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