NDT Advance Access published online on June 27, 2007
Nephrology Dialysis Transplantation, doi:10.1093/ndt/gfm314
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How much is catheter flow influenced by the use of closed luer lock access devices?
1Institute Biomedical Technology, Ghent University, Gent and 2Nephrology Section, AZ Werken Glorieux, Ronse Belgium
Correspondence and offprint requests to: S. Eloot, Institute Biomedical Technology, Ghent University, Campus Heymans–Block B, De Pintelaan 185, 9000 Ghent, Belgium. Email: sunny.eloot{at}ugent.be
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Abstract |
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Background. To reduce infection risks in patients on hemodialysis with a long term central venous catheter, different types of closed luer lock access devices are used on the arterial and venous catheter hub. Although those connectors create a mechanically and microbiologically closed system in between two dialysis sessions, no data are available on the resistance those connectors exert on the blood flow during dialysis. Therefore, in the present study, flow resistance was determined in three different connectors.
Methods. In an in vitro setup, different connectors were attached in between a male (Bellco BL 307 dialysis tubing) and female luer: BD Q-SyteTM (Becton-Dickinson, Utah, USA), second edition TegoTM (ICU Medical, CA, USA), and Swan-LockÛ connector (Codan, Lensahn, Germany). For a wide range of water flow rates, pressure-flow relationships were measured, simulating catheter inflow as well as catheter outflow, by reversing the flow direction. Resistances were compared to a simple male-female connection, as in a standard bloodline-catheter connection, and mathematical corrections were performed for the use of water instead of blood.
Results. For a blood flow of 500mL/min, simulating clinical dialysis, the additional pressure drop is 118mmHg (Becton Dickinson), 52mmHg (Codan), and 23mmHg (TegoTM) in the case of catheter inflow, while it is 74mmHg (Becton Dickinson), 40mmHg (Codan), and 27mmHg (TegoTM) in the case of catheter outflow. Resistances are also depending on the type of tubing as used during dialysis.
Conclusions. In conclusion, the TegoTM and Codan connector show promising results for the use on a catheter hub during and in between dialysis sessions. Whether those resistances are in the safe range without the incidence of blood hemolysis will soon be investigated in an in vivo study.
Keywords: haemodialysis; connection; catheter; infection; flow resistance
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Introduction |
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Ten percent of patients with a long-term central venous catheter for chronic haemodialysis develops a catheter- related blood stream infection, resulting from repeated exposure, or opening and manipulation of the catheter hub [1–4]. To reduce infection risks while handling the catheter hub, different types of closed luer lock access devices are presently available in the market. Those connectors create a mechanically and microbiologically closed system when attached to the arterial and venous catheter hub and remain in place during the dialysis treatment. Connectors are designed to ensure straight flow paths when attaching blood lines, such that blood flows up to 600 ml/min might be reached. The functional and microbiological efficacy was proven to last for up to one week and connectors are simply disinfected by swapping them [5–7].
The different connectors in the market aim to create an unobstructed fluid path in the open position, with an equivalent resistance compared with a direct connection of male and female luer. Since luer lock accesses with mechanical valves could cause haemolysis, connectors for use with dialysis blood flows are designed with a split septum of proven medical grade silicon.
Although proven to decrease and/or eliminate infection risk associated with catheter use [5–7], no data are available on the resistance those closed luer lock access devices exert on the blood flow during dialysis. Therefore, the present study set out to evaluate the flow resistance through three different closed luer lock access devices designed for application in haemodialysis and to compare them with a simple male–female connection as in a standard bloodline–catheter connection.
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Methods |
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Pressure–flow relationships in different catheter connectors designed for application in haemodialysis were investigated in vitro: BD Q-SyteTM (Becton–Dickinson, Utah, USA), second edition TegoTM (ICU Medical, CA, USA) and Swan Lock connector (Codan, Lensahn, Germany). Those luer lock connectors were attached in between a male and female luer, using a Bellco BL 307 tubing at dialysis machine side. Steady water flow, considered as a Newtonian substitute of blood, was performed by a rotary pump and measured gravimetrically as a mass variation on the balance during a pre-set time interval. Pressures up and downstream the catheter hub were measured using calibrated fluid filled pressure transducers (Becton–Dickinson Benelux, Erembodegem, Belgium).
The measurements were done for a wide range of water flow rates, simulating a catheter inflow (venous flow) as well as a catheter outflow (arterial flow) by reversing the flow direction. The measured data points were fitted using a quadratic regression analysis, as typical pressure-flow relation for an obstructed flow. Furthermore, the extra resistance as exerted exclusively by the closed luer lock access device was calculated as the difference between the pressure flow curves derived with and without the luer lock access device. Finally, since reverse osmosis (RO) water was used in the present experimental pressure-flow analysis, recalculations were performed to obtain pressure-flow relationships for blood flow. To obey dynamic similarity between pressure problems in fluids of different viscosity and density, dimensionless Reynolds numbers (Re) and Euler numbers (Eu) were kept equal in both models [8]:
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(kg/m3) and pressure p (Pa). Since human blood at 37°C has a viscosity of 3 mPa·s and density of 1054 kg/m3, while water at room temperature has a viscosity of 1 mPa·s and density of 998 kg/m3, the measured water pressure and flow must be increased by a factor of 2.81 and 8.34, respectively, to obtain the corresponding pressure-flow curve for the clinical setup using blood. In order to explain the experimental findings more in detail, the connectors were cut along the longitudinal axis to observe and make drawings of the internal geometry. Furthermore, the lumen of the connectors, as connected to different tubings with a luer lock and as currently used in dialysis, was evaluated.
Data were analysed using SigmaStat software (Jandel Scientific, San Rafael, CA, USA). Statistical analyses were carried out on the derived flow-pressure curves, using the Students t-test for paired samples when comparing venous and arterial flow results, and using Friedman repeated measures analysis of variance on ranks when comparing the results of the three different connectors. P < 0.05 was taken the limit of significant difference.
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Results and Discussion |
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The measured data points with corresponding regression lines are shown in Figure 1 for venous flow (Panel A) and arterial flow (Panel B) in the case without a connector and when a Becton–Dickinson, Codan, or TegoTM connector was attached in between the male and female luers. Data points show an accurate quadratic relation (R2 > 0.99) in between the water flow and pressure drop over the connection. During venous as well as arterial flow, the Becton–Dickinson connector resulted in the highest resistance, while the TegoTM connector presented the least resistance.
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Figure 2 shows the pressure drop, as originated exclusively from the closed luer lock access device. This curve was calculated as the difference between the pressure flow curves derived with and without the luer lock access device and after recalculations for the use of water instead of blood in the experiments. At a blood flow of 500 ml/min, the additional pressure drop was equal to 118 mmHg (Becton–Dickinson), 52 mmHg (Codan), and 23 mmHg (TegoTM) in the case of venous flow, while it was 74 mmHg (Becton–Dickinson), 40 mmHg (Codan) and 27 mmHg (TegoTM) in the case of arterial flow. Significant differences were found between the flow pressure relations for the different tested connectors for venous as well as for arterial flow (both P < 0.001). Furthermore, the pressure drop related to arterial flow was significantly smaller (P < 0.001) compared with that, during venous flow in the Becton–Dickinson and Codan connector, while it was significantly larger in the TegoTM connector.
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Figure 3 shows a photo and cross sectional view (not on scale) of the tested connectors, not attached to a luer device. After cutting the connectors along the longitudinal axis, internal dimensions of the hard plastic (black) and the silicon split septum (white) were added to the figure. Those pictures, however, fail to explain the experimental findings.
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By attaching the connectors to a Bellco BL 307 dialysis tubing, we could observe the opening section of the connections in order to explain the measured differences in pressure drop. Table 1 gives an overview of the opening sections inside the three connectors when attached to other currently used dialysis tubings. The different pressure drops over the three connector types were found attributable to the position and opening system of the silicon split septum. Furthermore, since this septum might cause a different obstruction in both flow directions, pressure losses and with it, pressure drops, were not found equal for arterial and venous flow. Finally, most connector-tubing connections showed a connection play after screwing (closed vs loosen connection), even when the luer lock is fully tightened (Table 1). This resulted in some cases, in an even higher flow constriction when the connector is in its most loosen position, as the male of the tubing connector is not able to fully open the split septum.
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While previous studies concerning the use of closed luer lock access devices on catheter hubs are only dealing with the microbiological efficacy avoiding catheter related infections, the present study set out to evaluate the occurrence of flow resistance. Although the silicon split septum was designed not to influence blood flow, the appliance of a closed luer lock access device was found to exert an additional resistance to flow, compared with the standard male-female luer connection. From the present experimental evaluation it can be concluded that the TegoTM and Codan connector show promising results for the use on a catheter hub during and in between dialysis sessions. Further investigation is, however, necessary to evaluate in vivo the occurrence of blood haemolysis and to predict the period of usage without ensuing any obstruction and/or leakage.
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Conclusion |
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In order to diminish catheter-related infections with chronic haemodialysis patients, different types of closed luer lock access devices were designed to attach to the arterial and venous catheter hub. Several studies showed their significance of being a microbiological barrier, but since those devices stay in place during dialysis, it is also important that blood flow is minimally influenced. The present study revealed that additional resistances to blood flow were minimal in the TegoTM and Codan connector, while they were significant in the Becton–Dickinson connector. Furthermore, the degree of resistance was even depending on the type of dialysis tubing connected. Whether those resistances are in the safe range without the incidence of blood haemolysis, will be investigated in an in vivo study as planned for the near future.
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Acknowledgements |
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The first author is working as post doctoral fellow for the Belgian Fund for Scientific Research-Flanders (FWO-Vlaanderen).
Conflict of interest statement. None declared.
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References |
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- Canaud B. Haemodialysis catheter-related infection: time for action. Nephrol Dial Transplant (1999) 14:2288–2290.
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- Casey AL, Worthington T, Lambert PA, et al. A randomized, prospective clinical trial to assess the potential infection risk associated with the PosiFlow((R)) needleless connector. J Hosp Infect (2003) 54:288–293.[CrossRef][Web of Science][Medline]
- Adams D, Karpanen T, Worthington T, et al. Infection risk associated with a closed luer access device. J Hosp Infect (2006) 62:353–357.[CrossRef][Web of Science][Medline]
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Accepted in revised form: 27. 4.07
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