3.3 Winged Infusion Sets (Butterfly) & Syringe Systems

3.3 Winged Infusion Sets (Butterfly) & Syringe Systems

Clinical Core: While standard multisample evacuated tube systems (ETS) are the mainstay of routine phlebotomy, difficult patient populations—including neonates, pediatric patients, frail geriatric individuals, oncology patients with sclerotic vessels, and patients with superficial dorsal hand veins—require specialized venipuncture systems. Mastering the technical mechanics of Winged Infusion Sets (WIS / Butterfly needles) and manual Syringe Systems, along with their strict safety and air-purge protocols, is essential for high-level clinical competency.

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Winged Infusion Sets (WIS / Butterfly Needles)

A Winged Infusion Set (WIS), colloquially known as a butterfly needle, is a specialized vascular access device designed for shallow, delicate, or difficult venipunctures.

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|                   WINGED INFUSION SET (BUTTERFLY) ANATOMY                   |
+-----------------------------------------------------------------------------+
|                                                                             |
|   [ Short Needle ]--[ Flexible Wings ]======[ 7"-12" Clear Tubing ]===[Hub] |
|     (1/2" - 3/4")      (Textured)           (0.5 mL Air Dead-Space)  (Luer) |
|           |                                                                 |
|           v                                                                 |
|   [ Transparent Flashback Chamber ] (Immediate visual confirmation of vein) |
+-----------------------------------------------------------------------------+

Physical Anatomy and Engineering Components

1. Short Stainless Steel Needle: Typically 1/2 inch to 3/4 inch (1.27 to 1.9 cm) in length, providing superior tactile control and maneuverability in shallow subcutaneous tissue compared to standard 1.0 to 1.5 inch ETS needles.
2. Flexible Textured Wings: Bilateral plastic wings color-coded by needle gauge (e.g., 21G Green, 23G Light Blue, 25G Royal Blue/White). Grasping the wings folded together allows the phlebotomist to manipulate the needle at an exceptionally low angle of entry. Once inserted, the wings rest flat against the patient's skin, stabilizing the needle.
3. Flexible Kink-Resistant Extension Tubing: Measures 7 to 12 inches (18 to 30 cm) of clear plastic tubing connecting the needle to a female Luer hub. The tubing isolates patient limb movement and tube-swapping manipulation from the needle tip, preventing needle dislodgement.
4. Transparent Flashback Chamber: Located directly behind the needle hub. The instant the needle bevel breaches the vein lumen, venous pressure pushes blood into the chamber, providing immediate visual confirmation (flashback) of successful intraluminal access before advancing an evacuated tube.
5. Engineered Safety Device: Integrated push-button retraction or active sliding shield that encapsulates the needle tip the moment it is withdrawn from the vein.

Clinical Indications for Winged Infusion Sets

• Pediatric and Neonatal Patients: Small vessel calibers requiring high tactile sensitivity and minimal needle movement.
• Geriatric and Oncology Patients: Fragile, rolling, thin-walled, or sclerotic veins prone to rupture or transfixion under rigid needles.
• Dorsal Hand and Wrist Venipunctures: Superficial hand veins lie immediately above delicate tendons, fascia, and periosteum, requiring a very shallow entry profile.
• Tremulous, Agitated, or Spastic Patients: Patients with Parkinson's disease, severe tremors, or developmental agitation; the flexible tubing absorbs patient motion without forcing the needle through the posterior vessel wall.

Butterfly Gauge Selection and Insertion Biomechanics

• 23-Gauge (Light Blue Wings): The universally recommended clinical standard for adult difficult venipunctures and dorsal hand collections.
• 21-Gauge (Green Wings): Used for larger hand veins or multi-tube collections with higher volume requirements.
• 25-Gauge (Royal Blue / White Wings): Reserved exclusively for neonatal scalp or tiny pediatric micro-veins. Clinical Caution: The extremely narrow bore of a 25G needle increases hydrodynamic shear stress; pulling blood through a 25G needle with strong vacuum significantly increases the risk of in vitro mechanical hemolysis.
• Insertion Angle: Fold the flexible wings together with the textured sides touching, bevel facing strictly UP. Enter the skin at a very shallow angle of 10 to 15 degrees (almost parallel to the skin surface). As soon as the blood flash appears in the tubing, lower the wings flat to the skin and stabilize.

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The Mandatory Butterfly Discard Tube Rule

One of the most heavily tested and clinically critical rules in diagnostic phlebotomy is the Mandatory Butterfly Discard Tube Rule when collecting coagulation specimens.

[ Butterfly 12" Tubing Contains ~0.5 mL Air ]
                     |
                     v (If Light Blue Sodium Citrate is Drawn First WITHOUT Discard)
[ 0.5 mL Air Pulled Into Light Blue Tube First ]
                     |
                     v
[ Vacuum Exhausts Early -> Tube Draws Only 4.0 mL Blood Instead of 4.5 mL ]
                     |
                     v
[ Blood-to-Anticoagulant Ratio Altered: 8:1 instead of 9:1 (Over-Citrated) ]
                     |
                     v
[ Excess Citrate Binds Lab Reagent Calcium -> FALSELY PROLONGED PT/INR & aPTT! ]

Detailed Biochemical and Physical Mechanism

1. The Dead-Space Air Phenomenon: A standard 12-inch butterfly tubing set contains approximately 0.3 to 0.5 mL of ambient air within its lumen.
2. The Underfill Consequence: When a light blue (3.2% sodium citrate) tube is attached as the very first tube of a draw, the evacuated tube's pre-measured negative pressure vacuum immediately pulls that 0.5 mL of dead-space air into the tube before blood arrives.
3. Ratio Disruption: The tube exhausts its vacuum prematurely, underfilling by exactly 0.5 mL (e.g., drawing only 4.0 mL of blood into a 4.5 mL draw tube containing 0.5 mL liquid citrate). This disrupts the strict 9:1 blood-to-anticoagulant ratio, creating an over-citrated specimen (~8:1 ratio).
4. Diagnostic Impact: The excess uncomplexed citrate in the specimen binds the calcium reagent during automated coagulation testing, resulting in falsely prolonged Prothrombin Time (PT/INR) and falsely prolonged Activated Partial Thromboplastin Time (aPTT). This can lead physicians to inappropriately halt anticoagulant therapy or administer unnecessary fresh frozen plasma.

The Mandatory Clinical Protocol

• Mandatory Discard Action: Whenever a light blue sodium citrate tube is the first or only tube to be drawn with a winged infusion set, the phlebotomist must first collect a non-additive discard tube (a plain red top without clot activator or a secondary non-diagnostic light blue tube).
• Purging the Air: Connect the discard tube to the holder just long enough for blood to fill the 12-inch tubing and enter the tube stopper (filling only 0.5 mL). The discard tube is removed and discarded into biohazard waste (it is never sent to the laboratory).
• Diagnostic Collection: Immediately insert the diagnostic light blue tube, which will now fill completely with pure whole blood to its exact target fill line, preserving the perfect 9:1 ratio.
• Exceptions: If blood culture bottles, plain red serum tubes, or SST tubes are ordered prior to the light blue tube, those preceding tubes automatically purge the dead space air from the tubing. In such multi-tube sequences, a separate discard tube is not required.

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Manual Syringe Collection Systems

While evacuated tube systems rely on fixed negative pressure, manual hypodermic syringes allow the phlebotomist to control the rate and strength of aspiration vacuum manually.

Clinical Indications for Syringes

• Collapsed Veins: Small, thin-walled, or elderly veins that instantly collapse under the aggressive negative pressure (-300 to -500 mmHg) of an evacuated tube.
• Low-Pressure Fragile Vessels: Veins in hypotensive, dehydrated, or burn patients where gentle, millimeter-by-millimeter plunger traction prevents vessel occlusion.
• Arterial Blood Gas (ABG) Collections: Specialized pre-heparinized syringes with self-filling arterial pressure.

Syringe Anatomy and Preparation Protocol

• Components: Calibrated plastic barrel (typically 3 mL, 5 mL, 10 mL, or 20 mL), rubber-tipped plunger creating an airtight seal, and a threaded Luer-Lok hub.
• "Popping the Plunger" (Breaking Factory Friction): Before attaching the needle, the phlebotomist must gently push the plunger forward and pull it backward to break the factory manufacturing seal and ensure smooth gliding resistance. Expel all residual air from the barrel by pushing the plunger completely forward against the base before needle attachment.
• Manual Aspiration Technique: Enter the vein at 15 to 30 degrees (or 10 to 15 degrees with a butterfly-syringe assembly). Upon seeing blood in the needle hub, brace your hand against the patient's arm and slowly, steadily draw back on the plunger. Match the rate of plunger retraction exactly to the rate of venous blood refill.
• The Hemolysis Danger: Pulling the plunger back too forcefully or rapidly creates high negative suction pressure that collapses the vein against the needle bevel or subjects erythrocytes to extreme hydrodynamic shear stress, causing severe in vitro mechanical hemolysis.

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OSHA-Compliant Safety Blood Transfer Devices

Once blood is successfully collected in a syringe barrel, it must be safely transferred into evacuated blood collection tubes for laboratory processing.

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|               OSHA SAFETY BLOOD TRANSFER DEVICE PROTOCOL                    |
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|                                                                             |
| [ Syringe Barrel ] === [ Luer-Lok ] <---> [ Safety Transfer Device Holder ] |
|                                                        |                    |
|                                                        v                    |
|                                            [ Evacuated Collection Tube ]    |
|                                            (Vertical Insertion Inside Hood) |
|                                                        |                    |
|                                                        v                    |
|    *** ALLOW VACUUM TO DRAW BLOOD NATURALLY -- NEVER PUSH PLUNGER! ***      |
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The Strict OSHA Prohibition on Direct Stopper Puncturing

Under the OSHA Bloodborne Pathogens Standard, phlebotomists are strictly prohibited from holding an evacuated tube in one hand and piercing its rubber stopper with a hypodermic needle attached to a syringe. This practice is a leading cause of catastrophic needlestick puncture wounds when the needle slips off the convex rubber stopper. Furthermore, forcing blood through a hypodermic needle pressurizes the tube, which can cause the rubber stopper to blow off, aerosolizing infectious blood into the phlebotomist's eyes and mucous membranes.

Step-by-Step OSHA Blood Transfer Protocol

1. Activate Needle Safety: Upon needle withdrawal from the vein, immediately activate the safety mechanism and remove the needle from the syringe hub using a one-handed safety decapper or sharps port.
2. Attach Transfer Device: Securely screw a single-use, needleless Safety Blood Transfer Device onto the Luer-Lok hub of the syringe.
3. Vertical Tube Insertion: Place the evacuated tubes vertically into the transfer hood, advancing the tube onto the internal recessed needle.
4. The Critical "No Plunger Pressure" Rule: Never depress the syringe plunger. Allow the evacuated tube's internal vacuum to pull the exact calibrated volume of blood out of the syringe naturally. Depressing the plunger creates massive hydrostatic shear pressure that forces erythrocytes across the internal cannula, resulting in gross specimen hemolysis, or overfills the tube, violating anticoagulant ratios.
5. Syringe Transfer Order of Draw: Tubes must be filled in the following order during syringe transfer to prevent clotting in the syringe barrel: (1) Blood Cultures, (2) Light Blue (Coagulation), (3) Serum tubes (Red/Gold SST), (4) Green (Heparin), (5) Lavender/Pink (EDTA), (6) Gray (Fluoride/Oxalate). Coagulation and culture tubes are transferred first because clotting factors begin activating in the syringe barrel the moment blood leaves the body.