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Your Curriculum: Medicine & Allied Subjects

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How We'll Work Together

1. Definition, classification, epidemiology (Bangladesh context)
2. Applied anatomy & physiology (clinically relevant only)
3. Aetiology & pathophysiology (with mechanisms - your strength)
4. Clinical features (history + examination)
5. Investigations (what, why, interpretation)
6. Differential diagnosis
7. Management (emergency → definitive → follow-up, national guidelines where relevant)
8. Complications & prevention
9. Referral criteria
10. Clinical pearls (ward, viva, lifelong practice)

• Medical textbook library (Harrison's, Davidson's, Kumar & Clark, Oxford Handbook, and others in the database)
• PubMed for recent evidence
• Bangladesh-specific context (NTP, IMCI, DOTS, EPI, national programmes)

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Ready to go!

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A1.5 — Practical & Procedural Skills

IV Cannulation | IV Infusion | IV Transfusion | IM / SC / ID Injections

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PART 1: INTRAVENOUS CANNULATION

Anatomy Basis

• Preferred veins (distal to proximal): dorsum of hand (metacarpal veins) → cephalic vein (antecubital fossa, lateral) → basilic vein (medial) → median cubital vein
• Avoid: dominant arm, flexion creases, feet (DVT risk), infected/bruised sites, AV fistula arm, mastectomy-side arm (lymphoedema risk), side with ongoing infusion
• Why cephalic at antecubital fossa is preferred: straight, superficial, easy to stabilise, large bore possible

Mechanism of Why It Works

• Cannula = Teflon/polyurethane catheter over steel needle (trocar)
• Bevel-up entry at 15-30° - needle punctures skin + vessel wall, blood flashback confirms intravascular position, cannula advanced while needle withdrawn
• Flashback chamber fills: venous blood (dark) confirms correct position (bright red = arterial - stop immediately)

Equipment (mnemonic: GASP-C-T)

• Gloves (non-sterile)
• Alcohol swab (70% isopropyl, dry 30 sec - "wet = contaminated")
• Syringe + normal saline flush (5-10 mL)
• Plaster / transparent dressing (Tegaderm)
• Cannula (correct gauge)
• Tourniquet

Cannula Gauge Guide (important for viva)

Step-by-Step Technique

1. Explain procedure, get consent
2. Position arm dependent (gravity fills veins), apply tourniquet 5-7 cm above site
3. Identify and palpate vein - "bounce" test
4. Clean with alcohol swab, allow to dry
5. Stretch skin distally (anchors vein, prevents rolling)
6. Insert bevel-up at 15-30°, watch for flashback
7. Lower angle to 5-10°, advance cannula 2-3 mm further, slide cannula off needle
8. Release tourniquet, apply pressure proximal to tip, withdraw needle fully
9. Attach Luer-lock cap or giving set, flush with 5 mL saline
10. Secure with transparent dressing, label with date+time+gauge

Complications & Mechanisms

Clinical Pearls

• Difficult veins: warm the arm (vasodilation), ask patient to clench fist, use nitro patch, ultrasound-guided
• Always label the cannula date - unlabelled cannula = assumed infected in ward
• Never recap the needle - straight to sharps bin (universal precaution, HIV/hepatitis)
• Flushing should be brisk with no resistance and no swelling = correctly sited

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PART 2: INTRAVENOUS INFUSION

Types of IV Fluids & Their Mechanisms

Crystalloids

• Crystalloids distribute by osmotic gradient and vascular permeability
• Only 1/4 of isotonic saline stays intravascular (hence 3:1 rule for blood loss replacement)
• Colloids (albumin, gelatin, starch) stay intravascular longer - maintain oncotic pressure

Colloids

• Albumin 4-5%: natural, used in SBP prophylaxis, hepatorenal syndrome
• Gelatin (Gelofusine/Haemaccel): synthetic, anaphylaxis risk
• Starches (Hetastarch): now avoided - AKI risk proven in trials

Infusion Rate Calculation (exam skill)

Drops/min = (Volume in mL × Drop factor) ÷ Time in minutes

• Standard giving set: 20 drops/mL
• Blood giving set: 15 drops/mL
• Paediatric/Burette set: 60 drops/mL

Complications of IV Infusion

• Fluid overload → pulmonary oedema (especially elderly, cardiac/renal disease) - monitor JVP, lung bases
• Electrolyte imbalance → excessive NS causes hyperchloraemic metabolic acidosis
• Phlebitis/infection (as above)
• Air embolism
• Hypothermia with large-volume rapid cold infusions - use blood warmer

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PART 3: BLOOD TRANSFUSION

Blood Products & Indications

• Each unit contains ~200-250 mL RBCs with ~60 g Hb
• Total blood volume ~5000 mL in 70 kg adult
• 60 g ÷ 5000 mL = ~1.2 g/dL rise (adjusted for dilution effect ≈ 1 g/dL)

Pre-Transfusion Checks (CRITICAL - exam + clinical)

1. Blood group (ABO + Rh)
2. Cross-match compatibility
3. Patient name + hospital ID matches blood bag label
4. Expiry date
5. Visual inspection (clots, discolouration, bubbles)

• Re-confirm patient identity (ask name + DOB, check wristband)
• Match blood bag label vs request form vs patient ID
• Document: time started, unit number, nurse signatures

Transfusion Technique

• Use 16-18G cannula (smaller gauge → RBC haemolysis from shear stress)
• Use blood-giving set with 170-200 µm in-line filter (removes clots, cell debris)
• First unit: start slowly (1 mL/kg/hr for first 15 minutes) - observe for reaction
• If no reaction: 4-6 mL/kg/hr
• Each unit should complete within 4 hours (bacterial proliferation risk after 4 hrs at room temperature)
• Pre-medicate with paracetamol ± chlorphenamine if prior febrile/allergic reactions

Transfusion Reactions (most important topic)

• TRALI = Lung injury from donor (immunological) = NO JVP rise, NO hypertension, NOT helped by diuretics
• TACO = overloAd = JVP raised, BP up, RESPONDS to diuretics

Blood Transfusion - Clinical Pearls

• Never add drugs to blood bag - incompatibility/haemolysis
• Only flush with normal saline (NOT dextrose - causes haemolysis)
• Massive transfusion (>10 units in 24 hrs): give FFP + platelets in 1:1:1 ratio with PRBC
• Jehovah's Witnesses: document refusal, offer cell salvage, iron infusion, erythropoietin, use restrictive threshold Hb 6 g/dL

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PART 4: INJECTIONS — IM / SC / ID

Comparison Table (most exam-tested)

Mechanism of Absorption Differences

Intradermal (ID) Injection - Mantoux Test

1. Inner aspect of forearm, 4-5 cm below antecubital fossa
2. Clean with alcohol, allow to dry
3. Insert bevel-up at 10-15°, advance 2-3 mm
4. Inject 0.1 mL tuberculin PPD → pale, raised wheal (8-10 mm) must form
5. No wheal = SC injection = test invalid, repeat other arm
6. Read at 48-72 hours (not immediately)

• ≥10 mm induration: Positive (general population)
• ≥5 mm: Positive in HIV, close TB contacts, CXR changes
• ≥15 mm: Positive in low-risk individuals
• Note: BCG vaccination causes false positive; prior TB also positive

Subcutaneous (SC) Injection - Insulin Example

• Abdomen (fastest absorption - preferred pre-meal)
• Outer thigh (slower)
• Upper arm
• Buttock (slowest)

1. Pinch skin fold between thumb and index finger (lifts SC tissue away from muscle)
2. Insert at 45° (lean patients) or 90° (adequate SC fat)
3. Do NOT aspirate (current evidence: no benefit, may cause tissue trauma)
4. Inject slowly, maintain pressure 5-10 sec, withdraw at same angle
5. Apply gentle pressure - do NOT rub (rubbing accelerates absorption unpredictably)

Intramuscular (IM) Injection

1. Clean skin with alcohol swab, dry
2. Pull skin 2.5-3.5 cm laterally (the "Z")
3. Insert 90° with quick, smooth motion
4. Aspirate (for IM - debate continues but still taught in BMDC curriculum for dorsogluteal to avoid intravascular injection)
5. Inject slowly (1 mL/10 sec)
6. Release Z-track after withdrawing needle → skin slides back, seals drug in muscle, prevents backtrack to SC → reduces pain and leakage

• Creates a zig-zag channel through tissue layers
• Drug cannot track back to SC layer (painful) or skin surface
• Particularly important for irritant drugs (iron dextran, hydroxyzine)

Complications of Injections

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SUMMARY MIND-MAP (Quick Revision)

IV ACCESS
├── Cannula: 14G(orange)→16G(grey)→18G(green)→20G(pink)→22G(blue)→24G(yellow)
├── Angle: 15-30° entry → lower to 5° to advance
├── Complication: Phlebitis, Extravasation, Air embolism, Haematoma
└── Change every 72-96 hrs

IV FLUIDS
├── NS = ECF expansion (1/4 stays intravascular), hyperchloraemic acidosis risk
├── RL = most physiological crystalloid
├── 5% Dextrose = free water (goes everywhere), NOT for resuscitation
└── Drops/min = (Vol × drop factor) ÷ time(min)

TRANSFUSION
├── PRBC: Hb<7 (or <8 cardiac); 1 unit = +1 g/dL Hb
├── 4-hr rule: complete each unit within 4 hours
├── Flush with NS only (not dextrose)
├── TRALI = immunological, no diuretics
└── TACO = overload, give diuretics; STOP transfusion first

INJECTIONS
├── ID: 5-15°, 0.1 mL, wheal required (Mantoux)
├── SC: 45-90°, ≤2 mL, no aspiration, no rubbing (insulin, heparin)
└── IM: 90°, Z-track, ≤5 mL, aspirate; avoid dorsogluteal (sciatic nerve)

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Viva Pearls

• "Why not give blood in dextrose?" → Dextrose causes osmotic haemolysis of RBCs
• "First sign of acute haemolytic reaction in anaesthetized patient?" → Haemoglobinuria (can't report pain)
• "Why Poiseuille's law matters clinically?" → Wider, shorter cannula = exponentially faster flow in emergencies
• "Why Mantoux read at 48-72 hrs not immediately?" → Type IV hypersensitivity (delayed, T-cell mediated) - takes 48-72 hrs to develop induration
• "Safest IM site?" → Ventrogluteal - no major nerves or blood vessels in the triangle
• "Why rotate insulin injection sites?" → Prevents lipodystrophy and ensures predictable absorption