Traces: Making Sense of Urodynamics Testing -- Part 3

Evaluation of Bladder Filling/Storage Functions



Urol Nurs. 2011;31(3):149-153. 

In This Article

Bladder Capacity: Definition

Bladder capacity may be defined in three contexts. Anatomic bladder capacity (maximum anesthetic bladder capacity) is defined as the volume that can be infused into the bladder during a cystoscopic procedure while the patient is under anesthesia (Abrams et al., 2002). This maneuver can be used to evaluate maximal capacity and bladder wall compliance in patients with interstitial cystitis or other painful disorders of the bladder. Because it is measured under spinal or general anesthesia, it tends to be significantly greater than both functional and cystometric capacity.

Functional bladder capacity is defined as the volume of urine accumulated in the bladder prior to voluntary micturition; it is typically evaluated by measuring the maximum, mean, or median voided volume recorded on a bladder diary (Haylen et al., 2010). Because functional bladder capacity represents the intravesical volume present when an individual makes a decision to urinate, it is prone to variability based on multiple factors, such as the magnitude of the desire to urinate and individual judgment based on considerations related to the availability of a toilet in the near future. Fitzgerald, Stablein, and Brubaker (2002) evaluated voiding diaries in 300 women with differing racial and ethnic backgrounds, and reported that the median voided volume was 330 ml. Latini, Mueller, Lux, Fitzgerald, and Kreder (2004) analyzed multiple variables from voiding diaries in 284 men without bothersome lower urinary tract symptoms and found that the median voided volume was 382 ml. Van Doorn and associates (2011) evaluated voiding parameters in 1688 Dutch men and found a similar mean voided volume in adult men of 400 ml. All three groups reported that mean voided volumes tended to be small in older adults, although 24-hour volumes remained unchanged. Van Doorn and associates (2011) followed patients longitudinally over a period of 6.5 years and found that median voided volumes declined from 400 ml to a median value of 245 ml as men aged. Fitzgerald et al. (2002) and Latini and colleagues (2004) also reported that median voided volumes varied based on racial or ethnic background. Assessment of functional capacity provides an estimate of the average or maximal voided volume, but it tends to be smaller than cystometric capacity. Technical factors, such as the use of continuous, supraphysiologic fill rates during urodynamics testing as compared to slower, intermittent natriuretic filling may account for this difference, including differences in filling rates (Klevmark, 2002). However, the largest difference may be attributable to the nature of the filling CMG, which attempts to reproduce lower urinary tract symptoms, such as urgency or urinary incontinence, compared to the non-clinical setting where patients learn to void at lower volumes to avoid experiencing these distressing symptoms.

Cystometric capacity is defined as intravesical volume at the end of the filling CMG (Abrams et al., 2002). It may occur when permission to void is granted, when the patient experiences terminal detrusor overactivity with involuntary voiding, when the patient with low bladder wall compliance reaches his or her detrusor leak point pressure and experiences leakage, or when lower urinary tract pain results in nociceptive urgency. As noted previously, cystometric capacity is not identical to functional bladder capacity. In many cases, cystometric capacity is higher than functional bladder capacity. For example, Harris, Cundiff, Theofrastous, and Bump (1996), and Bostrom, Jennumn, and Lose (2002) reported mean cystometric capacities of 570 ml to 617 ml in adult women. In contrast to these findings, Ertberg, Møller, and Lose (2003) noted that cystometric capacity tended to be lower in a group of 60 women who were incontinent, presumably caused by the provocative nature of the filling CMG. Similarly, Yoon and Swift (1998) compared cystometric capacity with voided volumes on voiding diaries and found that the mean cystometric capacity was 14.7% lower than the maximum voided volume recorded on 24-hour voiding diaries.


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