Measurement of the bladder pressure is one component of a urodynamic study. Normally, the viscoelastic properties of the bladder allow it to store increasing volumes of urine with little change in bladder pressure (compliance) until capacity is reached. There are two interrelated components of bladder compliance, the passive characteristics of the connective-tissue elements of the bladder and the active properties of the smooth muscle in the bladder. 
During normal voiding, a coordinated series of events occurs: concurrent relaxation of the pelvic floor muscles and external sphincter and relaxation of the bladder neck, followed immediately by sustained detrusor contraction. The resultant uroflowmetry pattern recorded shows a bell-shaped flow curve with a rapid rise to peak amplitude. Following voiding, the bladder pressure decreases rapidly, the pelvic floor muscles contract, and the bladder neck closes. Phasic increases in detrusor pressure (detrusor overactivity) may be associated with frequency, urgency, and urgency urinary incontinence in patients with idiopathic overactive bladder and neurogenic detrusor overactivity (see image below).
Poor compliance, defined as significant increases in bladder pressure with small increments in bladder volume, may lead to incontinence and place the upper urinary tract at risk for damage (see image below). Poor compliance is most commonly seen in patients with spinal cord injury (traumatic, compression by tumor, or related to surgical interventional for spinal malignancy) and those with myelomeningocele. Poor compliance may also occur after pelvic irradiation in both adults and children or after radical hysterectomy with or without adjuvant radiation therapy and can result from bladder fibrosis and contracture in patients previously treated for hemorrhagic cystitis caused by the use of oxazaphosphorine-alkylating agents. 
In patients with end-stage renal disease, bladder compliance decreases the longer the duration of dialysis continues.  Moreover, the presence of anuria contributes to further decreases in bladder capacity and compliance.
In patients with suspected bladder outlet obstruction, a pressure/flow study is used to confirm the diagnosis.  In this study, the detrusor pressure required to void is plotted against the resultant flow rate. A finding of a high voiding detrusor pressure with a low flow rate indicates bladder outlet obstruction.
Lastly, in patients with neurogenic bladder dysfunction, the detrusor leak point pressure is used to assess the risk for upper urinary tract damage. [5, 6] A detrusor leak point pressure of more than 40 cm H2 O is associated with an increased risk of upper urinary tract damage.
Abdominal pressure (Pabd): The pressure measurement obtained from a rectal catheter during a urodynamic study
Bladder compliance: The relationship between change in bladder volume and change in detrusor pressure (ΔDV/ΔDP). (The International Continence Society recommends two standard points be used for compliance calculations: (1) the detrusor pressure at the start of bladder filling and the corresponding bladder volume (usually zero) and (2) the detrusor pressure and corresponding bladder volume at cystometric capacity or immediately before the start of a detrusor contraction that causes significant leakage.)
Detrusor leak point pressure (DLPP): The lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increase in abdominal pressure.
Detrusor overactivity: A urodynamic observation characterized by involuntary detrusor contractions during the filling phase, which may be spontaneous or provoked
Detrusor pressure (Pdet): The true bladder pressure. It is calculated by subtracting the abdominal pressure (Pabd), measured with a rectal catheter, from the vesical pressure (Pves), measured with a catheter in the bladder. Pdet = Pves - Pabd
Filling cystometry: The method by which the pressure/volume relationship of the bladder is measured during bladder filling
Intravesical pressure (Pves): The pressure recording from a urodynamic catheter placed inside the bladder
Physiologic filling rate: A filling rate (during cystometry) that is less than the predicted maximum (see definition below)
Predicted maximum: The maximum rate of urine production, calculated using the predicted maximum body weight in kg divided by 4 and expressed as mL/min
Pressure at maximum flow: The lowest pressure recorded at maximum measured flow rate
Pressure/flow study: Measures the detrusor pressure required to void and the flow rate a given bladder pressure generates (The study can be useful in the evaluation of suspected bladder outlet obstruction.)
In patients with neurogenic lower urinary tract dysfunction (ie, spina bifida, spinal cord injury), bladder pressure monitoring as part of a urodynamic study is important to ensure that bladder pressures during filling remain within the safe range (< 40 cm H2 O) to decrease the risk of upper urinary tract damage.
In male patients with lower urinary tract symptoms, bladder pressure measurements and flow rates during voiding (pressure/flow study) are used to determine the presence of bladder outlet obstruction.
In patients with refractory lower urinary tract symptoms, bladder pressure monitoring can determine if involuntary bladder contractions (detrusor overactivity) is occurring during bladder filling.
In women with lower urinary tract symptoms after incontinence surgery, bladder pressure monitoring during voiding can help identify postoperative bladder outlet obstruction.
There are several contraindications to the use of bladder pressure to assess intra-abdominal pressure (IAP).  Bladder pressures should not be used in patients with intraperitoneal adhesions, pelvic fractures, abdominal packs, pelvic hematomas, or neurogenic bladder (including patients with spinal shock and Parkinson disease). These conditions may alter pressure readings in the bladder owing to a loss of bladder compliance or the inability of the bladder wall to move freely, leading to inaccuracies in measurement. In addition, the morbid obesity, pregnancy, or ascites can lead to chronic elevations in IAP, further complicating the diagnosis of IAH. 
The AbViser is contraindicated in patients with a history of bladder rupture or bladder wall repair within the prior 3 months.  In addition, the AbViser must be replaced at the time of urinary catheter and/or tubing change.
The Holtech Foley manometer should not be used for more than 7 days and should be changed when the Foley catheter or urine collection device is changed. 
Of note, there does not appear to be an increased risk of nosocomial urinary tract infection with systems using a closed transducer.
Urodynamics should not be performed if the patient has or is actively being treated for a urinary tract infection. In patients on clean intermittent catheterization, bacteria are often present in the urine (colonized) in the absence of an acute infection. A urine dipstick test is helpful; the presence of significant pyuria would suggest a urinary tract infection, and the procedure should be canceled and urine cultured.
In addition, a significant amount of stool in the rectal vault interferes with the abdominal pressure monitoring and therefore requires management prior to proceeding with the study.
Lastly, if the patient has cardiovascular issues and/or orthopedic hardware in place, the patient or the physician providing the cardiovascular and/or orthopedic care should be consulted regarding the need for prophylactic antibiotics.
Undergoing a urodynamic study can provoke anxiety in a patient. Issues such as modesty and concern regarding discomfort during and after the procedure may be worrisome to the patient.
It is ideal for the room where the procedure will be performed to be quiet and separate from busy patient flow areas. Avoid loud music and interruptions by other staff during the procedure. Also, all reasonable attempts to maintain patient modesty should be undertaken.
Lastly, it is important to engage the patient during the procedure, as it is imperative to document what the patient is sensing during the procedure (ie, urgency at the time of an involuntary detrusor contraction, sensation when he/she would first think of using the restroom, when he/she feels a strong urge to void that would prompt voiding).
In patients who void volitionally and are not on clean intermittent catheterization, urinalysis is recommended prior to urodynamic evaluation, as well as urine culture and treatment if urinalysis findings are positive.
In patients with an indwelling catheter and/or who are on clean intermittent catheterization, a urinalysis is obtained. If significant pyuria is present and/or the patient has symptoms of a urinary tract infection, a urine culture should be obtained.
The literature neither supports nor refutes the use of prophylactic antibiotics during IABP monitoring.
Urinary tract infection may occur after urodynamic evaluation. A prospective study evaluating pre-urodynamic urine cultures and urine cultures obtained on the third day after a urodynamic study demonstrated that, of the 35 women involved, 23 (66.7%) showed no evidence of a urinary tract infection before or after urodynamic evaluation. Of the remaining 12 women, 6 had bacteriuria in the post-cytometry urine sample, 2 women had a urinary tract infection in the pre- and post-cystometry urine samples, 3 women had pyuria with mixed organisms and repeat urine culture was negative for a urinary tract infection, and one woman (2.9%) developed a urinary tract infection following the urodynamic study. 
Bombieri et al performed a prospective study evaluating the incidence and natural history of urinary tract infections in 214 women undergoing urodynamic evaluation and noted a bacteriuria incidence of 7.9% after urodynamics.  Of the 17 women with bacteriuria, it was found to be transient in 4, persistent in 9, and late-developing in 4. Only one of the 17 women had symptoms. Advanced age was the only variable associated with bacteriuria after urodynamic evaluation. Thirty-four percent (34%) of the women undergoing urodynamic evaluation had irritative symptoms after the study.
Peschers et al performed a single blind prospective randomized study comparing a single postprocedure dose of cotrimoxazole to placebo after urodynamics.  Seventy women were prescreened to rule out a urinary tract infection and then underwent multichannel urodynamics with a single dose of cotrimoxazole or placebo after the procedure. Two women in the treatment group (2 of 37, 5.9%) and 2 in the placebo group (2 of 33, 6.1%) developed a urinary tract infection after the urodynamics. Unfortunately, the power of the sample size was too small to draw conclusions as to the efficacy of prophylaxis.
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- Periprocedural Care
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