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Arterial blood gas sampling is an essential component of the care of many Emergency Department patients. It provides key information regarding a patient’s oxygenation and acid-base status. Arterial cannulation allows for continuous and accurate blood pressure monitoring and frequent blood gas sampling in the care of the critically ill patient. There are many issues associated with obtaining and maintaining arterial access. Placement of an arterial line occurs less commonly than venous access. It is important to know when to obtain arterial access, where to obtain arterial access, and how to obtain arterial access. The use of an arterial line provides a more accurate blood pressure than using a noninvasive cuff.


Knowledge of the arterial anatomy is a key factor in the success of arterial puncture and cannulation. It is important to recognize that nerves and veins are in close proximity to the desired arteries in order to avoid complications. The anatomy and positioning for radial, brachial, femoral, and dorsalis pedis artery access are described below.


The radial artery is the preferred site for arterial puncture and cannulation. One reason is the comparative ease of identifying the anatomic location of this artery. A second reason is the collateral nature of the arterial blood supply to the hand provided by the radial and ulnar arteries (Figure 72-1). The ulnar artery is not often used due to its smaller size. Terminal branches of these two arteries meet in the palm of the hand to form the deep and superficial palmar arterial arches (Figure 72-1).

FIGURE 72-1.

Anatomic location of the radial and ulnar arteries. Collateral circulation is provided by the superficial and deep palmar arches.

The radial artery is just medial and proximal to the radial styloid process on the ventrolateral wrist (Figure 72-1). Dorsiflexing the wrist approximately 45° places the radial artery at its most superficial position to the skin and can aid in palpating the arterial pulse.1 Another notable landmark is the flexor carpi radialis tendon immediately medial to the radial artery. The recommended point of needle or catheter insertion is at the proximal flexor crease of the wrist and directly above the radial artery pulse.

Perform an Allen test to assess the adequacy of the collateral circulation to the hand prior to radial artery puncture or cannulation (Figure 72-2).2-4 Ask the patient to repeatedly close their hand tightly into a fist and open it to force blood out of the fingers while manually occluding the radial and ulnar arteries (Figure 72-2A). Continue this process for 1 minute. Ask the patient to open their hand. The fingers will blanch and become pale due to the occlusion of the arterial inflow. ...

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