Chapter 19
Arterial Lines

Arterial lines come with a steep learning curve. A failed attempt during an otherwise smooth induction can leave you with both a hematoma and a sense of defeat. But once you master this skill, it becomes one of the more satisfying procedures in our field. With strong palpation skills and a steady ultrasound hand, you can quickly become proficient. Unlike IVs, which sometimes rely on a bit of luck, arterial lines reward methodical, precise technique. They are ultimately more satisfying to master with experience.

As with any procedure, think first. Before you prep, step back and confirm:

is this an appropriate vessel to cannulate, and is this limb otherwise affected by the surgical procedure or positioning?
has the patient had a recent left heart cath via radial approach, or was their radial artery harvested for a coronary artery bypass?
is there an AV fistula on this side? and
does the patient have any vascular anomalies that might complicate placement?

While the Allen test isn’t strongly evidence-based, it may still provide useful information in high-risk patients. What matters most is forethought. I’m always impressed by trainees who assess the clinical context first, rather than rushing to grab a needle.

Set Yourself Up for Success

Arterial lines are typically placed during a narrow, chaotic window after induction: blood pressure may be soft, the room may be busy, OR staff may be haranguing you with questions or rushing to prep the patient. Reduce the scramble by preparing ahead: gather and open your supplies, set up your transducer, and unwrap any equipment you know you’ll need to use. Especially, if you are left on your own, consider running a low-dose phenylephrine drip to keep the blood pressure up while you do the procedure. It not only makes the procedure easier but also prevents you from having to pause your procedure and bolus a pressor, change gloves, etc.

Palpation Is an Acquired Skill

Use the tips of your fingers to palpate the artery. Keep a light touch, as too much force blunts your ability to distinguish the patient’s pulse from your own. If you can’t feel a pulse, don’t waste time waiting for one to magically appear. Switch to the other side or use an ultrasound.

Insert the Needle

Insert the needle at a ~45° angle, puncture the skin, and maintain a consistent trajectory. Once you begin to advance, resist the urge to shift directions. If you don’t get a flash within a reasonable depth (typically 2–3 mm), withdraw, slightly change your angle right or left, and try again. Continue withdrawing to skin and reattempting, fanning medial to lateral as you do so. As with central lines and intubation, if you don’t succeed, don’t become frustrated and start to jab the needle in random directions. Be methodical.

A practical tip: the artery is often a little more medial than you expect, and in women, it is more superficial. Elderly atherosclerotic patients are the most difficult, and you should have a low threshold to use an ultrasound in this patient population. Their distal arteries can sometimes be thick with plaque, so it helps to use the ultrasound to cannulate slightly more proximally than you normally would.

When you get flash, thread the wire immediately (assuming you’re using a catheter with a built-in wire). There’s no need to drop your angle or use the ultrasound to advance the needle. The arterial line kits with an embedded wire are specifically designed to minimize extra steps. The presence of flash means you’re in the vessel, and the wire should pass easily.

If the wire doesn’t advance, don’t force it. The wire may be up against the posterior wall, lodged within a plaque, or your needle has lost its place in the arterial lumen. Withdraw the wire and make small adjustments to your catheter.

Respect the Vessel

Recognize when it’s time to stop and reassess. Repeated attempts at the same site, especially when the wire or catheter will not pass, dramatically increase the risk of complications such as bruising, thrombosis, and ischemia. Arterial lines have a good safety profile until they don’t. That inflection point usually comes after too many failed passes in the same vessel.

If you’ve been left to attempt on your own, consider stopping after two to three attempts and asking for help. It shows humility and respect for the patient to not attempt multiple times in the same vessel and risk injury. Likewise, do not switch to alternate sites like brachial, axillary, or dorsalis pedis without discussing it. These locations carry higher complication risks and should always involve your supervising attending’s input. The brachial artery has no collaterals (unlike axillary or radial, which have more extensive collaterals).

Ultrasound is a powerful tool, but not a crutch. Ultrasound-guided arterial lines are excellent for improving your ultrasound skills and significantly reducing the number of attempts to successful arterial cannulation. That said, don’t let your reliance on ultrasound come at the cost of your blind palpation skills. As a trainee, I recommend reserving ultrasound guidance for more challenging cases or when a pulse is difficult to palpate. This ensures you maintain a broad “toolbox” of vascular access techniques. This is something that will serve you well in low-resource settings like the ER, the floor, or the trauma bay, where ultrasound may not be available.