If you suspect arterial insufficiency in the arm or hand, try to palpate the ulnar pulse as well as the radial and brachial pulses. Press deeply on the flexor surface of the medial wrist (Fig. 1). Partially flexing the patient's wrist may help you. The pulse of a normal ulnar artery may not be palpable.

FIGURE 1. Palpate the ulnar pulse.

The Allen Test 

The Allen test compares patency of the ulnar and radial arteries. It also ensures patency of the ulnar artery before puncturing the radial artery for blood samples. The patient should rest with hands in lap, palms up.

Ask the patient to make a tight fist with one hand; then compress both radial and ulnar arteries firmly between your thumbs and fingers (Fig. 2).

FIGURE 2. Compress the radial and ulnar arteries.

Next, ask the patient to open the hand into a relaxed, slightly flexed position (Fig. 3). The palm is pale.

FIGURE 3. Pallor when hand relaxed.

Release your pressure over the ulnar artery. If the ulnar artery is patent, the palm flushes within about 3 to 5 seconds (Fig. 4).

FIGURE 4. Palmar flushing—Allen test negative.

Test patency of the radial artery by releasing the radial artery while still compressing the ulnar artery

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