UROFLOWMETRY

• Electronic recording of the urinary flow rate throughout the course of micturition.
• Simple, diagnostic screening procedure used to calculate the flow rate of urine over time.
• Common, non-invasive urodynamic test used in the diagnostic evaluation of patients presenting with symptoms of Bladder Outflow Obstruction (BOO).
• Results from the test can suggest if the flow is normal or abnormal. Abnormal results are nonspecific for the cause of the disease.
• Abnormally low flow rate may be caused by obstruction or detrusor hypocontractility.

• Flow rate – volume of urine through urethra per unit time, expressed in ml/sec.
• Peak flow rate (Q Max) – maximum measured flow rate.
• Voided volume – total volume expelled through urethra.
• Flow time – Total time over which measurable flow occurs.
• Average flow rate – voided volume / flow time.
• Time to maximum flow – elapsed time from onset of flow to maximum flow.
• Intermittent flow – flow time should be measured carefully. The time intervals between the flow episodes are disregarded.

• Possible bladder outlet obstruction / symptoms of outlet obstruction.
• Women subjected to undergo surgery for stress incontinence.
• Elderly women to exclude residual urine, a cause of recurrent UTI.
• Pre-operative workup and post-operative follow up in case of urethral stricture, Benign Prostatic Hyperplasia (BPH) bladder neck obstruction.

• Weight transducer flow meter Weighs the urine voided - measuring the volume of urine voided and hence the urine flow rate by differentiation with respect to time.
• Ordinary pressure transducer The hydrostatic pressure exerted by a column of urine also can be applied to measure the weight of the urine voided.
• Rotating – disc flow meter Has a spinning disc on which urine falls.
  The disc rotates at a same speed by a servomotor, in spite of changes in the urine flow rate.
  The weight of urine tends to slow the disc speed.
The differing power needed to maintain disc rotation constant is proportion to the urine flow rate.



Urine flow clinics


• Uroflow studies should be performed in privacy when the patient has a normal desire to void and is relaxed.
• Patient is asked to drink 500 ml to 1 litre of fluid on arrival. They are asked to hold their urine until comfortably full - but not bursting to pass urine.
• Then patient is led into the flow room, having been made familiar about the equipment, the person is allowed to pass urine in privacy.
• Ideally 3 flows to be recorded on three occasions and each time after passing urine, their post-void residual urine recorded ultrasonographically.


Normal flow patterns
• A variety of normograms has been produced by various authorities, such as Von Garrelts (1958), Backman (1965), Gierup (1965), Siroky et al (1979), Kadow et al (1985) and Haylen (1990).
• The shape of the curve is unimodal i.e. monotonic increase, stable period, monotonic decrease.
• “Bell shaped”.
• Maximum flow is reached in first 30% of any trace and within 5 seconds (3-10 S) from the start of the flow.
• The flow rate may vary with amount of urine voided.
• The final phase of a normal flow trace shows a rapid fall from high flow, with a sharp cut off at the termination of the flow.
• The trace appearance may vary with paper speed. A paper speed of 25 cm/s is recommended.
• Urine flow rate is highly dependent on the volume voided.
• Flow rates are highest and more predictable with 200-400 ml urine volume.
• Detrusor muscle when stretched achieves an optimal performance, but when stretched further it becomes inefficient (> 400ml).
• Uroflow in an adult male is considered to be normal if it is bell shaped with a peak flow of 15 ml/sec or more on more than one occasion.
• Normally Uroflow in an adult female should be bell shaped with a peak flow rate of 25ml/sec
Similar peak flow rate or Q max but different flow curve shapes due to different voided volumes are shown below.


AHCPR Guidelines
• Flow rate measurements are inaccurate if the voided volume is less than 125 to 150 ml.
• Flow rate recording is the single best noninvasive urodynamic test to detect lower urinary tract obstruction. However there is no recommended "cut-off" value.
• The peak flow rate (PFR; Qmax) more specifically identifies patients with BPH than does the average flow rate (Qave).
• Although Qmax decreases with advancing age and decreasing voided volume, no age or volume correction is currently recommended for clinical practice.
• Patients with a Qmax > 15 ml/sec appear to have somewhat poorer treatment outcomes after prostatectomy than patients with a Qmax < 15 ml/sec.
• A Qmax of less than 15 ml/sec does not differentiate between obstruction and bladder decompensation.
• Age: 4 to 7
• The average flow rate for both males and females is 10 mL/sec.
• Age: 8 to 13
• The average flow rate for males is 12 mL/sec.
• The average flow rate for females is 15 mL/sec.
• Age: 14 to 45
• The average flow rate for males is 21 mL/sec.
• The average flow rate for females is 18 mL/sec.
• Age: 46 to 65
• The average flow rate for males is 12 mL/sec.
• The average flow rate for females is 15 mL/sec.
• Age: 66 to 80
• The average flow rate for males is 9 mL/sec.
• The average flow rate for females is 10 mL/sec.
• Artifacts can occur from abdominal straining or "waggling" of the stream.
Detrusor over activity
• Supra-normal pattern. Very high maximum flow rate may be achieved with an abnormally short time of 1-3 secs.
• The detrusor contraction may have already opened the bladder neck widely thus reducing the urethral resistance. Hence he/she is required only to relax the distal sphincter.




Bladder Outflow Obstruction (BOO)
• The flow curve has low maximum flow and also reduced average flow rates, with the Qave being more than half the Qmax.
• Maximum flow may be obtained quickly (3-10S) but the final phase decreases slowly.
• The obstruction may be compressive (BPH) or constrictive (urethral stricture).
BPH
• Shows a compressive pattern, the first third of the curve may appear normal, Qmax may be reduced.
• The final phase is elongated into a pronounced “tail” of reducing flow rate.




Stricture
• The later produces a “plateau” - shaped curve, with very meagre difference between Qmax and Qave.




Detrusor under-activity
• Produces low maximum flow rate.
• The time to reach the maximum flow is variable and usually occurs in the second half of the curve.
• The traces of both obstruction and detrusor under-activity may look similar, making it difficult to distinguish between the conditions.
• Requires urodynamic pressure flow study.

Irregular interrupted flow patterns - May occur secondary to straining in cases of obstruction or detrusor hypocontractility.

Artifacts – Cruising

• Patient moving their stream in relation to the central exit from the collecting tunnel.
• The “peaks” occur when the stream is moving down the side of the tunnel towards central exit.
• The “valleys” occur with impact point moving away from exit.
• This can be minimized with complex baffles in the tunnel.

• Patient may squeeze the penis or fore skin leading to series of “peaks”.
• Usually it is an effort to compensate for the reducing urine flow.
• Patient to be educated about proper urination.

• Increased daytime frequency Complaint by the patient who considers that he/she voids too often by day.
• Nocturia Complaint that the individual has to wake at night one or more times to void
• Urgency Complaint of a sudden compelling desire to pass urine which is difficult to defer.
• Urinary incontinence Complaint of any involuntary leakage of urine.
• Stress urinary incontinence Complaint of involuntary leakage on effort or exertion, or on sneezing or coughing.
• Urge urinary incontinence Complaint of involuntary leakage accompanied by or immediately preceded by urgency.
• Mixed urinary incontinence Complaint of involuntary leakage associated with urgency and also with exertion, effort, sneezing or coughing.
• Enuresis Any involuntary loss of urine. If it is used to denote incontinence during sleep, it should always be qualified with the adjective ‘nocturnal’.
• Nocturnal enuresis Complaint of loss of urine occurring during sleep.
• Continuous urinary incontinence Complaint of continuous urine leak.

• Urgency is the complaint of a sudden compelling desire to pass urine which is difficult to defer.
• Urgency, during filling cystometry, is a sudden compelling desire to void.
• Urge urinary incontinence is the complaint of involuntary leakage accompanied by or immediately preceded by urgency.

• Feel of an early and persistent desire to void.

• Aware of bladder filling but does not feel a definite desire to void.

• No sensation of bladder filling or desire to void.

• Perception of reduced urine flow usually compared to previous performance or in comparison to others. Splitting or spraying of the urine stream may be reported.

• Urine flow which stops and starts, on one or more occasions, during micturition.

• Difficulty in initiating micturition resulting in a delay in the onset of voiding after the individual is ready to pass urine.

• Measuring the Frequency, Severity and Impact of Lower Urinary Tract Symptoms
• Micturition time chart - Records only the times of micturitions, day and night, for at least 24 hours.
• Frequency volume chart (FVC) - Records the volumes voided as well as the time of each micturition, day and night, for at least 24 hours.
• Bladder diary - Records the times of micturitions and voided volumes, incontinence episodes, pad usage and other information such as fluid intake, the degree of urgency and the degree of incontinence.
• Daytime frequency - Number of voids recorded during waking hours and includes the last void before sleep and the first void after waking and rising in the morning.
• Nocturia - Number of voids recorded during a night’s sleep: each void is preceded and followed by sleep.
• 24-hour frequency is the total number of daytime voids and episodes of nocturia during a specified 24 hours period.
• 24-hour production is measured by collecting all urine for 24 hours.
• Polyuria - Measured production of more than 2.8 litres of urine in 24 hours in adults.
• Nocturnal polyuria - Increased proportion of the 24-hour output occurs at night.
• Nocturnal urine volume - Total volume of urine passed between the time the individual goes to bed with the intention of sleeping and the time of waking with the intention of rising.
• Maximum voided volume - Largest volume of urine voided during a single micturition and is determined either from the frequency/volume chart or bladder diary.

• Normal Detrusor Function remains unchanged and is defined as “allowing bladder filling with little or no change in pressure. No involuntary phasic contractions occur despite provocation”.
• Detrusor Overactivity is now defined as “an urodynamic observation characterized by involuntary detrusor contractions during the filling phase which may be spontaneous or provoked.
• Phasic Detrusor Overactivity is “defined by a characteristic wave form, and may or may not lead to incontinence”.
• Terminal Detrusor Overactivity is “defined as a single involuntary detrusor contraction occurring at cystometric capacity, which cannot be suppressed and results in incontinence usually resulting in bladder emptying”.
• Detrusor Overactivity Incontinence is a new term to describe “incontinence due to detrusor overactivity”.
• Detrusor overactivity with or without incontinence might have been simpler. The condition may also be sub-classified based on its etiology.
• Replacing detrusor hyperreflexia is the new term Neurogenic Detrusor Overactivity which is “when there is a relevant neurological condition (that causes the detrusor overactivity)”.
• Idiopathic Detrusor Overactivity is the new term used to replace detrusor instability and is used when involuntary detrusor contractions occur “when there is no defined cause”. Provocative Maneuvers are a new addition to the terminology of cystometry and are defined as “techniques used during urodynamics in an effort to provoke detrusor overactivity, for example, rapid filling, use of cooled or acid medium, postural changes and hand washing.
• Bladder Compliance is defined as the” relationship between change in bladder volume and change in detrusor pressure”. It is “calculated by dividing the volume change by the pressure change during that change in bladder volume”. The ICS recommends that two standard points be used for compliance calculations: the detrusor pressure at the start of filling (bladder volume=0) and the detrusor pressure and corresponding bladder volume at cystometric capacity or immediately before the start of any detrusor contractions that cause significant leakage.

• Cystometric Capacity has a new definition as “the bladder volume at the end of the filling cystometrogram, when “permission to void” is usually given. The cystometric capacity is the volume voided together with any residual urine”.
• Maximum Cystometric Capacity, in patients with normal sensation, is” the volume at which the patient feels he/she can no longer delay micturition and has a strong desire to void.
• Maximum Anesthetic Bladder Capacity has also been redefined as “the volume to which the bladder can be filled under deep general or spinal anesthetic and should be qualified according to type of anesthesia used, the speed of filling, the length of time of filling, and the pressure at which the bladder is filled”

• The Normal Urethral Closure Mechanism “maintains a positive urethral closure pressure during bladder filling even in the presence of increased abdominal pressure, although it may be overcome by detrusor overactivity.
• Incompetent Urethral Closure Mechanism is “defined as one which allows leakage of urine in the absence of a detrusor contraction”.
• As a clarification of the prior confusing term “unstable urethra” the new term Urethral Relaxation Incontinence is “defined as leakage due to urethral relaxation in the absence of raised abdominal pressure or detrusor overactivity.
• Urodynamic Stress Incontinence is “defined as the involuntary leakage of urine during increased abdominal pressure, in the absence of a detrusor contraction. This is the replacement term for “genuine stress incontinence.
• The Abdominal Leak Point Pressure is defined as “the intra-vesical pressure at which urine leakage occurs due to increased abdominal pressure in the absence of a detrusor contraction”.
• Detrusor Leak Point Pressure is defined as “the lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increased abdominal pressure”, “the lowest detrusor pressure at which urine leakage occurs in the absence of increased abdominal pressure from either decreased bladder compliance or detrusor overactivity”.
• Bladder Outlet Obstruction is “the generic term for obstruction during voiding and is characterized by increased detrusor pressure and reduced urine flow rate. It is usually diagnosed by studying the synchronous values of flow rate and detrusor pressure”.
• Dysfunctional Voiding is an “intermittent and/or fluctuating flow rate due to involuntary intermittent contraction of the peri-urethral striated muscle during voiding, in neurologically normal individuals”. This is a general term to describe what has been called “non-neurogenic neurogenic bladder or idiopathic detrusor sphincter dyssynergia” previously.
• The new finding of Non-Relaxing Urethral Sphincter Obstruction “occurs in individuals with a neurological lesion and is characterized by a non-relaxing, obstructing urethra resulting in reduced urine flow”. This condition is usually found in sacral and infra-sacral lesions such as with meningo-myelocele or after radical pelvic surgery.
• Acute Retention of Urine is a condition described as “a painful, palpable or percussable bladder, when the patient is unable to pass any urine”.
• Chronic Retention of Urine is defined as “a non-painful bladder, which remains palpable or percussable after the patient has passed urine. Such patients may be incontinent”. This condition supplants the poor past term of “overflow incontinence”. Typically the retention in these patients is >300ml.
• Benign Prostatic Obstructionis a form of bladder outlet obstruction; and may be diagnosed when the cause of outlet obstruction is known to be benign prostatic enlargement, due to histologic “benign prostatic hyperplasia”. Benign Prostatic Hyperplasia “is a term used and reserved for the typical histopathological pattern which defines the disease”. Benign Prostatic Enlargement is defined as “prostatic enlargement due to histologic benign prostatic hyperplasia. The term ‘prostatic enlargement’ should be used in the absence of prostatic histology”.
• Lower Urinary Tract Rehabilitation is defined as “non-surgical, non-pharmacological treatments for lower urinary tract function and include: Pelvic Floor Training, Biofeedback, Behavioral Modification and Electrical Stimulation.
• Intermittent Catheterization is described as Intermittent Self-Catheterization performed by the patient. Intermittent Catheterization performed by an attendant, Clean Intermittent Catheterization using washed or disposable catheters, and Aseptic Intermittent Catheterization using a sterile technique with sterile gloves and catheters. Indwelling Catheterization is also described as “an indwelling catheter in the bladder, urinary reservoir, or conduit for a period longer than one emptying”.
• Bladder Reflex Triggering “comprises various maneuvers performed by the patient in order to elicit reflex detrusor contraction by exteroceptive stimuli”. Bladder Expression consists of “various maneuvers aimed at increasing intravesical pressure in order to facilitate bladder emptying”. The most common of these are abdominal straining, Valsalva’s maneuver and Crede maneuver.

• The aim of Urodynamic Examination (UDE) is to reproduce the patient’s symptoms and relate them to any synchronous urodynamic events.

• Nitti notes three important principles:
  
  
  1. Study that does not duplicate the patient's symptoms is not diagnostic.
  2. Failure to record an abnormality does not rule out its existence.
  3. Not all abnormalities detected are clinically significant.

• To make a diagnosis
• To provide evidence to determine which to treat first in coexisting abnormalities
• To increase diagnostic accuracy
• To predict problems that follow treatment
• To assess results of treatment

• Urodynamics facility should be as private as possible for the patient to be able to replicate his or her usual voiding habits.
• As few observers as possible to minimize patient embarrassment.

• Adequate history and physical examination should be performed
• Indication and details of procedure explained
• Voiding diary completed
• Free uroflow obtained
• Serum creatinine, Urine culture reports
• Laxative given on night before study Patient Preparation on day of procedure
• Patients need to be counseled and be asked to sign a consent form.
• Parenteral antibiotic prophylaxis is necessary.
• Prior to catheterization asked to void.

• Oral antibiotics in patients requiring multiple instrumentation or those at high risk for UTI for 48 hours after study.

• Urinary tract infection and indwelling catheters may result in altered bladder dynamics
• Patients should stop medications or their impact on the urodynamic study should be taken into account.

• Catheters
  
  Epidural 3F with Filling catheter 8F or Dual channel catheter 6F Rectal catheter

• Pressure transducers - two types
  
  - External strain gauge type
  - Catheter tip mounted
  

• Tubing
  
  Flexible but not elastic
  
• Recording equipment
• Printing equipment

• Insertion of catheters
• Fixing of catheters
• Attaching the catheters to the transducers
• Measuring pressures correctly

PRESSURES

• Step 1: Setting zero Zero pressure is the surrounding atmospheric pressure
• Step 2: Calibration of transducers.
• Step 3: Establishing reference level

• Crucial that there be no air bubbles in any of the transducers or tubing

• Quality control ensured by:
1. Feasible initial pressure recording
ICS values
• Pves (cm H2O)
• Supine 10-20
• Sitting 15-40
• Standing 30-50
• Pdet 0-6 cm H20


2. Cough every minute during filling

Filling Rate
• Slow fill < 10 ml/min ("physiologic")
  Medium fill 10 to 100 ml/min
  Rapid fill > 100 ml/min
  
• Faster the bladder is filled, lower the bladder compliance and not representative physiologically
• Fluid used – saline
• Temperature of fluid – Room temperature

• Normal activity: Detrusor quiescent during filling. End filling pressure 10 cm H2O
• Detrusor overactivity: Phasic involuntary detrusor contractions which may be spontaneous or provoked. Abnormal only when it produces symptoms

• First sensation (50% of cystometric capacity)
• Normal desire to void (75% of cystometric capacity)
• Strong desire to void (90% of cystometric capacity)
• Urgency
• Abnormal sensation

• Reduced in infection, inflammation, scarring, chronic indwelling catheter, rapid fill rate.
• High compliance in diabetes, spinal shock.

• Leak/ no leak

• Cystometric capacity: Bladder capacity at end of filling when patient has normal desire to void.
• Maximum cystometric capacity: Patient feels he cannot delay voiding

• Detrusor activity Normal
  Underactive
  Acontractile
  
• Urethral function
  Various Indices calculated during Urodynamics
  BCI = Bladder contractility index:
  PdetQmax+5Qmax
  
  
  
  BOOI = Bladder outlet obstruction index:
  PdetQmax-2Qmax

OVERACTIVE BLADDER (OAB)

Definitions:

Overactive bladder is a symptom complex consisting of urgency, with or without urge incontinence, usually with frequency and nocturia. There should be no proven infection or other obvious pathology.

The diagnosis of OAB requires presence of Urgency and at least one other symptom.

The other names for OAB are Urgency syndrome and Urgency-Frequency syndrome.

Urgency is a complaint of sudden compelling desire to pass urine which is difficult to defer.

Urgency incontinence is a complaint of involuntary leakage accompanied or immediately preceded by urgency.

Detrusor overactivity (DO) is the urodynamic study (UDS) finding in patients with OAB.

Limitation of OAB Terminology

• OAB - Some patients have all the Symptoms, but there are no Involuntary Detrusor Contractions on conventional cystometry
• 10-45% of individuals with unstable Detrusor contractions may be asymptomatic.
• The term OAB – Does not indicate –
  – A specific condition
  – Nor is the cause obvious
  (Ref- Eckhardt et al .Urology 2001;58:966-971)
  

• Normal detrusor is not well coupled electrically – Normally transmission of electrical activity in a cell occurs without it spreading to adjoining muscle cell.
• Unstable bladders are well coupled allowing spread of electrical activity leading to synchronous contraction of detrusor causing tetanic contraction.
• Thus unstable bladders have better connectivity leading to propagation of uninhibited contraction.

• Neuroplasticity means the ability of nervous system to change - transmitters, reflexes or synaptic transmission with disease , injury or any change in the environment
• Ischemia to nerves leads to neuroplasticity and leads to Detrusor hyperactivity with impaired contractility (DHIC)
• Irreversible neuronal damage causing OAB also seen with Urinary Obstruction and Ageing

• an increase in metabolic demand with reduced blood flow to detrusor leading to anoxia and neuronal death
• There is an increase in Nerve Growth Factors (NGF) content in the detrusor muscles
• Increased NGF – leads to increase in size of efferent neurons in the pelvic plexus - causing urinary frequency
• NGF presence also leads to de-novo development of spinal micturition reflex leading to subsequent OAB.
• NGF is responsible for growth of sympathetic and sensory neurons
• With inflammation there is an increase in NGF content in bladder
• Repeated inflammatory stimuli of the bladder also leads to enlargement of bladder DRG ( dorsal root ganglion ) neurons of the spinal cord
• Relief of obstruction can lead to reversal of these neural changes

• These conditions lead to disturbance in brain circuits using serotonin (5-HT) neurotransmitter.
• 5-HT function is diminished in these conditions, causing low volume threshold for voiding with unstable bladder contractions.
• Reduced 5-HT neurotransmission in the CNS enhances bladder activity.

• OAB more common in females than males.
• Males have 52% higher rate of synthesis of 5-HT as compared to females.
• Women may be predisposed to both OAB and depression in part because levels of 5-HT in the brain are substantially lower in women than in men.

Definition: 

It is the complaint of involuntary leakage on effort or exertion, or on sneezing or coughing.

Approach to a patient with SUI:

SUI is a fairly straightforward and simple diagnosis. It does not need any complex test to prove it. Once the diagnosis is obvious, then the degree of bother is to be evaluated along with enquiry into the lifestyle of the patient. 

If the patient is using only few pads per day and her social life is not being altered by this problem, then conservative treatment is started straight away. Patient should be told to do pelvic floor exercises diligently for 6-8 weeks before re-evaluation of the symptom.

If the patient’s social lifestyle is significantly affected or her work involves moderate degree of exertion (eg-Aerobic instructor), then a surgical management is to be considered straightaway. In this situation, a prior Urodynamics will help before invasive therapy.


Urodynamics in SUI: 

Indications for UDS: 

1) Prior to invasive treatment
2) History of mixed incontinence 
3) In previously failed incontinence surgery where re-surgery is contemplated
4) Previous radical pelvic surgery
5) Associated obstructive voiding/abnormal post void residue
6) Associated neurologic disorders

Advantages of UDS prior to invasive treatment:

1) Confirmation of incontinence and its cause
2) Definition of detrusor activity during filling – to rule out poor compliance
3) Assessment of detrusor during voiding – to rule out obstruction or detrusor underactivity
4) Assessment of degree of sphincter weakness

Urodynamic procedure in SUI:

The urodynamic procedure has to be carried out either in sitting position or in standing position. In sitting position, if stress leak is not demonstrated, the patient is asked to flex and abduct one thigh to open the introitus. Patient has to be properly explained the need for this position and taken into confidence before proceeding further.

Urodynamic finding in SUI:

Urodynamic stress incontinence is the involuntary leakage of urine during filling cystometry occurring when the patient is asked to cough or do Valsalva manoeuvre. 

The important finding to be noted is the increase in abdominal pressure (Pves or Pabd) without any detrusor contraction (ie – nil or minimal change in Pdet).

The volume at which the SUI occurs is to be noted. The Pves value at which the stress leak starts is also important.

Intrinsic sphincter deficiency is thought to be present if the stress leak occurs at Pves of less than 60cm H20. 

Management of SUI:

The initial management of SUI includes teaching the patient a proper Keegel’s exercise, losing weight if obese and sometimes medication. The conservative approach is to be done for at least 6-8 weeks. If the patient continues to have significant symptoms affecting their social life, invasive treatment options are to be considered.

Mixed Urinary Incontinence:

Up to 12% women with apparently pure SUI can be shown to have Overactive bladder.

In mixed urinary incontinence, the frequency of SUI episodes is usually more compared to Urgency incontinence. However, patients are more likely to be troubled with urge urinary incontinence (UUI). This is because the UUI leak is a larger volume of leak leading to more pad usage and social embarrassment. 

The initial management of mixed urinary incontinence is again conservative. It includes conservative measures as described for UUI along with pelvic floor exercises and drugs for OAB. 

If the conservative treatment fails after 6-8 weeks trial, then Urodynamics is indicated prior to further invasive treatment.

Graph showing Detrusor overactivity (sporadic and terminal DO)

Graph depicting stress leak during Valsalva maneuver (Note the rise in Pabd and Pves without any rise in Pdet )

Urodynamics in Children

Urodynamics study is an invasive procedure causing considerable distress to the child and has an inherent risk of UTI and severe sepsis. Therefore it should be ordered only when other less invasive tests have not yielded the necessary information. Before an urodynamic study is performed, it is important for the child and the family to have full knowledge of the procedure. An explanatory leaflet should be provided so that parents will know what to expect and can explain the test to their child, or the child can read about it if he or she is old enough. A thorough history and clinical examination should be undertaken. Non invasive tests like uroflowmetry and ultra sonogram should always precede an urodynamic study in children. 

Uroflowmetry

Uroflowmetry consists of measurement of urine flow during voiding and is described in terms of rate (ml/sec) and curve pattern. It is the least invasive of all urodynamic methods and is therefore perfect for paediatric use. However it requires a cooperative child, and is generally not possible in children less than 4 yrs of age. It measures urine stream during the emptying phase and gives an idea about bladder function and outlet function. 

Age related uroflow nomograms are available separately for boys and girls depicting the maximum flow (Q max) in ml/sec. The normal curve pattern is ‘bell shaped’ or tower shaped some times and the flow ends usually within 10-15 sec (Figure 1). The normal Q max is generally above 10-15ml/sec. Values below 10ml/sec and a prolonged trace are suggestive of outlet obstruction, which may be anatomical (meatal stenosis, PUV) or functional (detrusor sphincter dyssynergia). Sometimes a staccato patter of uroflow is seen in these children with outlet obstruction. Over active bladder following prolonged obstruction causes a super normal curve while a lazy bladder causes a flat curve. 

Uroflow can be combined with post void residual volume measurements to exclude obstructive uropathy. When combined with EMG, it becomes a very useful tool to assess sphincter incoordination. Uroflow EMG is becoming a norm in children with recurrent UTI and VUR these days to identify underlying dysfunctional voiding. It can also be used to provide biofeed back in dysfunctional voiders, to show how to relax the sphincters while voiding.

Indications for Urodynamics

Urinary incontinence in children can be mainly divided in to three etiological categories; neuropathic, uropathic and non neuropathic bladder sphincter dysfunction. The indications for urodynamics in children include

• Neurogenic bladder dysfunctions following

       – Myelomeningocele, Spina bifida, sacral agenesis
       – Pelvic surgery for anorectal malformations
       – Transverse myelitis sequelae
       – Sacrococcygeal teratoma and other spinal tumour excision

• Urinary outflow obstructions
       – PUV, meatal stenosis following circumcision, Hypospadias
       – Traumatic urethral strictures

• Intractable bladder dysfunction with
      – Upper tract changes
      – Renal functional impairment

Urodynamics in Children: Preparation

Rarely is any premedication given either orally or intramuscularly, but the child is conscientiously attended to in order to minimize his or her fears. If possible, the child is instructed to come to the urodynamic suite with a full bladder to obtain an initial representative uroflow. The child is catheterized with a 8F double-lumen urodynamic catheter after a small amount of liquid Xylocaine (1%) has been injected into the urethra and held in place for a moment or two. 

Although urethral catheters are tolerated in newborns and adolescent children, children of the age group 3-10 find it very distressing and some times do not cooperate well. Once they start crying, it becomes difficult to obtain proper trace and artefacts start appearing. To circumvent this problem, it is becoming routine these days to insert suprapubic lines the previous day under GA. This is combined with a cystoscopy to assess the bladder status and exclude any obstructive pathology.

It is important to have rectal catheters to obtain a good abdominal pressure profile since children may cry, strain and cause a lot of artefacts during the procedure. To obtain a proper abdominal pressure the rectum must be empty. Since children with neurogenic bladder may also suffer from constipation it is essential to prescribe laxatives or enema for 2-3 days prior to the procedure.

Urodynamics in Children: Technical Differences

First, the intravesicular pressure is recorded. Then the bladder is drained and the residual urine is carefully measured. (Figure 2) Sometimes it is necessary to aspirate the catheter to get accurate information on the volume of residual urine. The rate of bladder filling per minute usually is selected by first calculating the child's predicted capacity and then dividing the result by 10 in order to fill the bladder slowly. 
The average capacity in millilitres for a child older than 2 years of age is determined by Koff’s Formula. In younger children weight of the child is used to assess this. 

Koff’s Formula: Volume (ml) = (Age + 2)30 ml

Fairhurst Formula: Volume (ml) = Wt(kg) x 7.5 ml

There are many other formulae to measure bladder capacity, however it is the author’s preference to use the above formulae due to its simplicity. It has been shown that more rapid filling rates may yield falsely low levels of detrusor compliance and may minimize uninhibited contractions in an attempt to avoid this problem, the bladder is filled slowly with saline warmed to 37°C. When it is important to determine very mild degrees of hyper tonicity, even slower rates of filling are used to measure its true incidence. During filling, it is helpful to try to divert the child's attention by asking unrelated questions, reading a story aloud, or showing a movie or cartoon. If the examiner wishes to elicit uninhibited contractions, the child is asked to cough; alternatively, a cold solution may be instilled at a rapid rate. 

In most of the centres supine position is preferred for urodynamics in children. In adolescent and cooperative children, sitting position is possible. Video urodynamics is essential in children as most of them have associated VUR or sphinteric incompetence. Non compliance may be missed in these children unless simultaneous video is undertaken. Although needle EMG electrodes are the standard recommendation, EMG patch electrodes are equally informative and less traumatic. Simultaneous EMG recording is very informative in children with voiding dysfunction and neurogenic bladder. 

Urodynamics in Children: Parameters measured

During Filling the following parameters are measured

• Bladder sensation, capacity at first desire; total Bladder capacity
•  Functional bladder capacity (Bladder volume with detrusor pressure <40cm)
•  Bladder compliance ∆V / ∆P
•  Uninhibited contractions (Figure 3)
•  Leak point pressure (pressure at which initial major leak occurs)
•  Detrusor Sphincter Dyssynergia: Increasing EMG activity before bladder contraction or with increase in filling (Figure 3) 
  

•  Whether the contraction is sustained until voiding is complete 
•  Whether abdominal pressure has been used to facilitate the emptying process 
•  Whether sphincter remained quiet throughout the voiding process on EMG
•  Whether the flow rate curve was bell-shaped 
•  Voided volume vs. with filled volume 
•  Whether the patient voided to completion (PVR)

Urethral Pressure Profile (UPP)

For measuring UPP a triple lumen catheter is required. This needs to be positioned accurately before the start of the procedure. It measures the passive resistance of a particular point within the urethra. Many factors contribute to this resistance, including the elastic properties of the tissues surrounding the lumen and the tension generated by the smooth and skeletal muscles of the urethra, which are constantly changing during the micturition cycle It is difficult to extrapolate data obtained when the bladder is empty and apply it to periods when the bladder is full, is responding to increases in abdominal pressure, or is in the process of emptying . Failure to recognize this fact leads to false assumptions and improper treatment. In view of this many centres use leak point pressure (LPP) (pressure at which leak occurs) instead of UPP

Video Urodynamics

Video urodynamics has gained popularity since its introduction in 1970. Visualization of the bladder and bladder neck during filling and of the urethra during voiding has added a dimension for more accurately integrating all aspects of lower urinary tract function and characterizing an abnormality. Incompetence of the bladder neck or pelvic floor or the location of any posterior urethral obstruction can be correlated with pressure measurements recorded simultaneously. Sometimes, aberrations noted on pressure monitoring of sphincter EMG tracings can be confirmed, enhancing these findings.

Ambulatory urodynamics 

This technique measures natural fill cystometry with the help of an ambulatory urodynamic monitor linked to a notebook computer. It has become available and feasible in children with the development of micro transducers mounted on small catheters positioned in the bladder. Data can be stored up to 24 hours at a time and analyzed later. When combined with techniques to monitor wetness, it can be a very effective way to determine the cause of incontinence. Intravesical pressures are measured via 5F suprapubic catheters inserted 24 hrs earlier. Factors assessed include: activity during fill, voiding pressures and flow, uroflow, PdMax, PVR, emptying efficiency (voided volume/capacity).

Urodynamics in Dysfunctional Voiding

The clinical features of bladder hyperactivity—urgency, frequency, and precipitate voiding—occur in about 60% to 70% of affected patients. These symptoms characterize the commonly occurring urgency-incontinence syndrome in children whose bladder instability elicits a weak or absent sphincteric response. Incontinence may vary in severity. Urodynamic study is not required in most cases for diagnosis; it may be safely reserved for children who fail an empiric trial of anticholinergic drug therapy. When performed, it confirms bladder instability with minimal evidence of dyssynergia or obstruction. Consequently, UTI is not a major feature of this subcategory. Ultrasonography of the urinary tract is characteristically normal except for bladder wall thickening, and VCUG, if performed to evaluate for UTI, typically demonstrates a smooth-walled bladder with capacity nearly appropriate for age. Children with bladder instability void normally to completion without residue, so the occurrence of a large residual urine volume should make the diagnosis suspect. One sign that is almost pathognomonic is Vincent's curtsey, so named because the child squats with the heel of one foot compressing the perineum and urethra to prevent urinary leakage. 

The small-capacity, hypertonic bladder subcategory is characterized clinically by more prominent symptoms and urodynamically by more obvious bladder-sphincter dyssynergia causing functional obstruction. UTIs commonly occur and are associated with prominent urgency and incontinence that characteristically persist after eradication of the infection. Typically, functional bladder capacity is observed to be reduced during urodynamic study or cystography. This appears to be the result of chronic repetitive functional obstruction during unstable contractions, which is reflected in radiographic studies that may show bladder wall thickening, saccules, and diverticula. Very severe spectrum of this disorder represents Hinman’s Syndrome, the non neurogenic neurogenic bladder.

Urodynamics in Neurogenic Bladder

A combination of bladder contractility and external sphincter activity results in three categories of lower urinary tract dynamics: synergic (19%), dyssynergic with and without detrusor hyper tonicity (45%), and complete denervation (36%). In the past these bladders are classified in to contractile, mixed and acontractile bladders. DSD occurs when the external sphincter fails to decrease or actually increases its activity during a detrusor contraction or a sustained increase in intravesical pressure as the bladder is filled to capacity. Frequently, a poorly compliant bladder with a high intravesical pressure occurs in conjunction with a dyssynergic sphincter, resulting in a bladder that empties only at high intravesical pressures Complete denervation is noted when no bioelectric potentials are detectable in the region of the external sphincter at any time during the micturition cycle or in response to sacral stimulation or a Credé manoeuvre. 

The categorization of lower urinary tract function in this way has been extremely useful because it reveals which children are at risk for urinary tract changes, which ones should be treated prophylactically, which need close surveillance, and which can be monitored at greater intervals. Aggressive observation and prompt intervention is essential to prevent upper tract deterioration in these children. A typical child for bladder augmentation is the one with small capacity non compliant bladder with deteriorating renal function and worsening hydronephrosis.

Urodynamics in Posterior urethral valves (PUV)

For many years, it has been recognized that most children treated for urethral valves have varying degrees of abnormal bladder function. Most often, this abnormality presents as urinary incontinence, with half of the boys still damp during the day well into late childhood. In the past, investigators assumed that this incontinence was primarily a result of incompetent sphincter function. However, with the application of modern urodynamics to paediatric urology, it has become increasingly obvious that primary vesical dysfunction is commonly present in association with urethral valves, that this vesical dysfunction does not necessarily abate after relief of the obstruction, and that, ultimately, this abnormal bladder function has a significant impact on prognosis. 

Three different types of vesical dysfunction has been categorised with the help of urodynamics. These include: bladder instability; non compliant bladder; and myogenic failure. Progressing from instability during infancy to findings more consistent with myogenic failure in older boys has been seen during observations. Regular monitoring with base line urodynamics starting from the age of four is becoming the norm these days. 

Urodynamics in Vesico ureteric reflux VUR

Studies of urodynamics are indicated for any child with a suspected secondary cause for reflux (e.g., valves, neurogenic bladder, non-neurogenic neurogenic bladder, voiding dysfunction). This is becoming even more important with the realization that a significant number of patients with reflux have bladder instability, inadequate urethral relaxation during voiding, and voiding dysfunction. Complete evaluations include cystometrography, flow studies with electromyography, and video recordings. Valid urodynamic values can be difficult to obtain in the face of massive reflux. When this is the case, ureteral occlusion catheters can be placed to eliminate the dampening effect of deleterious pressures that reflux offers the bladder. 
Conclusion

Urodynamics in children require several adaptations in view of the small bladder size and patient size. As stressed earlier, it should not be take lightly and should be supervised by the physician in charge of the patient. Because of the invasive nature and inherent sepsis risk, urodynamics should be recommended only after non invasive tests like uroflowmetry have been exhausted. Interpretation of urodynamics in children should be done cautiously as it can have a lot of fallacies and artefacts. EMG, rectal catheters and video are important tools in children to minimize artefacts. Identifying the high risk bladder, the small capacity non compliant bladder with high leak point pressure is of paramount importance. Prompt medical or surgical intervention with clean intermittent catheterisation (CIC) will save these children from renal failure in the long term. 

Figure 1. Normal Uroflowmetry 

Figure 2. Principles of Urodynamics

GLOSSARY


BPH - Benign Prostatic Hyperplasia
CIC - Clean Intermittent Catheterization
DO - Detrusor Overactivity
EMG - Electromyography
OAB - Overactive Bladder
Q max/PFR - Peak Flow Rate
Q ave - Average Flow Rate
UDS - Urodynamic Study
Vcomp - Voided Volume
PVR - Post Void Residue