Arterial Lines: A Guide for Patients and Families

If you or a family member is in the intensive care unit (ICU) or recovering from major surgery, you may notice a catheter in the wrist or another location connected to a monitor that shows a continuous wave-form and blood pressure reading. This is an arterial line (often called an “A-line”). It is one of the most common monitoring devices in critical care, and it is distinctly different from a standard IV line.

This guide explains what arterial lines are, why they are used, how they work, what the safety rules are, and what to expect.

What Is an Arterial Line?

An arterial line is a thin catheter (plastic tube) placed directly inside an artery — a blood vessel that carries oxygenated blood away from the heart, under high pressure. Unlike intravenous (IV) lines, which go into veins, arterial lines are placed in arteries.

The catheter is connected via a small tube filled with fluid to a pressure transducer (a sensor) and then to the bedside monitor. The transducer converts the pulsatile pressure of arterial blood into an electrical signal that the monitor displays as a continuous waveform.

Where Is an Arterial Line Placed?

The most common location is the radial artery at the wrist — the same artery you feel when you take your pulse at the wrist. The radial artery is preferred because:

It is accessible and easy to secure
It has a good collateral blood supply (backup circulation from the ulnar artery), making it safer than most sites
Complications from radial arterial lines are rare

Other sites used when the radial artery is not suitable:

Femoral artery (groin) — common in emergencies; allows large catheter size
Brachial artery (inside the elbow) — used when radial is not accessible
Dorsalis pedis artery (top of the foot) — used in some cases
Axillary artery (armpit) — less common, used in specific situations

Why Is an Arterial Line Used?

Arterial lines are placed when:

Continuous blood pressure monitoring is needed

A blood pressure cuff on the arm gives a reading every few minutes at best. In the ICU or during major surgery, blood pressure can change drastically within seconds — from medications, fluid shifts, position changes, or the underlying illness. An arterial line provides a beat-to-beat continuous blood pressure reading, allowing the care team to respond instantly.

This is particularly important for patients:

Receiving vasoactive medications (drugs that raise or lower blood pressure)
With severe hemodynamic instability (shock, sepsis, major trauma)
Undergoing major cardiac, vascular, or neurosurgical procedures
Requiring very tight blood pressure control (e.g., after brain aneurysm repair or aortic surgery)

Frequent arterial blood sampling is needed

Arterial blood gases (ABGs) — measurements of oxygen, carbon dioxide, and acid-base balance — require arterial blood, not venous blood. In patients on mechanical ventilators, or with severe lung disease or metabolic disturbances, ABGs may be needed hourly or more frequently.

Without an arterial line, each ABG requires a needle stick into an artery — painful, time-consuming, and impractical at high frequency. The A-line allows painless, immediate blood sampling at the bedside as often as needed.

Other tests can also be run from the arterial line, reducing the need for separate venipunctures.

How It Works: Reading the Monitor

The arterial line connects to a pressure transducer zeroed to atmospheric pressure. When your heart beats:

The waveform rises to the systolic pressure (the peak — the higher number in a blood pressure reading)
It then falls to the diastolic pressure (the lower number)
The mean arterial pressure (MAP) is calculated automatically and is often the most important number the care team watches

The monitor shows a continuous wave — a sharp upstroke with each heartbeat, followed by a slower decline. The shape of the waveform provides clinical information beyond just the numbers.

The numbers are more accurate than a blood pressure cuff, especially in patients who are very ill, have poor peripheral circulation, or are receiving vasoactive medications that alter circulation.

Critical Safety Rules for Arterial Lines

This section is important. Arterial lines have different safety rules from standard IV lines, and understanding these rules protects you or your family member.

1. Arterial lines are for monitoring and blood sampling only — NOT for standard IV medications or fluids

A standard IV line is designed to deliver medications and fluids into a vein. Injecting medications into an artery can cause catastrophic tissue damage, loss of limb, and death. Arterial blood flow goes to tissues at high velocity and pressure — medication accidentally injected into an artery can cause intense arterial spasm and tissue ischemia.

Arterial lines are color-coded and labeled specifically to prevent accidental injection. If you have a care team member who is unfamiliar with your lines, it is appropriate to ask: “Is that line arterial or venous?” before any injection.

2. An arterial line that disconnects is an emergency

Arterial blood is under high pressure (the same pressure that pumps blood to your entire body). If an arterial line becomes disconnected or a connection loosens:

Blood loss can be rapid and significant — up to several hundred milliliters per minute from a disconnected radial A-line
This can happen under sheets, blankets, or behind the arm where it is not immediately visible
Bedside monitors have alarm systems specifically for A-line disconnection (a rapid pressure drop triggers an alarm)

If you are a patient: Do not pull on or manipulate any line near your wrist or arterial access site. Alert your nurse if you feel anything wet or if you hear an alarm.

If you are a family member: If you notice unexpected bleeding or wetness near the access site, call for the nurse immediately. Do not attempt to reconnect lines yourself.

3. Keep the wrist position stable

Arterial waveform quality depends on the catheter remaining correctly positioned in the artery. Significant wrist bending or rotation can cause the waveform to become dampened or distorted, making readings unreliable. A wrist splint or positioning board is often used to keep the wrist in a neutral position. Do not remove or reposition this without nurse guidance.

4. The access site must remain visible

The dressing at the arterial access site should be transparent so nurses and physicians can see the site at all times. Notify your nurse if the dressing becomes soaked, loose, or obscured.

What to Expect When an Arterial Line Is Placed

For planned placement (e.g., before surgery)

The procedure is explained to you and consent is obtained
The wrist (or other site) is cleaned and a sterile drape is placed
Local anesthetic is injected to numb the area — this is the most uncomfortable part, similar to a dental injection
After the area is numb, the catheter is placed into the artery using a needle
Placement typically takes 5–10 minutes in experienced hands
A dressing is applied and the catheter is secured to the skin

Sensations during placement

You will feel the local anesthetic injection (a brief burning/stinging)
After the local anesthetic takes effect, you may feel pressure but minimal pain
You may feel brief sharp pain if the artery is difficult to find or if multiple passes are needed — this is brief
After placement, the area should be numb or mildly tender but not significantly painful

For emergency placement

In emergencies, placement may occur more rapidly and with less preparation. Local anesthesia is still used when time permits.

Discomfort and Mobility with an Arterial Line

Most patients with a radial arterial line at the wrist can:

Move their arm freely (avoiding extreme wrist flexion)
Use their arm for limited activities as their condition permits
Sleep normally

A wrist splint may feel restrictive but is there for a reason. Ask your nurse whether it can be temporarily removed for hygiene or repositioning — in many cases it can be removed briefly with monitoring.

Femoral arterial lines require the leg to be kept relatively still and limit walking. They are generally removed as soon as the clinical situation allows.

How Long Does an Arterial Line Stay In?

Arterial lines are removed as soon as continuous monitoring or frequent blood sampling is no longer needed. This is typically:

Post-surgical patients: When they are stable and transferred out of the ICU
Medical ICU patients: When hemodynamic stability is achieved and frequent ABG sampling is no longer needed

Routine removal within 3–7 days is standard, earlier if the clinical situation allows. Arterial lines do not stay in indefinitely — they carry infection risk (though lower than central venous catheters) and can affect arterial blood flow with prolonged use.

Arterial Line Removal

Removal is simple:

The catheter is withdrawn
Firm pressure is applied to the site for 5–10 minutes (longer if you are on anticoagulation or have bleeding issues) — arterial bleeding requires more time than venous
A pressure dressing may be applied and left in place for several hours
After removal, the site should be inspected for hematoma (a blood collection under the skin), which is a common minor complication managed with continued pressure

After removal, you may notice:

A bruise at the site — normal; may take a week or more to resolve
Mild tenderness — normal, resolves in days
The pulse at the wrist remains intact — check with your nurse if you are concerned

When to Alert the Nurse

While the arterial line is in place, tell your nurse or call for help immediately if you notice:

Bleeding from or around the access site
The site or hand appears significantly more pale, blue, or cold than normal
Numbness, tingling, or significant weakness in the hand on the side of the arterial line
Pain at the site that is worsening rather than stable
Any wetness or dampness near the site, especially if sudden
A monitor alarm you cannot identify

After the ICU: Transitioning

When an arterial line is removed and you are transferred out of the ICU, standard blood pressure monitoring transitions back to a cuff. You may notice this feels less precise — that is expected. The A-line was appropriate for your level of illness; standard monitoring is appropriate as you improve.

This guide is for educational purposes. Arterial line management protocols vary by institution and by patient condition. In all critical care situations, the decisions of your clinical care team regarding monitoring and access take priority. In an emergency, always call for your nurse or use the emergency call system immediately.