chest accompanied by hypotension and bradycardia, which improve with IV fluid administration. Upon stabilization, the chest X-ray reveals clear lung fields. The primary concern in such trauma cases, especially with abdominal involvement, is internal bleeding or organ injury that may not be evident on X-ray. The presence of normal lung fields does not rule out significant injuries such as hemothorax, pneumothorax, or abdominal organ injury. The most appropriate immediate diagnostic step is to perform an EFAST (Extended Focused Assessment with Sonography for Trauma).
EFAST is a rapid bedside ultrasound examination aimed at identifying free fluid, which in the context of trauma, is usually blood. It is particularly useful because it is non-invasive, quick, and can be performed in unstable patients without needing transport. This examination can help to identify conditions such as hemoperitoneum, hemothorax, or pneumothorax that may not be visible on an initial X-ray. The decision tree favored EFAST over other options such as CECT abdomen or chest, since those require a more stable patient due to the need for transport and time for imaging, whereas EFAST can be conducted in the resuscitation area promptly and repeatedly if necessary.