Radial Artery Cannulation 

Arterial cannulation is a commonly performed procedure in the management of patients who are critically ill. Approximately 8 million arterial catheters are placed yearly in the United States.^[1] An indwelling arterial catheter allows for continuous blood pressure (BP) monitoring, frequent blood sampling, and arterial blood gas measurement.

Arterial catheters can be placed at the bedside and have been found to be relatively safe, with a low incidence of serious complications.^[1] Arteries used for catheterization include the radial, ulnar, brachial, axillary, femoral, posterior tibial, and dorsalis pedis. Of these, the radial artery is most commonly used in both adults and children.^{[2, 3]} The radial artery is chosen primarily because of the superficial nature of the vessel and ease of maintenance of the site.^[2] Despite the common use and relative ease of radial artery cannulation, one must be cognizant of the potential risks involved.

For information on umbilical arterial catheterization, see Clinical Procedures topic Catheterization, Umbilical Artery.

• Arterial blood gas sampling
• Frequent blood sampling
• Continuous invasive BP monitoring
• Inability to use indirect BP monitoring (eg, severe burns, morbid obesity)

Strict ^{[2, 3]}

• Inadequate circulation to the extremity
• Raynaud syndrome
• Thromboangiitis obliterans (Buerger disease)
• Full-thickness burn over insertion site
• Skin infection over insertion site

Relative ^{[2, 3]}

• Uncontrolled coagulopathy
• Systemic anticoagulation
• Inadequate collateral flow from ulnar artery on Allen test
• Atherosclerosis

• For urgent placement of a radial arterial catheter in a patient who is critically ill, anesthesia is generally not required. In the conscious patient, local anesthesia can be provided with 1% lidocaine (without epinephrine) at the injection site. For more information, see Local Anesthetic Agents, Infiltrative Administration.
• If the patient is combative or if maintaining stability of the extremity is difficult, sedation or general anesthesia may be required. For more information, see Procedural Sedation.

• Sterile gloves
• Sterile gauze, 2 X 2 inch or 4 X 4 inch
• Arm board of appropriate size for the patient (eg, neonate, pediatric, adult)
• Sterile towels
• Skin preparation solution (4% chlorhexidine gluconate or povidone iodine)
• Needle, 25 or 27 gauge (ga), with syringe, for local anesthetic
• Syringe, 5 mL, that contains heparinized flush
• Radial artery cannula of appropriate size for the patient

  • Use a 20-ga peripheral artery catheter kit, shown below, for large children and adult patients.Radial artery catheter kit.
  • Use a 22- to 24-ga angiocatheter, like the one shown below, for infants and neonates.Angiocath used for radial artery cannulation in infants and small children.
• Adhesive tape
• Steri-Strips
• Needle holder
• Nylon suture, 5-0
• Intravenous tubing T-connector
• Tegaderm or other clear, semipermeable sterile dressing
• Stopcock, 3-way
• Pressure tubing
• Pressure transducer kit

• With the patient lying supine, the arm should be maintained in neutral position with the palm up and the wrist adequately exposed.
• Hyperextension of the wrist to 30° using a rolled-up towel or roll of gauze, as shown below, may allow easier cannulation of the radial artery by decreasing the tortuosity of the vessel.^[2] Positioning of wrist for radial artery cannulation.
• An IV board or other rigid flat surface may be used and the hand and forearm secured to the board with tape.

Allen test

Prior to radial artery cannulation, many experts recommend performance of the Allen test. This procedure, originally described by the American physician Edgar Van Nuys Allen in 1929, is a simple bedside test designed to evaluate for adequate collateral circulation to the hand via the ulnar artery. The test is performed as follows:

• Elevate the hand and ask the patient to make a fist for 30 seconds while applying simultaneous pressure to the ulnar and the radial arteries so as to occlude them, as in the image below. Allen test: Occlusion of both radial and ulnar arteries while patient makes a fist.
• Ask the patient to open the hand. It should appear blanched, as depicted in the image below.Allen test: Radial and ulnar arteries occluded after hand is opened.
• Release pressure over the ulnar artery and time the return of color to the palm in seconds, as shown.Allen test: Release of pressure on ulnar artery and observation for color return to hand within 5-10 seconds.
• If color returns to the hand within 5 seconds, 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 Allen test is positive (abnormal). In this case, the collateral blood supply to the hand may not be sufficient, and an alternate site of arterial cannulation should be used.^[3]

A modified Allen test has been described for use in unconscious or anesthetized patients who are unable to make a fist on demand.^[4] This test uses an Esmarch bandage to exsanguinate the hand; the rest of the test is performed as described above.

The value of the Allen test is controversial, and a negative Allen test may not guarantee adequate collateral circulation to the hand. Several reports exist of permanent ischemic injury, after radial artery cannulation, following a negative (normal) Allen test.^{[5, 6, 7]} Alternatively, a positive (abnormal) Allen test may not correlate with inadequate collateral circulation. 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.^[8] Other studies have shown poor correlation of results of the Allen test with distal blood flow as demonstrated by fluorescein dye injection or photoplethysmography.^{[9, 10]} Given the controversy surrounding the results of the Allen test, some experts recommend a Doppler evaluation of collateral flow be completed in all high-risk patients prior to cannulation.^[2]

Anatomy

The radial artery lies between the brachioradialis tendons and flexor carpi radialis tendons, approximately 1-2 cm from the wrist, medial to the bony head of the distal radius. Anatomy is shown in the image below.

The initial puncture site should be as distal as possible, but at least 1 cm proximal to the styloid process, in order to avoid puncture of the retinaculum flexorum and the small superficial branch of the radial artery.

Technique

The accepted percutaneous techniques for radial artery cannulation are referred to as over-the-wire and over-the-needle. The over-the-wire technique is generally used in adults and larger children. The over-the-needle technique is most commonly used in infants and neonates. As a last resort, a surgical cutdown technique can be used for cannulation of the radial artery. For safety reasons, the cutdown technique should be performed only by a trained surgeon or another individual who has special training in vascular access. The cutdown technique is not described here.

Over-the-wire technique

This method is similar to the over-the-needle technique described below but includes the use of the modified Seldinger technique, with advancement of a guidewire through the needle into the vessel lumen, prior to catheter advancement. The commercially available Arrow radial arterial catheterization system is commonly used for this technique (Arrow International, Inc., Reading, Pa). This kit includes a needle introducer, catheter, feeding tube assembly, and guidewire with actuating lever.

The modified Seldinger guidewire technique has been associated with increased overall success for arterial cannulation and has been recommended as the initial technique in female patients.^[11] This method should not be used routinely in neonates and infants because the radial artery diameter is too small to allow easy advancement of the guidewire.

• Perform Allen test or Doppler study to ensure adequacy of ulnar collateral circulation.
• Position the wrist and hand as described in the Positioning section. The hand may be secured using an arm board with the wrist in dorsiflexion prior to the procedure.
• Identify the radial artery by palpation.
• Perform surgical scrub and put on sterile gloves.
• Clean the skin over the wrist in a sterile fashion using 4% chlorhexidine gluconate or povidone iodine and establish a sterile field around the site using sterile towels or drapes as shown below. Radial artery prepared and draped in sterile fashion.
• If 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 to not create a wheal so large that it obscures landmarks or the pulse.
• Check the arterial catheterization catheter and needle (shown below) for proper function prior to use.Radial artery catheter.
• Puncture the skin over the radial artery using the arterial catheterization catheter and needle at an angle of 30-45° from the skin with the needle bevel up, as depicted in the images below. Introduction of radial artery catheter. Angle of introduction of radial artery catheter.
• Advance the arterial catheterization catheter and needle as shown below, toward the artery at an angle of 30-45° from the skin until a flash of blood is noted in the clear hub of the introducer needle. This initial flash is obtained when the needle tip, which protrudes beyond the end of the catheter, has entered the vessel lumen. Flashback of blood into radial artery catheter hub. Illustration of radial artery catheter entering artery.
• Stabilize the introducer needle and carefully advance the guidewire using the actuating lever, as shown.Advancement of guidewire into radial artery. Illustration showing advancement of guidewire into radial artery.
• Advance the guidewire distally as far as possible into the vessel lumen.
• If resistance is encountered while advancing the guidewire, do not retract the guidewire, as this may damage the guidewire. Instead, withdraw the entire unit and attempt a new puncture.
• Once the guidewire has been introduced as far as possible, advance the needle and catheter assembly 1-2 mm farther into the vessel.
• Hold the introducer needle in place and advance the catheter forward over the guidewire and into the vessel.
• Hold the catheter in place and remove the needle, guidewire, and feeding tube assembly, as shown below.Stabilization of catheter while introducer is removed.
• Confirm that the catheter remains in the vessel lumen by monitoring for blood return at the hub. Blood should flow freely from the end of the catheter hub after the needle, guidewire, and feeding tube assembly are removed, as shown. Stabilization of catheter while introducer is removed.
• Attach the intravenous tubing T-connector and syringe filled with heparinized flush to the end of the catheter, being careful not to dislodge the catheter. Pressure transducer attached to radial artery catheter.
• Flush the radial artery catheter slowly with 1-2 mL of heparinized flush and monitor for infiltration. If the catheter is within the artery, the skin around the insertion site blanches during catheter flushing.
• Secure the angiocatheter hub to the skin with Steri-Strips, tape, or suture.Radial artery cannula sutured in place.
• Cover the site with sterile Tegaderm or other clear semipermeable sterile dressing.Sterile dressing applied over radial artery cannula.
• Attach the T-connector to the pressure transducer.Inline 3-way stop-cocks attached for blood sampling.
• Check pulse wave form on the monitor to ensure good wave form. If the pulse wave form appears dampened initially, this may be secondary to arterial spasm. If this occurs, wait for arterial spasm to resolve.

Over-the-needle technique

This method involves the placement of the angiocatheter directly into the arterial lumen in a manner similar to that of an intravenous catheter. This method is the preferred method in neonates and infants, as the small vessel diameter in these patients makes threading the guidewire into the vessel lumen difficult.

• Perform Allen test or Doppler study and prepare the wrist as described above.
• Check the angiocatheter assembly for proper function prior to use.
• Puncture the skin over the radial artery using the angiocatheter and needle with the needle bevel up, as shown in the image below. Introduction of Angiocath into radial artery.
• Advance the angiocatheter and needle slowly toward the artery at an angle of 30-45° as shown from the skin until a flash of blood is noted in the angiocatheter needle hub. This initial flash is obtained when the needle tip, which protrudes beyond the end of the catheter, has entered the vessel lumen. Flashback of blood into Angiocath hub. Illustration of Angiocath entering radial artery.
• Lower the angiocatheter and needle to an angle of 10-20° from the skin and advance both forward another 1-2 mm to ensure that the catheter tip is within the radial artery lumen.
• Confirm that the angiocatheter and needle remain in the vessel lumen by monitoring for blood return at the hub.
• If a flash of blood is noted initially, but no blood flow is seen after advancement, the posterior wall of the vessel may have been punctured. In this situation, withdraw the angiocatheter and needle slightly until blood flow returns.
• While holding the needle stable, advance the angiocatheter over the needle and into the radial artery lumen until the angiocatheter hub is at the level of the skin. Stabilization of catheter while removing needle introducer.
• Inability to advance the catheter into the lumen may indicate failure to puncture the radial artery centrally. In this situation, the radial artery may have been punctured on the lateral wall, which typically results in hematoma formation.
• Remove the needle from the angiocatheter. Blood should flow freely from the end of the angiocatheter hub when the needle is removed.
• Attach the intravenous tubing T-connector and syringe filled with heparinized flush to the end of the catheter hub, being careful not to dislodge the catheter. Pressure transducer attached to radial artery catheter.
• Flush the radial artery catheter slowly with 1-2 mL of heparinized flush and monitor for infiltration. If the catheter is within the artery, the skin around the insertion site blanches during catheter flushing.
• Secure the angiocatheter hub to the skin with Steri-Strips, tape, or suture.Radial artery cannula secured in place with Steri-Strips.
• Cover the site with sterile Tegaderm or other clear semipermeable sterile dressing.Sterile dressing applied over radial artery cannula.
• Attach the T-connector to the pressure transducer and check pulse wave form on the monitor to ensure good wave form. If the pulse wave form appears dampened initially, this may be secondary to arterial spasm. If this occurs, wait for arterial spasm to resolve.

• Prior to starting the procedure, flush the needle introducer with heparinized flush to facilitate flashback of blood up to the needle hub upon entry of the artery.
• By puncturing the artery from a slight lateral-to-medial direction, the operator can stabilize the artery against the flexor carpi radialis tendon.
• A subcutaneous infiltration of lidocaine or similar anesthetic around the puncture site may reduce vessel spasm.^[3]
• Making a small nick in the skin with a No. 11 scalpel blade at the site of needle insertion may avoid catheter kinking on the skin during advancement.^[3]
• If unable to pass the guidewire into the artery, try rotating the needle 90-180° in an attempt to eliminate an intimal flap blocking passage of the wire.^[2]
• If difficulty is encountered advancing the catheter into the lumen, the “liquid stylet” method might help. To perform, fill a 10-mL syringe with 5 mL of sterile normal saline and attach it to the catheter hub. Aspirate 1-2 mL of blood into the syringe, and then slowly inject the fluid from the syringe into the vessel as the catheter is advanced behind the fluid wave.^[12]
• After several failed attempts at cannulation, the artery may spasm, making further attempts more difficult. If this occurs, allow the artery to recover for a short time before reattempting cannulation.
• Papaverine added to the arterial line fluid in a concentration of 30 mg/250 mL has been shown to prolong the patency of the peripheral arterial catheters in children and neonates.^{[13, 14]}
• Remove the radial artery catheter at the first signs of circulatory compromise or clot formation (eg, cyanosis in fingers tips, dampening pulse waveform on monitor). Do not flush the catheter in an attempt to remove clots.
• Remove the cannula as soon as it is no longer needed.

Common complications ^[1]

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

Less common complications ^[1]

• Localized catheter site infection (0.72%)
• Hemorrhage (0.53%)
• Sepsis (0.13%)
• Permanent ischemic damage (0.09%)
• Pseudoaneurysm formation (0.09%)

Rare complications ^[1]

• Paralysis of median nerve
• Suppurative thromboarteritis
• Air embolism
• Compartment syndrome
• Carpal tunnel syndrome