Cystometry

Did You Know?

• Cystometric analysis helps determine the source of urinary problems and a normal CMG effectively rules out primary vesical dysfunction.
• The procedure is contraindicated in patients with an active UTI because results may be skewed and the infection may spread.
• Potential risks include trauma to the bladder and urethra, which may result in hematuria.

Procedure

The procedure lasts between fifteen minutes and one hour. One or two catheters are inserted into an emptied bladder through the urethra. With two catheters, one transfers liquid and the other is a manometer; a single specialized catheter can perform both functions. An additional rectal catheter may be placed. The bladder is filled with saline, and the patient is asked to note when liquid is felt, when the bladder feels full, and when urgency to void occurs. The patient then voids while flow and pressure are recorded and plotted against each other.

Results

A cystometrogram is the main output of cystometry, plotting bladder volume on the horizontal axis against internal pressure on the vertical. In healthy individuals, the graph shows a series of spikes, with their lowest points tracing a curve that looks like exponential growth. These spikes mark bladder contractions from the micturition reflex. The lower edge of the plot indicates the pressure required to urinate. For the first few hundred milliliters, very little pressure is needed. Pressure then rises for the next 200 to 300 milliliters, and beyond that, it increases steeply.