Chapter 46

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.

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 located in close proximity to the desired arteries in order to avoid complications. The anatomy and positioning for radial, brachial, and femoral arterial access is described below.

The radial artery is the preferred site for arterial puncture and cannulation. One reason is the comparative ease of identifying the anatomical 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. Terminal branches of these two arteries meet in the palm of the hand to form the deep and superficial palmar arterial arches (Figure 46-1).

###### FIGURE 46-1

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

The radial artery can be found just medial and proximal to the radial styloid process on the ventrolateral side of the wrist (Figure 46-1). Dorsiflexing the wrist approximately 60 degrees can aid in palpating the arterial pulse. Another notable landmark is the flexor carpi radialis tendon that runs immediately medial to the radial artery. The recommended point of needle or catheter insertion is at the proximal flexor crease of the wrist.

A modified Allen test should be performed to assess the adequacy of the collateral circulation to the hand prior to radial artery puncture or cannulation (Figure 46-2).1,2 Ask the patient to close their hand tightly into a fist to force blood out of the fingers (Figure 46-2A). Manually occlude the radial and ulnar arteries (Figure 46-2A). Ask the patient to open the hand. The fingers should be blanched due to the occlusion of the arterial inflow. Release the finger occluding the ulnar artery (Figure 46-2B). Measure the time it takes for blushing of the palm to occur. It is considered normal if it is < 7 seconds, equivocal at 8 to 14 seconds, and abnormal if > 14 seconds.1

###### FIGURE 46-2

The modified Allen test. A. The distal radial and ulnar arteries are occluded. B. The radial artery remains occluded while determining if the ulnar artery can supply adequate blood flow to the hand.

An alternative method of evaluating the collateral circulation involves the use of a pulse oximeter with ...

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