Radial artery puncture can lead to thrombosis of the distal artery. Because 12% of hands have inadequate collateral flow because of an incomplete palmar arch (Fig. 208-1), to minimize the risk of permanent ischemic damage to the hand, many experts suggest confirming adequate collateral circulation before puncture. Even if there is excellent collateral flow, the nondominant hand should be used, if possible. However, other experts have questioned the value of testing for collateral circulation. At least one large case series of patients demonstrated the safety of radial artery cannulation without testing for collateral circulation with the modified Allen test in patients without major peripheral arterial disease (Slogoff and colleagues, 1983).

Figure 208-1 Anatomy of radial and ulnar arteries at wrist and superficial palmar arch.

Modified Allen Test

The Allen test, used to evaluate ulnar collateral flow, was first described in 1929. To minimize falsely abnormal results, the modified Allen test can be used:

1 The hand should be at least room temperature (>70° F). It can be warmed in water, if necessary. The patient should hold his or her arm above heart level, and then open and close the hand several times to exsanguinate it. Next, the patient should clench the fist tightly. The clinician then compresses both the radial and ulnar arteries (Fig. 208-2A). (In a comatose or anesthetized patient, the hand can be elevated and clenched passively by an assistant.)

2 After a minute is allowed for blood to drain from the hand, the fist should be lowered below the level of the heart, unclenched (Fig. 208-2B), and pressure on the ulnar artery (Fig. 208-2C) released. Care should be taken to avoid hyperextension of the wrist or fingers, which can lead to a falsely abnormal test result. When the pressure on the ulnar artery is released, the cadaveric color of the entire hand should return to its normal color within 6 seconds (Fig. 208-2D). Color usually returns to the palm first, and then to the entire hand. If any area of the hand does not rapidly (within 6 seconds) return to normal color, this is a positive modified Allen test. The thumb, index finger, and thenar eminence are the areas most commonly involved in a positive test. These areas often have inadequate collateral blood flow and may be entirely dependent on the radial artery for perfusion.

Figure 208-2 Modified Allen test. A, Hand is elevated and fist clenched while radial and ulnar arteries are occluded for 1 minute. B, Hand is lowered and fist is unclenched. Hand is cadaveric. C, Ulnar artery compression is released while radial artery compression is continued. In a negative test, the entire hand regains color within 6 seconds. D, Positive test. With inadequate collateral perfusion from the ulnar artery, the hand remains cadaveric as long as radial artery compression is maintained. When inadequate collateral perfusion is demonstrated, another puncture or cannulation site should be considered.

An abnormal or equivocal modified Allen test result, although it may not preclude arterial puncture or cannulation, should alert the clinician to potential complications, a need for caution when performing the procedure, and a need to monitor the patient closely postprocedure. Various types of noninvasive studies are also useful for further patient evaluation. Hand-held Doppler ultrasonography or pulse oximetry can be used to rapidly assess perfusion with techniques more sensitive and specific than the modified Allen test. If time allows, formal arterial Doppler ultrasonography, either portable or in the radiology department, can be used to further evaluate the collateral circulation or direct the puncture.

Pulse Oximetry Evaluation

This is especially useful in the unconscious patient.

1 Place the sensor of a pulse oximeter with a visual pulse waveform display on the patient’s thumb.

2 While examining the waveform on the monitor, occlude the radial artery. If the waveform remains unchanged after radial artery occlusion, the patient has adequate collateral circulation, probably from the ulnar artery.

Assessment of Dorsalis Pedis Collateral Circulation

To minimize the risk of permanent ischemic damage to the distal foot, some experts suggest confirming adequate collateral circulation before dorsalis pedis artery puncture is attempted.

1 The foot should be at least room temperature (>70° F). It can be warmed in water, if necessary.

2 After locating and palpating the dorsalis pedis artery (Fig. 208-4), occlude it with compression.

3 Blanch the great toenail by compressing for several minutes.

4 Release pressure on the nail and observe for flushing. A rapid return of color indicates adequate collateral flow.

Figure 208-4 Location of the dorsalis pedis artery.

note: In most persons, collateral circulation of the foot is provided by a branch of the posterior tibial artery. Hand-held Doppler ultrasonography can be used to assess collateral flow between the dorsalis pedis and posterior tibial arteries in a manner similar to that used in the palmar arch.

Preprocedure Patient Preparation

The clinician and patient should be in a comfortable position that can be maintained for 10 to 15 minutes. The procedure, its necessity, alternatives (if there are any), and possible complications should be explained to the alert patient. In nonemergent situations, informed consent should be obtained (see the sample patient consent form online at www.expertconsult.com). The patient should be prepared for some discomfort.

Technique

1 Rinse the syringe with a small amount (1 or 2 mL) of heparin and then empty it through the needle. For glass syringes, this step not only coats the syringe with heparin, it eliminates the dead space in the syringe and needle. Although heparin does not adhere to plastic syringes, performing this step with plastic syringes will displace any air and fill the dead space.

note: Certain kits contain syringes that are already heparinized (often containing a pellet of lyophilized heparin) and the plunger should not be moved.

2 Following universal blood and body fluid precautions, prepare the skin in an aseptic manner and put on sterile gloves.

3 The clinician should use his or her nondominant hand to palpate the selected artery with the balls of two or three fingers, and immobilize it with these fingers along its course.

4 Optional: Local anesthetic (lidocaine) can be injected for a particularly anxious patient to minimize hyperventilation artifact. However, use minimal amounts to avoid anatomic distortion, which could make it difficult to palpate and puncture the pulse.

5 Holding the barrel of the syringe like a pencil in the dominant hand, keep the needle bevel up.

6 Depending on the site selected, perform the puncture.

• Radial artery puncture: Dorsiflex the supine wrist (about 30 degrees) of the patient’s nondominant hand and rotate it outward (externally), slightly. The wrist should be supported by a firm surface, such as an assistant’s hand, a rolled towel or washcloth, or a 500-mL intravenous (IV) fluid bag. Insert the needle where the pulse is most prominent—

to 1 inch proximal to the wrist crease—at a 40- to 60-degree angle to the skin. Direct it slowly in the long axis of the artery toward the pulsation (Fig. 208-5).

Figure 208-5 This patient is left-hand dominant. Palpate the patient’s radial pulse with your left hand. While holding the heparinized syringe with your right hand (reverse hands if left-handed), puncture the skin at approximately a 60-degree angle to the skin, directing the needle toward the radial pulsation.

note: Avoid “spearing” (going through) the artery. Osteomyelitis and large hematomas can result from “spearing” the artery.

• Brachial artery puncture: Place the patient’s elbow on a rolled towel or washcloth. Slightly hyperextend and supinate the arm (palm up) with the patient’s wrist in the anatomic position but rotated slightly outward. The brachial artery pulsation should be palpable in the medial aspect of the antecubital fossa (Fig. 208-6), lateral to the medial epicondyle, but medial to the biceps tendon. Insert the needle at about a 45- to 60-degree angle, slightly above the elbow crease, in the antecubital fossa or slightly proximal to it. Aim along the long axis of the artery toward the pulsation.

• Femoral artery puncture (Fig. 208-7): With the patient in a supine position and legs straight, rotated slightly outward, insert the needle 1 to

inches distal to the inguinal ligament at about the inguinal crease. It should be at a 60- to 90- degree angle to the distal skin and aimed toward the pulsation (Fig. 208-8). Avoid puncturing lateral to the pulsation because the femoral nerve could be damaged.

• Dorsalis pedis artery puncture (Fig. 208-9): With the patient in a supine position, insert the needle where the pulse is most prominent, at a 45- to 60- degree angle to the sole of the foot. Aim toward the pulsation.

7 Although penetration into the artery can occasionally be sensed, puncture is usually detected when blood enters the syringe. It should enter the syringe spontaneously without withdrawing the plunger if the syringe is specifically designed for arterial puncture. With plastic syringes or in severely hypotensive patients, slight aspiration may be necessary. Otherwise, attempt to avoid aspiration to decrease the chance of obtaining venous blood. If blood is not obtained during the insertion, slowly withdraw the needle and stop when blood appears.

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