📚 L9 Antidepressants I

📚 Lecture Overview

This summary covers the clinical principles of blood transfusion, detailing major blood group systems, compatibility requirements, and the specific indications for various blood components and derivatives. It explores immediate and delayed transfusion complications, distinguishing between immunologic and non-immunologic reactions, and outlines the management of massive transfusions. Mastering these concepts is essential for ensuring patient safety and recognizing life-threatening transfusion reactions.

🎯 Key Concepts & Definitions

• Blood Components: Products separated from whole blood by physical means (e.g., packed RBCs, platelets, fresh-frozen plasma, cryoprecipitate).
• Blood Derivatives: Commercially prepared, fractionated, and heat- or chemically-treated plasma products (e.g., albumin, immune globulins, coagulation factor concentrates).
• Platelet Refractoriness: The failure to achieve an adequate increase in platelet count after two consecutive transfusions of single-donor platelets.
• Alloimmunization: An immune response stimulated by foreign antigens (such as HLA or RBC antigens) from genetically different individuals, often due to prior transfusion or pregnancy.
• Massive Transfusion: The administration of blood components exceeding or equaling the patient's total blood volume within 24 hours ($≥ 10$ units of whole blood or $20$ units of packed RBCs in adults).
• TRALI: Transfusion-Related Acute Lung Injury; a life-threatening, non-cardiogenic pulmonary edema triggered by donor antibodies attacking recipient white blood cells.
• TACO: Transfusion-Associated Circulatory Overload; a cardiogenic pulmonary edema caused by rapid or excessive volume expansion during transfusion.

📖 Main Content

1. Blood Grouping and Compatibility

• RBC Antigens: Red blood cells possess surface antigens with varying biochemical, phenotypic, and immunological characteristics. The major clinically important systems include ABO, Rh, Kell, Kidd, and Duffy.
• Antibodies: Naturally occurring antibodies (anti-A and anti-B) are present without prior sensitization. Development of most other allo-antibodies (such as anti-D) requires prior sensitization via transfusion or pregnancy.
• Compatibility Rule: Any blood component containing > 2 ml of RBCs must be compatible with the patient's plasma.

2. Blood Components: Storage, Indications, and Yields

Whole Blood

• Indications: Acute hypovolemia with active red cell loss, and exchange transfusion (e.g., in sickle cell crises or Hemolytic Disease of the Newborn [HDN]).
• Limitations: It is not a source of functional platelets or granulocytes, as these deteriorate within 24 hours of refrigerated storage.

Packed Red Blood Cells (PRBCs)

• Indications: Treatment of symptomatic anemia.
• Yield: One unit of packed RBCs increases Hemoglobin (Hb) by 1 g/dl in an average-sized adult.
• Storage: Stored in a blood bank refrigerator at 2–6°C for up to 35 days.

Platelets

• Source: Separated from whole blood shortly after collection via centrifugation (random donor/platelet concentrates) or collected by apheresis (single donor).
• Yield: One unit of platelets increases the platelet count by 5,000–10,000/cmm³.
• Storage: Stored at room temperature on a platelet shaker for up to 5 days.
• Indications:
• Therapeutic: Bleeding associated with thrombocytopenia or qualitative platelet defects.
• Prophylactic:
  • Major surgery or invasive procedures: Transfuse if count is $≤ 50 × 10^9/L$.
  • Ocular or neurosurgery: Transfuse if count is $≤ 100 × 10^9/L$.
  • Stable, non-bleeding, afebrile patient: Transfuse if count is $< 10 × 10^9/L$.
  • Stable, non-bleeding, febrile patient (Temp $>38°C$): Transfuse if count is $< 20 × 10^9/L$.

Platelet Refractoriness

• Definition: Inadequate platelet increment following two successive single-donor platelet transfusions.
• Mechanisms:
• Non-immune mediated: Fever, infection, splenomegaly, DIC, massive bleeding, or drugs that accelerate platelet destruction.
• Immune-mediated: Alloimmunization to HLA or human platelet antigens (HPA) due to repeated transfusions or multiparity.
• Management: Transfuse HLA-compatible or cross-match compatible platelets.

Granulocytes

• Source: Collected by apheresis from donors mobilized with G-CSF.
• Indications: Neutropenia (Absolute Neutrophil Count [ANC] $< 0.5 × 10^9/L$) with documented infection, or defective granulocyte function (e.g., Chronic Granulomatous Disease).

Fresh-Frozen Plasma (FFP)

• Indications: Correction of multiple clotting factor deficiencies (bleeding or pre-procedure), DIC, liver disease, massive transfusion, plasma exchange (e.g., TTP), and rapid reversal of warfarin.
• Contraindications: Should not be used for volume expansion or nutritional protein replacement.
• Storage: Must be separated and frozen within 8 hours of donation to preserve labile coagulation factors. Stored at $-20°C$ to $-80°C$ for up to 1 year.

Cryoprecipitate

• Composition: Formed from a fraction of plasma; contains Factor VIII, fibrinogen, Factor XIII, and von Willebrand Factor (vWF).
• Indications: Fibrinogen deficiency, dysfibrinogenemia, Factor XIII deficiency, DIC, and urgent treatment of Hemophilia A or von Willebrand disease when factor concentrates are unavailable.

3. Blood Derivatives

These are commercially fractionated, heat- or chemically-treated plasma products designed to eliminate viral transmission.

• Rh Immune Globulin: Prevents anti-D sensitization in Rh-negative pregnant women carrying Rh-positive fetuses to prevent HDN; also used for immunomodulation in ITP.
• Albumin: Used for volume expansion in hypovolemia, acute liver failure (provides oncotic pressure and binds excess bilirubin), cardiopulmonary bypass hemodilution, extensive burns, and prior to exchange transfusions in HDN to prevent kernicterus.
• Intravenous Immune Globulin (IVIG): Used for passive antibody prophylaxis, primary immunodeficiencies, immunomodulation (refractory ITP), and specific infections/neuropathies (HIV-related thrombocytopenia, CMV pneumonitis, Guillain-Barré syndrome).
• Recombinant & Concentrated Coagulation Factors:
• Recombinant Factor VIIa (rVIIa): Factor VII deficiency, refractory hemophilia A/B, or high inhibitor levels.
• Factor VIII Concentrate / Recombinant FVIII: Hemophilia A and vWD.
• Factor IX Complex (Prothrombin Complex): Contains F IX, II, VII, and X; indicated in hemophilia B and factor X or VII deficiencies.
• Recombinant Factor XIII: Factor XIII deficiency.

4. Transfusion Complications

Immediate Immunological Complications

1. Febrile Non-Hemolytic Transfusion Reaction (FNHTR):
   - Features: Temp increase of $> 1°C$ (diagnosis of exclusion). Chills, rigors, tachycardia, tachypnea.
   - Mechanism: Cytokines/pyrogens accumulated in the bag during storage are passively transferred to the recipient.
   - Management/Prevention: Slow transfusion, give paracetamol. Prevent with leukodepletion (leukoreduction) and plasma removal.
2. Mild Allergic Reaction:
   - Features: Localized erythema, pruritus, flushing, and urticaria near the IV site.
   - Mechanism: IgE antibodies against donor plasma proteins trigger histamine release.
   - Management: Antihistamines; can resume transfusion if symptoms resolve.
3. Anaphylactic Reaction:
   - Features: Dyspnea, wheezing, laryngeal edema, hypotension, shock. Fever is absent.
   - Mechanism: IgA-deficient patient with pre-formed anti-IgA antibodies reacting to IgA in donor plasma.
   - Management: Stop transfusion immediately. Administer adrenaline, corticosteroids, and airway support.
4. Acute Hemolytic Transfusion Reaction (AHTR):
   - Features: Fever, chills, flank/back pain, dyspnea, hypotension, hemoglobinuria, renal failure, DIC.
   - Mechanism: ABO incompatibility (mismatched blood). Pre-formed IgM antibodies fix complement, causing intravascular hemolysis.
   - Management: Stop transfusion. Support blood pressure and renal perfusion with IV fluids and pressors. Induce diuresis to maintain urine output $> 100 ml/hour$. Check patient identity, repeat cross-match, and run hemolysis labs (Positive DAT, low hematocrit, high LDH, high bilirubin).
5. Transfusion-Related Acute Lung Injury (TRALI):
   - Features: Acute non-cardiogenic pulmonary edema, hypoxia, fever, hypotension, and bilateral pulmonary infiltrates on chest X-ray within 6 hours of transfusion. Normal CVP.
   - Mechanism: Donor leukoagglutinins (anti-HLA or anti-granulocyte antibodies, typically from multiparous female donors) activate recipient neutrophils, injuring pulmonary endothelium.
   - Management: Discontinue transfusion, provide aggressive ICU supportive ventilation, and manage fluid balance.

Delayed Immunological Complications

1. Delayed Hemolytic Transfusion Reaction (DHTR):
   - Features: Occurs 1–3 weeks post-transfusion. Triad of fever, hyperbilirubinemia, and anemia. Positive DAT. No hemoglobinuria (hemolysis is extravascular).
   - Mechanism: Anamnestic antibody response in a previously sensitized patient.
   - Management: Self-limiting; monitor hemoglobin. Prevent by avoiding the specific antigen in future transfusions.
2. Post-Transfusion Purpura (PTP):
   - Features: Sudden, severe thrombocytopenia 5–10 days post-transfusion.
   - Mechanism: Recipient antibodies against platelet-specific antigen HPA-1a destroy both donor and autologous platelets.
   - Management: IVIG or plasma exchange.
3. Transfusion-Associated Graft-versus-Host Disease (TA-GvHD):
   - Features: Occurs 4–30 days post-transfusion. Fever, maculopapular rash (may progress to toxic epidermal necrolysis), diarrhea, abnormal LFTs, and profound pancytopenia (hypocellular bone marrow). Extremely high mortality.
   - Mechanism: Donor T-lymphocytes engraft and attack recipient tissue in immunocompromised patients.
   - Prevention: Gamma-irradiation of blood products (2500 cGY) to inactivate donor lymphocytes. Note: Leukoreduction does NOT prevent TA-GvHD.

Non-Immunological Complications

1. Bacterial Sepsis:
   - RBCs: Usually contaminated by cold-growing bacteria (Yersinia enterocolitica, Pseudomonas).
   - Platelets: Stored at room temperature, making them highly susceptible to Gram-positive cocci (Staphylococci, Streptococci).
   - Management: Stop transfusion, administer broad-spectrum antibiotics, support blood pressure.
2. Transfusion-Associated Circulatory Overload (TACO):
   - Features: Cardiogenic pulmonary edema, dyspnea, orthopnea, congested neck veins, elevated CVP, and hypertension. Risk is highest in children, elderly, and cardiac patients.
   - Management/Prevention: Stop transfusion, administer oxygen and diuretics. Transfuse at-risk patients slowly (1–4 ml/kg/hour) and never exceed 4 hours per unit.
3. Hemosiderosis (Iron Overload):
   - Features: Bronze skin, hepatic fibrosis, diabetes, and heart failure in patients receiving chronic transfusions ($> 20$ units). Each unit of RBCs contains 200–250 mg of iron.
   - Management: Iron chelation therapy (indicated if serum ferritin $> 1000 ng/ml$).

5. Massive Transfusion Sequelae and Management

Massive transfusion causes several metabolic and physiological derangements that require preemptive management:

• Hypothermia: Caused by rapid infusion of cold blood. Prevent with blood warmers.
• Dilutional Coagulopathy: Dilution of platelets and clotting factors causes bleeding. Prevent by using a balanced 1:1:1 ratio of packed RBCs, platelets, and FFP.
• DIC: Triggered by activation of the intrinsic coagulation pathway. Prevent with FFP transfusion.
• Acidosis: Caused by the citric acid preservative in stored blood. Prevent with IV sodium bicarbonate.
• Electrolyte Disturbances:
• Hypocalcemia & Hypomagnesemia: Citrate preservative in blood bags chelates calcium and magnesium. Prevent with IV calcium gluconate and IV magnesium sulfate.
• Hyperkalemia: Stored RBCs leak potassium into the supernatant over time. Correct with IV insulin + glucose.

📊 Visual Learning

Diagram 1: Management of Acute Hemolytic Transfusion Reaction (AHTR)

Diagram 2: Classification of Transfusion Complications

Diagram 3: Metabolic Sequelae of Massive Transfusion

💡 Important Points to Remember

• The 1 g/dl Rule: One unit of PRBCs raises adult hemoglobin by 1 g/dl (or hematocrit by 3%).
• Platelet Yield: One unit of platelets raises the recipient's platelet count by 5,000–10,000/cmm³.
• Storage Differences: PRBCs must be refrigerated (2–6°C); platelets must be kept at room temperature with continuous agitation on a shaker to maintain viability.
• FFP Use: FFP contains all clotting factors but contains no cells. It is contraindicated for simple volume expansion or nutritional support.
• The TA-GvHD Rule: Leukoreduction filters out white blood cells to prevent FNHTR and HLA sensitization, but only gamma-irradiation prevents TA-GvHD by destroying the proliferative capacity of donor T-cells.
• Anaphylaxis vs. Other Reactions: Anaphylaxis is characterized by the absence of fever and occurs in IgA-deficient patients.
• TRALI vs. TACO: TRALI is non-cardiogenic (normal CVP, donor HLA antibodies, fever, hypotension). TACO is cardiogenic (high CVP, fluid overload, hypertension, neck vein distension).
• Bacterial Culprits: Red cell bags grow cold-loving Gram-negatives (Yersinia, Pseudomonas); platelet bags grow room-temperature Gram-positives (Staph, Strep).
• Iron Burden: Each unit of RBCs delivers 200–250 mg of iron. Chelation is indicated after 20 units or when ferritin exceeds 1000 ng/ml.

⚠️ Common Exam Questions

Common Exam Traps & Tricks

1. The "Leukoreduction prevents TA-GvHD" Trap:
   - The Trick: Examiners will present an immunocompromised patient and ask how to process the blood to prevent TA-GvHD, listing "leukoreduction" as an option.
   - The Truth: Leukoreduction is insufficient. You must select gamma-irradiation (2500 cGY) to prevent TA-GvHD.
2. Distinguishing TRALI from TACO in MCQs:
   - The Trick: Both present with acute respiratory distress and pulmonary infiltrates after transfusion.
   - The Clue: Look at the Central Venous Pressure (CVP) and Blood Pressure. TRALI features normal/low CVP and hypotension. TACO features elevated CVP, hypertension, and jugular venous distension.
3. DAT Status in Hemolytic Reactions:
   - The Trick: Question asks to differentiate AHTR and DHTR based on DAT (Direct Antiglobulin Test).
   - The Truth: Both AHTR and DHTR have a positive DAT. The difference is that AHTR has intravascular hemolysis (hemoglobinuria/hemoglobinemia) and IgM complement fixation, whereas DHTR has extravascular hemolysis (no hemoglobinuria/hemoglobinemia, delayed onset, IgG-mediated).
4. Massive Transfusion Electrolyte MCQ:
   - The Trick: A question states that massive transfusion leads to "hypercalcemia" due to rapid infusion of calcium-containing blood.
   - The Truth: Massive transfusion causes hypocalcemia because the citrate preservative chelates the patient's ionized calcium.
5. Platelet Prophylaxis Thresholds:
   - The Trick: A stable, non-bleeding, afebrile patient has a platelet count of $12 × 10^9/L$. The question asks if transfusion is indicated.
   - The Truth: No. For stable, afebrile, non-bleeding patients, the threshold for prophylactic transfusion is $< 10 × 10^9/L$. If they are febrile ($>38°C$), the threshold becomes $< 20 × 10^9/L$.

📝 Quick Review Checklist

I can differentiate between blood components (RBCs, Platelets, FFP, Cryoprecipitate) and blood derivatives (Albumin, IVIG).
I know the exact storage temperatures and maximum shelf-lives for PRBCs (2–6°C, 35 days), Platelets (room temp on shaker, 5 days), and FFP ($-20°C$ to $-80°C$, 1 year).
I can state the expected therapeutic yields of 1 unit of PRBCs (Hb increases by 1 g/dl) and 1 unit of platelets (count increases by 5,000–10,000/cmm³).
I understand the prophylactic platelet transfusion thresholds for surgery ($≤ 50$), neurosurgery ($≤ 100$), stable afebrile ($< 10$), and stable febrile ($< 20$) patients.
I can explain the immunological mechanism of anaphylactic reactions (anti-IgA in IgA-deficient recipients) and how it differs from FNHTR.
I can clinically distinguish TRALI (non-cardiogenic, normal CVP, donor antibodies) from TACO (cardiogenic, high CVP, fluid overload).
I know that gamma-irradiation is the only way to prevent TA-GvHD, and that leukoreduction does not prevent it.
I can list the key complications of massive transfusion (hypothermia, dilutional coagulopathy, DIC, acidosis, hypocalcemia, hyperkalemia) and how to manage each.
I understand the difference between intravascular hemolysis (AHTR, IgM, hemoglobinuria) and extravascular hemolysis (DHTR, IgG, no hemoglobinuria).