A 68-year-old woman with severe aortic stenosis undergoes elective aortic valve replacement. Intraoperatively, after 4 hours of cardiopulmonary bypass, she receives 6 units of packed red blood cells, 4 units of fresh frozen plasma, and 1 unit of platelet concentrate. Post-operatively, she develops oozing from the surgical site, petechiae on the lower limbs, and haematuria. Laboratory investigations show: PT 18 seconds (INR 1.8), aPTT 52 seconds, platelet count 45,000/μL, fibrinogen 0.8 g/dL (normal 2–4 g/dL). What is the most likely diagnosis and the next immediate step in management?

Explanation

## Clinical Scenario Analysis This patient has undergone major cardiac surgery with prolonged cardiopulmonary bypass (4 hours) and received large-volume transfusion (6 PRBCs, 4 FFP, 1 platelet unit). She now presents with bleeding manifestations (oozing, petechiae, haematuria) and a characteristic laboratory pattern. ## Laboratory Interpretation | Parameter | Patient Value | Normal Range | Interpretation | |-----------|---------------|--------------|----------------| | **PT (INR)** | 1.8 | <1.2 | Mildly prolonged | | **aPTT** | 52 sec | 25–35 sec | Prolonged | | **Platelets** | 45,000/μL | 150,000–400,000 | Thrombocytopenia | | **Fibrinogen** | 0.8 g/dL | 2–4 g/dL | **Severely low** | **Key Point:** The combination of **low fibrinogen (0.8 g/dL) with only mildly prolonged PT/aPTT and moderate thrombocytopenia** in the context of massive transfusion is pathognomonic for **dilutional coagulopathy**, not DIC. ## Why Not DIC? **High-Yield:** In DIC, fibrinogen is consumed rapidly and is typically <0.5 g/dL (often undetectable), PT/aPTT are markedly prolonged (INR >2.5), and there is evidence of microangiopathic haemolytic anaemia (schistocytes on blood smear). This patient's INR of 1.8 is only mildly elevated, inconsistent with DIC. Additionally, DIC would show elevated D-dimer and low haptoglobin, which are not mentioned. **Clinical Pearl:** Dilutional coagulopathy occurs because: 1. Large volumes of crystalloid and colloid are infused during CPB 2. RBC transfusions contain minimal clotting factors 3. FFP transfusions lag behind RBC requirements 4. Platelets are consumed by the bypass circuit itself The result is a **dilution** of clotting factors and platelets, not consumption. ## Management Algorithm ```mermaid flowchart TD A[Massive transfusion + bleeding]:::outcome --> B{Fibrinogen <1.5 g/dL?}:::decision B -->|Yes| C[Dilutional coagulopathy]:::outcome C --> D[Transfuse cryoprecipitate]:::action D --> E[Target fibrinogen >1.5 g/dL]:::action B -->|No| F{PT/aPTT markedly prolonged + low Hb?}:::decision F -->|Yes| G[DIC]:::outcome G --> H[Treat underlying cause + FFP]:::action A --> I{Acute respiratory distress + normal CXR initially?}:::decision I -->|Yes| J[TRALI]:::urgent J --> K[Stop transfusion, O2, supportive care]:::action ``` **Mnemonic: FIBRIN FIRST** — Fibrinogen is the first factor to fall in dilutional coagulopathy; Cryoprecipitate is the fastest way to restore it. ## Correct Management **Transfuse 2 units FFP and 1 unit cryoprecipitate** because: - FFP (200 mL/unit) provides all clotting factors to address the prolonged PT/aPTT - **Cryoprecipitate (10 mL/unit, contains 150–250 mg fibrinogen per unit)** is the most efficient way to raise fibrinogen rapidly - 1 unit of cryo raises fibrinogen by ~40 mg/dL; this patient needs to reach >1.5 g/dL - Platelets may also be transfused if count remains <50,000/μL in an actively bleeding patient [cite:Harrison 21e Ch 181; Perioperative Blood Transfusion Guidelines]