Safe placement of central venous catheters
*E-mail: sundaramradha{at}doctors.org.ukEditor—We read with interest the recent paper on central venous catheter (CVC) tip position using the carina as a radiological landmark1 having recently completed a similar retrospective audit of 139 CVCs in an adult intensive care setting. Similar to Stonelake and Bodenham, we found a high incidence of CVC tips below the carina with 50 (35.9%) right-sided and 8 (5.7%) left-sided so placed. Similarly, more than half of the left-sided catheters that were above the carina had a steep angle of incidence to the vertical, a risk factor for erosion and perforation, whereas the vast majority of right-sided catheters in a similar position had a shallow angle to the vertical.
The optimal position of the CVC tip remains the subject of debate,2 but the package inserts of many CVCs give strong warnings about the absolute requirement for the catheter to lie outside the pericardium to avoid the risk of pericardial tamponade, advice mirrored by the FDA in the United States. Although perforation and tamponade are very rare with little data available regarding overall incidence, these warnings are hard to ignore.
Stonelake and Bodenham contend that it is particularly difficult to satisfy all criteria for safe placement of left-sided catheters and this is supported by our results. However, they then go on to suggest that the most important determinant of final tip position for a left-sided catheter should be the angle of incidence between the catheter tip and the vessel wall and that this should take precedence over intracardiac tip placement and other risk factors. We question whether this is always necessary or desirable, especially given the lack of evidence to support the real risk of perforation and the underestimation of the incidence of morbidity arising from catheter-related thrombosis.3 4
In addition to an acute angle of incidence between catheter and a simulated membrane, an in vitro study identified perforation risk factors as stiff catheter material (e.g. polyethylene), multiple lumens and bevelled tip design.5 Where left-sided placement is unavoidable, modification of these risk factors can reduce the risk of perforation without resorting to intracardiac placement. Proximal CVC tip placement is unlikely to be associated with a high risk of perforation if used only in the short term for pressure monitoring or the infusion of isotonic fluids. Regular aspiration of blood from the catheter lumen or lumens can also help to confirm that the catheter tip is not abutting against the vessel wall.
To site a left-sided catheter such that there is a shallow angle between the catheter and the vessel wall will in many instances require that the catheter tip be placed low in the SVC. Stonelake and Bodenham divide the great veins and upper right atrium into three zones representing different areas of significance for CVC placement and suggest different ideal tip locations for right- and left-sided catheters. However, the SVC is a relatively short structure, measuring on average 6 cm, and precise placement is technically difficult and probably not achievable. The final position of the catheter tip is checked by chest radiograph but the exact anatomy cannot be identified by this method, hence the use of the carina as a radiological surrogate for the pericardial reflection.6 In an intensive care setting, where semi-erect and kyphotic projections are used, patient rotation about the axial plane commonly occurs and can make a significant difference in the perception of tip position relative to the carina. In our study, disagreement between radiologists over the exact location of some CVC tips illustrates this point.
Furthermore, most CVC insertions are performed in the trendelenburg or supine positions, and the catheter tip can change position as the patient is moved with subsequent radiographs showing descent of the abdominal contents and diaphragm and a change in the catheter position relative to the mediastinal contents.7 Many catheters may consequently be in the right atrium.
Finally, despite current guidelines which stress the importance of siting the catheter tip outside the right atrium, both studies demonstrate a high proportion of CVCs with their tips below the carina. We question whether encouraging further insertion of left-sided catheters would only add to the confusion and suggest greater improvements in patient safety would be achieved by further underlining the importance of ensuring all catheter tips are sited in the SVC.
Glasgow, UK
Editor—We thank Dr Sundaram and colleagues for their interest in out paper. Our main purpose was to highlight the issue of catheter tip position as important in clinical practice, particularly for the longer term catheter. In the absence of definite evidence on which to base practice, and the limitations of plain chest X-rays in determining catheter tip position, operators can only work on general principles individualized to each patient.
Leeds, UK
*E-mail: Andy.Bodenham{at}leedsth.nhs.uk
References
1 Stonelake PA and Bodenham AR. The carina as a radiological landmark for central venous catheter tip position. Br J Anaesth 2006; 96:335–40
2 Fletcher SJ and Bodenham AR. Safe placement of central venous catheters: where should the tip of the catheter lie? Br J Anaesth 2000; 85:188–91
3 Collier PE, Blocker SH, Graff Dm, Doyle P. Cardiac tamponade from central venous catheters. Am J Surg 1998; 176:212–14[CrossRef][Web of Science][Medline]
4 Cadman A, Lawrance JAL, Fitzsimmons L, Spencer-Shaw A, Swindell R. To clot or not too clot? That is the question in central venous catheters. Clin Radiol 2004; 54:349–55
5 Gravenstein N and Blackshear RH. In vitro evaluation of relative perforating potential of central venous catheters: comparison of materials, selected models, number of lumens and angles of incidence to simulated membrane. J Clin Monit 1991; 7:1–6[CrossRef][Web of Science][Medline]
6 Schuster M, Nave H, Piepenbrock S, Pabst R, Panning B. The carina as a landmark in central venous catheter placement. Br J Anaesth 2000; 85:192–4
7 Nazarian GK, Bjarnason H, Dietz CA Jr, Bernadas CA, Hunter DW. Changes in catheter tip position when a patient is upright. J Vasc Interv Radiol 1997; 8:437–41[Web of Science][Medline]
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