The “optimal” positioning of a chronic dialysis catheter tip has been long debated, with a myriad of conflicting recommendations from various organizations such as the US Food and Drug Administration and the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (KDOQI).1,2 Considering that in 2009, an estimated 571,000 patients had end-stage renal disease, and 57% of those patients who needed dialysis needed at least one dialysis catheter, it stands as no surprise that an agreement of optimal catheter tip position is of paramount importance.3,4 Despite the preponderance of patients affected, optimal catheter tip position remains a moving target. In fact, up until 2006, KDOQI guidelines recommended placing the dialysis catheter tip in the superior vena cava (SVC) in order “not to cause cardiac perforations.”5,6

The changing recommendations are not meritless. As a result of updated practices, such as the mandatory use of fluoroscopy and suggested ultrasound guidance for venous access, as well as the evolution of catheter design and materials, the risk of cardiac and venous perforations has significantly decreased.7-10 In recent literary reviews and the most current iteration of KDOQI guidelines, the recommended catheter tip position was in the “mid-atrium with arterial lumen facing the mediastinum.”10,11

However, even these recommendations are marred by inaccuracy because they make no distinction between the different tip designs of the currently available dialysis catheters and dynamic interplay between catheter function, side hole design, and resulting complications.12-14

In this article, we will introduce a new concept: the functional tip (Figure 1). This concept is aimed at allowing accurate placement of various dialysis catheters while taking into consideration the different chronic dialysis catheter tip designs.

RECOMMENDATIONS FOR ACCURATE TIP PLACEMENT

Recommendation No. 1.  Do not place the catheter tip too deep in the right atrium, so as to avoid touching the floor of the atrium. If the catheter tip touches the atrial floor, there is increased risk of atrial mural thrombus, perforation, and arrhythmias (Figure 2).1,10

Recommendation No. 2.  Do not place the catheter too high. Side holes in the SVC may cause suction of the venous wall, positional occlusion, and/or malfunction.10,15 Positioning of the dialysis catheter tip within the SVC may also lead to higher recirculation rates.16,17 Damage to the vessel wall and thrombus creation can cause delayed vascular stenosis and occlusion (Figure 3).18

In addition, the whipping motion of the split-tip catheter during high-flow dialysis may further damage the vessel wall if the catheter terminates within the SVC; thus, accurate placement of split-tip catheters is of great importance.18

The chronic dialysis catheter should be placed with the side holes outside of the SVC. The anatomic location of the cavoatrial junction is well-established; however, its precise position on fluoroscopy and conventional chest radiography has been far more difficult.19 The complex, three-dimensional heart proves to be unfavorable to conventional anatomic landmark localization on a twodimensional modality. Multiple investigators have tried to establish criteria, using simple landmarks such as the carina, to allow radiologists to be more precise when attempting to place devices at the lower superior vena cava.20,21 These criteria have proven cumbersome and inaccurate, given the complex anatomical variations from one patient to the next.19 In our experience, even dedicated chest radiologists struggle to establish the precise location of catheter tips on chest radiographs. Placing the functional tip of the catheter within the right atrium allows the interventionist higher certainty of final catheter tip position.

We see that the tip of the catheter determines how low or how deep the catheter may be advanced. In contradistinction, the most proximal side holes determine how high the catheter may be placed, which brings us to the concept of the “functional tip” or “functional catheter length.”

THE FUNCTIONAL TIP

The functional tip is the part of the catheter from the most proximal side hole to the catheter tip (Figures 1, 2C, 3B, and 4). The catheter functional length or functional tip is the part of the catheter where all the action takes place. All catheters proximal to the functional length are, in essence, identical and serve as a simple blood conduit. Their length changes according to the total catheter length. Therefore, there should be only one tip—the functional tip.

Recommendation No. 3.  Place the catheter so that the entire functional length is within the right atrium, but not too deep to avoid touching the floor of the right atrium.

Another important caveat to take into consideration is superior migration of the dialysis catheter when the patient is erect or semierect, as catheters are usually placed in the supine position.17,22 One should envision the position of the patient during dialysis, because it is in this setting that the location of the functional length is clinically relevant. Superior migration of the catheter tip is magnified in obese patients and in women with large, pendulous breasts as result of soft tissue movement upon erect posture.1,22,23 In obese patients, the catheter may be placed deeper within the right atrium; however, care should be maintained not to touch the right atrial floor. One way to minimize migration is to create a shorter and more lateral tunnel. This lateral tunnel reduces the downward migration of the external part of the catheter when the patient sits up.

CONCLUSION

The debate should probably center around where to place the functional tip rather than where to place the physical catheter tip. We believe that the catheter should be placed so that the functional length is as high as possible within the right atrium during dialysis. This allows all the activity to take place within the right atrium, potentially improving catheter function, reducing thrombosis and positional occlusion, and possibly reducing fibrin sheath formation and delayed venous damage.

Michael Tal, MD, MBA, is Associate Clinical Professor. Yale Diagnostic Radiology,Yale University School of Medicine in New Haven, Connecticut. He has disclosed that he is a consultant to Covidien. Dr. Tal may be reached at michael.tal@aya.yale.edu.

Tamir Friedman, MD, is with Yale Diagnostic Radiology, Yale University School of Medicine in New Haven, Connecticut. He stated that he has no financial interests related to this article.

Hamid Mojibian, MD, is Associate Professor of Radiology, Yale University School of Medicine in New Haven, Connecticut. He stated that he has no financial interests related to this article.

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