Disseminated intravascular coagulation Study Guide

📖 Core Concepts Disseminated Intravascular Coagulation (DIC) – uncontrolled clotting throughout the bloodstream that blocks tiny vessels and consumes clotting components, leading to both thrombosis and bleeding. Acute vs. Chronic DIC – Acute: rapid, severe clotting (e.g., endotoxic shock). Chronic: slow, often in cancer, with intermittent bleeding. Hemostatic Balance – normal clotting (thrombin → fibrin) is counter‑balanced by fibrinolysis (plasmin → fibrin breakdown). DIC tips the balance toward massive thrombin generation and later fibrinolysis. Key Laboratory Hallmarks – prolonged PT/aPTT, falling platelet count, low fibrinogen (or “normal‑high” acute‑phase), high D‑dimer/fibrin degradation products, possible schistocytes. International Society of Thrombosis and Haemostasis (ISTH) Scoring – points for underlying disease, platelet count, D‑dimer, PT, fibrinogen; ≥5 = overt DIC. --- 📌 Must Remember Incidence: 1 % of all admissions; 20‑50 % of septic patients; 31 % of severe trauma; 6‑7 % of cancer patients. Mortality: 20‑50 % overall; higher in septic‑associated DIC. Platelet Trend: rapid decline = hallmark. Fibrinogen: low → consumptive DIC; normal/elevated → acute‑phase response, does not exclude DIC. D‑dimer: always elevated in overt DIC (reflects fibrinolysis). Treatment Priority: control the precipitating cause first; replace blood products as needed; heparin only in selected chronic/slow cases. --- 🔄 Key Processes Trigger → Tissue Factor Exposure Vascular injury → TF on endothelium/monocytes binds VIIa → extrinsic tenase → activates IX & X → thrombin surge. Excess Thrombin Generation Massive conversion of fibrinogen → widespread fibrin clots. Consumption Phase Platelets trapped in clots → thrombocytopenia. Clotting factors depleted → bleeding tendency. Dysregulated Fibrinolysis Thrombin‑driven plasminogen → plasmin → rapid fibrin breakdown → high D‑dimer. Fibrin degradation products act as anticoagulants, worsening bleeding. Feedback Loop Natural inhibitors (e.g., antithrombin) consumed → unchecked clotting → self‑amplifying cycle. Complement/Kinin Activation Plasmin activates complement & kinin → shock, hypotension, ↑ vascular permeability. --- 🔍 Key Comparisons Acute DIC vs. Chronic DIC Onset: sudden (shock, amniotic embolism) vs. insidious (cancer). Bleeding: prominent in acute; intermittent in chronic. Anticoagulation: rarely used in acute; heparin sometimes considered in chronic. DIC vs. Thrombotic Thrombocytopenic Purpura (TTP) Primary driver: systemic coagulation activation (DIC) vs. ADAMTS13 deficiency (TTP). Lab: prolonged PT/aPTT in DIC; usually normal in TTP. Peripheral smear: schistocytes present in both, but more marked thrombocytopenia & coagulation abnormalities point to DIC. Low Fibrinogen vs. Acute‑Phase Elevation Low: consumptive DIC, predicts severe bleeding. Normal/high: inflammatory response; does not rule out DIC. --- ⚠️ Common Misunderstandings “Normal fibrinogen = no DIC.” – Acute‑phase reactants can mask low levels. Look at trends and other labs. “All DIC patients bleed.” – Early/acute forms may present with thrombosis; bleeding appears after consumption. “Heparin cures DIC.” – Anticoagulation is adjunctive, only in selected chronic cases; primary therapy is treating the underlying cause. “Schistocytes are diagnostic.” – They are supportive but not sensitive or specific; rely on the full lab picture. --- 🧠 Mental Models / Intuition “Fire‑hose model” – Imagine a fire hose (thrombin) turned on full blast: everything downstream (fibrin, platelets, factors) gets soaked, then the hose bursts (bleeding). “Two‑phase roller coaster” – Phase 1 = clot‑formation surge; Phase 2 = fibrinolysis surge. Recognize which phase the patient is in by dominant symptoms (thrombosis vs. bleeding) and lab trends. “Score‑first, treat‑second” – Run the ISTH score quickly; if ≥5, commit to full DIC management while hunting the trigger. --- 🚩 Exceptions & Edge Cases Liver Disease – Can mimic DIC labs (prolonged PT/aPTT, low platelets) but lacks the consumptive fibrinogen drop and high D‑dimer typical of true DIC. HELLP Syndrome – Similar labs in pregnancy; differentiate by obstetric context and presence of hemolysis, elevated liver enzymes, low platelets. Cancer‑related Chronic DIC – May have relatively stable platelet counts; anticoagulation sometimes beneficial but bleeding risk remains high. --- 📍 When to Use Which Blood Product Choice Platelet transfusion: active bleeding or before invasive procedure when platelet < 50 × 10⁹/L. Fresh frozen plasma (FFP): PT/aPTT markedly prolonged or when clotting factor replacement is needed. Cryoprecipitate: fibrinogen < 1 g/L (≈100 mg/dL) or clinically significant hypofibrinogenemia. Heparin – Consider only in slow‑developing (chronic) DIC with predominant thrombosis and no active major bleeding. --- 👀 Patterns to Recognize Sudden PT/aPTT + platelet drop + high D‑dimer → classic overt DIC. Sepsis + worsening organ function + schistocytes → high suspicion for DIC. Cancer patient with intermittent bleeding + modest lab changes → think chronic DIC. Rapid rise in fibrinogen after a low value → acute‑phase response, not resolution. --- 🗂️ Exam Traps “Normal fibrinogen rules out DIC.” – Wrong; acute‑phase elevation can mask low levels. “Only bacterial infections cause DIC.” – Incorrect; trauma, malignancy, viral/fungal infections, massive tissue injury also trigger. “Heparin is always contraindicated.” – Misleading; low‑dose heparin may be used in chronic, low‑bleeding risk scenarios. “Schistocytes are pathognomonic for DIC.” – Not specific; they appear in TTP, HUS, mechanical heart valves. “ISTH score ≥5 = treatment required immediately.” – True for overt DIC, but always address underlying cause first; score guides urgency, not sole treatment decision.