Overview of anatomy and physiology related to vascular access: peripheral veins

Campus Vygon

19 Apr, 2023

VADs (Vascular Access Devices) can be inserted in various areas of the body via a selection of veins. Some venous access sites can result in more complications. It is therefore important to carefully select the vein for access.

The purpose of this article is to detail and describe the veins most used for access and subsequent vascular access device insertion.

 

Structure of the vein

 

Structure of the veinImage 1: Structure of the vein

 

The main function of veins is to carry waste products and deoxygenated blood away from tissues and organs. They help to eliminate waste products from the body and return deoxygenated blood back to the heart for re-oxygenation.

Veins are blood vessels that possess three layers of tissue. They include the tunica intima, tunica media, and tunica externa (Image 1).

 

The internal layer

The internal layer (tunica intima) is made up of squamous epithelium cells known as endothelium along with a basement membrane and a layer of elastic tissue (internal elastic lamina).

The purpose of the endothelium is to facilitate blood flow along the vessel and to prevent the adhesion of blood cells to the vessel wall (Tortora and Derrickson, 2021). This layer is important when inserting a needle during vascular access, as trauma can disrupt the lining and encourage platelets to adhere to the vessel wall. This can then result in thrombus formation.

There are other factors that can lead to damage of the endothelium cells. These include inserting a device in areas of flexion (such as over joints), poor device securement or dressing which can result in continuous catheter movement and vein intima damage. (Gorski, 2021).

 

The middle layer

The middle layer (tunica media) is composed of elastic tissue and smooth muscle fibres that run in a circular manner around the lumen of the vein. It also has an external lamina, which consists of elastic tissue (Tortora and Derrickson, 2021). This layer is sensitive to changes in temperature as well as mechanical or chemical irritation and this can cause the vessel to spasm.

It is important to note that this layer is also prone to, what is called, the stress relaxation phenomenon.

Because a tourniquet is used during some catheter insertion procedures, the muscle fibres elongate to accommodate the increased volume of blood. The pressure increases but then reverts to normal. When the tourniquet is subsequently removed, the volume and pressure fall suddenly and, within several minutes, normal pressure is re-established.

Therefore, if an obstruction is encountered during advancement of a cannula or midline, it may mean that adequate time has not been left between tourniquet removal and vein flow recovery time. Tourniquets can also cause veins to become unpalpable if left in place for an extended length of time. This can be due to smooth muscles over-stretching (Hadaway, 2001).

 

The tunica adventitia

The final layer is the tunica adventitia. This layer is composed of connective tissue, collagen, and nerve fibres. The nerve fibres are fibres of the sympathetic nervous system. The purpose of this layer is to support the vessel (Tortora and Derrickson, 2021).

 

Valves

Valves are structures found within the veins. They are formed by the endothelial lining of the Tunica Intima and are found in most veins apart from the larger veins of the vasculature. Their function is to allow unidirectional flow of blood back to heart and to prevent pooling in the peripheral circulation.

Valves can be visualised by ultrasound. They can sometimes be palpated. Occasionally valves can cause difficulties when threading guidewires through the veins.

 

Veins used for short peripheral catheters

Dorsal hand veins

 

Dorsal veins of the handImage 2: Dorsal veins of the hand

 

The small digital veins flow along the lateral portion of the fingers. The digital veins join to form the dorsal metacarpal veins which are easily visualised and palpated. The dorsal digital veins from the adjacent sides of the fingers unite to form three dorsal metacarpal veins. These form a dorsal venous network opposite the middle of the metacarpus.

The dorsal venous network of the hand lies within the superficial fascia on the dorsum (back) of the hand. The dorsal venous network is formed by the dorsal metacarpal veins which eventually give rise to the cephalic vein and basilic vein.

Although the hand is an area of flexion, these veins remain popular for peripheral venous cannulation as they are often prominent. As previously mentioned, devices placed in areas of flexion can irritate and damage the intima of the vein, potentially resulting in mechanical phlebitis.

 

Forearm veins

The superficial venous arch in the dorsum of the hand drains into the cephalic vein and basilic vein (Image 2).

The basilic vein in the forearm is usually a large vein. It is sometimes overlooked because of its position on the posterior medial aspect of the forearm. It can be easily palpated so it is an option for midlines and EDC device insertion if the area of flexion at the antecubital fossa can be avoided.

The median antebrachial veins ascend anteriorly in the forearms to join the basilic vein or medial cubital veins (sometimes both). The medial antebrachial ascends from the wrist. These veins might appear suitable for cannulation but because they are usually situated between two branches of the median nerve, performing venepuncture at this site can be extremely painful. The basilic and cephalic veins then continue into the forearm.

The median cubital vein continues to run diagonally across the antecubital fossa connecting the basilic vein and the cephalic veins (Scales, 2005). There is a great variation in the pattern of veins in this area and sometimes, the median cubital vein is not always visible.

 

Antecubital fossa

Often prominent in the antecubital fossa, the median cubital vein is commonly used for venepuncture and cannulation. It has a small diameter and a variable course. It is not a vein recommended for midline or PICC insertion due to being in an area of flexion, which is known to potentially lead to mechanical phlebitis (Gorski, 2021).

 

Veins of the upper arm

Deep veins in the upper arm can be used for the insertion of midlines and PICCs and arm / PICC ports. These are:

  • Cephalic vein
  • Brachial vein
  • Basilic vein
Main veins of the armImage 3: Main veins of the arm

 

Cephalic vein

The cephalic vein extends from the radial side of the wrist and runs along the lateral part of the upper arm. It then travels along the pectoral-deltoid groove and joins the axillary vein. It is usually smaller than the basilic vein and may be tortuous as it ascends the upper arm. The accessory cephalic vein joins the cephalic vein at the lateral border of the arm. There is an added risk of stricture formation at the junction or the accessory cephalic and the main cephalic vein. This can make PICC insertion or arm port insertion challenging and so is a less desirable vein selection for these devices (Bodenham et al., 2016).

As midline catheters do not extend beyond the axillary line, the cephalic vein of the upper arm remains a suitable access vein for midline catheters. However, the diameter of the veins should be considered to ensure an adequate catheter to vein ratio (CVR) (Sharp, 2016).

 

Brachial vein

The brachial vein is a deep vein in the arm; this vessel is paired closely with the brachial artery and brachial nerves. It carries the greatest risk of damage to adjacent structures (nerve and artery) and, therefore, should only be accessed with ultrasound guidance to minimise the risk of nerve damage.

 

Basilic vein

The basilic vein begins along the ulnar side of the forearm. Along its course, other veins connect to it, including a branch from the cephalic vein (median cubital vein). This vein joins the basilic vein near the elbow. The basilic vein continues to travel up in a groove between the biceps brachii and pronator teres muscles. It continues to cross the brachial artery and runs up and along the edge of the biceps brachii. Below the level of the axilla, the basilic vein then travels deeper into the arm. Here it is joined by the deep brachial veins from the middle of the inner arm. Together, these veins become the axillary vein.

The optimal vein of choice for PICC and arm port insertion is the basilic vein because it is the largest of the three vessels and provides a straight and direct route to the Superior Vena Cava.

 

CONCLUSION

Vessel health and preservation (VHP) should always be considered when choosing a vein for device placement. The most appropriate vein and insertion site should be selected to best accommodate the device being placed. Both vein and insertion site should be selected with the patient and healthcare team and based on the projected treatment plan. You should always choose the most appropriate site that is likely to last the full length of prescribed therapy.

Although the practitioner should use their professional judgement to select the most appropriate vein for cannulation, this decision should be based on patient history and anatomy and the availability of ultrasound guidance and fluoroscopy.

Considerations about forearm placement VASAV - V - Assess the vein quality A - ANTT S - Smallest device / Largest vein A - Avoid areas of flexion V - Ensure a good vein purchase (2/3 of the device should reside in the vein)

Considerations about upperarm placement MACUA : M - Mid upper arm (ZIM) A - ANTT C - Catheter to Vein Ration (CVR - leave 1/3 of the vein lumen free) U - Ultrasound guidance A - Ensure tip does not extend beyond the axillary vein

References
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