Axillary Arterial Lines

Hemodynamic monitoring of critically ill patients is incomplete without arterial catheters. These allow us to have accurate blood pressure monitoring and ease of checking arterial blood gases.

Traditionally the radial artery has been used most extensively. Since pulsations from the artery can easily be palpated on the arm, it is the most readily accessible artery for this procedure.

With ultrasound guidance becoming standard of care for all vascular procedures, we have better alternatives than the radial artery. Though a radial arterial line is also best done using ultrasound, the relatively small size of the vessel and its proximity to the wrist makes it very vulnerable to malfunction and inaccuracy. In my experience, radial arterial catheters are good for 24–48 hours in most patients. There is also convincing data that blood pressure measurements from the radial artery may not be as accurate as those from femoral arterial catheters.

The axillary artery is larger and easily accessible via ultrasound guidance. It is close to the pectoralis minor muscle, which divides it into three parts. I favor the axillary artery for arterial puncture and arterial catheter placement in most critically ill patients.

Anatomy and ultrasound

Most patients have this artery very superficial (0.5 to 2.0 cm beneath the skin), and with ultrasound it is easy to differentiate it from the axillary vein. Either compressibility or color Doppler can be used for this purpose. In the axilla, the axillary artery is surrounded by the brachial plexus. This is usually more proximal, and the risk of nerve injury is minimal if the procedure is done properly.

Use ultrasound to scan the arm to assess the size and anatomy of the axillary artery. If artery size is too small (less than 0.2 cm), it may be difficult to cannulate with a guidewire. In those cases the femoral artery is better (usually its diameter is larger). It is important to scan and obtain images prior to scrubbing in for the procedure.

Technique

Keep the patient’s arm at 90 degrees. After full sterile precautions are taken, local anesthesia can be given with lidocaine at the site. Using a needle (e.g., Argon Arterial Line) from the kit, the axillary artery can be accessed easily under real-time ultrasonographic guidance. Arterial blood is pulsatile and bright red. Using Seldinger technique, the guidewire is passed into the artery. The needle is then removed leaving the guidewire in the vessel. Always check the position of the guidewire with ultrasound — it should be easily visible in the cross-sectional and longitudinal views. The arterial catheter is then guided over the guidewire and the guidewire is removed. The arterial line is then secured with sutures and dressed.

If done properly, there is a 99% chance of successful access to the axillary artery on the first attempt. In comparison to the femoral artery, I find it easier to manipulate the guidewire, as it has a relatively straight path. The femoral artery goes beneath the inguinal ligament, and in some patients the guidewire gets stuck in that path.

Why axillary in obese patients

With our population getting more obese, femoral artery access is relatively difficult (the abdominal pannus covers the groin). In obese patients the femoral artery is also deeper. Even in most morbidly obese patients, the axillary artery is still less than 2.5 cm deep, as the medial side of the arm doesn’t gain as much subcutaneous fat.

Axillary arterial blood pressure (like femoral arterial pressure) is more accurate than radial arterial pressure, as these are more central vessels. Since the catheters are long, there is very little chance of losing waveform or accuracy with prolonged use. I have not had to remove a single one of these for malfunction so far. Infection risk is also minimal if strict sterile precautions are used.

Safety and collateral circulation

There is a common misconception that axillary artery puncture or catheterization has risks of compromising arm circulation. This is not true. The axillary artery has six major branches, and collateral circulation is provided via the dorsal scapular, subscapular, and anterior and posterior humeral circumflex arteries to the arm. As long as the procedure is done proximally (close to the axilla, above the teres minor muscle), it is very safe. Care should be taken in brachial artery punctures (the axillary artery becomes the brachial artery below the teres minor muscle), as there can be a risk of arm ischemia.

Takeaway

I find axillary arterial punctures and catheterizations a very important tool for hemodynamic monitoring of critically ill patients in my ICU. With ultrasound use, it is easy, safe, and can be used effectively to provide better care to our patients.