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Intravenous Fluids - Comprehensive Overview

1. Classification

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2. Crystalloid Solutions

Composition of Commonly Used Crystalloids

Key Crystalloids and Their Indications

• The most widely used, despite being a misnomer (not truly "normal" - plasma Na is ~140 mEq/L, not 154)
• High Cl- content (154 mEq/L) causes hyperchloremic metabolic acidosis when given in large volumes
• Associated with increased perioperative acute kidney injury risk
• Specific indications: hypochloremic metabolic alkalosis (e.g., from vomiting), diluting packed RBCs before transfusion, DKA initial resuscitation

• A balanced salt solution; more physiologic ionic composition
• Contains lactate (metabolized to bicarbonate by the liver)
• Preferred for most perioperative fluid replacement
• Avoid in hyperkalemia (contains 4 mEq/L K+) and liver failure

• Most balanced crystalloid; pH 7.4
• Replaces Cl- with acetate and gluconate instead of lactate
• Preferred in patients with liver dysfunction and in DKA (some evidence of more rapid normalization of physiology)

• Equivalent to free water after glucose metabolism
• Used for pure water deficits (hypernatremia), maintenance fluids in Na-restricted patients
• Never use for resuscitation - becomes hypotonic, causes cerebral edema

• Used in severe symptomatic hyponatremia and raised intracranial pressure
• Must be given slowly through a central line; risk of osmotic demyelination if Na corrected too fast (>10-12 mEq/L per 24h)

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3. Colloid Solutions

Safety warning: HES preparations are restricted or banned in many countries for ICU use due to RCT data showing increased acute kidney injury and mortality in septic patients. Albumin remains the safest colloid when one is needed.

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4. Crystalloid vs. Colloid: Key Debate

1. Crystalloids in sufficient volumes are equally effective as colloids for restoring intravascular volume
2. Colloids require 3-4x less volume for the same hemodynamic effect
3. Large-volume crystalloid (>4-5 L) causes tissue edema - impairing wound healing, bowel function, and oxygen transport
4. Concerns that colloids worsen pulmonary edema in increased-permeability states are generally unfounded
5. For hemorrhagic and septic shock, crystalloids are the initial fluid of choice

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5. Fluid Compartments and Distribution

• Isotonic crystalloid (NS, LR): Distributes throughout the extracellular compartment (~25% stays intravascular, ~75% goes interstitial)
• Colloid: ~80% remains intravascular
• D5W / hypotonic: Distributes throughout total body water (~10% intravascular)

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6. Clinical Indications by Scenario

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7. Monitoring Fluid Therapy

• Urine output: Target >0.5 mL/kg/h (adult); >1 mL/kg/h (child). A urine output >30 mL/h is generally satisfactory.
• Electrolytes: Check regularly during prolonged IV fluid therapy
• Clinical signs: JVP, skin turgor, mucous membranes, capillary refill
• Serum lactate: Marker of tissue perfusion in shock
• Caution: Osmotic diuresis from glycosuria can give falsely reassuring urine output despite hypovolemia

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8. Complications

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Quick Reference: "4-2-1 Rule" for Maintenance Fluids

• 4 mL/kg/h for first 10 kg
• 2 mL/kg/h for next 10 kg
• 1 mL/kg/h for each kg above 20

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IV Cannula - PG Surgery Practical Viva

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Q1. What is an IV cannula? What is it also called?

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Q2. What are the parts of an IV cannula?

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Q3. What material is the cannula made of?

• Polyurethane (most modern cannulas) - lower thrombogenicity, more flexible
• Older designs: polyvinylchloride (PVC) or Teflon (FEP - fluorinated ethylene propylene)

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Q4. What is the colour code and gauge of IV cannulas? What is gauge?

Memory tip: "Old Grandma Will Give Pink Biscuits Yesterday" - Orange, Grey, White, Green, Pink, Blue, Yellow, Violet

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Q5. What size do you use for a routine surgical patient? For emergency?

• Routine elective surgery: 18G (Green) - adequate for fluids and blood transfusion
• Emergency / trauma / major surgery: 16G (Grey) or 14G (Orange) - at least 2 large-bore cannulas
• Children: 22G-24G
• Neonates: 24G-26G

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Q6. What is the principle behind gauge and flow rate?

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Q7. What are the preferred sites for IV cannulation?

Order of preference (upper limb preferred over lower):

1. Dorsum of hand - cephalic vein, dorsal venous arch (most common)
2. Forearm - cephalic vein (lateral), basilic vein (medial), median antebrachial vein
3. Antecubital fossa - median cubital vein (good size, easy access; but limits elbow movement - avoid if possible for long-term)
4. Arm - cephalic/basilic vein upper arm
5. External jugular vein - emergency when peripheral access fails
6. Foot / great saphenous - last resort (high phlebitis risk)
7. Scalp veins - in neonates/infants

Preferred insertion site characteristics:

• Straight segment of vein (not over a valve/bifurcation)
• Away from joints (to avoid kinking)
• Y-junction of two veins (easier cannulation)

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Q8. What are the contraindications to IV cannulation at a particular site?

• Cellulitis / local infection / burns at the site
• AV fistula in that limb (dialysis patients - never cannulate that arm)
• Ipsilateral to axillary lymph node dissection (lymphoedema risk - Note: recent evidence suggests this may not be an absolute contraindication, per American Society of Breast Surgeons 2021)
• DVT in that limb
• Haematoma at site
• Phlebitis from previous cannula

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Q9. Describe the procedure of IV cannulation step by step.

1. Explain procedure and obtain consent; position patient (arm at heart level or slightly dependent)
2. Apply tourniquet 5-10 cm proximal to intended site; ask patient to pump fist
3. Select vein - inspect and palpate; choose straight segment
4. Clean site with 2% chlorhexidine swab; allow to dry (30 seconds)
5. Wear gloves; remove cannula cap
6. Apply distal traction with non-dominant hand to anchor vein
7. Hold cannula with bevel up, at 10-30° angle to skin
8. Insert through skin toward vein; advance until first flashback (blood in flashback chamber)
9. Flatten angle, advance 1-2 mm further to ensure tip is fully in vein
10. Withdraw needle slightly, observe second flashback (blood flows into cannula)
11. Thread cannula fully into vein over needle, release tourniquet
12. Apply pressure over vein proximal to cannula tip, withdraw needle fully
13. Attach cap/bung or IV line; flush with 10 mL normal saline to confirm patency
14. Secure with transparent dressing; label with date and time

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Q10. What is the significance of "first" and "second" flashback?

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Q11. Why flush with normal saline? Why not heparin?

• Flushing confirms patency and checks for extravasation (swelling = cannula not in vein)
• Normal saline is standard for flushing peripheral cannulas
• Heparin locks are used in central venous catheters and PICC lines, not peripheral cannulas
• Routine heparinisation of peripheral cannulas is not recommended (no evidence of benefit, risk of HITT)

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Q12. What are the complications of IV cannulation?

Local Complications:

Systemic Complications:

VIP Score (Visual Infusion Phlebitis Score):

• 0 = No signs
• 1 = Faint erythema or pain at site
• 2 = Erythema + pain at site
• 3 = Erythema + pain + induration/streaking
• 4 = Purulent exudate

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Q13. How long can a peripheral IV cannula remain in situ?

• Standard recommendation: 72-96 hours (3-4 days), then re-site
• However, current evidence (and some guidelines) supports clinically indicated replacement rather than routine replacement - i.e., change only when signs of complication (phlebitis, infiltration, blockage) develop
• Risk of infection rises significantly beyond 96 hours

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Q14. What are the types of IV cannulas?

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Q15. What is the difference between a peripheral cannula and a central venous catheter (CVC)?

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Q16. Quick fire viva answers:

• Why upper limb over lower limb? Lower limbs have higher phlebitis, DVT risk; impair mobility
• Why avoid joints? Cannula kinks, blocks, and causes positional flow issues
• Why bevel up during insertion? Reduces resistance; creates a clean incision; allows better flashback visualization
• Angle of insertion? 10-30° (flatten after first flashback)
• Why press proximally when withdrawing needle? Prevents blood spillage and air entry
• Why not cannulate AV fistula arm? Risk of infection, thrombosis, and disrupting the fistula used for dialysis
• Why label cannula? To track how long it has been in situ (change every 72-96 h)
• What if there is swelling on flushing? Extravasation - cannula is not in vein; remove immediately

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