A post-operative patient presenting with sudden hypotension and tachycardia raises suspicion for intra-abdominal bleeding or fluid collection. The FAST (Focused Assessment with Sonography in Trauma) scan is a rapid, bedside ultrasound tool designed to detect free fluid in the abdomen, pericardium, and pelvis. It is non-invasive, immediately available, and can be performed repeatedly, making it ideal for unstable patients. CT or MRI require patient stability and more time, while chest X-ray assesses thoracic pathology and is less useful for acute abdominal assessment. Thus, the FAST scan provides the quickest and most critical information to guide further management in the surgical setting.
Reference: Schwartz's Principles of Surgery, Brunicardi, 11th Edition.