Abstract
Conventional urodynamics (laboratory cystometry) is considered the ‘gold standard’ for measuring bladder function. However, it is a static short test, typically 20–30 minutes, and is considered ‘nonphysiological’. It involves rapid retrograde filling of the bladder in a laboratory setting, which does not always allow reliable reproduction of symptoms. Ambulatory urodynamic monitoring (AUM) relies on physiological bladder filling with natural stressors, including patient mobilisation over a longer time frame, to monitor bladder function which can then be directly compared to presenting symptoms. It is a useful additional test for women in whom conventional urodynamics fails to reproduce or explain the lower urinary tract symptoms of which they complain [1]. AUM is performed through a portable system which allows information to be recorded digitally, and downloaded and reviewed during or at the end of the test. The trace can then be expanded or compressed without loss of information.
8.1 Introduction
Conventional urodynamics (laboratory cystometry) is considered the ‘gold standard’ for measuring bladder function. However, it is a static short test, typically 20–30 minutes, and is considered ‘nonphysiological’. It involves rapid retrograde filling of the bladder in a laboratory setting, which does not always allow reliable reproduction of symptoms. Ambulatory urodynamic monitoring (AUM) relies on physiological bladder filling with natural stressors, including patient mobilisation over a longer time frame, to monitor bladder function which can then be directly compared to presenting symptoms. It is a useful additional test for women in whom conventional urodynamics fails to reproduce or explain the lower urinary tract symptoms of which they complain [1]. AUM is performed through a portable system which allows information to be recorded digitally, and downloaded and reviewed during or at the end of the test. The trace can then be expanded or compressed without loss of information.
8.2 Differences between Ambulatory Urodynamic Monitoring and Conventional Cystometry
AUM is performed in accordance with the International Continence Society (ICS) Standardisation of Ambulatory Urodynamic Monitoring [2]. ‘Ambulatory’ refers to the nature of the urodynamic monitoring rather than the mobility of the subject and, although it records the same measurements as conventional urodynamics, it differs principally in the following ways:
AUM is performed over a longer period of time (usually up to 4 hours) and facilitates more than one cycle of bladder filling and voiding.
It utilises natural bladder filling. (A standard fluid intake, such as 200 ml half-hourly, is recommended.)
It takes place outside the urodynamics laboratory.
Its portability allows better reproduction of a patient’s normal activities of daily living. These may include manoeuvres tailored specifically to the patient to identify the presence of involuntary detrusor and/or urethral activity and/or to provoke incontinence.
8.4 Performing the Test
Care in setting up the equipment, providing advice to patients on the information they should record during the test, and observation of them and troubleshooting are as important in making the diagnosis as the objective measurements obtained, which should not be interpreted in isolation. Checks on signal quality and pressure subtraction are highly important at the start, at regular intervals during the test and again before the test terminates.
8.5 Preparation of the Patient
Information explaining the AUM test including preparation for the test should be sent to patients prior to their appointment. Patients should attend wearing loose comfortable clothing with separate tops and bottoms, and empty their bowel beforehand if possible. Urinalysis is undertaken to exclude urinary tract infection. Concise explanation of the test should be done, and verbal or written consent is taken when the patient attends.
The following would be contraindications:
acute urinary tract infection
reduced cognitive ability
inability to follow instructions
inability to complete a symptom diary
severe constipation.
8.6 Equipment and Technique
The following are important components of the equipment required for AUM:
analysing system and software, urinary flowmeter, electronic incontinence pad or leakage conductance system
catheter transducers
patient symptom and event/activity diary.
8.7 The Recording System and Software
The recording unit (Figure 8.1) should be small and lightweight to allow patients freedom of movement. It should have a facility to mark bladder symptoms and events on the trace to support interpretation of the recording which is supplemented with a written or wireless patient diary. Many systems can measure pressures (pves, pabd, pdet, pura, pclos) with a facility to provide EMG (electromyography). The recorder is connected (either manually or via Bluetooth®) to a urinary flowmeter to allow simultaneous recording of pressure flow. The addition of an electronic pad worn by the patient or a leakage conductance system to supplement patients recording of events and symptoms will facilitate detection of incontinence and diagnosis. Recording units come with an over-the-shoulder strap for patient comfort which should mean minimal interference during physical activities and reduce chances of transducer damage, disconnection or loss.
Figure 8.1 Example of recording unit
A high-quality digital memory will allow storage and compression of large amounts of data in addition to allowing for expansion of the recorded trace during the subsequent analysis. Many of the new systems allow more than 24 hours of investigation data to be downloaded, analysed and presented in less than a couple of minutes. Review of recorded data can be made throughout the test using wireless online technology with a Bluetooth® recorder.
An example of software can be seen in Figure 8.2.
Figure 8.2 Example of software
8.7.1 The Catheter Transducers
Good quality calibrated catheters to record intravesical and intra-abdominal pressures are vital to ensure robust data for analysis. Solid-state microtip transducer catheters (Figure 8.3) produce fewer movement artefacts compared to water-filled catheters, allowing the patient to have greater mobility which is essential given the ambulatory nature of the test, and have reasonable responsiveness to rapid changes in pressure. The main disadvantages are that they are not of single-use type and therefore require a decontamination process, and they carry a risk of signal loss as there is no fixed reference point. Concerns about decontamination processes and hospital-acquired infection have encouraged the widespread use of single-use transducer catheters in general; commercial manufacturers have sought to improve fluid-filled and air-charged catheter transducers such that many of the AUM systems on the market now use those as viable alternatives to solid-state transducers. Fluid-filled transducers respond quickly to pressure changes but remain sensitive to catheter and patient movement artefacts, however, which can make them less than ideal in an ambulatory setting. Nonetheless, when appropriately secured, they do produce good quality traces. Air-charged catheters (Figure 8.4) are easier to calibrate and have the advantage of being less sensitive to patient and especially catheter movements. However, their response can be slower and relatively damped, especially to rapid pressure changes (e.g. with coughing). Additionally, the catheters are less flexible and are not always well tolerated. This can lead to the test being abandoned early because of symptoms of pain and haematuria which limit their use to 2 hours and decrease the utility of the test. These types of catheters are rarely used in clinical practice.
