Equipment
Antiseptic—70% isopropanol (disposable gauze
wipes soaked in isopropanol are available)
Sterile cotton gauze pads
Sterile syringe or vacuum tube holder
Disposable needle—the gauge of the needle should
be appropriate to the size of the vessel to be
entered. A "butterfly" needle (a short needle
attached to a flexible plastic tube that ends in a
syringe hub) may be used. Two-sided needles
are required when vacuum tube containers are
used.
Tourniquet
Specimen tubes
Procedure
1. Have the patient sit or lie down.
2. Prepare the specimen tubes and the syringe
assembly and place them beside the patient.
3. Select the arm to be used for the procedure.
Position the arm so that it is straight, well
supported, and comfortable. Position yourself
so that you are comfortable and have ready
access to the puncture site.
4. Place the tourniquet 6-10 cm above the elbow to
distend the veins. By palpation, identify a vein
in the antecubital area that is of adequate size,
pliant, and well seated (visual inspection alone
will not detect many excellent deeper veins). If
the veins are difficult to palpate, blood flow to
the arm may be accentuated by wrapping the
arm in a warm towel for 10 min prior to the
procedure. Also, limited forearm exercise (for
example, making a fist) can be used in an effort
to "bring out" a vein. Do not massage or slap
the arm.
5. Release the tourniquet before proceeding.
6. Cleanse the puncture site with antiseptic and
allow it to air dry or wipe it dry with a sterile
gauze pad.
7. Reapply the tourniquet.
8. Hold the skin taut over the puncture site by
applying downward tension on the forearm with
the thumb of the free hand. The free hand may
provide additional support for the patient's arm.
9. Hold the syringe assembly in the line of the vein
to be punctured at an angle approximately 30ş
with the arm. The bevel of the needle should be
up, the cutting tip down.
10. Puncture the skin and underlying vein, using a
steady, moderately fast movement. The needle
should be advanced no deeper than the estimated
distance needed to enter the lumen of the vein.
A slight give can usually be felt when the vein is
entered. Also blood can often be seen at the
needle hub.
11. Apply negative pressure by puncturing the
vacuum tube or by gently retracting the syringe
plunger. Blood should flow freely into the tube
or syringe. If the flow is irregular, rotate the
needle to reposition the bevel. Sometimes the
needle tip has passed through the vein - the
lumen can be reentered by pulling the needle
backward slightly.
12. Remove the tourniquet once blood is flowing
into the tube or syringe to prevent venous stasis
at the puncture site.
13. Once the specimen has been collected, remove
the needle and immediately apply pressure to the
site, using a sterile gauze pad until the bleeding
stops. The patient may apply the pressure with
his or her free hand. Do not allow the patient to
bend his or her arm as this reopens the incision
in the vein.
14. Specimen tubes containing anticoagulants must
be mixed promptly and may be inverted with one
hand while applying pressure to the venipuncture
site with the other.
15. Apply a sterile adhesive bandage.
Sources of Variability
1. Increased capillary hydrostatic pressure causes
water to shift from the intravascular into the
interstitial space. Blood cells, plasma proteins,
and protein-bound constituents will be present in
increased concentrations in this setting because
they will be distributed in a reduced volume of
plasma water. It can result from a systemic
increase in capillary pressure such as is seen
with prolonged standing, or from local effects,
most notably a prolonged time of application of
Specimen Collection Procedures A-4
BLOOD, VENOUS: ANTECUBITAL VEIN
