Scientific background
Urinary incontinence (UI) can dramatically influence the physical, psychological and social wellbeing of affected individuals, their families and carers and has considerable resource implications for the health service. The estimated prevalence of UI in general population studies varies from 5% to 69% with most estimates between 25% and 45%. In middle aged and older women daily incontinence estimates vary from 5% to 15% [
1]. The majority of these women have stress urinary incontinence (SUI), 50%, or mixed urinary incontinence (MUI), 36% [
2]. A 2004 UK study estimated the annual cost to the National Health Service of treating clinically important UI in women at £233m [
3].
Urodynamic testing is one of several methods that may be used in the assessment of UI to guide management decisions, including whether surgical intervention is indicated. This group of investigations is used to evaluate the function of the lower urinary tract and can be invasive (requiring catheterisation) or non-invasive [
4]. The most commonly used invasive urodynamic test (IUT) is multi-channel cystometry;[
5] this looks at the pressure/volume relationships during bladder filling and emptying, with a view to defining a functional, as distinct from symptomatic, diagnosis. Whilst this is the most commonly used IUT, videocystometry and ambulatory bladder pressure monitoring are also used. Non-invasive tests include frequency/volume charting, mid-stream urine culture, urine flow rate and residual urine volume measurement by ultrasound [
6].
The current position of IUT in the diagnostic pathway is not agreed, and practice varies considerably. In a UK survey in 2002 only half of the units surveyed had guidelines on indications for the tests, and 84.5% carried out cystometry in all women with incontinence [
5]. Current guidance from the National Institute for Health and Clinical Excellence (NICE) suggests that cystometry is not required prior to conservative treatments, and that there is no evidence to support its use prior to surgery where the diagnosis of SUI is likely [
7]. NICE, the National Institute for Health Research - Health Technology Assessment (NIHR-HTA) programme, the Cochrane Collaboration and the International Consultations on Incontinence (ICI) have all recently undertaken systematic reviews on the subject of urodynamic testing, and all emphasize the lack of high quality primary research confirming clinical utility [
4,
7‐
10]. Patients and clinicians working together in a project associated with the James Lind Alliance (JLA) have identified IUT as a research priority and, along with NICE, have recommended further research to answer the question of whether the use of IUT, prior to initial or subsequent treatments, affects the outcomes and cost effectiveness of interventions in women with UI [
7,
10].
The costing report associated with the NICE clinical guideline on UI used an estimated charge of £176 for each IUT. Consequently, the annual potential saving from eliminating IUT prior to conservative treatment was estimated at approximately £3 m and savings from a more rational use of IUT before surgery for SUI at approximately £321,000 [
7]. These calculations are based on 2002 -2007 figures. Changes in available operative techniques have led to dramatic alterations in surgical practice as recorded in the NHS's Hospital Episode Statistics (HES) which showed a 54% increase in surgery for SUI over the last ten years [
11]. These data along with 2008-09 national tariff costs for IUT of £425 suggest that the savings from a more rational use of IUT prior to surgery are likely to be substantially greater.
A randomised controlled trial (RCT) of IUT versus less invasive procedures prior to surgery would provide gold-standard evidence of the clinical and cost-effectiveness of this expensive procedure. However, prior to proceeding to a full scale RCT, a feasibility pilot study is deemed necessary for several reasons;
The use of IUT is widely established in clinical practice; many experts consider it a mandatory investigation, particularly prior to surgery [
12,
13]. So we need to establish whether sufficient clinicians are in equipoise and willing to recruit and randomise patients to a RCT. There is growing evidence in favour of pilot studies involving collection of both quantitative and qualitative data prior to embarking on this type of definitive RCT [
14].
Patients may not see the importance of 'testing a test' and are usually willing to undergo even invasive investigations in the belief that they guide their clinician and themselves to the most appropriate management. Trials reported in 2000 and 2001 randomizing radiography investigations for low back pain were only able to recruit 23% and 51% of patients approached to enter the randomised arms [
15,
16]. By assessing patients' willingness to undergo randomisation, potential barriers and facilitators to participation can be identified and used to modify the design of the definitive trial.
Given these uncertainties, before carrying out a definitive trial, it is essential to undertake a pilot study to estimate the extent of the potential recruitment problems described above and to provide robust estimates of the variability of the proposed outcome measures and of the likely rates of eligibility, recruitment, randomisation and retention of participants.