How is urodynamic study performed in bladder pressure assessment?

Updated: Jan 16, 2020
  • Author: Pamela I Ellsworth, MD; Chief Editor: Bradley Fields Schwartz, DO, FACS  more...
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The steps below are part of a urodynamic study, and bladder pressure is being measured during all phases of the study to assess for compliance and detrusor overactivity during filling, bladder outlet obstruction during voiding, and decreased contractility during voiding.

Patients who void volitionally are asked to arrive with a full bladder. A bladder scan is used to document the bladder volume. If the patient has at least 150 mL in his/her bladder and has the desire to void, a uroflow is obtained. The patient is then catheterized with a urodynamic catheter, typically a 10F or smaller, via sterile technique with Xylocaine topical jelly, and the postvoid residual is recorded. A rectal catheter is then placed.

Electromyography (EMG) electrodes, often patch electrodes (they are more comfortable and easier to use), are applied to the perineum. The transducers are equalized according to the recommendations of the individual urodynamic machine/company.

A cough test is performed to ensure that the catheters are functional.

The bladder is filled with room-temperature sterile saline (or contrast material if videourodynamic evaluation is being performed). The physiologic flow rate is used (see definition), since cold water and rapid filling can provoke involuntary detrusor contractions. Furthermore, supraphysiologic filling rates can result in loss of compliance.

The procedure may be performed with the patient sitting, semi-erect, or standing.

The catheters are calibrated so that zero corresponds to atmospheric pressure. If detrusor overactivity is noted at the onset of bladder filling, the rate is decreased.

The patient is asked to comment when he/she feels the first urge to void and whether he/she has any sensation of urgency or is leaking during filling. When the patient feels that he/she has reached capacity, inflow is stopped, and the patient is permitted to void. The patient then voids into the uroflow meter, and the flow pattern and EMG activity are recorded. The maximum detrusor pressure during flow, as well as the maximum flow rate, is often assessed.

A pressure flow study is generated by plotting the various bladder pressures and corresponding flow rates during voiding. Once voiding is complete, the bladder is emptied, and, if present, the postvoid residual is recorded.

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