CRNI Exam

This chapter maps the superficial and deep veins of the upper extremity, the nerves and arteries that lie close to them, and the route from the arm to the heart. It also explains why tip position matters and how the lymphatic system relates to vein selection. Vein selection, nerve injury and catheter tip questions draw heavily on this anatomy.

Superficial veins lie in the subcutaneous tissue and are the veins used for short peripheral catheters. From distal to proximal:

Metacarpal (dorsal hand) veins: formed by the union of digital veins on the back of the hand. They are easy to see and suit short, nonirritating therapies, and they are the preferred site in chronic kidney disease (stage 3b to 5) to preserve forearm and upper arm veins for future dialysis access. They are uncomfortable, move with hand use, and are fragile in older adults.

Cephalic vein: runs up the radial (thumb) side of the forearm, then along the lateral upper arm, and joins the axillary vein near the shoulder through a sharp angle at the deltopectoral groove. In the forearm it is large and accessible, but at the lateral wrist it lies close to the superficial radial nerve, so the radial side of the wrist (roughly the distal 10 to 12 cm) should be avoided.

Median cubital vein: crosses the antecubital fossa connecting the cephalic and basilic veins. It is ideal for venipuncture for laboratory specimens but is a poor site for a short peripheral catheter because the elbow is an area of flexion, which causes mechanical phlebitis, dislodgement and occlusion, and because the vein may be needed for later blood draws or PICC insertion.

Exam Tip: When a question asks for the best site for a short peripheral catheter in an adult, the answer is usually a forearm vein away from joints, such as the cephalic or basilic vein in the mid-forearm. Distractors include the antecubital fossa, the radial side of the wrist, the dorsal foot and the arm with a dialysis fistula.

Deep veins run alongside arteries and are not visible. The brachial veins, usually paired, accompany the brachial artery in the upper arm, and the median nerve lies very close to this bundle. The brachial vein is a second-choice PICC vein because of the risk of arterial puncture and median nerve injury. The basilic vein (first choice) is more superficial and separate from the bundle, while the cephalic vein (last choice for PICCs) is smaller and has a sharp junction with the axillary vein that makes catheter advancement difficult and malposition more likely.

Memory Aid: For PICC vein choice remember "B-B-C": Basilic, Brachial, Cephalic, in that order.

Nerve injury from venipuncture is uncommon but can be permanent, and the exam tests where it happens and what to do.

The first sign of nerve contact is usually a sudden electric, shooting or tingling pain radiating along the arm or into the fingers. The correct action is to stop and remove the needle or catheter immediately, never to reposition while the patient reports paresthesia. Then assess sensation and movement, document, notify the provider, and choose a different site.

Common Trap: A distractor may suggest withdrawing the needle slightly and redirecting when the patient reports shooting pain. Redirecting continues the injury. Stop the procedure and remove the device.

Central vascular access devices (CVADs) end in the central circulation, ideally at or near the cavoatrial junction, where the superior vena cava (SVC) meets the right atrium, in the lower third of the SVC. A PICC inserted in the basilic vein follows this path:

1. Basilic vein in the upper arm.
2. Axillary vein (the basilic becomes the axillary at the lower border of the teres major).
3. Subclavian vein (the axillary becomes the subclavian at the outer border of the first rib).
4. Brachiocephalic (innominate) vein, formed where the subclavian joins the internal jugular vein.
5. Superior vena cava, formed by the joining of the right and left brachiocephalic veins.
6. Cavoatrial junction and right atrium.

The left brachiocephalic vein is about two to three times longer than the right and crosses the chest more horizontally. As a result, left-sided catheters travel a longer and more tortuous path, have more contact with vessel walls, and carry a higher risk of tip malposition and thrombosis. Right-sided insertion, especially through the right basilic vein, gives the most direct route. Even so, handedness, prior surgery, an existing dialysis access, radiation or lymph node dissection may make the left side appropriate per organizational policy.

Common malpositions include the tip turning up into the internal jugular vein, crossing into the opposite brachiocephalic or subclavian vein, coiling in the axillary vein, or advancing too far into the right atrium or ventricle. Tip location is confirmed before first use by chest radiograph or ECG-based tip-location technology.

Why does the tip location matter? The SVC carries high blood flow (about 2 L/min in adults), which rapidly dilutes vesicants, hyperosmolar parenteral nutrition and irritating solutions and reduces endothelial damage. A tip too high, in the brachiocephalic or subclavian vein, increases the risk of thrombosis and vessel erosion. A tip too low, inside the right atrium or ventricle, can irritate the conduction system.

The heart's electrical impulse begins in the sinoatrial (SA) node, located in the wall of the right atrium near the entrance of the SVC. It spreads through the atria to the atrioventricular (AV) node, then through the bundle of His, the bundle branches and the Purkinje fibers to the ventricles. Because the SA node lies in the right atrium near the SVC junction, a guidewire or catheter tip that advances into the right atrium or ventricle can trigger premature atrial or ventricular contractions, atrial fibrillation or, rarely, ventricular tachycardia.

During insertion, sudden palpitations or an irregular rhythm on the monitor suggest the guidewire or catheter is too deep; pulling it back a few centimeters usually resolves the dysrhythmia. ECG-based tip-location systems take advantage of the same anatomy: the P wave grows taller as the tip approaches the SA node and is maximal near the cavoatrial junction, then becomes biphasic (with a negative deflection) if the tip enters the atrium.

Clinical Scenario: During a bedside PICC insertion with ECG tip guidance, the patient reports a fluttering feeling in the chest, and the monitor shows frequent premature contractions. The P wave has become biphasic. The inserter withdraws the catheter slightly until the P wave returns to its maximal upright height and the ectopy stops, then secures it at that external length and documents it. The fluttering and the biphasic P wave both signaled a tip in the right atrium.

The lymphatic system returns excess interstitial fluid and protein to the circulation, absorbs dietary fat and transports immune cells through lymph nodes. Lymph drains through lymphatic vessels into nodes and finally into the thoracic duct (left side) and the right lymphatic duct, which empty into the subclavian veins near their junctions with the internal jugular veins.

When axillary lymph nodes are removed or irradiated (for example after breast cancer surgery), lymph drainage from that arm is impaired, raising the risk of lymphedema. Evidence on restrictions is mixed, so INS guidance is to decide on venipuncture, catheter placement and blood pressure measurement on the affected side per organizational policy, the patient's history and the patient's preference. Lymphedema itself makes veins hard to find, raises infection risk and impairs healing.

• Use forearm veins for short peripheral catheters; avoid the antecubital fossa, the radial side of the wrist and the volar wrist.
• PICC vein choice is basilic first, then brachial (near the brachial artery and median nerve), then cephalic.
• Sudden electric or shooting pain during insertion means nerve contact: stop and remove immediately.
• The central path runs basilic, axillary, subclavian, brachiocephalic, SVC, cavoatrial junction; the left brachiocephalic is longer.
• Tips in the right atrium or ventricle can cause dysrhythmias because the SA node sits near the SVC junction.