Central venous access: anatomy and ultrasound

As a simulated patient in a recent course on ultrasound guided central venous access I learnt the basics of gross and surface anatomy of the venous system; the use of ultrasound imaging to view blood vessels; and the use of ultrasound guidance for venepuncture and insertion of central venous and peripherally inserted central catheters. This quiz covers gross, surface, and ultrasound anatomy of the internal jugular vein with regard to central venous access.

Consider the clinical scenario of a patient who has recurrent deep vein thrombosis and cannot receive oral anticoagulants. The patient will need central venous access to place a filter in the inferior vena cava to prevent pulmonary embolism.

Questions

(1) Where would you find the internal jugular vein, and what are the main relations to avoid?

(2) What features distinguish a vein from an artery in an ultrasound image?

(3) How can you tell that a vein is being punctured by a needle in an ultrasound image?

(1) The internal jugular vein runs in the carotid triangle then deep to the sternocleidomastoid and the sternoclavicular joint. The internal or common carotid artery and vagus nerve accompany this vessel in the carotid sheath and are at risk of damage. If attempting puncture low in the neck, the lung and subclavian artery are also at risk.

(2) A vein is non-pulsatile, compressible, and increases in diameter on valsalva manouvre.

(3) When a needle impinges on a vein its wall will become deformed in the real time ultrasound image.

Introduction

Central veins, such as the superior vena cava and inferior vena cava are accessed through major veins in the anterior triangle, axilla, and femoral triangle. The target vessels in these areas are the femoral, axillary, subclavian, and internal jugular veins. Access to central veins is necessary for many purposes, such as haemodialysis, giving chemotherapy, and monitoring central venous pressure or pulmonary capillary wedge pressure.

The internal jugular vein and femoral triangle are accessed in the anterior triangle of the neck and femoral triangle respectively. The axillary and subclavian veins are more difficult to access and are located in the axilla and anterior chest wall. Usually the internal jugular vein is found using the landmark method: an introducer needle is advanced while palpating the carotid artery until a flashback and aspiration of (venous) blood.

With the landmark method, however, structures that accompany the vein or lie close to it, such as arteries, nerves, and other organs are at risk of damage. Also the vein may not lie in the expected region, be thrombosed, or be atretic, especially if there is a history of insertion of a central venous catheter, and in these cases landmark venous puncture will fail. Real time two dimensional imaging of the target vessel and local anatomy has obvious advantages.

Anatomy is useful

The neck can be divided into an anterior and posterior triangle, with the former subdivided into the submental, submandibular, carotid, and muscular triangles. In the anterior triangle of the neck, the internal jugular vein leaves the skull via the jugular foramen along with the 9th, 10th, and 11th cranial nerves. On the surface, this point relates to the intertragic notch,¹inferior to the tragus and antitragus on the ear (fig 1). The internal jugular vein then traverses the carotid triangle (fig 2), before running deep to the sternocleidomastoid about halfway down its anterior border.

Fig 1 Surface anatomy of the internal jugular vein; a intertragic notch; b internal jugular vein; c sternocleidomastoid; d internal jugular vein between sternal and clavicular heads of sternocleidomastoid; e subclavian vein passing under the clavicle; f anterior triangle of the neck; g posterior triangle of the neck. The red triangle shows the area where intravenous access is obtained

At the sternoclavicular joint the internal jugular vein passes between the sternal and clavicular heads of the sternocleidomastoid (the site where the jugular venous pressure is assessed and central venous access obtained). Inferior to this it joins the subclavian vein and continues downward as the brachiocephalic vein. The left brachiocephalic vein passes across posterior to the manubrium, to join the right brachiocephalic vein and form the superior vena cava before entering the right atrium.

Fig 2 The anterior triangle of the neck; a sternothyroid and thyrohyoid muscles; b omohyoid; c sternocleidomastoid; d submandibular gland; e carotid triangle

In the neck, the internal jugular vein is accompanied by the vagus nerve and common carotid (fig 3) or internal carotid artery. These structures are enclosed in deep cervical fascia called the carotid sheath. The common carotid artery divides into the external and internal carotid arteries at the superior border of the thyroid cartilage and only the internal carotid artery remains in the carotid sheath with the vagus nerve and the internal jugular vein.

Fig 3 Contents and relations of the carotid sheath; a common carotid artery; b vagus nerve; c internal jugular vein; d sternocleidomastoid; e omohyoid (reflected); f sternothyroid muscle; g thyrohyoid muscle; arrow shows superior root of ansa cervicalis (reflected); # superior thyroid artery

The internal or common carotid artery, depending on the level, usually lies medial to the internal jugular vein with the vagus nerve posteriomedially between these two vessels. The ansa cervicalis (fig 3), from nerves C1, C2 and C3, travels on the anterior aspect of this sheath to supply the infrahyoid muscles of the neck. The accessory nerve travels with the carotid artery, internal jugular vein, and vagus nerve outside the carotid sheath and passes deep to the sternocleidomastoid muscle.

Ultrasound visualisation

Ultrasound imaging uses high frequency sound waves to produce a two dimensional, real time, greyscale image of tissues. Different views will be produced depending on the angle at which the beam passes through the vessels-a bit like a histology section. For venepuncture of the internal jugular vein it is best to get a cross sectional transverse image (fig 4) of the vessels as this allows the operator to visualise the target vessel and structures to be avoided, especially the common carotid artery.

Fig 4 Shows a cross sectional view of (a) the internal jugular vein and (b) the common carotid artery. Note the unique triangular shape of the internal jugular vein

A black and white ultrasound image of an artery and a vein can be confusing to the untrained eye. But arteries and veins on an ultrasound image can be distinguished by the difference in their appearances. Firstly, know the anatomical relations of the internal jugular vein, and ensure the probe is correctly oriented. To do this there will be a mark on the probe that corresponds to a mark on one side of the image on the screen. This avoids confusion between lateral and medial. The ultrasound image reflects basic histology-in general the vein is bigger with a wider lumen and a thinner wall. This may be difficult to see in the image, however, and patients with hypovolaemia will have the vein smaller than the artery.

Arteries are pulsatile, but veins are not. But remember that pulsation can be transmitted from the artery or, with the internal jugular vein, the jugular venous pulse may be visible. A better observation, therefore, is that with light pressure from the probe a vein is compressible and the artery is not. Also the internal jugular vein often has a unique triangular shape on a cross sectional ultrasound image (fig 4). So by looking at position, shape, pulsation, and compressibility it is possible to identify correctly the internal jugular vein with confidence. Once you have identified the internal jugular vein the next step is to gain venous access by venepuncture with a 21 gauge introducer needle and syringe.

Venepuncture with guidance

To gain percutaneous access, remember that the ultrasound beam is narrow, and, unless using a guide, you should attempt to puncture the vessel in the beam's field.

To do this, centralise the target vessel on the screen, and hold the needle at a 60° angle to the skin. As you advance the needle through the skin the vessel wall will become deformed as the needle encroaches on it (fig 5). As the needle punctures the vessel, its wall will spring back to the original position.

Fig 5 Showing deformation of the vessel wall (a) when the access needle encroaches on it

To ensure the needle is in the lumen, withdraw some blood. Then remove the syringe, and advance the guide wire into the vessel. Now the vessel is safely punctured get a longitudinal view by rotating the probe 90°, and watch the guide wire pass along the lumen as you advance it to ensure that you have not inadvertently cannulated a local artery.

Central venous access is done often and has potentially serious and costly complications for the patient and the health service. Several studies and a more recent meta-analysis have shown that ultrasound guidance makes the procedure quicker and safer for patients.² This seems obvious because it allows visualisation of the target vein, structures to be avoided, and the passage of the needle from the skin to the target vessel and confirmation of guide wire in the vein. This does not devalue the importance of being skilled in the landmark method because this may be necessary in emergency or in situations of technical failure.²

A good understanding of venous anatomy is therefore essential when attempting to gain central venous access, with or without ultrasound guidance. This is an excellent example of the link between anatomy and clinical practice. Based on available evidence, the UK National Institute for Health and Clinical Excellence recommends the use of ultrasound guidance for central venous access, meaning this technique may well soon be standard practice.² An implication is that more junior staff with the right training may be doing such procedures in the future.

1. Backhouse KM, Hutchings RT. A colour atlas of surface anatomy. Weert, Netherlands: Wolfe Medical Publications, 1986: 80-2.
2. Hind D, Calvert N, McWilliams R, Davidson A, Paisley S, Beverley C, et al. Ultrasonic locating devices for central venous cannulation: meta-analysis. BMJ 2003;327:361-70.