NDT Advance Access originally published online on November 1, 2005
Nephrology Dialysis Transplantation 2006 21(4):1134-1135; doi:10.1093/ndt/gfi247
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In vivo quantification of central venous catheter leak
Email: mohsen.agharazii{at}crhdq.ulaval.caSir,
In the June issue of Nephrology Dialysis Transplantation, we reported the results of an in vitro experiment aimed at quantifying the heparin leak that occurs as a result of central venous catheter heparin lock [1]. Our results showed an early catheter leak of 
0.7 ml during the first 30 s after performing a catheter lock. Continuous late catheter leak was substantial in this experiment (75% within 30 min); however, its relevance to in vivo conditions was unknown. We would like to report now briefly the results of an in vivo experiment in a single patient who agreed to have a modified lung scan to confirm a possible catheter leak.
A routine nuclear medicine lung perfusion scan is usually performed following intravenous injection of Tc99m-labelled albumin macro-aggregates (MAAs). These MAA particles become ‘trapped’ in the terminal alveolar arterioles of the lungs since the particles are in the range of 15 µm in diameter and capillaries are only in the range of 7 µm in diameter. Therefore, the radioactivity distribution recorded by a gamma camera over the chest area represents lung perfusion.
With the patient positioned under the camera, as if for an anterior view of a lung scan, we filled the dialysis catheter lumens with MAAs diluted in a 4.5 ml solution (2.2 ml in the arterial lumen and 2.3 ml in the venous lumen). Images were taken every minute for 30 min (Figure 1). Once this process was completed, the MAAs in both catheter lumens were flushed and a final imaging of the lungs was performed. The rationale for this procedure was that any leak from the catheter would be detected by an accumulation of radioactivity in the lungs. In addition, quantification of the degree of lung uptake would allow for a relative quantification of any leak. A time/activity curve (Figure 2) of the lung area was used to quantify the relative catheter leak over time. The value at the end of the curve, following a rapid rise obtained after complete flushing of the catheter, represents the entire lock volume (100% value) from which the percentage of the leak can be calculated at any time point.
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The results show an almost 20% leak that occurred initially without any detectable continuous leakage over the following 30 min (Figure 2). The slight continuous decrease of the curve, seen prior to the flushing, is probably due to the physical radioactive decay of the tracer (half-life of 6 h) as well as slow disintegration of MAAs. In our case, the 20% leak represents 0.9 ml. The results of the present experiment confirm the magnitude of initial leak that we quantified in our previous in vitro study. However, in contrast to our in vitro experiment, this single in vivo experiment showed no evidence of continuous late catheter leak. It is possible that in vivo, higher blood density prevents any significant late catheter leak.
In conclusion, the results of this single in vivo experiment show an important initial catheter leak that occurs soon after performing a catheter lock. In clinical conditions where there is a high risk of bleeding, we advise using a heparin lock with caution.
Conflict of interest statement. None declared.
1 Division of Nephrology2 Division of Nuclear Medicine Centre Hospitalier Universitaire de Québec Hôtel-Dieu de Québec Hospital and Department of Medicine Faculty of Medicine Laval University Québec Canada
References
- Agharazii M, Plamondon I, Lebel M, Douville P, Desmeules S. Estimation of heparin leak into the systemic circulation after central venous catheter heparin lock. Nephrol Dial Transplant 2005; 20: 1238–1240
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