Equipment
The necessary equipment for an arterial puncture is
usually available as a packaged, sterilized set.
Antiseptic—povidone-iodine
Local anesthetic—lidocaine hydrochloride
Sodium heparin solution
Sterile cotton gauze pads
Sterile syringes and plungers
Disposable needles—a 25-gauge needle is used when
administering the anesthetic. A medium bore
needle (e.g., 21-gauge) is usually used for the
actual puncture
Specimen containers—almost always the syringe
itself will serve as the specimen container
Procedure
1. Identify the artery by its pulsations.
2. Cleanse the skin over the puncture site using the
antiseptic. Allow it to air dry.
3. The use of local anesthesia is not required but is
encouraged. Infiltrate the skin and soft tissue at
the puncture site with the anesthetic.
4. Draw 1 ml of sodium heparin solution into the
syringe and with it thoroughly lubricate the
barrel. Test the plunger to assure easy mobility,
then expel the heparin, leaving the dead space
filled with residual heparin.
5. Change the needle on the syringe. For puncture,
the needle gauge should be appropriate to the
caliber of the artery to be entered.
6. Position the arm so that it is well supported and
comfortable. Dorsiflexion of the wrist is useful
and may be achieved by placing a rolled towel
under the patients vein.
7. Hold the needle parallel to the artery at an angle
of 45-60 degrees, bevel up.
8. Puncture the skin and underlying artery, using a
steady, moderately fast movement. The needle
should be advanced no further than the estimated
distance needed to enter the lumen of the artery.
A slight give can usually be felt when the artery
is entered.
9. Arterial blood usually fills the syringe under its
own pressure but slight negative pressure
generated by gentle retraction of the syringe
plunger may be needed. Once the specimen has
been collected withdraw the needle and immedi-
ately compress the puncture site for at least 5
min using a sterile gauze.
10. If air has been aspirated into the syringe, expel
it.
11. Remove the needle, place an airtight cap over
the tip of the syringe, and place the syringe into
ice.
12. Transport the specimen immediately.
Sources of Variability
1. Contract with air, even as air bubbles within the
syringe, will result in substantial alterations in
the partial pressure of oxygen (pO
2
) in the speci-
men. Because the pO
2
of arterial blood is
always subatmospheric in patients who are not
receiving oxygen therapy, exposure to air for
even short periods will cause the pO
2
to
increase. Air bubbles should be expelled from
the syringe, and the tip of the syringe should be
capped securely.
2. Because carbon dioxide is readily absorbed into
heparin solution, a large volume of heparin in
the collection syringe (as can happen in small
syringes with large dead spaces) will cause a
decrease in the partial pressure of carbon dioxide
in the specimen. Minimize the residual heparin
in the syringe prior to obtaining the specimen.
3. Cellular respiration in a blood specimen leads to
a decrease in its pO
2
. Cooling the specimen by
immersing it in ice water effectively slows this
process. Immediate delivery and processing of
the specimen further reduces the likelihood of
significant oxygen consumption.
Medical Considerations
1. Local anesthesia can greatly reduce the discom-
fort experienced by the patient so its use is
encouraged.
2. Local trauma from an arterial puncture is usually
minimal when arm arteries are used. In adults,
femoral arteries are frequently atherosclerotic.
Consequently, puncture of these arteries can lead
Specimen Collection Procedures A-2
BLOOD, ARTERIAL: RADIAL ARTERY
