The carina is clearly visible on most chest X-rays and so is used as a landmark to help determine central venous catheter (CVC) location
Correct positioning of a CVC tip depends on the side of entry
Correct positioning of a CVC tip also depends on the intended use of the catheter
Identifying the exact position of a catheter tip is limited by the quality of the X-ray
Catheter positioning
Positioning the tip of a central venous catheter (CVC) within the superior vena cava (SVC) at or just above the level of the carina is generally considered acceptable for most short-term uses, such as fluid administration or monitoring of central venous pressure. Ideally the distal end of a CVC should be orientated vertically within the SVC.
CVCs placed for the purpose of long term chemotherapy may be placed more inferiorly at the cavo-atrial junction - the junction of the SVC and right atrium (RA). Catheters used for haemodialysis may be placed at the cavo-atrial junction or even in the RA itself.
Positioning the catheter tip too proximally, for example in the right or left brachiocephalic veins, is associated with increased risk of line infection and thrombosis.
Anatomy
The lower part of the SVC is surrounded by the pericardial reflection; this is where the upper pericardium folds back on itself to form a sac. Positioning a CVC tip within the SVC and below the level of the pericardial reflection is associated with a small risk of pericardial tamponade.
Neither the SVC nor the pericardial reflection are visible on a chest X-ray. As the carina is a visible structure, which is located above the level of the pericardial reflection, it can be used as an anatomical landmark to help determine the level of a CVC tip within the SVC and above the pericardial reflection.
The pericardial reflection is located below the level of the carina
The cavo-atrial junction is located approximately the height of two vertebral bodies below the level of the carina
Right-sided catheters
CVCs are most commonly inserted via the right internal jugular vein. Right internal jugular catheters are positioned on the right side of the neck, and pass vertically from a position above the clavicle.
The tip is projected over the anatomical location of the SVC - approximately 1.5 cm above the level of the carina
This is an ideal position for right-sided catheters for fluid administration and venous pressure monitoring, but not for long-term chemotherapy or dialysis
Catheters inserted into the subclavian vein pass below the clavicle and then curve into the SVC.
The catheter passes below the level of the clavicle
The distal catheter is orientated vertically
The tip is located 1 cm above the level of the carina
Left-sided catheters
Left-sided catheters approach the SVC at a shallow angle such that they may abut the right lateral wall of the SVC (see next page). They may need to be inserted further so the distal end obtains a vertical orientation. This may mean locating the tip below the level of the carina. In this position the risk of vessel wall erosion is reduced, but with a small increased risk of pericardial tamponade.
This left subclavian catheter is located with its tip below the level of the carina
Positioning the tube vertically avoids abutment of the tip against the right lateral wall of the SVC
Long-term catheters
Catheters which are used for long-term administration of chemotherapy drugs (inserted either from the right or left) are usually positioned more inferiorly, at the level of the cavo-atrial junction. These catheters are usually inserted by radiologists or other specially trained staff.
This peripherally inserted central catheter (PICC) is correctly located with its tip at the level of the cavo-atrial junction - approximately the height of two vertebral bodies below the level of the carina
This is often considered a preferable location for long-term catheters
Radiographic quality
Obtaining good quality X-rays in patients with CVCs is often technically difficult. Variance of radiographic quality factors, such as patient rotation or incomplete inspiration, means that identifying anatomical landmarks is often difficult. If in doubt about catheter location, ask a senior colleague or a radiologist.
