What is bladder pressure assessment?

Updated: Jan 16, 2020
  • Author: Pamela I Ellsworth, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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Answer

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. [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. Detrusor overactivity.

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. Decreased bladder compliance.

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 for upper urinary tract damage. [11, 12] A detrusor leak point pressure of more than 40 cm H2 O is associated with an increased risk of upper urinary tract damage.


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