Technical Aspects

Urodynamic laboratories use various instruments and techniques (Figure 3-2.5). There are a variety of catheters, such as microtip, air-charged, fiberoptic, and water-infused. Our department uses water-infused catheters. Microtip catheters are primarily used by urogynecologists. Intravesical pressure is measured by placing a catheter into the bladder that both fills the bladder and detects the pressure. The catheter has two lumens: one for filling and another for monitoring pressure. A triple-lumen catheter is used when urethral pressure is simultaneously monitored. Because the rectum and bladder are in close proximity and the intraabdominal pressure experienced by both organs is equal, abdominal pressure is measured with a rectal balloon catheter. Vaginal pressure monitoring may be used in women; however, the vagina is subject to many anatomical changes that may alter pressure transmission. The vagina should be used if there are anatomical changes of the rectum. The rectal tube should be soft and moderately sized, with a maximally distensible balloon. After instrumentation, the bladder is filled. Historically, both liquid and gas have been used as the filling medium. Gas is inexpensive and allows rapid filling. However, it is unphys-iologic, compressible, and easily provokes detrusor overactivity, and is not suitable for studying voiding and leakage. The liquid filling medium may be saline, water, or radi-

Pves r^_Pdet

Figure 3-2.4. Urodynamic algebra.

Figure 3-2.5. Multichannel urodynamic unit.

Figure 3-2.5. Multichannel urodynamic unit.

ographic contrast. The bladder can be filled either ante-gradely or retrogradely. The latter is used more often in the office setting because of time considerations. The temperature of the liquid should be either room or body temperature. According to the International Continence Society (ICS), the filling rate is considered fast (>100mL/min), medium (10-100mL/min), or slow (<10/min).6 Natural bladder filling averages 1 to 2 mL/min. Rapid infusion may induce involuntary contractions or give the appearance of decreased compliance. A rapid infusion rate is used to provoke occult detrusor instability,to provoke contractions in a patient who did not demonstrate them at a slower infusion rate, or to determine the presence of sensation in a large bladder.8 Slow infusion is used for children and adults with small functional capacity or unusual sensitivity to filling at medium filling rates. At Cleveland Clinic Florida, we use room-temperature sterile water as a filling medium, with a filling rate of 60 mL/min in adults and 30 mL/min in patients with suspected overactive (unstable) bladder. A triple-lumen 7-French catheter is used for filling and pressure measurements. Catheter sizes larger than 8 French are discouraged, because they may impede voiding. The patient's bladder is filled in the supine or sitting position, and the patient is then asked to void in either a standing or sitting position.

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