The Subclavian Vein

The subclavian vein (SCV) has a wide calibre (1-2cm diameter in adults) and is thought to be held open by surrounding tissue. In severely shocked patients, however, it may be safer to perform a venous cutdown (eg. onto the long saphenous vein) or use the EJV which may be accessible. In conscious patients the subclavian route is often preferred (since head movement does not affect it) and also in trauma patients with suspected cervical spine injury. Subclavian cannulae are easier to secure which reduces subsequent movement and dislodgment. Whilst a high success rate for placement can be achieved, serious complications occur more commonly than with the other routes. Subclavian puncture should be avoided in patients with abnormal clotting since it is difficult to apply pressure to the subclavian artery following accidental puncture.

Anatomy. The SCV lies in the lower part of the supraclavicular triangle (figure 2.) and drains blood from the arm. It is bounded medially by the posterior border of the sternocleidomastoid muscle, caudally by the middle third of the clavicle, and laterally by the anterior border of the trapezius muscle. The SCV is the continuation of the axillary vein and begins at the lower border of the first rib. Initially the vein arches upwards across the first rib and then inclines medially, downwards and slightly forwards across the insertion of the scalenus anterior muscle into the first rib to enter the thorax where it joins with the IJV behind the sternoclavicular joint.

Anteriorly, the vein is covered throughout its entire course by the clavicle. It lies anterior to, and below the subclavian artery as it crosses the first rib. Behind the artery lies the cervical pleura which rises above the sternal end of the clavicle.

Preparation and positioning. The patient should be supine, both arms by the sides, with the table tilted head down to distend the central veins and prevent air embolism. Turn the head away from the side to be cannulated unless there is cervical spine injury. Normally the right SCV is cannulated since the thoracic duct is on the left and may occasionally be damaged during SCV cannulation.

Technique. Stand beside the patient on the side to be cannulated. Identify the midclavicular point and the sternal notch. The needle should be inserted into the skin 1cm below and lateral to the midclavicular point. Keeping the needle horizontal, advance posterior to the clavicle aiming for the sternal notch. If the needle hits the clavicle withdraw and redirect slightly deeper to pass beneath it. Do not pass the needle further than the sternal head of the clavicle.

Complications. Any of the complications described above can occur but pneumothorax (2-5%) or rarely haemothorax or chylothorax (fatty white fluid in the pleural cavity due to leakage of lymph from thoracic duct) are more common with this route than the others. Occasionally the catheter may pass up into either jugular or the opposite SCV rather than into the chest. This will not give reliable CVP readings and infusion of some drugs (hypertonic solutions/vasoconstrictors) may be contra-indicated.

Practical problems specific to the subclavian route

• Keep hitting the clavicle: Check that you are starting from the correct position. Redirect the needle slightly more posterior whilst being careful not to enter the chest. Try bending the needle slightly to encourage it to pass beneath the clavicle. Try placing a pillow under the shoulders or getting someone to pull gently down on the arms.
• Cannot find the vein: direct the needle a little more cephalad
• Fail after repeated attempts: DO NOT PERSIST since the likelihood of complications increase. Try an alternative route ON THE SAME SIDE unless chest radiography is available to exclude any possible pneumothorax.
• The catheter tip is not in the chest: Usually detected on chest X-ray, or if the fluid level in the CVP manometer does not rise and fall with breathing. A simple test that may increase the suspicion of jugular placement is to rapidly inject 10ml of fluid into the catheter whilst listening with a stethoscope over the neck. An audible 'whoosh' or thrill under the fingers suggests the catheter has entered the jugular vein. If this is positive, in the presence of a CVP reading which does not change with respiration, then the position of the cannula must be questioned. 

The Internal Jugular Vein

The internal jugular vein (IJV) is a potentially large vein commonly used for central venous access which drains blood from the brain and deep facial structures. Cannulation is associated with a lower incidence of complications than the subclavian approach. Unlike the subclavian route, failure on one side does not prevent the operator from trying the other side although this should be discouraged if arterial puncture had occurred. Many approaches have been described depending upon the level in the neck where the vein is entered. High approaches reduce the risk of pneumothorax but increase the risk of arterial puncture the opposite being true of a low approach. A middle level approach is described below.

Anatomy. The sigmoid venous sinus passes through the mastoid portion of the temporal bone, emerging from the jugular foramen at the base of the skull as the IJV. It passes vertically down through the neck within the carotid sheath. The vein initially lies posterior to the internal carotid artery, before becoming lateral and then anterolateral to the artery. It is able to expand laterally to accommodate increased blood volume. It joins the SCV behind the sternal end of the clavicle to enter the chest as the innominate vein (figure 2).

Preparation and positioning. The patient should be supine, both arms by the sides, with the table tilted head down to distend the central veins and prevent air embolism. Slightly turn the head away from the side to be cannulated for better access (turning it too far increases the risk of arterial puncture).

Technique. Stand at the head of the patient. Locate the cricoid cartilage and palpate the carotid artery lateral to it at this level. Keeping a finger gently over the artery, insert the needle at an angle of 30-40^o to the skin and advance it downward towards the nipple on the same side (in a woman guess where the nipple would be if she were a man). Always direct the needle away from the artery under your finger. The vein is usually within 2-3cm of the skin. If the vein is not found, redirect the needle more laterally.

Complications. With experience this route has a low incidence of complications. Arterial puncture is easily managed by direct pressure. Pneumothorax is rare providing the needle is not inserted too deeply.

Practical problems

• Cannot feel the artery. Check the patient! Try the carotid on the other side. It is safer to consider a different approach rather than 'blindly' try to find the jugular.
• Arterial puncture. Remove needle and apply firm pressure over the puncture site for 10 minutes.
• Cannot find the vein. Recheck your position. Ensure that you are not pressing firmly on the artery as this can compress the vein next to it. Try tipping the patient further head down if possible. If the patient is hypovolaemic, and central venous access is not immediately required to correct it, give intravenous fluids and wait until the veins are fuller. Try inserting the needle a little closer to the artery but beware of puncture. 

(Continued ...)

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