Arterial Puncture

Indications
Arterial blood samples can provide important information regarding respiratory and acid&base status, including arterial pH, pCO, pO and bicarbonate levels. Such information is often sought in patients to assess respiratory and metabolic status, in those with significant respiratory compromise, and in others who are severely ill.

Contraindications
Although there are no absolute contraindications arterial puncture should beperformed with extreme care in patients with the following bleeding disorders or anticoagulation, severe arterial disease in the area, as evidenced by diminished pulse or audible bruit, evidence absent collateral flow in areas where it normally
exists, and previous vascular surgery in the area. Do not perform arterial puncture through skin that appears infected. When frequent blood sampling is anticipated, it may be preferable to inser an indwelling arterial catheter rather than performing repeated arterial punctures.

Equipment
Prepackaged arterial blood gas kit including:
- Antiseptic sponge or solution
- Heparinized 5-ml syringe with 20- or 22-gauge needles
- Syringe stopper
- Gauze pads
- Syringe, and 25- or 27-gauge needles for anesthesia
- Local anesthetic solution


Technique


The blood sample is obtained with a 5-ml syringe, the barrel of which has been coated with heparin. If a prepackaged kit is used, the syringe already contains heparin. When preparing the syringe yourself, draw 2ml of heparinized saline solution (1000IU/ml) into the syringe. Draw back the plunger to coat the barrel and needle, and then eject the remaining heparin. Select an arterial puncture site. Common sites
are the radial, brachial and femoral arteries. The radial artery at the wrist is the most commonly used location (Look Figure), though the femoral artery is often preferred in patients in circulatory shock. For the radial artery, palpate the pulse
at the wrist, placing the hand in approximately 60 degrees of dorsiflexion. Avoid hyperextending the wrist, as this may place excessive traction on the artery, making the pulse more difficult to feel. The brachial pulse can be felt on the flexor aspect of the elbow, just proximal to the antecubital fossa. The femoral artery enters the thigh after passing beneath the inguinal ligament; the pulse can be felt in the groin, midway between the anterior-superior iliac spine and the pubic symphysis.

When the radial artery is considered, the Allen test should be performed to ascertain the adequacy of collateral ulnar flow. Perform the test as follows:
1. Palpate the radial and ulnar pulses at the wrist.
2. Compress both the arteries while having the patient repeatedly make a tight fist.
3. Instruct the patient to release the fist, and observe for blanching of the palm.
4. Release your compression of the ulnar artery, noting the time it takes for blanching to resolve. This should normally occur within 5-10 seconds.
When return of normal color to the palm is delayed, the adequacy of ulnar collateral flow can be questioned, and radial artery puncture should not be performed. The Allen test requires a cooperative patient. Moreover, even a normal Allen test does not guarantee the adequacy of collateral circulation.

Prepare the skin overlying the puncture area with antiseptic solution. In the awake patient, you may elect to anesthetize the skin by introducing a small volume of 1% plain lidocaine via a 25- or 27-gauge needle to make a small wheal. Alarge wheal may obscure the pulse. Palpate the pulse with the index and middle
fingers of the non-dominant hand. Puncture the skin over the artery between these two fingers. Advance the needle at approximately a 458angle to the skin, parallel to the vessel. When the artery is entered, allow the syringe to fill with the force
of arterial pressure. Obtain at least 3ml of blood for analysis. If no blood is encountered or the blood does not readily advance the syringeís piston, withdraw the needle and redirect it. Once blood sampling is completed, withdraw the needle and apply pressure over the puncture site for at least 5 minutes. If the patient has a
coagulopathy or is on anticoagulation therapy, apply pressure for 10ñ15 minutes. Expel any air bubbles present in the sample through the needle holding it upright, then plug the needle or cap the syringe to maintain anaerobic conditions.


Complications
Hematoma formation is the most common complication. This can be avoided by conscientious application of pressure after the procedure is completed. In any event, such bleeding is usually minor. Infection at the site is another potential complication. Serious infections, however, are uncommon. Although it has been postulated that the femoral site is at particular risk to infection because of proximity to the groin and perineum,no studies substantiate this.
Puncture may induce arterial spasm, which in turn can produce ischemia and thrombus formation. Such spasm usually causes transient ischemia, without significant sequelae in most cases. Nerve or venous injury from the needle is a potential complication. The femoral vein and nerve lie immediately to the medial and lateral sides of the artery, respectively. The median nerve lies just to the ulnar side of the brachial artery at the antecubital crease.

Reference
Clark VL, Kruse JA. Arterial catheterization. Crit Care Clin 1992;8:687-697.