A central line provides rapid access to the right side of the heart, which allows drugs to be rapidly delivered to the rest of the body. A central line has many applications, including: a chemotherapy port, emergency delivery of drugs or large volumes of fluid, total parenteral nutrition, pacemaker leads, etc.
Let's begin with the skeleton. The clavicles and sternum have been dissected from the 3D window, and rib 1 is the only rib included. From the first and second costal cartilages you can infer the position of the manubrium and the sternal angle. At any time, you may add back the skin or rotate the image using the Skin opacity tool or the Rotate tool. Remember to use mouse-overs with the "Highlight" tool activated in order to identify structures. In the cross-sectional images, identify the first rib and clavicle.
Let's look at the major veins that drain into the superior vena cava. The subclavian veins and internal jugular veins are commonly used for a central line. Look at their relationships to the clavicle and first rib in the cross-sectional images. The veins have different names based on location. To see where the same vessel changes name, use mouse-overs to trace the veins from the thorax to their origin.
This YouTube video discusses the instrumentation and techniques for infra- and supra-clavicular approaches to the subclavian vein. The anatomy of the procedure is discussed between minutes 5:40 and 7:35.
Test your recall of the video by answering the questions embedded in this more detailed exploration of the anatomy.
Start working on the left side. Omit the right-side structures to provide a clear view during image rotation. Add in the left clavicle. Your target is the subclavian vein, between the clavicle and first rib. Rotate the image 60° to the left to see the path of your needle into the vein. Add in some skin to see where you are.
Now let's add some structures that should be avoided. First the arteries. (Remember to use mouse-overs to identify them). Rotate the image through 360° to confirm that the axillary artery and vein are very close together throughout their distal course beyond the first rib.
Click on the green box to see the answer. To activate a link in the answer right, or control, click the link and choose "open"
Where do you see a gap between the subclavian vein and artery?
When you rotate the image to 90° to the left or 90° to the right. Look where the vessels cross the rib.
On the cross-sectional images, use mouse-overs with the "Highlight" tool activated to identify the muscle that separates the subclavian artery and vein.
Add the anterior scalene muscle. Rotate 360° to confirm that the anterior scalene separates the subclavian artery and vein.
Now look at 0° as we remove the clavicle and then remove the subclavian vein. Mouse-over the transverse image to see the relationships between the clavicle, subclavian vein, muscle and subclavian artery. You can access the subclavian vein where it crosses the first rib because the anterior scalene muscle will protect the artery from your needle, should you go too deep.
What else would be protected by the anterior scalene muscle?
Add in the brachial nerve plexus. These nerves supply the arm and shoulder. Your patient will let you know if you hit it!
Which nerve lies on the anterior surface of the anterior scalene muscle and would be at risk of injury by your procedure?
Add in the phrenic nerve (controls the phrenic diaphragm and one's ability to breathe).
Observe how the Lung extends above the first rib. If your needle advances too deep it will enter the pleural cavity.
What would be the result of puncturing the lung?
A pneumothorax, which would let air enter to the pleural cavity thereby decreasing lung capacity. Because of this you would not attempt a central line if the contralateral lung was compromised by pneumothorax, hemothorax, or dysfunctional hemidiaphragm.
Lastly, note a major lymphatic vessel that drains most of the body, the thoracic duct.
What would injuring this vessel cause?
A chylothorax, which allows lymph to enter the pleural cavity and thereby decreasing lung capacity.
Add back the entire skeleton for one final look. Rotate the view around as much as you like!
Now try to apply your knowledge and interpret the following sonographic images used for the ultrasound-guided approach to the placing a central line.
This YouTube video reviews the anatomical principles and demonstrates three different approaches to the Jugular vein.
Test your recall of the video by answering the questions embedded in this more detailed exploration of the anatomy.
Let's begin with the bones and the sternocleidomastoid muscle on one side. Now, add the internal jugular vein and common carotid artery on both sides. Rotate the 3D image and examine the cross-sectional images to answer the following questions.
Which vessel has the closest relationship to the sternocleidomastoid muscle?
The internal jugular vein is just deep to the sternocleidomastoid muscle throughout its course.
Which vessel is medial to the internal jugular vein?
The common carotid artery.
There are several ways to locate the internal jugular vein.
You can feel the pulse of the common carotid artery near the medial border of the sternocleidomastoid at the level of the hyoid bone and thyroid cartilage. The internal jugular vein lies lateral to this location. Relax the sternocleidomastoid muscle and gently push the medial border in a lateral direction to feel the pulse.
What would happen if you gently massaged the artery at this location? Why?
The heart rate would decrease, because the bifurcation of the common carotid artery and associated carotid sinus are located near here. Stimulation of the carotid sinus (cranial nerve IX) is interpreted as an increase in blood pressure, which activates the vagus nerve (cranial nerve X) to slow the heart.
To orient yourself for the anterior approach shown in the movie, draw a line from the mastoid process to the groove between the sternal and clavicular heads of the sternocleidomastoid muscle. (The clavicular head is highlighted; the sternal head is not). The internal jugular vein lies just deep to the sternocleidomastoid muscle, where the heads split. This method is generally combined with method 1 to avoid the common carotid artery. The landmarks for the anterior approach are typically easier to find in obese or edematous patients.
Find the location of a palpable groove between the lateral border of the sternocleidomastoid and the anterior scalene (Clavicle removed for clarity). You can find this groove on your person by resting your chin in the palm of your left hand and placing the fingers of your right hand on the lateral, right side of the neck. Turn your head against the resistance of the left hand and feel the sternocleidomastoid muscle pop up on the right. Palpate the lateral border of the muscle. Then relax your neck and with the tips of your right fingers press into the grove between the sternocleidomastoid and the anterior scalene muscle. The groove posterior to that is bounded by the middle and anterior scalene muscles.
Which structures are located between the anterior and middle scalene muscles?
The brachial plexus and subclavian artery.
This method is more difficult with obese patients and many clinicians favor methods 1 and 2 because they can be used with any patient.
Now apply your knowledge to interpret the following sonographic images used for the ultrasound-guided approach to placing a central line.
This video provides more relevant clinical details.
Note: The risk of pneumothorax is much greater than the risk of damaging the phrenic nerve or thoracic duct when putting in a subclavian central line. However, it is more difficult to control the bleeding if the subclavian artery is punctured than if the common carotid artery is punctured. The common carotid artery is more accessible to compress without a surgical procedure. This is why some clinicians prefer a jugular central line.