Arterial Line Placement Technique

Identification of vessels

Vessels may be identified by means of either or both of the following methods ^[16] :

• Palpation over anatomic landmarks
• Ultrasound guidance

Choice of site and approach

Arterial line placement can be performed via multiple methods. The choice of approach is determined on the basis of location, operator preference, and available equipment. The most commonly used methods are the following ^[17] :

• Catheter over needle
• Catheter over wire (including direct Seldinger and modified Seldinger techniques)

Arterial cutdown for arterial access is not recommended. It should be considered a last resort, to be performed only by physicians with sufficient training and skill to perform the procedure and manage complications. Discussion of cutdown technique is beyond the scope of this article.

For radial artery cannulation, either the catheter-over-needle technique or the catheter-over-wire technique may be used. The latter is more common in adults and larger children; the former is more common in infants and neonates. As a last resort, a surgical cutdown can be performed for cannulation of the radial artery.

For femoral artery cannulation, the catheter-over-wire technique is preferred. The puncture site for the femoral artery should be below the inguinal ligament to allow control of bleeding and prevention of bleeding into the pelvis. The catheter-over-needle technique can also be used for femoral artery cannulation, either alone or in combination with an over-the-wire technique (ie, Seldinger) if a longer indwelling catheter is desired.

Many experts recommend that an Allen test be performed before radial artery cannulation is initiated. This is a simple bedside test designed to evaluate for adequate collateral circulation to the palmar arches of the hand. In most patients, the palmar arches are supplied by both the radial artery and the ulnar artery. This collateral circulation allows perfusion of the hand should either of these vessels be injured.

To perform the Allen test, the examiner elevates the hand and asks the patient to make a fist for 30 seconds. With the patient’s hand in a fist, the examiner applies simultaneous pressure to the ulnar and radial arteries so as to occlude them (see the image below).

The patient is then asked to open the hand, which should appear blanched as a consequence of the occlusion of the radial and ulnar arteries (see the image below).

Next, the pressure over the ulnar artery is released (see the image below), and the time it takes for color to return to the hand is measured (in seconds).

A modified Allen test has been described for use in unconscious or anesthetized patients who are unable to make a fist on demand. ^{[3, 18]}  In this variant, an Esmarch bandage is used to exsanguinate the hand; the rest of the test is performed as already described.

According to one view, Allen test results may be interpreted as follows ^[3] :

• If color returns to the hand within 5 seconds, the result of the Allen test is negative (normal) and the radial artery can safely be cannulated
• If color does not return to the palm within 5 seconds, the test result is positive (abnormal), in which case the collateral blood supply to the hand may be insufficient and an alternate cannulation site may be warranted

According to another view, Allen test results may be divided into the following three categories ^[10] :

• Return of perfusion to the hand in less than 7 seconds - Normal
• Return of perfusion in 8-14 seconds - Equivocal
• Return of perfusion in more than 14 seconds - Abnormal

In addition to disagreement about precisely what constitutes an abnormal result, there has been some debate in the literature about whether an Allen test is needed before radial artery puncture and how well it predicts complications. Patients with abnormal test results have safely undergone radial artery cannulation, and patients with normal results have experienced hand ischemia. ^{[19, 20]}

Overall, although the Allen test is not perfect, it should be performed before arterial puncture if time permits, and alternative puncture sites should be considered if the results are abnormal. Given the controversy surrounding the results of this test, however, some experts recommend Doppler evaluation of collateral flow in all high-risk patients before cannulation. ^[21]

Once the patient is properly positioned, palpate the artery, and confirm with ultrasonography (US) or Doppler US. US can be particularly helpful for identifying and accessing arteries in patients who have small vessels, have had previous arterial lines or attempts in the same area, or are hypotensive. ^{[4, 22, 23, 24, 25, 26, 27, 28, 29]} US guidance reduces the number of attempts, shortens the time to cannulation, reduces complications, and identifies anatomic variations. ^{[4, 22, 23, 24, 25, 26, 27, 28, 30, 16]} US can also help distinguish veins, which collapse with gentle pressure of the probe, from pulsating arteries.

Given the increasing availability of US for bedside use, it is reasonable to recommend that US guidance be employed when available. ^[26] Barriers identified as prohibiting the use of US guidance for vascular access include lack of equipment, perceived increases in procedure time, and concern regarding possible loss of traditional vessel identification skills. ^[31] If standard US is not available, a handheld Doppler device can facilitate location of the artery.

Vessels can be visualized both out of plane (short axis, perpendicular to the vessel) and in plane (long axis, parallel to the vessel). Both the short-axis view and the long-axis view can be used for ultrasound-guided arterial cannulation. ^[32] The short-axis view is useful for identifying surrounding structures; however, the operator must be mindful of advancing the probe along the vessel to maintain visualization of the needle tip while accessing the vessel. The long-axis view is useful for visualizing the continuous length while the vessel is being cannulated. ^[26]

An ultrasound device with a high-frequency linear-array transducer ultrasound probe and a sterile probe cover are needed in addition to the standard setup (see the image below). Often, placing the machine on the patient's contralateral side is helpful. The depth and gain of the screen should be optimized for visualization of blood vessels. Depending on the quality of the ultrasound machine screen, dimming the lights in the procedure room may facilitate identification of structures.

A small amount of lubricant should be placed into the sterile sheath before insertion of the ultrasound probe. After the probe has been inserted into the sheath, sterile rubber bands can be used to secure the sheath tightly over the transducer and keep the lubricant in place (see the image below). Additional lubricant is then used on the patient’s skin to optimize visualization of the structures.

For the short-axis view, the probe is placed perpendicular to the course of the artery and oriented so that movements on the ultrasound machine's screen correspond to movements of the needle in the patient (see the first image below). Arteries can generally be distinguished from surrounding veins, in that they appear pulsatile and less compressible in comparison (see the second image below). The middle mark on the probe should be placed over the target vessel. It is important to advance the probe proximally with the tip of the needle so as to avoid complications. The needle will appear hyperechoic in comparison with surrounding structures.

After the needle is inserted through the skin, the subcutaneous tissues will be displaced as the needle is advanced (see the first image below). Arteries without significant atherosclerotic disease will compress similarly until the anterior wall of the artery is punctured and the needle enters the lumen of the vessel. Correct placement is also confirmed via flash or return of blood. Once the needle is successfully in the lumen of the vessel (see the second image below), the provider can proceed with one of the aforementioned techniques for catheter insertion.

The long-axis view is obtained by placing the probe parallel to the artery (see the first image below). The artery should appear pulsatile, as in the short-axis view (see the second image below). This technique is advantageous in that it allows visualization of a longer segment of the artery and the needle at the same time without the ultrasound probe having to be advanced proximally during the procedure (see the third image below).

In patients with smaller vessels, such as pediatric and neonatal patients, the long-axis view may help to avoid puncture of the posterior wall due to the relatively greater size of the needle as compared with  the artery. Once the needle is successfully in the lumen of the vessel (see the image below), the provider can proceed with one of the aforementioned techniques for catheter insertion.

The catheter-over-needle approach is the most basic method for placing an arterial line. Much as with peripheral intravenous (IV) placement, a needle with an integrated catheter is placed into the arterial lumen, and the catheter is advanced over the needle. This technique is best suited for use when the artery is located superficially, as is the case with the radial artery. It is the preferred method for radial artery cannulation in neonates and infants; the small vessel diameter in these patients makes threading a guide wire into the vessel lumen difficult.

For the catheter-over-needle approach, position the patient as described previously (see Patient Preparation). Identify the artery by means of palpation or US (or both). Clean the area with povidone-iodine or chlorhexidine, don sterile gloves in a sterile fashion, and drape the field with sterile towels or drapes.

Palpate the artery with the second and third digits (see the image below; the hand is left undraped to provide orientation), or visualize the artery with an ultrasound device in the nondominant hand. Inject 1-2 mL of lidocaine 1% without epinephrine at the site of insertion. Make sure not to distort the anatomy with a significant skin wheal.

Puncture the skin proximal to your fingers over arterial pulsations, advancing the needle at a 30-45° angle toward the pulsation with its bevel facing up (see the images below). If the artery is not punctured, make sure to withdraw the needle back to the skin before repositioning the needle. When employing US guidance, remember to follow the tip of the ultrasound device with the tip of the needle in the short-axis view. The long-axis view can be advantageous in that it allows visualization of the length of the artery and needle during cannulation.

Observe the hub of the needle for a flash of bright red blood, which signifies arterial puncture (see the images below). Once a flash has been obtained, lower the needle-catheter assembly to an angle of 10-20° from the skin, and insert the needle 1-2 mm further to advance the catheter into the lumen of the artery.

Stabilize the needle (see the first image below), and advance the catheter over the needle into the artery until the hub is at the level of the skin (see the second image below). If any resistance is felt, reposition the needle until free blood flow is obtained, and then try to advance the catheter. Never pull the catheter back over the needle; this can shear the catheter tip and lead to embolization of the catheter or a foreign body in the subcutaneous tissues.

After the catheter has been advanced into the artery, remove the needle and attach the catheter to an appropriate arterial line tubing (see the image below).

 Secure the catheter in place with sutures, tape, or adhesive strips (see the first image below), and apply a semipermeable sterile dressing over the site (see the second image below).

If the catheter cannot be advanced into the lumen but free return of blood exists, attempt to cannulate the vessel by using a guide wire and placing the catheter over the wire (see Catheter-Over-Wire Technique ). If a longer catheter is desired, the catheter-over-needle technique can be combined with the catheter-over-wire technique (see Catheter-Over-Wire Technique and Combination Technique).

The other main option for arterial line placement is the catheter-over-wire method, which includes the Seldinger and modified Seldinger techniques. The Seldinger and modified Seldinger techniques are similar in that they both involve entering the artery with a needle, advancing a wire into the artery through the needle, and then threading a catheter over the wire into the artery. Whereas the Seldinger technique uses separate components, the modified Seldinger technique uses an integrated needle-catheter-wire system.

Catheter-over-wire techniques can be used for superficial arteries (eg, the radial artery) and are preferred for the femoral artery. This method should not be used routinely for radial artery cannulation in neonates and infants, because the diameter of the vessel is too small to allow easy advancement of the guide wire.

Seldinger technique

Position, prepare, and drape the patient as previously described. Inject local anesthetic. Open the arterial line kit, and check the guide wire to make sure that it flows freely through the introducer needle. Palpate the artery with the second and third digits of the nondominant hand (see the image below).

Attach the finder needle to a syringe. Puncture the skin proximal to your fingers over arterial pulsations, advancing the needle at a 30-45° angle toward the pulsation (see the images below). Sometimes, making a small puncture in the epidermis with a larger needle at the site of the desired cannulation will decrease friction.

Advance the needle with slight negative pressure until free return of blood is visualized in the syringe (see the image below). If initial return of blood is observed but the flow then ceases, the posterior wall of the vessel may have been punctured. Withdraw the needle slightly to try to restore blood flow to the needle.

Once free flow of blood is obtained, remove the syringe.  Advance the guide wire into the artery (see the image below). If any resistance is encountered in advancing the guide wire, stop advancing the wire, reposition the needle, and attempt to cannulate the vessel again. If any resistance to repositioning the guide wire in the needle is met or if the guide wire is stuck in the needle, remove the needle and the wire together and start again.

Before removing the needle, make a small skin incision with a scalpel at the site of needle entry into the skin (see the images below). Do not make a stab incision of the sort used in central line placement; such an incision may damage the underlying artery.

Remove the needle while holding the guide wire in place. Then, advance a catheter over the wire into the artery (see the images below). If advancement of the catheter becomes difficult, a twisting motion can be used to facilitate catheter passage. A dilator is usually not necessary; if it is used, it should be employed only to dilate the tract, not to enter the artery; the latter can cause excessive bleeding.

Once the catheter is in place, remove the guide wire. Appropriate positioning of the catheter is confirmed by return of pulsatile blood from the catheter hub. Attach the catheter to appropriate arterial line tubing (see the image below). Secure the catheter in place with sutures, tape, or occlusive dressing.

Modified Seldinger technique

The modified Seldinger technique is similar to the standard Seldinger technique; however, the needle, catheter, and guide wire are all parts of a single unit. The description below addresses the use of this technique for line placement in the radial artery.

Position, prepare, and drape the patient as previously described. Inject local anesthetic. Open the arterial line kit. Assemble the catheter and wire (see the first image below). Make sure the guide wire moves smoothly and confirm that the wire is fully retracted (see the second image below).

Puncture the skin over the radial artery with the catheter and needle at an angle of 30-45° to the skin with the needle bevel facing up (see the image below).

Advance the needle until a flash of blood is seen in the needle hub; this initial flash is obtained when the needle tip, which protrudes beyond the end of the catheter, has entered the vessel lumen (see the images below).

Stabilize the needle, and carefully advance the guide wire into the artery by moving the actuating lever as far forward as possible (see the images below). If any resistance to advancing the guide wire is encountered, stop advancing the wire, remove the entire unit, and attempt another puncture. Do not try to retract the guide wire; doing so may shear the tip of the wire.

When the guide wire is in place, grasp the hub of the catheter, and advance the catheter over the needle and wire and into the vessel. If difficulty is encountered in passing the catheter, advance the needle 1-2 mm, and reattempt catheter placement. Once the catheter has been advanced, hold the catheter hub in place, and withdraw the needle and guide wire as a single unit (see the images below).

Confirm that the catheter remains properly positioned in the vessel lumen by monitoring for return of blood at the hub. Blood should flow freely from the end of the catheter hub after the needle and guide wire are removed. 

Attach the catheter to appropriate arterial line tubing, connectors, and transducers. Secure it in place with sutures, tape, or occlusive dressing. (See the images below.)

If a longer catheter is needed, first gain access with the catheter-over-needle technique (see Catheter-Over-Needle Technique), and then use the Seldinger technique to replace the shorter catheter with a longer one.

To perform this combination technique, place a wire through the shorter catheter after placement and remove the shorter catheter while holding the wire in place (see the image below).

Next, advance the longer (eg, 5-in. [12.7-cm]) catheter, and remove the guide wire once the longer catheter is in place (see the image below). Once proper positioning of the 5-in. catheter within the arterial lumen is confirmed, remove the guide wire. Confirm placement with free-flowing blood, then attach the appropriate tubing and cover with a sterile dressing.

Common complications of arterial line placement are as follows ^{[2, 33, 34]} :

• Temporary radial artery occlusion (19.7%)
• Hematoma/bleeding (14.4%)

Less common and rare complications include the following ^{[2, 33, 34]} :

• Localized catheter-site infection (0.72%)
• Hemorrhage (0.53%)
• Hematoma (14% radial, 6% femoral) ^[34]
• Sepsis (0.13%) ^[35]
• Permanent ischemic damage
• Pseudoaneurysm formation (0.09%) ^[36]
• Permanent occlusion (0.09%)
• Arteriovenous fistula
• Air embolism
• Compartment syndrome
• Carpal tunnel syndrome
• Paralysis of median nerve ^[37]
• Femoral artery dissection
• Suppurative thromboarteritis

A 2014 meta-analysis by O'Horo et al suggested that arterial catheters may be an insufficiently recognized cause of catheter-related bloodstream infection (CRBSI). ^[35]  The risk of arterial CRBSI was found to be higher with the femoral site than with the radial site. In some cases, complications of indwelling catheters (eg, in the radial artery) may necessitate open surgical intervention for management. ^[38]

Overall, the more serious complications of arterial line placement are exceedingly rare when correct procedural techniques are used. ^[39]