Nephrol Dial Transplant (2007) 22: 3061–3064
doi:10.1093/ndt/gfm314
Advance Access publication 27 June 2007

Technical NoteSee http://www.oxfordjournals.org/our_journals/ndtplus/

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

Abstract
Background. To reduce infection risks in patients on
hemodialysis with a long term central venous catheter,different types of closed luer lock access devices areused on the arterial and venous catheter hub. Althoughthose connectors create a mechanically and microbiologically closed system in between two dialysis
sessions, no data are available on the resistance thoseconnectors exert on the blood flow during dialysis.
Therefore, in the present study, flow resistance wasdetermined in three different connectors.
Methods. In an in vitro setup, different connectors wereattached in between a male (Bellco BL 307 dialysis
tubing) and female luer: BD Q-SyteTM (BectonDickinson, Utah, USA), second edition TegoTM(ICU Medical, CA, USA), and Swan-LockÛ connector (Codan, Lensahn, Germany). For a wide range ofwater flow rates, pressure-flow relationships weremeasured, simulating catheter inflow as well ascatheter 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 thecase 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 acatheter hub during and in between dialysis sessions.
Whether those resistances are in the safe range without
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@ugent.bethe incidence of blood hemolysis will soon beinvestigated in an in vivo study.
Keywords: haemodialysis; connection; catheter;
infectionflow resistanceIntroduction
Ten percent of patients with a long-term central venous
catheter for chronic haemodialysis develops a catheterrelated blood stream infection, resulting from repeatedexposure, or opening and manipulation of the catheter
hub [1–4]. To reduce infection risks while handling thecatheter hub, different types of closed luer lock accessdevices are presently available in the market. Thoseconnectors create a mechanically and microbiologicallyclosed system when attached to the arterial and venous
catheter hub and remain in place during the dialysis
treatment. Connectors are designed to ensure straightflow paths when attaching blood lines, such that bloodflows up to 600 ml/min might be reached. The
functional and microbiological efficacy was proven tolast 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 anequivalent 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 designedwith a split septum of proven medical grade silicon.
Although proven to decrease and/or eliminate
infection risk associated with catheter use [5–7], nodata are available on the resistance those closed luer
lock access devices exert on the blood flow during
dialysis. Therefore, the present study set out toevaluate the flow resistance through three different
closed luer lock access devices designed for applicationin haemodialysis and to compare them with a simple
male–female connection as in a standard bloodline–catheter connection.

ß The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.
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Sunny Eloot1, Jean-Yves De Vos2, Remi Hombrouckx2 and Pascal Verdonck1

3062

S. Eloot et al.
A 220Methods200Re ¼UDEu ¼p  U2

180
pressure drop (mmHg)

160
1401201008060
Codan
Becton Dickinson
Tego
no connector

402000200

400

600

800

1000

1200

B 220
200180pressure drop (mmHg)

160
140
120
1008060

Codan
Becton Dickinson
Tego
no connector

402000200

400

600

800

1000

1200

water flow (mL/min)½1

with fluid velocity U (m/s), cross sectional diameter D (m),fluid viscosity  (Pa.s), fluid density  (kg/m3) and pressurep (Pa). Since human blood at 378C has a viscosity of 3 mPasand density of 1054 kg/m3, while water at room temperature
has a viscosity of 1 mPas and density of 998 kg/m3, themeasured water pressure and flow must be increased by afactor of 2.81 and 8.34, respectively, to obtain thecorresponding pressure-flow curve for the clinical setup
using blood.
In order to explain the experimental findings more indetail, the connectors were cut along the longitudinal axis toobserve and make drawings of the internal geometry.
Furthermore, the lumen of the connectors, as connected todifferent tubings with a luer lock and as currently used indialysis, was evaluated.
Data were analysed using SigmaStat software (JandelScientific, San Rafael, CA, USA). Statistical analyses werecarried out on the derived flow-pressure curves, using theStudents t-test for paired samples when comparing venous
and arterial flow results, and using Friedman repeatedmeasures analysis of variance on ranks when comparing
the results of the three different connectors. P < 0.05 wastaken the limit of significant difference.

Results and discussion
The measured data points with corresponding regression lines are shown in Figure 1 for venous flow

Fig. 1. Measurement results (symbols) of pressure and water flow in
different types of connectors and without any connector for venousflow (catheter inflow) (Panel A) and arterial flow (catheter outflow)(Panel B).
Regression analysis for water inflow (Panel A):
Becton Dickinson: y ¼ 0.00035x2 þ 0.0595x; R2 ¼ 0.999
Codan: y ¼ 0.00015x2 þ 0.0518x; R2 ¼ 0.997
Tego: y ¼ 0.00011x2 þ 0.0383x; R2 ¼ 0.999
No connector: y ¼ 0.00009x2 þ 0.0269x; R2 ¼ 0.999
Regression analysis for water outflow (Panel B):
Becton Dickinson: y ¼ 0.00029x2 þ 0.0402x; R2 ¼ 0.999
Codan: y ¼ 0.00013x2 þ 0.0450x; R2 ¼ 0.999
Tego: y ¼ 0.00012x2 þ 0.0378x; R2 ¼ 0.999
No connector: y ¼ 0.00012x2 þ 0.0199x; R2 ¼ 0.999(Panel A) and arterial flow (Panel B) in the casewithout a connector and when a Becton–Dickinson,
Codan, or TegoTM connector was attached in between
the male and female luers. Data points show anaccurate quadratic relation (R2 > 0.99) in between thewater 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 leastresistance.
Figure 2 shows the pressure drop, as originatedexclusively from the closed luer lock access device.
This curve was calculated as the difference between
the pressure flow curves derived with and without theluer lock access device and after recalculations forthe use of water instead of blood in the experiments.

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Pressure–flow relationships in different catheter connectors
designed for application in haemodialysis were investigatedin vitro: BD Q-SyteTM (Becton–Dickinson, Utah, USA),second edition TegoTM (ICU Medical, CA, USA) and Swan
Lock connector (Codan, Lensahn, Germany). Those luer lockconnectors were attached in between a male and female luer,
using a Bellco BL 307 tubing at dialysis machine side. Steadywater 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 waterflow 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 aquadratic regression analysis, as typical pressure-flow relation for an obstructed flow. Furthermore, the extra resistanceas 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 thepresent experimental pressure-flow analysis, recalculations
were performed to obtain pressure-flow relationships forblood 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]:Influence of closed luer lock access devices
120

venous flow Codan
venous flow Becton Dickinson
venous flow Tegoarterial flow Codan
arterial flow Becton Dickinson
arterial flow Tego

100Pressure drop (mmHg)

3063

806040
20050

100

150

200

250

300

350

400

450

500

Blood flow (mL/min)Fig. 2. Additional pressure drop as originated from a catheter
connector during arterial and venous blood flow.

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 thecase 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 flowpressure 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 andCodan connector, while it was significantly larger in
the TegoTM connector.
Figure 3 shows a photo and cross sectional view (noton scale) of the tested connectors, not attached to aluer device. After cutting the connectors along thelongitudinal axis, internal dimensions of the hardplastic (black) and the silicon split septum (white)were added to the figure. Those pictures, however, failto explain the experimental findings.
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 theopening 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 bothflow 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 vsloosen connection), even when the luer lock is fullytightened (Table 1). This resulted in some cases, in aneven 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.
While previous studies concerning the use of closed
luer lock access devices on catheter hubs are only

Fig. 3. Photo and cross sectional view of the tested connectors. Theinternal dimensions are indicated in black (hard plastic) and white(silicon split septum).

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 accessdevice was found to exert an additional resistance toflow, 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 acatheter hub during and in between dialysis sessions.
Further investigation is, however, necessary to evaluate
in vivo the occurrence of blood haemolysis and topredict the period of usage without ensuing any
obstruction and/or leakage.

Conclusion
In order to diminish catheter-related infections withchronic haemodialysis patients, different types of closed
luer lock access devices were designed to attach to thearterial and venous catheter hub. Several studies
showed their significance of being a microbiologicalbarrier, but since those devices stay in place during
dialysis, it is also important that blood flow is
minimally influenced. The present study revealed

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S. Eloot et al.

Table 1. Overview of the opening size of the three connectors attached to different dialysis tubings
Tubings

Connection play

Opening section

Codan

Tego

BDCodan

Tego

BELLCOBL 307
A5656-4 Formula 2000 BL307
BL 360

yes
yes
no

yes
yes
no

yes
yesno

C: half open L: half open
C: half open L: half open
half open

C: open L: 3/4 open
C: open L: 3/4 open3/4 open

C: open L: open
C: open L: open
open

FRESENIUS
CVVH-set
For Bellco Multimat

yes
yes

yes
yes

yesno

C: open L: 1/4 open
C: open L: 1/4 open

C: open L: half open
C: open L: half open

C: open L: open
openALLMED
For Bellco

yes

yes

yes

C: open L: 1/4 open

C: open L: half open

C: open L: open

yesno

yes

C: open L: half open

3/4 open

C: open L: opennonono

1/4 open

3/4 openopenBELDICO
Y-piece for single lumen catheter
GAMBRO
AK10/100/200/95

Columns 2–4 indicate whether there is some connection play, after attachment to dialysis tubing, while columns 5–7 indicate the opening
section. In the case of ‘connection play’, distinction is made between the opening section in the most closed position (C) and most loosen
position (L). The opening section is indicated as being open, 3/4 open, half open, or 1/4 open.

that additional resistances to blood flow were minimalin the TegoTM and Codan connector, while they
were significant in the Becton–Dickinson connector.
Furthermore, the degree of resistance was evendepending on the type of dialysis tubing connected.
Whether those resistances are in the safe range without
the incidence of blood haemolysis, will be investigatedin an in vivo study as planned for the near future.
Acknowledgements. 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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Received for publication: 17.1.07
Accepted in revised form: 27.4.07

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