The Role of Ambulatory Urodynamics in Spinal Cord Injury

Anne P. Cameron


Nat Rev Urol. 2011;8(6) 

Abstract and Introduction


Bladder management is an important aspect of the management of patients with spinal cord injury (SCI). A device capable of performing ambulatory urodynamics on individuals with SCI has recently been developed; however, the benefit of ambulatory urodynamics in patients with SCI is disputed.


A new device has been developed to perform ambulatory urodynamics on individuals with SCI.[1] The hand-held device was tested on 28 patients, and the results were recently published.[1] However, many clinicians question the usefulness of ambulatory urodynamics compared to standard urodynamics, and a group in The Netherlands has recently gone so far as to state that there is no primary role for this investigation in patients with SCI.[2]

In individuals with SCI, bladder management is of the utmost importance, given their risk of incontinence, bladder stones, urinary tract infections and upper tract deterioration.[3] Urodynamics are a key part of the routine follow-up[4] of these individuals and can be used to diagnose poor compliance, high-pressure storage or neurogenic detrusor overactivity (NDO), all of which can lead to these complications.[3] Some would argue that conventional urodynamic evaluation is an artificial situation, in which the bladder is filled too rapidly and the patient is immobile, neither of which is physiologically normal.[5] Furthermore, a typical urodynamics investigation lasts less than 20 minutes, and provides only a brief snapshot of lower urinary tract function.

Ambulatory urodynamics are similar to conventional urodynamics except that they are carried out over a prolonged period of time (usually several hours), during which the patient performs their usual daily activities. Bladder filling is accomplished with the patient's own urine production instead of fluid filling with a catheter. A pressure-sensing catheter is placed in the bladder and, typically, also in the rectum, to measure abdominal pressure. Electromyography (EMG) patches can also be used.[1,5]

Kim et al.[1] have developed a new ambulatory urodynamic monitoring system, using a personal device assistant (PDA) for data collection. They tested their device in 28 patients with SCI and compared the results to standard urodynamics techniques. Their device is novel as it measures abdominal pressure using surface EMG patches, and alerts itself to leakage by means of impedance changes in two sensors on the urethral catheter. These measures, along with rectal and bladder pressures, are stored and analyzed in the handheld PDA. The study found that the rate of NDO was higher when using ambulatory urodynamics than standard urodynamics (60.7% versus 32.1%; P <0.05). Furthermore, abdominal EMG was able to replace the use of a rectal catheter.

However, this study was not without its limitations: all the patients underwent the "ambulatory" urodynamics testing while confined to their hospital bed, and all had a filling cystogram performed before the ambulatory study, possibly resulting in increased bladder irritation from undergoing two studies in the same day. This could have caused the increased rate of NDO observed in the second test. The authors concluded that their system for performing ambulatory urodynamics could be a useful tool when standard urodynamics fail to diagnose a patient's symptoms.

In Neurourology and Urodynamics, Martens et al.[2] discuss their study of 27 patients with SCI who had symptoms suggestive of NDO. They underwent both conventional and ambulatory urodynamics on the same day, with the ambulatory portion lasting 6 hours, during which they were allowed to perform their usual activities. A larger number of patients were diagnosed with detrusor overactivity during the ambulatory study, but the increase in bladder pressure measured during detrusor contractions did not differ. The authors hypothesized that false-positive results for NDO would be much more common with ambulatory urodynamic testing, owing to the high possibility of catheter movement as the patients are moving and causing artifact. They concluded that, although conventional urodynamics techniques might underdiagnose NDO in a minority of patients, a good clinical assessment of the patient combined with standard urodynamics is sufficient to make an accurate diagnosis of NDO in patients with SCI.

The increased sensitivity of ambulatory testing to detect detrusor overactivity has also been reported by other authors.[5,6] Stress urinary incontinence (SUI), however, is not better measured on ambulatory urodynamics.This has been shown in a randomized crossover trial of 106 women.[5] The results of this trial confirm what many already believe—that if stress incontinence is present, it can be reliably detected during standard urodynamics. This is in contrast to incontinence due to detrusor overactivity, which is not always present during urodynamic studies.

Notably, neither of these studies has taken into account the high cost and substantial bother associated with using bladder tests of long duration. Ambulatory testing is likely to be uncomfortable for the patient, and the use of multiple catheters could trigger episodes of autonomic dysreflexia.

In my experience, a good 3-day voiding or catheter volume diary and a thorough history, combined with standard urodynamics, is sufficient to diagnose NDO in patients with SCI. If a patient has neither SUI (which can be reliably detected on standard urodynamics) nor NDO, but has incontinence at bladder volumes below their maximum capacity, it is reasonable to assume that they have detrusor overactivity. Their treatment should then be adjusted accordingly, with either increased medical therapy or more invasive treatment such as botulinum toxin injections or bladder augmentation.


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