The effect of patient position during
urodynamics studies in children: Another
variable to consider!
By Angela Buffett-Fairen, RN; Joao Pippi Salle, MD, PhD; and Armando J. Lorenzo, MD
Issues in Incontinence: Spring/Summer 2008
It is well known that patients suffer from urinary symptoms and incontinence in positions that differ
from the somewhat artificial conditions created by conventional urodynamic studies. This poses a
problem in analysis of the data, particularly when we consider that one of the main goals of such studies
is to reproduce the patient’s state when experiencing symptoms or abnormal bladder dynamics,
allowing the healthcare provider to gain insight into the pathophysiology of the underlying problem and
to devise sound treatment options.
Background
It is interesting that the effect of position, even though theoretically appealing and despite
standardization efforts in the field, 1 has been relatively under-evaluated in the pediatric population.
Prior to our recently published prospective study, 2 children at our institution were mostly tested in
supine or semi-recumbent position. We recognized that some children’s incontinence history did not
correlate with our urodynamic findings. For example, many parents described their child’s urinary
symptoms as being damp to wet every day even when the child was compliant with the catheterization
regimen, whereas our urodynamic testing demonstrated that the child had the potential of being
continent, with no leakage detected during multiple tests when the child was supine. To our knowledge,
no literature has discussed from a pediatric perspective the effects of position changes in urodynamic
testing. This led us to further look into patient position as a clinically important variable.
A few articles addressing effects of postural changes on urodynamic parameters within the adult
population have been published in recent years. In women with urge incontinence, mixed incontinence,
and urgency, Arunkalaivanan et al.3 demonstrated significant changes in bladder dynamics associated
with leakage and detrusor overactivity while patients were seated. Al-Hayek et al. 4 reviewed 16 articles
that sought to determine the best patient position during urodynamic testing to observe detrusor
overactivity in preoperative patients with stress incontinence and prostatic obstruction; all but 2
articles, by Ramsden et al. (Br J Urol. 1977;49:633–9) and Choe et al. (J Urol. 1999;161:1541–4)
supported the conclusion that detrusor overactivity increases when urodynamic testing is performed
with the patient vertical. Despite compelling evidence that these and other studies 5-7 are applicable to
patients with incontinence, it is difficult to transfer their findings in urodynamic parameters from the
adult to the pediatric population, since children’s underlying physical and mental development and
maturity is certainly different.
There are important issues to consider when ordering and evaluating urodynamic studies in a pediatric
population. The purpose of urodynamic testing in children is to ensure the preservation and
maintenance of kidney function and also to assess a child’s urinary incontinence status. An important
number of children who undergo urodynamic testing have underlying neurological conditions, such as
myelomeningocele and sacral agenesis, or have experienced a spinal-cord injury resulting in a
neurogenic bladder. However, there are some children who undergo urodynamic testing due to a
history of persistent and/or difficult to treat lower urinary tract symptoms or incontinence (in many
cases thought to be secondary to “dysfunctional voiding”) with no known neurogenic etiology.
Underlying conditions as well as age and developmental status can be deciding factors in whether or not
a child can tolerate position changes and the number of consecutive urodynamic tests that can be
performed. The child may not be able to stand or sit for long periods due to pain and discomfort
associated with the underlying condition. A child’s physical size may not permit sitting on a commode
for long periods; this can influence urodynamic findings by causing the study to be terminated prior to
acquiring adequate results. Furthermore, a child’s development and maturation can have some bearing
on repeating urodynamic tests with the patient in another position. It is sometimes difficult for young
children to comprehend the importance of repeat testing, and they will permit the healthcare provider
to perform only 1 test. It is therefore of value to get the most out of 1 well-performed test,
administering it under conditions that optimize the chances of acquiring the most relevant information.
Study design
In the absence of published information, we tested the hypothesis that position changes can increase a
child’s intra-abdominal pressure and, therefore, have the potential to influence bladder storage capacity
and behavior. In a large pediatric center and in non-randomized fashion we prospectively enrolled 48
children who were able to tolerate consecutive urodynamic tests while sitting and supine. All subjects
were referred to the urodynamics department by in-house pediatric urologists.
We divided the subjects into 2 equal-number groups: The first group consisted of children who were
supine during the first test and sitting during the second test; the second group began testing in a sitting
position and were supine during the second test. Study variables included demographics (such as age,
sex), underlying pathologies, medications, surgical interventions, medical history (such as
catheterization routine, voiding and bowel habits, incontinence history, water/fluid consumption,
history of urinary tract infections), and pertinent physical findings. Urodynamic testing was performed
by 2 experienced nurses utilizing the same equipment. Subjects had an average age of 10.4 years, and
there was no statistically significant difference in male:female ratio or in sedation requirements of the 2
groups. Almost 30% of subjects were being assessed for cause of urinary incontinence while the others
were already diagnosed with neurogenic bladders. Fifty-seven percent of the subjects were ambulatory.
Results
Two pediatric urologists, blinded to the subjects’ positions during urodynamic testing, extracted the
data for analysis. They noted higher average intravesical and abdominal pressures in sitting subjects. As
we reported in the Journal of Urology, 2 between the 2 positions there was no statistically significant
difference in maximum bladder capacity, detrusor leak-point pressure, or detrusor pressure at 20 cm
H2O and 30 cm H2O. Discrepancies noted with position changes included more detrusor overactivity
and stress or urge incontinence in sitting subjects. It is interesting that there was a trend for lower
Valsalva leak-point pressure in sitting subjects. These findings have potentially important clinical
repercussions, as the differences in results may have to be considered in the decision-making process
for treating urinary incontinence.
Discussion
Acknowledged limitations of the study included a bias in the selected population and the sample size:
We selected children who could tolerate position changes, and the enrolled number was relatively
small. Certainly, the generalization of our findings is difficult to extrapolate to all children who undergo
urodynamic tests. With those limitations in mind, what can we learn from our results?
● Position likely plays an important role in urodynamic findings, in both children and adults.
● The patient’s position during testing is a clinically important variable; standardization of terms and
procedures should take this into account.
● Our findings should be corroborated and expanded upon; researchers should attempt to find patient
populations particularly affected by positional changes.
● The therapeutic implications should be evaluated.
Urodynamic testing enables the urologist to gain a greater understanding of a patient’s bladder
dynamics during the filling and emptying phases. Appropriate analysis is essential for good clinical and
research endpoints. By uncovering variables such as patient position that impact on results, we may
better define good urodynamics practices for both pediatric and adult populations.
References
1. Nevéus T, von Gontard A, Hoebeke P, Hjälmås K, Bauer S, Bower W, et al. The standardization of
terminology of lower urinary tract function in children and adolescents: report from the Standardisation
Committee of the International Children’s Continence Society. J Urol. 2006;176:314-24.
2. Lorenzo AJ, Wallis MC, Cook A, Buffett-Fairen A, Bozic D, Bägli DJ, et al. What is the variability in
urodynamic parameters with position change in children? Analysis of a prospectively enrolled cohort. J
Urol. 2007;178:2567-70. Epub 2007 Oct 22.
3. Arunkalaivanan AS, Mahomoud S, Howell M. Does posture affect cystometric parameters and
diagnoses? Int Urogynecol J Pelvic Floor Dysfunct. 2004;15:422-4; discussion 424. Epub 2004 Jul 1.
4. Al-Hayek S, Belal M, Abrams P. Does the patient’s position influence the detection of detrusor
overactivity? Neurourol Urodyn. 2008;27:279-86.
5. Arnold EP. Proceedings: Cystometry—postural effects in incontinent women. Urol Int. 1974;29:185-6.
6. Godec CJ, Cass AS. Cystometric variations during postural changes and functional electrical stimulation
of the pelvic floor muscles. J Urol. 1980;123:722-5.
7. Shukla A, Johnson D, Bibby J. Impact of patient position on filling phase of urodynamics in women. Int
Urogynecol J Pelvic Floor Dysfunct. 2006;17:231-3. Epub 2005 Jul 7.