The Guiding Significance of Urodynamic Studies for Clean Intermittent Catheterization (CIC)
01
Urodynamic studies can be divided into non-invasive and minimally invasive methods.
Non-invasive methods: Measurement of uroflow rate combined with bladder residual volume by ultrasound is convenient and can guide the frequency and interval of clean intermittent catheterization (CIC).
Minimally invasive methods: Techniques such as cystometry and pressure-flow studies (CMG/PFS) allow more precise evaluation of CIC indications and contraindications. They measure parameters including maximum cystometric bladder capacity, bladder compliance, detrusor overactivity during filling, and weakened detrusor contraction during voiding, thereby guiding CIC use and evaluating its efficacy.
Application:
● The uroflow-residual urine method for CIC is suitable for patients who retain partial voluntary voiding function.
● Free uroflow measurement is a simple, non-invasive test that objectively reflects lower urinary tract voiding function. Uroflow represents the entire bladder emptying process and provides insight into the function of the bladder, bladder neck, urethra, and urethral sphincter, as well as their interactions during voiding.
Key parameters observed:
● Maximum flow rate (Qmax)
● Average flow rate
● Voided volume
● Voiding time
● Flow duration
● Curve pattern
It is recommended to report uroflow results using maximum flow rate in combination with voided volume and residual urine, with flow rates precise to 1 mL/s and volumes to 1 mL.
02
Post-void residual urine (PVR) refers to the urine remaining in the bladder after voiding. There are several methods to measure PVR, including direct catheterization, color Doppler ultrasound, and portable ultrasound devices.
● Direct catheterization immediately after voiding (within 5 minutes) provides the most accurate measurement, using a graduated container to measure urine volume. However, catheterization is invasive and carries a risk of urinary tract infection. During urodynamic studies, if cystometry is performed, catheterization can be used to measure residual urine.
● Transabdominal ultrasound is a simple, non-invasive method to determine PVR, though it requires access to an ultrasound device.
Clinical significance:
● Persistently elevated PVR usually indicates increased bladder outlet resistance, decreased detrusor contractility, or a combination of both.
● A normal PVR does not rule out urethral obstruction or detrusor-sphincter dyssynergia; therefore, PVR alone cannot distinguish whether residual urine is due to detrusor dysfunction or bladder outlet obstruction (BOO).
Detrusor underactivity is characterized by decreased contraction strength (myogenic decompensation) and often by poor maintenance of contraction. This condition may be primary or idiopathic, or secondary to BOO, infrequent voiding, or neurogenic bladder dysfunction.
Additional considerations: Sensory threshold, first sensation of bladder filling, cystometric bladder capacity, and PVR are often interrelated indicators, reflecting the complex interaction between bladder sensation, contractility, and outlet function.