## FAST Examination: Principles and Limitations ### Four Views of FAST | View | Anatomical Location | Clinical Significance | |---|---|---| | **Pericardial** | Pericardial sac | Detects hemopericardium; indicates cardiac/great vessel injury | | **Perihepatic (Morrison's pouch)** | Right upper quadrant, between liver and kidney | Most **sensitive** for free fluid; first site to accumulate fluid in supine patient | | **Perisplenic** | Left upper quadrant, between spleen and kidney | Detects left-sided hemorrhage | | **Pelvic** | Pelvis, pouch of Douglas | Also highly sensitive; fluid collects here due to gravity | **Key Point:** Option B is the INCORRECT statement — Morrison's pouch (perihepatic view) is classically described as the **most sensitive** location for detecting free intra-abdominal fluid on FAST, NOT the most specific. It is the first place free fluid accumulates in a supine patient due to anatomical positioning and gravity, making it the highest-yield view for early hemorrhage detection. ### FAST Sensitivity and Specificity **High-Yield (ATLS 10th Edition):** - **Perihepatic (Morrison's pouch) view:** Most **SENSITIVE** — fluid accumulates here first in the supine patient; detects as little as 100–200 mL - **Pelvic view:** Also highly sensitive, particularly for smaller volumes of fluid pooling in the dependent pelvis - Calling Morrison's pouch "most specific" is factually incorrect; specificity refers to the ability to rule out false positives, which is not the defining characteristic of this view - Overall FAST sensitivity: 73–100% for detecting ≥500 mL free fluid ### Why the Other Options Are Correct (and NOT the answer) - **Option A:** A positive FAST in a hemodynamically **unstable** patient IS sufficient to mandate immediate exploratory laparotomy without further imaging — this is a core ATLS principle. No CT is needed when the patient is in hemorrhagic shock with a positive FAST. - **Option C:** The pericardial view correctly assesses for hemopericardium, which may indicate cardiac or great vessel injury — this is accurate. - **Option D:** Free fluid in the pelvis is indeed a highly sensitive location for detecting intra-abdominal hemorrhage, as fluid pools dependently — this is accurate. **Clinical Pearl:** The classic teaching is that Morrison's pouch is the **most sensitive** single view on FAST. Labeling it "most specific" is a factual error and represents the exception (incorrect statement) in this all-except question. **Mnemonic — FAST Sensitivity Hierarchy:** - **Morrison's pouch** = most sensitive (first to show fluid in supine patient) - **Pelvic view** = also highly sensitive (dependent pooling) - **Pericardial view** = detects life-threatening cardiac tamponade [cite: ATLS 10th Edition, Ch 5; Schwartz's Principles of Surgery, 11th Ed, Ch 7]
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