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Overview

Practice Essentials

Bladder pressure is measured during all phases of a urodynamic study to assess for compliance and detrusor overactivity during filling and bladder outlet obstruction and decreased contractility during voiding. Various measurement techniques have been used, including manometry, “homemade” indwelling urinary catheter systems, and commercial intra-abdominal pressure (IAP) monitoring devices.

Indications

Indications for bladder pressure measurement include the following:

To identify bladder outlet obstruction in patients with lower urinary tract symptoms.
To detect detrusor overactivity during bladder filling in patients with refractory lower urinary tract symptoms.
To assess the risk of upper urinary tract damage in patients with neurogenic bladder.

Contraindications

A urodynamic evaluation should not be performed in a patient with a urinary tract infection. In addition, a significant amount of stool in the rectal vault interferes with abdominal pressure monitoring.

Bladder pressure measurement should not be used to assess IAP in patients with intraperitoneal adhesions, pelvic fractures, abdominal packs, pelvic hematomas, or neurogenic bladder. Note that morbid obesity, pregnancy, or ascites can lead to chronically elevated IAP.

Procedure planning

For patients who void volitionally, urinalysis is recommended before urodynamic evaluation, as well as urine culture and treatment if urinalysis findings are positive. In patients with an indwelling catheter or who are receiving clean intermittent catheterization, a urinalysis is obtained. If significant pyuria is present or the patient has symptoms of a urinary tract infection, a urine culture should be obtained.

Urinary tract infection may occur after a urodynamic study; however, the literature does not support the routine use of prophylactic antibiotics.^[1]

Forms of cystometry

A simple cystometry can be performed with a catheter and a syringe or manometer held 15 cm above the symphysis pubis. The advantage of this method is that it is inexpensive and readily available; however, exact measurements of bladder pressure and determination of compliance are not possible.

Single-channel cystometry involves recording intravesical pressure during filling with a single catheter. A major disadvantage of the single-channel technique is that increases in IAP may result in elevated detrusor pressure readings.

Multichannel cystometry is performed with the use of a second catheter to measure IAP. The catheter may be placed in the vagina or, more commonly, the rectum.

Bladder pressure assessment methods

A limitation of manometry via a Foley catheter is the need for repeated breaking of the closed system (Foley-drainage bag seal) to obtain a pressure reading.

Limitations of “homemade” indwelling urinary catheter systems include concerns with sterility and lack of quality control, standardization, and data reproducibility.

Commercially available IAP monitoring devices include the following:

AbViser
Bard IAP monitoring device
UnoMeter Abdo-Pressure kit

Research is ongoing with implantable bladder pressure monitors.^{[2, 3]}

Bladder pressure monitoring in abdominal compartment syndrome

In patients at risk for abdominal compartment syndrome, the clinical examination is unreliable for assessing IAP.^[4] Thus, bladder pressure monitoring is used as a surrogate for IAP monitoring.^[5]

The most reliable method for monitoring IAP is via pressure transduction through a catheter within the peritoneal cavity.^[6] Less invasive options include pressure transduction through a tube placed in the stomach, bladder, or rectum.

Background

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 2 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.^[7]

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).

Detrusor overactivity.

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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.^[8]

Decreased bladder compliance.

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In patients with end-stage renal disease, bladder compliance decreases the longer the duration of dialysis continues.^[9]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.^[10]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 of upper urinary tract damage.^{[11, 12]}A detrusor leak point pressure of more than 40 cm H₂O is associated with an increased risk of upper urinary tract damage.

Definitions

Abdominal pressure (P_abd): 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 2 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 an 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 (P_det): The true bladder pressure. It is calculated by subtracting the abdominal pressure (P_abd), measured with a rectal catheter, from the vesical pressure (P_ves), measured with a catheter in the bladder. P_det = P_ves - P_abd.

Filling cystometry: The method by which the pressure/volume relationship of the bladder is measured during bladder filling.

Intravesical pressure (P_ves): 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.)

Indications

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 H₂O) 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) are 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.

Contraindications

There are several contraindications to the use of bladder pressure to assess intra-abdominal pressure (IAP).^[13]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, 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.^{[14, 15]}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.^[16]

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.^[17]

In addition, a significant amount of stool in the rectal vault interferes with 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.

Best Practices

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, sensation when he/she feels a strong urge to void that would prompt voiding).

Procedure Planning

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.

Complications

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.^[18]

Dass et al performed a prospective study to evaluate the incidence of bacteriuria after urodynamic studies in 140 women.^[19]None of the participants received prophylactic antibiotics. Thirty women (21.4%) had asymptomatic bacteriuria before the urodynamic study and were excluded. Among the remaining 110 women, infection occurred in 4 (3.6%) after the urodynamic study. Advanced age (older than 60 years) was found to be a significant risk factor for infection.

In a randomized, controlled, double-blind trial, Hirakauva et al evaluated the efficacy of antibiotic prophylaxis with levofloxacin, trimethoprim-sulfamethoxazole (TMP-SMX), or nitrofurantoin in 217 women.^[20]All patients had negative urine cultures before the urodynamic study. A urine culture performed 14 days after the study revealed asymptomatic bacteriuria in 5 women who received placebo, one who received levofloxacin, one who received TMP-SMX, and one who received nitrofurantoin. Symptomatic bacteriuria occurred in one woman in the placebo group. The investigators concluded that antibiotic prophylaxis does not reduce the incidence of urinary tract infection.

In general, the literature neither supports nor refutes the use of prophylactic antibiotics during intra-abdominal pressure monitoring to prevent urinary tract infection.^[1]

Periprocedure

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