📈 Chapter 137: Arterial Line

Indications · Sites (radial, femoral, dorsalis pedis) · Modified Allen test · Over-the-needle vs Seldinger · Transducer setup · Complications (thrombosis, ischemia, infection) · Damping

🔍 Core Concepts: Arterial Line

📌 Indications
Continuous BP monitoring in unstable patients, titration of vasoactive drugs, frequent ABG sampling, hypertensive emergencies, post-cardiac surgery.
📍 Preferred Sites (Children)
Radial artery (most common), femoral artery, dorsalis pedis, posterior tibial. Avoid end arteries (brachial, temporal) – risk of distal ischemia.
✋ Modified Allen Test
Assesses ulnar collateral circulation. Positive test (flush <15 sec) → radial artery can be cannulated safely. Negative → choose other site.
🔧 Insertion Techniques
Over-the-needle (catheter-over-needle, like IV). Seldinger (needle → wire → dilator → catheter) for larger arteries (femoral).
📊 Transducer Setup
Zero at phlebostatic axis (4th ICS, mid-axillary). Square wave test for dynamic response (fast flush). Damping = under/overdamped waveform.
⚠️ Complications
Thrombosis, distal ischemia (rare if collateral flow), hematoma, infection, arterial spasm, pseudoaneurysm, nerve injury.
🧼 Line Care
Transparent dressing, daily site inspection, remove as soon as not needed. Continuous flush (heparinized saline 1-5 U/mL) to maintain patency.

📊 Stepwise Arterial Line Insertion (Radial Artery)

1
Perform modified Allen test
Compress radial and ulnar arteries, ask patient to open hand (blanched). Release ulnar – if hand flushes within 5-15 seconds (positive test), radial cannulation safe.
2
Prepare & position
Extend wrist (gentle dorsiflexion) on arm board. Clean with chlorhexidine. Use local anesthesia (lidocaine). Use ultrasound if pulses difficult.
3
Insertion (over-the-needle technique)
Palpate radial pulse with non-dominant hand. Insert catheter at 30-45° angle toward pulse. Look for flash of bright red, pulsatile blood. Lower angle to 10-15°, advance catheter over needle.
4
Secure & connect
Remove needle. Connect to transducer system (primed, zeroed). Secure with suture or tape. Apply transparent dressing. Flush with heparinized saline.
5
Confirm waveform & zero
Check for normal arterial waveform (sharp upstroke, dicrotic notch). Zero transducer at phlebostatic axis. Perform square wave test (fast flush) – 1-2 oscillations normal.