Arterial Line Placement Technique
- Author: Alex Koyfman, MD; Chief Editor: Vincent Lopez Rowe, MD more...
The radial artery is preferred for securing arterial blood and for cannulation to provide continuous blood pressure (BP) monitoring and arterial blood sampling. If the radial artery cannot be cannulated, the femoral artery offers a viable alternative.
Arterial line placement can be performed via multiple methods. The choice of methods is determined by location, operator preference, and available equipment. The most commonly used methods are the following:
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.
With either the catheter-over-needle approach or the catheter-over-wire approach, meticulous attention must be paid to preparing the cannulation site with chlorhexidine to minimize the risk of infection and to firmly securing the final intra-arterial catheter with sutures.[3, 23, 24]
As with central venous line placement, real-time ultrasonographic guidance can decrease the number of attempts and amount of time required to place an arterial line.[25, 26, 22]
Many experts recommend that an Allen test be performed before radial artery cannulation is initiated. This procedure 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 this 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, 27] 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 :
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 :
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 is 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.[6, 28, 29, 30, 31]
One study showed that, in the absence of peripheral vascular disease, the Allen test was not predictive of ischemia of the hand during or after radial artery cannulation. Other studies have shown poor correlation between Allen test results and distal blood flow as demonstrated by fluorescein dye injection or photoplethysmography.[32, 33]
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.
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 Positioning). Identify the artery by palpation. 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 digit of your nondominant hand (see the image below; the hand is left undraped to provide orientation). 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.
Observe the hub of the needle for a flash of bright red blood, signifying 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, and advance the catheter over the needle into the artery until the hub is at the level of the skin. 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 images below.)
Secure the catheter in place with sutures, tape, or adhesive strips, and apply a semipermeable sterile dressing over the site (see the images 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).
Determine the location of the femoral artery by palpating the arterial pulse approximately 2.5 cm below the inguinal ligament. Prepare the overlying skin with chlorhexidine. Anesthetize the skin with a 10-mm intradermal wheal of local anesthetic. Identify the course of the vessel by palpating with the index and middle finger of the nondominant, gloved hand.
Puncture the skin at an angle of 45° to the skin and the vessel (see the image below). Advance the needle slowly until pulsating blood flow is appreciated. Continuation of pulsating blood confirms that the needle is still within the arterial lumen. If flow ceases, slowly retract the needle in case both walls of the vessel have been punctured. If withdrawal does not produce blood flow and the needle must be redirected, first withdraw the needle to just below the level of the dermis, then reintroduce it.
If the artery is not easily punctured or if difficult cannulation is anticipated (eg, in an obese patient), the artery can be located by using Doppler ultrasonography.
Make a small nick in the skin at the needle entry site to facilitate passage of the catheter through the skin. Advance the needle-catheter assembly through the skin until a flash of blood is obtained (indicating that the needle, which protrudes beyond the catheter tip, has entered the artery). Advance the needle-catheter complex an additional 2 mm to ensure that the catheter tip has entered the artery. Advance the catheter into the vessel while holding the needle stationary.
Finally, remove the needle (see the image below). Successful artery cannulation is confirmed by pulsatile blood flow from the catheter when the needle is removed. Suture the catheter in place to ensure immobilization. Apply a sterile dressing, labeled with the date of placement, over the catheter.
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. The modified Seldinger technique has been associated with increased overall success for arterial cannulation and has been recommended as the initial technique in female patients. 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.
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 image below).
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, and 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 image 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 image below). If advancement of the catheter becomes difficult, a twisting motion can be used to facilitate catheter passage. 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.
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.
Prepare and anesthetize the skin, locate the vessel, and insert the needle as previously described for the catheter-over-needle technique (see the image below). Because of the real deep location of the femoral artery, the needle should be inserted at a 45° angle.
Once the needle is in the artery, use a guide wire insertion adapter to advance the wire through the lumen of the needle (see the image below). Ensure that the guide wire passes easily, without resistance.
After the guide wire has been advanced to within several centimeters of the end of the needle, remove the needle over the wire, taking care never to let go of the wire.
Make a small nick in the skin at the site of guide wire insertion to facilitate passage of the catheter through the skin (see the image below).
Make sure that the wire fits tightly into the end of the catheter, so that the catheter will enter the arterial lumen smoothly (this may be problematic, especially in patients with synthetic femoral grafts and in patients with advanced atherosclerosis). Advance the catheter over the guide wire and into the vessel (see the image below).
Remove the guide wire, leaving the catheter in place. Successful artery cannulation is confirmed by pulsatile blood flow from the catheter when the wire is removed.
Suture the catheter in place to ensure immobilization. Apply a sterile dressing, labeled with the date of placement, over the catheter.
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 the wrist and hand as previously described (see Periprocedural Care). The hand may be secured on an arm board with the wrist in dorsiflexion before the procedure. Identify the radial artery by palpation.
Perform a surgical scrub, and put on sterile gloves. Clean the skin over the wrist in a sterile fashion with 4% chlorhexidine gluconate or povidone iodine, and establish a sterile field around the site with sterile towels or drapes (see the image below).
If local anesthesia is desired, inject local anesthetic around the anticipated puncture site, using 1-2 mL of 1% lidocaine (without epinephrine) and a 25- or 27-gauge needle. Be careful not to create a wheal so large that it obscures landmarks or the pulse.
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 image 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 (see the image below).
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.)
Check the pulse wave form on the monitor to ensure that a good waveform is obtained. A pulse waveform that appears dampened initially may be secondary to arterial spasm. If this occurs, wait for the arterial spasm to resolve.
In the catheter-over-needle technique (see above), the initial insertion should be performed with a 2.5-in. catheter. Often, a longer (eg, 5-in.) catheter is desirable, in that it allows permanent placement of the catheter. In such a case, the 5-in. catheter may be inserted initially and advanced over the needle once continuing arterial flow persists.
Not infrequently, however, difficulties are encountered in attempting to insert the longer catheter into the femoral artery via the catheter-over-needle technique. In such cases, the catheter-over-needle technique can be combined with the catheter-over-wire technique as follows.
Employ the catheter-over-needle technique with a 2.5-in. catheter (see Catheter-Over-Needle Technique). When the artery is cannulated, remove the needle, and insert a guide wire into the catheter (see the image below).
When the guide wire is in place, remove the 2.5-in. catheter from the vessel over the wire, leaving only the guide wire in place. Next, advance a 5-in. catheter into the vessel over the guide wire (see the image below). Once proper positioning of the 5-in. catheter within the arterial lumen is confirmed, remove the guide wire.
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