## Livor Mortis: Formation and Fixation Timeline **Key Point:** Livor mortis is the purple-red discoloration of dependent tissues caused by gravitational settling of deoxygenated blood and hemolysis. It progresses through phases: appearance → blanching → fixation. ### Phases of Livor Mortis Development | Phase | Timeline | Characteristics | Blanching | | --- | --- | --- | --- | | **Appearance** | 30 min – 2 hours | Faint purple-red in dependent areas | Fully blanches | | **Intensification** | 2–6 hours | Darker, more extensive | Still blanches | | **Fixation** | 8–12 hours | Dark purple-red, fixed pattern | **Non-blanching** | | **Late changes** | >24 hours | May fade; green discoloration (putrefaction) | Non-blanching | ### Mechanism of Fixation 1. **Early phase (0–6 hrs):** RBCs remain intact; gravitational settling is reversible → blanching occurs with pressure. 2. **Transition (6–8 hrs):** RBC membranes begin to rupture; hemoglobin leaks into tissue fluid. 3. **Fixed phase (8–12 hrs):** Hemoglobin is now bound in tissue; pressure cannot redistribute blood → **no blanching**. **High-Yield:** The **8–12 hour window** is when livor becomes fixed and is a critical forensic PMI marker. After this point, blanching cannot occur even with pressure. ### Forensic Significance **Clinical Pearl:** If livor mortis is blanching after 12 hours, suspect: - **Hypothermia** (slows metabolic processes) - **Carbon monoxide poisoning** (bright cherry-red livor; carboxyhemoglobin is stable) - **Anemia** (pale livor) - **Recent death** (livor not yet fixed) **Mnemonic: FIX at 8–12** — **Fixation** occurs at **8–12 hours**.
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