What is the role of CMG in the workup of overactive bladder (OAB) in children?

Updated: Apr 01, 2019
  • Author: Pamela I Ellsworth, MD; Chief Editor: Edward David Kim, MD, FACS  more...
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Cystometrography (CMG), also known as filling cystometry, is the component of the urodynamic study that is used to assess the bladder during filling. CMG provides information on the pressure/volume relationship of the bladder during bladder filling.

The bladder should be filled with body-temperature 0.9% sterile saline at a rate of 5-10% of the child’s expected bladder capacity per minute to a maximum rate of 10 mL/min. Contrast material may also be used if fluoroscopic imaging is planned. The bladder capacity is measured during filling cystometry. The cystometric bladder capacity is the bladder volume at the end of the filling CMG, when the child is given permission to void.

The cystometric capacity is the volume voided together with any residual volume. The maximum cystometric capacity in patients with normal sensation is the bladder volume at which the patient feels that he or she can no longer delay voiding (strong desire to void).

The term bladder compliance refers to the relationship between the change in bladder volume and the change in detrusor pressure.

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