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Hello writer, critique the article “Foley Drainage Tubing Configuration Affects Bladder Pressure: A Bench Model Study “utilizing the information below. Discuss the findings associated with the article by reviewing the discussion and implications/recommendations for practice and summary assessment Describe how these findings will support an small test of change.
Discussion
• Are all major findings interpreted and discussed?
• Are the interpretations consistent with the results and with the study’s limitations?
• Does the report address the issue of the generalizability of the findings?
Implications/Recommendations
•Do the researchers discuss the implications of the study for clinical practice or further research-and are those implications reasonable and complete?
Summary Assessment
•Despite any identified limitations, do the study findings appear to be valid-do you have confidence in the truth value of the results?
•Does the study contribute any meaningful evidence that can be used in nursing practice or that is useful to the nursing discipline?
It is very important answer all of the questions below, and identify them in the paper as a subtitles or titles, but related to the article that I’m going to insert with this request. Remember all of the questions above please answer them from the article “Foley Drainage Tubing Configuration Affects Bladder Pressure: A Bench Model Study “.

UROLOGIC NURSING / January-February 2014 / Volume 34 Number 1 33
Foley Drainage Tubing
Configuration Affects Bladder
Pressure: A Bench Model Study
Wilhelm K. Schwab, David E. Lizdas, Nikolaus Gravenstein, and Samsun Lampotang
Wilhelm K. Schwab, PhD, was an Engineer
with a career-long interest in understanding
how things work and how to make them work
better. He worked with the University of
Florida Clinical and Translational Research
Informatics Program (CTRIP), Gainesville,
FL. He passed away on September 7, 2012.
David E. Lizdas, BSME, is a Mechanical
Engineer, the Center for Safety, Simulation, &
Advanced Learning Technologies, Depart –
ment of Anesthesiology, University of Florida
College of Medicine, Gainesville, FL.
Nikolaus Gravenstein, MD, is an
Anesthesiologist, the Department of
Anesthesiology, University of Florida College
of Medicine, and the Center for Safety,
Simulation, & Advanced Learning Tech –
nologies, Department of Anesthesiology,
University of Florida College of Medicine,
Gainesville, FL.
Samsun Lampotang, PhD, is an Engineer
and Professor of Anesthesiology, the
Department of Anesthesiology, University of
Florida College of Medicine, and the Center
for Safety, Simulation, & Advanced Learning
Technologies, Department of Anesthe si –
ology, University of Florida College of
Medicine, Gainesville, FL.
Funding/Support: This study was carried out at the University of Florida Center for Safety,
Simulation & Advanced Learning Technologies (CSSALT), and was supported by institutional
and departmental sources. Part of this material was presented in poster form at the American
Society of Anesthesiologists Annual Meeting, October 15-19, 2011, Chicago, IL.
Acknowledgements: We would like to thank Dr. Robert Williams (deceased) and Mrs. Rosita
Williams for their generous support of the Center for Safety, Simulation, & Advanced Learning
Technologies, which made this study possible.
Research
© 2014 Society of Urologic Nurses and Associates
Schwab, W.K., Lizdas, D.E., Gravenstein, N., & Lampotang, S. (2014). Foley drainage
tubing configuration affects bladder pressure: A bench model study. Urologic
Nursing, 34(1), 33-37. doi:10.7257/1053-816X.2014.34.1.33
A bench model was created to measure and analyze pressures in a simulated
bladder and an actual urine drainage system. Fluid-filled dependent (generally
U-shaped) loops in the urine drainage tubing generated back-pressure (in units
of cm H2O), directly related to the difference in fluid meniscus heights (in units of
cm) across the dependent loop that interfered with emptying of the simulated
bladder. If the results obtained with a simulated bladder occur in actual bladders
with indwelling urinary catheters, retained urine volume (that can promote urinary
tract infection) will increase with larger differences in meniscus heights across the
dependent loop due to increased back-pressure. Dependent loops in urine
drainage tubing should be avoided. If the dependent loops cannot be avoided or
a configuration without dependent loops cannot be maintained, they should be
routinely emptied of urine, especially if the bag-side meniscus is higher than the
bladder-side meniscus.
Key Words: Dependent loop, bladder distention, drainage, catheterassociated
urinary tract infection (CAUTI), Foley catheter,
back-pressure.
In a recent surgery, one
author of this study noted
poor urine flow after kidney
reperfusion in a liverkidney
transplant patient; however,
after straightening the urine
drainage tubing to empty the
urine that had accumulated in
the generally U-shaped dependent
loop in the Foley drainage
tube, the rate of urine outflow
from the bladder appeared to
increase. This sequence of events
raised a simple question with
clinical implications: could
potentially harmful back-pressures
sometimes exist in urine
drainage systems that are considered
as passive drains that reliably
channel urine from the bladder
to the urine collection bag? At
a minimum, obstruction to urine
outflow may cause patient discomfort
and may also predispose
a patient to a catheter-associated
urinary tract infection (CAUTI).
Informal experimentation with a
commercial urine drainage system
led to the hypothesis that significant
back-pressures might
arise in clinical practice, and consequently,
to the bench experiments
described herein.
Garcia et al. (2007) described
a cessation of drainage in urine
drainage systems with fluid-filled
dependent loops due to backpressure
created by fluid trapped
in the loop. Dependent loops in
bladder drainage tubing significantly
increase the risk of CAUTI
(Maki & Tambyah, 2001). As a
34 UROLOGIC NURSING / January-February 2014 / Volume 34 Number 1
was connected to the bladder
with an IV bag trochar via one of
the IV bag’s access ports. The
Foley catheter was inserted in
the other port and sealed to prevent
leakage around it. The
drainage tubing and vented collection
bag (Bard Medical
Division) were hung from a perforated
board to simulate typical
clinical orientations and height
relationships of the various components
(see Figure 1, a).
Instrumentation and
Software
Pressures were measured
using disposable invasive blood
pressure transducers (Edwards
Life Sciences, Irvine, CA) at –
tached to a Component Moni –
toring System monitor and pressure
modules (Model M1006A,
Philips, Andover, MA) at locations
shown in Figure 1, a. Data
were captured at approximately
two-second intervals. The pressure
sampling line for the blad-
Research Summary
Background
Urinary retention and bladder distention can lead to urinary
tract infection. The excess drainage tubing in a urine
drainage system will droop and form a generally U-shaped
loop (a dependent loop) where urine will collect. If the urine is
allowed to collect, the meniscus on the bag side will rise higher
than the bladder-side meniscus, indicating back-pressure
that impedes bladder emptying.
Objective
To determine if the back-pressure impeding bladder
emptying is linearly proportional to the difference in meniscus
heights across a fluid-filled dependent loop.
Methods
An instrumented bench model was built to measure and
analyze the pressures in a simulated bladder drained via an
indwelling urinary catheter connected to a urine drainage and
collection system.
Results
The back-pressure (in units of cm H2O) impeding bladder
emptying was found to be linearly related (R2 = 0.998) to
the difference in meniscus heights (in units of cm), meaning
that a taller difference in meniscus heights indicates a larger
back-pressure opposing bladder emptying, resulting in larger
retained urine volume.
Conclusions
Assuming that results with a simulated bladder apply to
actual bladders drained with indwelling urinary catheters, a)
clinicians should avoid dependent loops in the drainage tubing,
b) if dependent loops are found or cannot be avoided
because a configuration without dependent loops cannot be
maintained because the excess drainage tubing keeps falling
down and re-forming a dependent loop, drain the urine that
collects in the dependent loops frequently.
Level of Evidence – VI
(Polit & Beck, 2012)
measure to avoid CAUTI, Trautner
and Darouiche (2004) and Kwak
et al. (2010) recommend ensuring
dependent drainage as appropriate
management of Foley
drainage systems. The urge to
void generally occurs near a bladder
volume of 150 mL, and an
accumulating bladder volume is
associated with physical discomfort
(Sulzbach, 2002).
Materials and Methods
Purpose
The primary purpose of the
study was to determine the relationship
between the back-pressure
exerted on the simulated
bladder and the difference in
meniscus heights; the hypothesis
was that the relationship would
be linear.
Bench Model
A bench model (see Figure 1,
a) of the urinary system was constructed
and drained using a Foley
catheter (Bardex I.C. 930116, 16
Fr, Bard Inc., Covington, GA),
urine drainage tubing, and a urine
collection bag. An infusion pump
(Alaris PC 8015 Series, CareFusion,
San Diego, CA) was used as a
model for the kidneys and
ureters, and a 500 mL soft IV fluid
bag represented the bladder
(Baxter, Deerfield, IL). The pump
Figure 1.
Time sequence showing the initially empty drainage tubing (a),
and the progression (b to d) of fluid toward its first crested
configuration (d). Note the inflation of the simulated bladder at top
left as the fluid climbs the bag-side leg of the dependent loop.
UROLOGIC NURSING / January-February 2014 / Volume 34 Number 1 35
der pressure was fluid-filled, and
the sampling line for the air
space in the drainage tubing was
air-filled. Fluid meniscus heights
were measured relative to the
floor using a metal yardstick with
centimeter gradations (AE141,
Swanson Tool Co., Frankfort, IL).
Protocol
After zeroing the pressure
transducers, each repetition consisted
of two phases. Phase 1 is
analogous to the initial placement
of a catheter and ends
when fluid first enters the collection
bag; it occurs with the deepest
possible loop (see Figure 2,
“Start”). Phase 2 consists of
measurements with a sequence
of progressively more shallow
loops, allowing collection of data
on multiple dependent loop
depths. The loop depths were
chosen to mimic the spectrum
that is observed clinically with
different patient positions and
tubing routing.
For each measurement of
pressures and meniscus heights,
we allowed the distal (downstream)
bag side meniscus to
crest and allow fluid to drip into
the collection bag as is observed
in clinical practice when there is
a dependent loop present. Pres –
sures and heights of the fluid
menisci were recorded. Measure –
ments were done at the end
of Phase 1 and for each of the
seven successive configurations
in Phase 2.
Phase 1.
• Clamp the Foley catheter 1
cm distal to the bladder and
arrange the tubing in the first
configuration (see Figure 2,
“Start”) having the deepest
possible loop.
• Transfer approximately 420
mL of tap water with yellow
food coloring into the bladder.
• Start the data collection software
and unclamp the Foley
catheter.
• Start the infusion pump at
900 mL/hour to simulate
urine production. This rate
(900 mL/hour) was chosen
for efficiency because there
is little resistance in the system.
The simulated “urine”
flow rate is not intended to
be a clinical one.
• When the downstream men –
is cus crests and fluid enters
the collection bag (see Figure
2, “Configuration 1”), record
pressures and meniscus
heights as described above.
Phase 2.
Each of the remaining seven
predetermined drainage bag positions
(see Figure 2, “Con fig ura –
tions 2 to 8”) proceeded as follows:
• Advance the collection bag
to the new position to reduce
the depth of the loop and
pour out some fluid into the
urine collection bag.
• Wait for the return of a crested
configuration with stable
pressures, and record meniscus
heights and pressures as
described above.
A typical pressure versus
time profile from this protocol is
shown in Figure 3.
Results
Filling of the Drainage
Tubing: Evolution and
Locations of the Fluid
Menisci
The urine drainage tubing is
initially empty (see Figure 1, a).
However, gravity causes fluid to
accumulate at the bottom of the
generally U-shaped dependent
loop in the urine drainage tubing
(see Figure 1, b). Once the fluid
level rises sufficiently to occlude
the drainage tubing, the air in the
bladder-side portion of the tubing
is trapped between the fluidfilled
Foley catheter and the
bladder-side meniscus. Because
air is essentially incompressible
at pressures present in the system,
the bladder-side meniscus is
almost stationary, and fluid is
forced to climb the bag-side portion
of the dependent loop (see
Figure 1, c and d). Advancement
of the fluid is driven by the pressure
of the air in the bladder-side
limb, which ultimately must be
provided via the bladder.
Figure 2.
The initially empty drainage tubing (“Start”) and its first and
successive (numbered 1 to 8) crested configurations at
which meniscus heights and bladder and air space pressures
were recorded. White arrow points to meniscus.
36 UROLOGIC NURSING / January-February 2014 / Volume 34 Number 1
Pressure vs. Time
Pressures
During each repetition of the
experiment, the bladder (primed
with 420 mL of fluid) is initially
able to freely drain, but as fluid is
forced to climb the ascending
limb of the dependent loop, bladder
pressure increases, peaking
as the fluid reaches the crest at
the collection bag. After cresting,
new fluid added to the system
displaces fluid into the collection
bag. Figure 3 shows a typical
pressure versus time profile.
Start and stop times from the laboratory
notes, pressures captured
by our recording system, and
meniscus elevations measured
with a metal meter ruler were
used to plot the relationships
between the air space pressure
(Figure 4; R2 = 0.998) and the
bladder pressure (R2 = 0.999),
respectively, versus the vertical
distance from the bladder-side
meniscus to the bag-side meniscus
in the drainage tubing.
Meniscus heights were measured
at the center of the drainage tubing
during time periods emphasized
(in gold) in Figure 3.
Discussion
The primary objective was to
mimic the spectrum of what is
observed in the clinical setting to
study the relationship between
the geometry of the drainage tubing
dependent loop and the bladder
pressure required to move
urine into the collection bag. The
worst-case clinical scenario is to
hang the urine collection bag
directly adjacent to the Foley
catheter, creating the deepest
dependent loop and allowing the
maximum possible difference in
meniscus elevation; this configuration
results in a bladder pressure
of 40.8 cm H2O (30 mmHg).
Understanding the physics of
urine-filled dependent loops
facilitates visual monitoring of
the pressures in a urine drainage
system. Preventing the formation
of loops, or at least minimizing
their depth, minimizes the outflow
pressure thresholds that
need to be overcome for urine to
flow into the collection bag,
thereby minimizing 1) bladder
Figure 3.
Typical Pressure versus Time (Minutes) Profile for the Experiment
Pressure (cm Water)
Time (Minutes)
40
30
20
10
10 20 30 40 50
Bladder
Air Space
1
2 3
4
5
6
7
8
Note: The emphasized (gold) portions of the graph correspond to the eight crested
configurations (numbered 1 to 8 in Figure 2) during which heights and pressures
were recorded.
Figure 4.
Measured Pressures in the Bladder and Air Space versus the
Difference in Heights of the Menisci
Pressure vs. Difference in Meniscus Elevation
40
30
20
10
0
Pressure (cm Water)
Meniscus Elevation Difference (cm)
0 10 20 30 40
Slope Bladder = 0.98658 cm Water/cm
Intercept Bladder = 1.2407 cm Water
R2Bladder = 0.99856
Slope Air Space = 0.97298 cm Water/cm
Intercept Air Space = 0.47603 cm Water
R2 Air Space = 0.99835
Pressure
Bladder (IV Bag)
Air Space
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