Phlebotomy

Phlebotomy is a technique in which a needle is temporarily inserted into a vein to provide venous access for venous blood sampling.[1, 2, 3]  Veins have a three-layered wall composed of an internal endothelium surrounded by a thin layer of muscle fibers, which in turn is surrounded by a layer of connective tissue.

Identification of the optimal site for venous access (see Technical Considerations) involves both visual and tactile evaluation. After applying a venous tourniquet, the physician should inspect and palpate potential sites, starting with the nondominant extremity. On palpation, the vein should be soft and bouncy, it should refill after being depressed, and it ideally should be well supported by the surrounding tissue.

Phlebotomy is commonly performed with either an evacuated tube system (eg, Vacutainer; BD, Franklin Lakes, NJ) or a syringe and needle or winged butterfly needle device (see Technique).

Indications for phlebotomy include the following:

• Blood sampling
• Short-term infusion (via butterfly needle)

Contraindications for phlebotomy include the following:

• Evidence of cellulitis or abscess
• Venous fibrosis on palpation
• Presence of a hematoma
• Presence of a vascular shunt or graft
• Presence of a vascular access device

Anatomy

The superficial veins of the upper extremities, particularly those in the antecubital fossa, are the ones most commonly selected for phlebotomy because they are usually readily visible and easily palpable. The antecubital fossa contains four veins (see the images below). Of these, the median cubital vein is usually the vein of choice for phlebotomy: It is typically more stable (less likely to roll), it lies more superficially, and the skin overlying it is less sensitive than the skin overlying the other veins.

In many cases, the metacarpal veins are easily visualized and palpated (see the image below). However, obtaining needle access on the dorsal hand is more painful, and the metacarpal veins are more likely to roll and collapse on vacuum application than the antecubital veins are.

It appears that the device used to collect blood is the strongest independent predictor of hemolysis in blood samples drawn in the emergency department (ED). An ED study suggested that the most effective strategy to reduce the rate of hemolysis in the ED is to use butterfly needles for phlebotomy rather than intravenous catheters.[4]

Review the phlebotomy order and the patient’s written consent. Review the procedure with the patient, inform him or her about the tests for which the blood samples are being collected, and allow the patient to ask questions and express any preferences he or she may have for a site or side. Ask the patient if he or she ever experienced complications with phlebotomy in the past or is allergic to latex.

Equipment used for phlebotomy includes the following:

• Single-use nonsterile gloves
• Tourniquet
• Skin disinfectant (eg, chlorhexidine 0.5% in 70% alcohol or 70% alcohol swab or solution)
• Evacuated tube system with needle and adapter (eg, Vacutainer; BD, Franklin Lakes, NJ; see the first image below) or syringe and needle or winged butterfly needle device
• 21-gauge (green) or 22-gauge (black) needles are recommended in adults; a 23-gauge (light-blue) winged butterfly device is recommended in young children or in patients with small and fragile veins
• Blood collection tubes (see the second and third images below)
• Gauze
• Hypoallergenic tape (paper is preferred)

To alleviate potential anxiety, approach the patient in a professional, calm, and confident manner. If the patient is very anxious about the pain he or she expects to feel, a topical anesthetic cream may be applied 1 hour before phlebotomy.

Position the patient in a supine or sitting position with the arm resting on a flat surface. Make sure that the arm is positioned on a padded surface to increase comfort.

Verify the patient’s identity against the laboratory requisition, using local patient identification standards. Assemble the required equipment for this blood draw, and verify that the correct number and type of blood bottles are available. Wash your hands with soap and water before putting on a pair of nonsterile single-use gloves.

Phlebotomy is commonly done with an evacuated tube system (eg, Vacutainer; BD, Franklin Lakes, NJ; see the first video below) or a syringe and needle or winged butterfly needle device (see the second video below).

Apply a tourniquet 10 cm proximal to the chosen site (see the image below), and have the patient lower the arm while clenching and releasing the fist repeatedly for 15-30 seconds so as to engorge the veins.

Gently tapping on the vein may facilitate its identification. On palpation (see the image below), the vein should be soft and bouncy, it should refill after being depressed, and ideally, it should be well supported by the surrounding tissue.

Use a skin disinfectant to prepare the skin (see the image below), and apply firm pressure to the skin with the swab. Allow the skin to dry for 30 seconds. You may not repalpate the skin after it has been disinfected.

Assemble the blood collection device (see the image below), inspect it for any breaks or irregularities, and expose the needle.

With your nondominant thumb, apply traction to the skin a few centimeters distal to the chosen site of needle insertion (see the image below).

Inform the patient that you are about to introduce the needle, then insert the needle, with the bevel facing up (see the image below), at an angle of 15-30°. Once the needle has entered the vein (as signaled by decreased resistance), reduce the angle further, and advance the needle another 3-5 mm into the vein.

If a winged butterfly device is used, grasp it by the wings and introduce the needle into the vein, with the bevel facing up, at an angle of 10-15° (see the first image below). Once the needle is in the vein, a flashback of blood will be visible in the device’s chamber and tubing (see the second image below). Reduce the angle further, and advance the needle another 3-5 mm into the vein.

Switch hands, and hold the vacuum adapter device or the syringe with your nondominant hand so that you can use your dominant hand to pull the plunger or insert and release the vacuum tubes (see the image below).

Once a tube has filled up with blood, invert it slowly a couple of times to ensure that the blood mixes with the anticoagulant or additive without causing mechanical hemolysis (see the image below).

Release the tourniquet, apply gauze over the needle entry site, and withdraw the needle (see the image below). Either cover the needle with the safety needle cover or immediately place the device and needle in a sharps container.

Instruct the patient to keep the arm straight, and apply—or have the patient apply—direct pressure on the gauze for at least 5 minutes (see the image below).

If a syringe was used for drawing blood, use the needle remover on the sharps container to remove the needle, then use an adapter to transfer the blood into the sample tubes (see the image below).

Finally, verify the patient’s identity again, and compare it to the preprinted labels. Apply the correct labels to the blood collection tubes while at the patient’s bedside or in the room. Inspect the phlebotomy site. If no bleeding is observed, apply a paper tape over the gauze, or place an adhesive bandage over the puncture site. Discard waste and single-use items, and send the collected blood tubes to the lab.

Complications of phlebotomy include the following:

• Hematoma formation - To prevent this complication, keep the arm straight, and have the patient apply direct pressure to the gauze for at least 5 minutes (patients receiving anticoagulant therapy might require longer application of pressure)
• Nerve injury - Severe pain is a sign that a nerve was touched by the needle; if this occurs, remove the needle and apply direct pressure
• Arterial puncture - If this occurs, remove the needle and apply direct pressure for at least 10 minutes; if a pulsatile mass persists, consider arterial duplex ultrasonography
• Syncope - Some patients manifest a vasovagal response during or just after phlebotomy; thus, phlebotomy in a patient with a history of periphlebotomy should be done in the supine position; using a topical anesthetic and having the patients look away from the phlebotomy site, equipment, and blood filled tubes may be helpful
• Phlebitis or cellulitis (rare when aseptic technique is used for phlebotomy)