Arterial Access: Overview 

1. Choice of Cannula Sites 

Arterial cannulation is commonly performed for continuous blood pressure monitoring and arterial blood sampling. The choice of site depends on accessibility, safety, and patient factors. 

Common Sites:

1. Radial artery (most common)
– Advantages: Superficial, easily compressible, low risk of ischemia due to collateral circulation.
– Hazards: Rare ischaemia, thrombosis.
– Note: Perform Allen’s test before cannulation to ensure Ulna pulse present. 

Femoral artery 
Advantages: Large vessel, easy access in emergencies. 
Hazards: Higher infection risk, retroperitoneal hematoma, difficult compression. 

Brachial artery 
Advantages: Larger vessel than radial. 
Hazards: No collateral circulation, high risk of limb ischemia, possible nerve injury. 

Dorsalis pedis or posterior tibial artery 
Advantages: Alternative lower limb access. 
Hazards: Small vessels, higher thrombosis risk, difficult compression. 
 
2. Hazards and Complications 

Thrombosis → distal ischaemia 
Haemorrhage or haematoma 
Infection / sepsis 
Embolism (air or thromboembolism) 
Nerve injury 
Ischaemia / necrosis 
Pseudoaneurysm or arteriovenous fistula 
 
3. Arterial Waveforms 

Normal Arterial Waveform:
– Sharp systolic upstroke
– Systolic peak – Dicrotic notch (aortic valve closure)
– Gradual diastolic runoff
– Normal BP values: Systolic 90–120 mmHg, Diastolic 60–80 mmHg, MAP 70–100 mmHg 

Abnormal Waveforms:  

1. Damped waveform: Flattened peaks, loss of dicrotic notch (causes: air bubbles, kinks, clot, no fluid in transducer)  
2. Overdamped waveform: Slow upstroke, absent dicrotic notch (causes: long tubing, air in line)  
3. Underdamped waveform: Exaggerated peaks/troughs (causes: stiff tubing, resonance)  
4. Abnormal physiologic patterns:
– Low systolic/narrow pulse: Shock, hypovolemia
– High systolic/wide pulse: Aortic regurgitation
– Slow upstroke: Aortic stenosis 

 

4. Reasons for Removing an Arterial Cannula 
No longer needed for monitoring or ABGs 
Complications: hematoma, thrombosis, infection, ischemia 
Malfunction: blockage, leakage, inaccurate readings 
Prolonged duration 
Patient mobility/comfort 
 
Summary: