10.2 Venepuncture, Peripheral Cannulation & Blood Sampling

Anatomical Site Selection & Venous Assessment

Venepuncture and peripheral intravenous (IV) cannulation are invasive procedures that require meticulous anatomical knowledge, aseptic non-touch technique (ANTT), and systematic vein selection to minimise patient discomfort and complications.

Primary Venous Landmarks in the Antecubital Fossa

1. Median Cubital Vein: The primary and preferred site for venepuncture. Located centrally in the antecubital fossa, it is typically large, superficial, well-anchored by surrounding fascia, and possesses a lower risk of accidental nerve or arterial injury.
2. Cephalic Vein: Located along the lateral aspect of the forearm and antecubital fossa. It is well-suited for both venepuncture and peripheral cannulation, though it may roll if not properly anchored during insertion.
3. Basilic Vein: Located along the medial aspect of the forearm and antecubital fossa. Although often large and prominent, it lies in close anatomical proximity to the brachial artery and median nerve. Puncture of the basilic vein carries a higher risk of accidental arterial puncture or nerve damage.

Contraindicated Sites & Clinical Risk Factors

Nurses must avoid selecting veins in limbs with any of the following clinical conditions:

• Lymphoedema or Axillary Node Clearance: Avoid the affected side due to impaired lymphatic drainage and elevated infection risk.
• Arteriovenous (AV) Fistula or Graft: Absolutely contraindicated for venepuncture or IV insertion to preserve vascular access for haemodialysis.
• Stroke-Affected or Paresic Limb: Impaired sensation and venous return increase complication risks.
• Active Infection, Cellulitis, or Extensive Burns: Prevents introducing pathogens into the systemic circulation.
• Limb with Existing Intravenous Infusions: Sampling proximal to an active IV infusion causes hemodilution and spurious laboratory results.

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Tourniquet Technique & Hemoconcentration Avoidance

Proper tourniquet application increases venous pressure, causing target veins to engorge and become distended.

• Placement Distance: Apply the tourniquet 7 to 10 cm (3 to 4 inches) proximal to the intended puncture site.
• Tightness: The tourniquet must restrict venous return while maintaining arterial inflow (radial pulse must remain palpable).
• The One-Minute Rule: Tourniquet application time must not exceed 1 minute. Leaving a tourniquet on for longer than 60 seconds causes hemoconcentration—the localized accumulation of large molecules, cellular elements, and protein-bound substances due to fluid shifting out of the vascular space.
• Laboratory Artifacts: Prolonged tourniquet application leads to spuriously elevated readings for potassium (hyperkalaemia), calcium, total protein, and coagulation factors, alongside potential haemolysis.
• Release Timing: Release the tourniquet as soon as blood begins flowing into the first vacuum tube during venepuncture, or immediately after venous access is established prior to flushing a peripheral cannula.

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Standard Order of Draw for Blood Sampling

To prevent cross-contamination of tube additives that can cause erroneous laboratory test results, blood sample tubes must be filled strictly according to the international Clinical and Laboratory Standards Institute (CLSI) and NHS UK standard order of draw.

• Inversion & Mixing: Immediately following collection, tubes containing additives must be gently inverted 5 to 10 times (do not shake vigorously) to ensure thorough mixing without causing mechanical haemolysis.
• Sodium Citrate Specifics: Light Blue tubes must be filled precisely to the fill indicator line to maintain the exact 9:1 blood-to-anticoagulant ratio required for valid coagulation testing.

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Peripheral Intravenous Cannulation: Gauge Selection & Indications

Selecting the appropriate peripheral intravenous cannula (PIVC) gauge depends on vein caliber, required flow rate, and clinical indication.

• Flushing & Maintenance: Peripheral cannulae must be flushed with 0.9% Sodium Chloride before and after medication administration, or at least every 24 hours to maintain patency.
• Visual Infusion Phlebitis (VIP) Score: Cannula sites must be assessed at least every shift using the VIP scale (Score 0: Healthy site; Score 1: Slight pain/redness; Score 2: Two signs present—remove cannula; Score 3-5: Advanced phlebitis/thrombophlebitis).

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Complication Identification & Emergency Management

Nurses must vigilantly monitor IV sites for four primary local complications:

1. Phlebitis: Inflammation of the vein intima caused by mechanical irritation, chemical irritation (hypertonic drugs), or infection. Symptoms include warmth, erythema, localized tenderness, edema, and a palpable venous cord. Action: Immediately remove cannula, record VIP score, apply warm compress, and re-site in the opposite limb.
2. Infiltration: Inadvertent leakage of a non-vesicant IV solution or medication into surrounding subcutaneous tissue. Symptoms include cool skin, swelling, pallor, tightness, and pain around the insertion site. Action: Stop infusion, remove cannula, elevate the extremity, and apply a cool or warm compress depending on the solution.
3. Extravasation: Inadvertent leakage of a vesicant solution (e.g., chemotherapy agents, potassium chloride, concentrated vasopressors, calcium gluconate) into tissue, causing blistering, tissue necrosis, and sloughing. Action: Stop infusion immediately, disconnect tubing, attempt to gently aspirate residual drug through cannula, do NOT flush, notify the medical team, initiate specific antidote protocols, elevate limb, and document extensively.
4. Haematoma: Inadvertent perforation of the vein wall or inadequate pressure applied following cannula/needle removal, leading to localized blood collection. Symptoms include localized swelling, bruising, and pain. Action: Apply direct pressure, elevate limb, and apply ice pack.