Anatomy, Physiology, and Vascular Assessment
Domain 2: Anatomy, Physiology, and Vascular Assessment
This domain tests whether you can identify safe target veins, recognise structures at risk, and use assessment findings-not guesswork-to choose a site.
Core anatomy and rules
- Upper limb superficial veins: dorsal venous network, cephalic vein (lateral), basilic vein (medial), median cubital vein, and median forearm vein. The cephalic and basilic systems connect via the median cubital vein.
- The basilic vein in the medial upper arm lies near the brachial artery and median nerve; deep brachial access carries arterial and nerve injury risk. The cephalic vein is safer distally but may be tortuous or small proximally.
- Central veins: internal jugular, subclavian, axillary, and brachiocephalic join to form the SVC; the SVC meets the right atrium at the cavoatrial junction, the preferred tip position for central catheters.
- Assess visually, by palpation, and by ultrasound: diameter, depth, compressibility, valves, tortuosity, thrombosis, arterial proximity, and flow. A compressible, round, thin-walled, non-pulsatile lumen with low-pressure flow is venous.
- Physiology matters: low venous pressure, valve incompetence, and hypovolaemia change lumen size; tourniquet use improves filling but should be released promptly.
Worked example
Ultrasound shows a 4 mm vessel in the medial arm at 0.6 cm depth, but it is pulsatile and non-compressible. Reasoning: do not cannulate. It is likely the brachial artery. Move laterally to the cephalic vein or choose another limb; map the artery and nerve before needle entry.
Traps
Choosing visible veins only; failing to identify the artery; assuming deeper is safer; ignoring valves and tortuosity; and assessing without ultrasound when access is difficult.