L9 Antidepressants I

📚 Lecture Overview

This summary covers the essentials of blood transfusion medicine, detailing major blood group systems, compatibility principles, and specific indications and storage conditions for various blood components and derivatives. It outlines the clinical presentation, pathophysiological mechanisms, and management of both immediate and delayed transfusion complications (immune vs. non-immune). Furthermore, it details the diagnostic criteria and metabolic/hemostatic complications associated with massive transfusion protocols.

🎯 Key Concepts & Definitions

Naturally Occurring Antibodies: Pre-existing plasma antibodies (such as Anti-A and Anti-B) present without prior red cell exposure or sensitization.
Alloantibodies: Immune antibodies produced only after prior exposure/sensitization to foreign antigens via transfusion or pregnancy.
Platelet Refractoriness: Failure to achieve an adequate increase in recipient platelet count following two consecutive single-donor platelet transfusions.
TRALI (Transfusion-Related Acute Lung Injury): Non-cardiogenic pulmonary edema triggered by donor leukocyte antibodies damaging recipient alveolar endothelium within 6 hours of transfusion.
TACO (Transfusion-Associated Circulatory Overload): Cardiogenic pulmonary edema caused by rapid or excessive volume administration during blood product transfusion.
TA-GvHD (Transfusion-Associated Graft-versus-Host Disease): A high-mortality complication where immunocompetent donor T-lymphocytes attack host tissues in an immunocompromised recipient.
Massive Transfusion: Administration of blood components exceeding the patient's total blood volume within 24 hours (≥10 units of whole blood or ≥20 units of packed RBCs in adults).

📖 Main Content

1. Blood Groups & Compatibility Rule

Major Systems: ABO, Rh, Kell, Kidd, and Duffy.
Core Compatibility Rule: Any blood component containing > 2 mL of RBCs must be compatible with the recipient's plasma.

2. Blood Components

Component	Storage Conditions	Key Indications	Expected Increment / Clinical Notes
Whole Blood	2–6°C for up to 35 days	Acute hypovolemia with RBC loss, exchange transfusion (e.g., sickle cell crisis, HDN)	Functional platelets and granulocytes deteriorate within < 24 hours.
Packed RBCs (PRBCs)	2–6°C for up to 35 days	Symptomatic anemia	1 Unit increases Hb by 1 g/dL in an average adult.
Platelets	Room temp with continuous agitation for up to 5 days	Bleeding with thrombocytopenia/platelet defects; prophylaxis prior to invasive procedures	1 Unit increases platelet count by 5,000–10,000/mm³.
Granulocytes	Room temp (apheresis after donor G-CSF mobilization)	Neutropenia (ANC < 0.5 × 10⁹/L) with documented infection; chronic granulomatous disease	Short shelf-life; used when infection is refractory to antimicrobial therapy.
Fresh-Frozen Plasma (FFP)	Frozen at -20°C to -80°C for up to 1 year	Multiple clotting factor deficiencies, DIC, liver disease, massive transfusion, TTP, rapid warfarin reversal	Must be frozen within 8 hours of donation to preserve labile factors. Do NOT use for volume expansion.
Cryoprecipitate	Frozen storage (derived from plasma fraction)	Hypofibrinogenemia, dysfibrinogenemia, Factor XIII deficiency, DIC, urgent hemophilia A / vWD treatment	Contains Factor VIII, Fibrinogen, Factor XIII, and vWF activity.

Platelet Prophylaxis Thresholds:

≤ 50,000/mm³: Major surgery or invasive procedures.
≤ 100,000/mm³: Ocular surgery or neurosurgery.
< 10,000/mm³: Stable, non-bleeding, afebrile patient.
< 20,000/mm³: Stable, non-bleeding patient with fever (> 38°C).

3. Blood Derivatives

Commercially fractionated plasma products subjected to viral inactivation (heat/chemical treatment):
- Rh Immune Globulin (RhIG): Given to Rh-negative mothers with Rh-positive fetuses to prevent anti-D alloimmunization and HDN; also used in refractory ITP.
- Albumin: Used for volume expansion in hypovolemia, acute liver failure, extensive burns, cardiopulmonary bypass surgery, and pre-exchange transfusion in HDN (binds free bilirubin to prevent kernicterus).
- IVIG: Used for passive prophylaxis, primary immunodeficiencies, ITP, HIV-related thrombocytopenia, CMV interstitial pneumonitis, and Guillain-Barré syndrome.
- Recombinant Factor Concentrates:
- Recombinant Factor VIIa (rVIIa): Factor VII deficiency, refractory hemophilia A/B with inhibitors.
- Factor VIII / IX Concentrates: Hemophilia A (Factor VIII) and Hemophilia B (Factor IX).
- Prothrombin Complex (Factor IX Complex): Contains Factors II, VII, IX, and X.

4. Transfusion Complications Matrix

A. Immediate Immunologic Complications

Febrile Non-Hemolytic Transfusion Reaction (FNHTR):
- Most common transfusion reaction.
- Diagnosis: Temperature rise > 1°C (diagnosis of exclusion).
- Mechanism: Pre-stored cytokines passively transferred from donor component.
- Management: Slow transfusion rate; administer antipyretics (paracetamol).
- Prevention: Leukodepletion (leukoreduction) of blood components.
Mild Allergic / Urticarial Reaction:
- Mechanism: IgE antibodies reacting against plasma proteins in donor plasma.
- Presentation: Localized erythema, pruritus, and urticaria near IV site. No fever.
- Management: Antihistamines. Transfusion may resume if symptoms clear.
Anaphylactic Reaction:
- Mechanism: IgE anti-IgA antibodies in an IgA-deficient recipient reacting against donor IgA.
- Presentation: Bronchospasm, stridor, laryngeal edema, hypotension, shock. Fever is ABSENT.
- Management: Stop transfusion immediately; give adrenaline, corticosteroids, and airway/circulatory support.
Acute Hemolytic Transfusion Reaction (AHTR):
- Mechanism: ABO incompatibility; IgM antibodies activate complement causing rapid intravascular hemolysis.
- Presentation: Chills, flank/back pain, chest pain, hypotension, shock, acute renal failure, DIC.
- Lab Results: Positive Direct Antiglobulin Test (DAT+), low hematocrit, elevated LDH, elevated indirect bilirubin, hemoglobinemia, and hemoglobinuria.
- Management: Stop transfusion. Fluid resuscitation and pressors to keep urine output > 100 mL/hr.
Transfusion-Related Acute Lung Injury (TRALI):
- Mechanism: Donor anti-HLA or anti-granulocyte antibodies (often from multiparous female donors) damage recipient pulmonary capillary endothelium.
- Presentation: Non-cardiogenic pulmonary edema, hypoxemia, fever, bilateral pulmonary infiltrates within 6 hours. Normal CVP.
- Management: Stop transfusion; supportive ICU care (mechanical ventilation).

B. Delayed Immunologic Complications

Delayed Hemolytic Transfusion Reaction (DHTR):
- Mechanism: Anamnestic IgG response 1–3 weeks post-transfusion in a previously sensitized patient.
- Presentation: Triad of fever, hyperbilirubinemia, and anemia. Hemolysis is extravascular (no hemoglobinuria). DAT is positive.
Post-Transfusion Purpura (PTP):
- Mechanism: Anti-HPA-1a antibodies destroy host platelets 5–10 days post-transfusion.
- Management: IVIG or plasma exchange.
Transfusion-Associated Graft-versus-Host Disease (TA-GvHD):
- Mechanism: Donor lymphocytes engraft and attack recipient tissue (occurs 4–30 days post-transfusion).
- Presentation: Fever, maculopapular rash, profuse diarrhea, liver dysfunction, and profound pancytopenia (bone marrow aplasia).
- Prevention: Gamma-irradiation of blood products (2500 cGy). Note: Leukoreduction does NOT prevent TA-GvHD.

C. Immediate Non-Immunologic Complications

Bacterial Contamination & Sepsis:
- PRBCs: Cold-tolerant Gram-negative bacteria (Yersinia, Pseudomonas).
- Platelets: Gram-positive bacteria (Staphylococcus, Streptococcus) due to room-temperature storage.
Transfusion-Associated Circulatory Overload (TACO):
- Mechanism: Volume overload causing cardiogenic pulmonary edema, high CVP, elevated BP, cyanosis, and jugular venous distension.
- Management: Stop transfusion, give oxygen and diuretics. Infuse at slow rates (1–4 mL/kg/hr, max 4 hours per unit) in high-risk patients.

D. Delayed Non-Immunologic Complications

Transfusion-Transmitted Infections (TTIs): HBV, HCV, HIV-1/2, HTLV-I/II, CMV, EBV, Parvovirus B19, Syphilis, Malaria, Prions (CJD).
Hemosiderosis (Iron Overload):
- Occurs after > 20 PRBC transfusions (each unit supplies 200–250 mg iron).
- Presentation: Bronze skin, hepatic fibrosis, diabetes mellitus, cardiac failure.
- Management: Iron chelation therapy when serum ferritin exceeds 1000 ng/mL.

5. Massive Transfusion & Sequelae

Defined as administering ≥ 10 units of whole blood or ≥ 20 units of PRBCs in 24 hours.

Massive Transfusion Complications & Prophylaxis:
├── Hypothermia                 ──> Prevent with Blood Warmers
├── Dilutional Coagulopathy     ──> Transfuse 1:1:1 Ratio (PRBC : FFP : Platelets)
├── Consumption Coagulopathy    ──> Transfuse Fresh Frozen Plasma (FFP)
├── Metabolic Acidosis          ──> Administer Sodium Bicarbonate
├── Hypocalcemia & Hypomagnesemia ─> Administer IV Calcium Gluconate & Mg Sulfate (Citrate Toxicity)
└── Hyperkalemia                ──> Administer IV Insulin + Glucose (K+ leakage from stored RBCs)

📊 Visual Learning

Diagram 1: Classification of Transfusion Reactions

graph TD A[Transfusion Reactions] --> B[Immediate Reactions] A --> C[Delayed Reactions] B --> D[Immunologic] B --> E[Non Immunologic] D --> F[FNHTR and AHTR] D --> G[TRALI and Anaphylaxis] E --> H[TACO and Sepsis] C --> I[DHTR and TAGvHD] C --> J[Iron Overload]

Diagram 2: Acute Hemolytic Transfusion Reaction Mechanism

sequenceDiagram participant D as Donor RBC participant P as Patient Plasma participant C as Complement System P ->> D: Anti A or Anti B binds D ->> C: Activates complement cascade C ->> D: Intravascular cell lysis D ->> P: Releases free hemoglobin

Diagram 3: Complications of Massive Transfusion

mindmap root("Massive Transfusion Complications") "Metabolic Sequelae" "Hypocalcemia from citrate" "Hyperkalemia from stored RBCs" "Metabolic acidosis" "Hemostatic Issues" "Dilutional coagulopathy" "DIC from pathway activation" "Physical Effects" "Hypothermia from cold blood"

💡 Important Points to Remember

1 Unit PRBC raises Hb by 1 g/dL; 1 Unit Platelets raises platelet count by 5,000–10,000/mm³.
FNHTR is the most common transfusion reaction; it is prevented by leukoreduction.
TA-GvHD prevention requires gamma-irradiation (2500 cGy); leukoreduction is ineffective for preventing TA-GvHD.
Anaphylactic transfusion reactions occur in IgA-deficient patients with anti-IgA antibodies; no fever is present.
TRALI causes non-cardiogenic pulmonary edema (low/normal CVP, hypotension); TACO causes cardiogenic pulmonary edema (high CVP, hypertension).
AHTR involves intravascular hemolysis (IgM, complement activation, hemoglobinuria); DHTR involves extravascular hemolysis (IgG, anamnestic response, no hemoglobinuria).
Citrate toxicity in massive transfusions binds divalent cations, leading to hypocalcemia and hypomagnesemia.
Potassium leakage from aging stored RBCs during massive transfusion leads to hyperkalemia.
Platelets are stored at room temperature with continuous agitation for up to 5 days, making them susceptible to Gram-positive bacterial contamination.
Each unit of PRBCs contains 200–250 mg of iron; iron chelation should be considered after 20 units or when serum ferritin exceeds 1000 ng/mL.

⚠️ Common Exam Questions & Traps

Exam Traps & Examiner Tricks:

The TA-GvHD Prevention Trap:
- Trick: Examiners will ask how to prevent TA-GvHD in an immunocompromised patient and offer "Leukoreduced blood" as an option.
- Trap: Selecting leukoreduction. Leukoreduction prevents FNHTR and CMV, but ONLY gamma-irradiation prevents TA-GvHD by inactivating donor lymphocytes.
Intravascular vs. Extravascular Hemolysis:
- Trick: A patient presents 10 days post-transfusion with fever, jaundice, falling Hb, and a positive DAT, but normal urine color.
- Trap: Diagnosing AHTR. This is DHTR (an extravascular process caused by IgG, meaning free hemoglobin is NOT excreted in urine). AHTR occurs immediately and presents with hemoglobinuria.
TRALI vs. TACO Differentiation:
- Trick: Presenting a dyspneic patient post-transfusion with bilateral pulmonary infiltrates and asking for the diagnosis based on blood pressure and neck veins.
- Trap: TRALI features hypotension and normal/low CVP (non-cardiogenic). TACO features hypertension, elevated CVP, and jugular venous distension (cardiogenic).
Massive Transfusion Electrolyte Confusions:
- Trick: Asking which electrolyte abnormalities occur during rapid, massive transfusion of PRBCs.
- Trap: Confusing calcium and potassium directions. Citrate binds calcium → HYPOcalcemia. Stored RBC breakdown releases potassium → HYPERkalemia.

📝 Quick Review Checklist

I can differentiate between intravascular (AHTR) and extravascular (DHTR) hemolytic reactions.
I know the storage temperature and shelf-life for PRBCs, Platelets, and FFP.
I can identify the prophylactic platelet transfusion thresholds for different surgical procedures.
I understand the clinical and hemodynamic differences between TRALI and TACO.
I know why gamma-irradiation (and not leukoreduction) is required to prevent TA-GvHD.
I can list all metabolic and electrolyte complications of massive transfusion and their preventive measures.
I understand the laboratory findings expected in acute ABO incompatibility (+ve DAT, elevated LDH/bilirubin, low Hct, hemoglobinuria).

📚 L9 Antidepressants I