Ambulatory urodynamics: do they help clinical management?


Correspondence: Ms E. Gorton, Royal Surrey County Hospital, Guildford, Surrey GU2 5XX, UK.


Objective To assess the contribution of ambulatory urodynamics to the treatment of women with urinary incontinence.

Design A retrospective casenote review of all women referred from the urogynaecology clinic for ambulatory urodynamic monitoring from 1 April 1994 to 31 December 1997.

Setting A teaching hospital tertiary referral centre urodynamic laboratory.

Participants Notes were retrieved of 71 women, 80% of whom had had the investigation because the conventional cystometrogram had been normal.

Results Technical difficulties occurred in 30 traces, two of which were not interpretable. Detrusor instability was diagnosed in 32 women, including three women who also had stress incontinence (42% of interpretable traces). Of these, 20 women were treated with anticholinergics compared with nine of 37 women where detrusor instability was not diagnosed. None of the women with detrusor instability were offered anti-incontinence surgery, compared with five of those where the bladder remained stable. Less than half the women who were treated with anticholinergic medication improved, but none were considered suitable for more aggressive treatment.

Conclusions Although the diagnosis of detrusor instability may be increased by ambulatory urodynamics, this does not always translate into more effective treatment. Ambulatory urodynamic testing does not yet result in clinical improvements in diagnosis and treatment.


Urodynamic investigations are widely recommended in the diagnosis and treatment of women with urinary incontinence. It has long been recognised that there is a discrepancy between the woman's history and urodynamic findings and for this reason the bladder has been dubbed an ‘unreliable witness’1,2. However, conventional dual channel cystometry requires rapid bladder filling in an unnatural setting and so is unphysiological. Since the introduction of ambulatory urodynamic testing, a number of researchers have shown that urodynamics performed over a longer period under more physiological conditions are more likely to detect detrusor instability than conventional urodynamic investigations3–5. Some authors have even gone as far as to state that ambulatory monitoring should be mandatory when conventional urodynamics have failed to provide a diagnosis6.

However, ambulatory monitoring is expensive, both in equipment and time. There has been surprisingly little research into the use of ambulatory monitoring in clinical practice. The aim of this study was to review the role of ambulatory urodynamic tests in clinical management, to see how treatment was altered following the test, and where possible to determine the outcome of that treatment.


This was a retrospective case note review of women who had undergone ambulatory urodynamic investigations at a tertiary referral centre in urogynaecology between April 1994 and December 1997. From the notes, data were extracted about the woman's main symptoms, results of previous cystometry, and treatment prior to the ambulatory urodynamic tests. The treatment following ambulatory urodynamic investigations was noted and the outcome of treatment at the time of the last follow up visit was recorded. Where there was no follow up information in the hospital chart, the woman was contacted and asked to provide further information on any treatment she had had elsewhere, and her current symptoms.

Women were referred for ambulatory monitoring when conventional urodynamic investigations were normal or failed to explain their clinical symptoms. Ambulatory urodynamic testing were performed using the Urolog system, with 6F Gaeltec vesical and rectal catheters and a Urilos pad to record urinary leakage. The catheters were secured with tape to the woman's inner thigh and she was asked to undertake activities that would normally provoke leakage. She was encouraged to drink and the investigation usually continued for 3 to 4 hours. As the equipment did not include a channel for separate flow rates, no pressure flow data were available. A single dose of 200 mg trimethoprim was given at the start of the test, and she was encouraged to drink at least 2 L over the course of the next 24 hours to prevent urinary tract infection. The women were asked to keep a diary of their symptoms.

All ambulatory traces were interpreted by urogynaecology fellows and treatment decisions were made by them under the direct supervision of the consultant. A trace was considered to show detrusor instability if detrusor contractions were seen in conjunction with symptoms of urgency.


Overall 79 patients had ambulatory monitoring; of these 73 women were referred from the urogynaecology clinic and six patients (two men and four women) were referred from other clinics. As detailed documentation of symptoms was available only for women who had been referred from the urogynaecology clinic the other patients were not considered. Notes could not be traced for two women, so the final sample was 71 women. The characteristics of these women, including the main indication for performing ambulatory urodynamic investigations, are summarised in Table 1.

Table 1.  Characteristics of the women. Values are given as n (%), mean [SD] or median (interquartile range).
 n= 71
Age (years)52.2 [14.1]
  Nulliparous10 (14)
  Multiparous61 (86)
  Previous surgery for incontinence or prolapse19 (27)
  Previous anticholinergic treatment18 (25)
  Urge incontinence16 (23)
  Stress incontinence18 (25)
  Mixed symptoms27 (38)
  Frequency and urgency7 (10)
  Continuous incontinence3 (4)
  Enuresis1 (1)
  Duration of symptoms (years)4.2 {2–13.3}
Indication for ambulatory monitoring 
  Normal conventional urodynamics56 (79)
  Clinical and urodynamic diagnoses different12 (17)
  Conventional urodynamics difficult to interpret3 (4)
  Unable to void during test6 (8)
  No. of voids2 {1–3}
  Volume voided (mL)250 {170–400}

Technical difficulties occurred during a substantial number of traces: the bladder line was out for at least part of the test (11), inability to accurately complete a diary or it had been subsequently lost (9), inability to void during the test (4), poor subtraction between the abdominal pressure trace and the intravesical trace (7), investigation abandoned as the women were distressed (2), and the Urilos pad did not work although it was found to be very wet at the end of the test (1). Some women had a combination of factors, so there were 30 traces in which some technical difficulty was noted. In two women the ambulatory monitoring was impossible to interpret. One developed a severe rash following administration of the prophylactic antibiotic and she requested termination of the test; and in the other woman the bladder line had fallen out shortly after commencing the investigation which was not realised until the test had been completed. Neither of these women agreed to have the study repeated, both were lost to follow up, and further attempts to contact them were unsuccessful.

A summary of the treatment and follow up of the other 69 women is shown in Table 2. Those diagnosed as suffering detrusor instability included five women who had detrusor contractions greater than 20 cm H2O without documented urgency. In these women it was thought that urgency had been poorly documented.

Table 2.  Results of urodynamic monitoring and treatment of the women. Values are given as n or median (interquartile range).
Diagnosis and treatmentsNo. of womenNo. who improved
No. of successful examinations69
Duration of examination (h)3.6 (3.4)
Detrusor instability2913
  Anticholinergic drugs175
  Anterior repair11
  No treatment73
Genuine stress incontinence41
  Anticholinergics and colposuspension10
  No treatment10
Mixed incontinence31
  Anticholinergic drugs20
  Anterior repair and anticholinergic  
Normal ambulatory urodynamics3314
  Anticholinergic drugs72
  Anticholinergics and colposuspension11
  Anterior repair21
  No treatment122

Women who had detrusor instability were more likely to have anticholinergic treatment prescribed than those who did not (61% compared with 24%); however, the treatment was successful in less than half of either group.

Twelve women had conventional urodynamic investigations repeated between three months and four years after the ambulatory monitoring. In four of these women the repeat investigation was because of continuing symptoms after surgery. Two of these women had stress incontinence on the pre-operative cystometrogram and detrusor instability was detected post-operatively. One woman had a normal ambulatory trace and a normal postoperative conventional cystometrogram despite debilitating urgency and urge incontinence. The other woman had ambulatory monitoring that had shown mixed incontinence. After her anterior repair she had a repeat conventional cystometrogram that showed stress incontinence, but she was treated with oxybutynin with symptomatic relief. Five of the women who did not have surgery between their ambulatory urodynamics and the repeat conventional monitoring had detrusor instability on their ambulatory monitoring. This was confirmed in two of the women on repeat cystometrogram, but not in the other three. All these women continued to suffer symptoms of incontinence despite anticholinergic treatment.

Three of the women who had repeat conventional urodynamics had a normal ambulatory test. All had stress incontinence demonstrated on their repeat investigation, with one woman having detrusor instability as well.


In deciding treatment the woman's history, including her previous treatment and the severity of her symptoms, are just as important as the results of investigations. In a retrospective review it can be difficult to assess the contribution that each of these factors makes to the final decision regarding treatment. In our unit ambulatory urodynamic investigations were mainly used when conventional urodynamic tests had been normal. The results of ambulatory urodynamics seemed to have a negative effect on the decision to advise surgery, as none of the women who had detrusor instability underwent surgery for stress incontinence, although two women had anterior repair for prolapse. The diagnosis of detrusor instability had less effect on the selection of medical therapy. Although detrusor instability was associated with greater use of anticholinergic medication, almost a quarter of women with a stable bladder were also given anticholinergic drugs empirically because of symptoms of urgency and urge incontinence.

The percentage of symptomatic women showing detrusor contractions (42%) was similar to the 38%–69% of asymptomatic volunteers who have been shown to have detrusor contractions on ambulatory monitoring7–9. With such a high incidence of abnormality in asymptomatic individuals, it is difficult to know how to interpret detrusor contractions in women with symptoms. The diagnosis of detrusor instability was not always helpful: even when further treatment with anticholinergic drugs or physiotherapy (including bladder drill) was tried less than half of these women were improved. Most of the women were treated before tolterodine was available, and so it is hoped that improvements in anticholinergic therapy will improve the outcome for these women. Augmentation cystoplasty was not considered suitable for any of these women. Other authors have shown that although more than 50% of women will be happy with the results of augmentation cystoplasty, it has a significant complication rate and some women will continue to suffer incontinence even after such a major procedure10.

Some authors have noted that the incidence of ‘false positive’ detrusor contractions seen on ambulatory urodynamic traces can be reduced both by meticulous attention to the woman's diary, counting only detrusor contractions that occur with urgency, and by the use of two transducers within the bladder11. Diary information was incomplete in a significant number of women in the study, and other writers have also noted poor compliance in the use of event buttons and diaries12.

It has long been recognised that detrusor instability reduces the success of surgery for stress incontinence. From this it has been suggested that the 10% of women who develop de novo detrusor instability post-operatively may have had pre-existing undiagnosed detrusor instability. In our study none of the women who had detrusor instability were offered surgery, even when they also had stress incontinence. Although we feel that these women have avoided a possibly harmful operation, in other studies neither pre-operative symptoms nor the results of ambulatory monitoring predicted symptoms or urodynamic findings post-operatively12. Thus it is possible that some women have been denied an operation which may have helped them. Conversely, although our numbers were small, it is apparent that the absence of detrusor instability on ambulatory monitoring pre-operatively was no protection against developing symptoms of urgency and urge incontinence post-operatively.

In 48% of our women we were unable to reach a diagnosis by ambulatory monitoring. In an earlier study of symptomatic patients van Waalwajk van Doorn et al.3 were able to make a diagnosis in 95% of those who had ambulatory monitoring compared with 68% of those who had conventional monitoring. This improvement may have been due to technical differences as they were able to perform monitoring for a much longer period (mean 5 hours 55 minutes, range 2 hours 30 minutes to 23 hours 42 minutes), or it may reflect a different population (only 13 of their 100 patients were women). They do not discuss how the ambulatory results affected treatment. In a recent study comparing proposed treatment with actual treatment after ambulatory monitoring, approximately 60% of the women received different treatment after ambulatory monitoring13. Swithinbank et al.14 found that treatment was altered by the results of the ambulatory urodynamic studies in 91% of 92 patients. Neither of these studies determined how many patients were improved by the change in treatment.

For some women a normal result of ambulatory urodynamic testing may be reassuring. Often it is not so much her current symptoms that are distressing, but she is more concerned about the possibility of deterioration with age15. Research in other fields however has shown that patients are not necessarily reassured by normal test results, even in the absence of symptoms16.

Ambulatory urodynamic testing will undoubtedly play an important part in research, increasing our understanding of normal bladder physiology. However, its clinical role is at present limited and suggestions are premature that it is mandatory in any woman where the diagnosis is unclear. Logical treatment of women with urinary symptoms but no diagnosis on ambulatory monitoring includes the use of diaries and pad tests to confirm incontinence followed by empirical treatment based on her history. A randomised controlled trial of ambulatory monitoring against empirical therapy is required to determine the best treatment for this group of women. As our research has suggested that only 40% of women improve following ambulatory monitoring, a trial with 100 women in each arm would be required to have an 80% chance of detecting a 20% difference between ambulatory monitoring and empirical treatment at the 5% significance level.