1. Date of download: 6/29/2016 Copyright © 2016 McGraw-Hill Education. All rights reserved. Interpretation of multichannel urodynamic evaluation: cystometrogram. A catheter is placed in the bladder to determine the pressure generated within it (Pves). The pressure in the bladder is produced from a combination of the pressure from the abdominal cavity and the pressure generated by the detrusor muscle of the bladder. Bladder pressure (Pves) = pressure in abdominal cavity (Pabd) + detrusor pressure (Pdet). A second catheter is placed in the vagina (or rectum if advanced-stage prolapse is present) to determine the pressure in the abdominal cavity (Pabd). As room-temperature saline is instilled into the bladder, the patient is asked to cough every 50 mL and the external urethral meatus is observed for leakage of urine around the catheter. The volume at first desire to void and the bladder capacity is recorded. Additionally, the detrusor pressure (Pdet) channel is observed for positive deflections to determine if there is detrusor activity during testing. The detrusor pressure (Pdet) cannot be measured directly by any of the catheters. However, from the first equation, we can calculate the detrusor pressure (Pdet) by subtracting the abdominal pressure (Pabd) from the bladder pressure (Pves): Detrusor pressure (Pdet) = bladder pressure (Pves) − pressure in abdominal cavity (Pabd) I. Urodynamic Stress Incontinence (USI) Urodynamic stress incontinence is diagnosed when urethral leakage is seen with increased abdominal pressure, in the absence of detrusor pressure. a. +USI (Column 1): Abdominal pressure is generated with Valsalva maneuver or cough. This pressure is transmitted to the bladder, and a bladder pressure (Pves) is noted. The calculated detrusor pressure is zero. Leakage is observed, and diagnosis of USI is assigned. b. No USI (Column 2): Abdominal pressure is generated with Valsalva maneuver or cough. This pressure is transmitted to the bladder, and a bladder pressure (Pves) is noted. The calculated detrusor pressure is zero. Leakage is not observed. The patient is not diagnosed as having USI. II. Detrusor Overactivity (DO) Detrusor overactivity is diagnosed when the patient has involuntary detrusor contractions during testing with or without leakage. a. +DO (Column 3): Although no abdominal pressure is observed, a vesicular pressure is noted. A calculated detrusor pressure is recorded and noted to be present. A diagnosis of DO is made regardless of whether leakage is seen. b. +DO (Column 4): In this example, an abdominal pressure is observed as well as a vesicular pressure. Using only the Pabd and the Pves channels, it is difficult to tell whether or not the detrusor muscle contributed to the pressure generated in the bladder. On subtraction, a calculated detrusor pressure is recorded. Thus, a diagnosis of DO is made, again regardless of whether leakage is seen. In addition to these channels, occasionally a channel to detect electromyographic activity is used. Pabd = pressure in abdominal cavity; Pdet = detrusor pressure (calculated); Pves = bladder pressure. Legend : From: Chapter 23. Urinary Incontinence Williams Gynecology, 2e, 2012 From: Chapter 23. Urinary Incontinence Williams Gynecology, 2e, 2012