Urodynamics in Children

Fig. 1

Room set-up. Toddler is relaxed in supine position while watching a video. Catheters are in place. Fluoroscopy unit is in position

An experienced team of professionals who are comfortable working with children is the cornerstone to a well-performed urodynamics study. Nursing staff that are welcoming to children, competent in pediatric catheter placement, and well-versed in the urodynamic set up will decrease stress for the family and child, as well as the time to conduct the study. More than one staff member may be required for a second pair of hands, especially in younger children who may be uncooperative and move frequently, which can dislodge catheters and disrupt readings. Child Life specialists can be beneficial and should be utilized frequently, if available. Parental involvement also can alleviate the child’s anxiety, and additional lead aprons are needed for them if fluoroscopy is employed.

Pre-study room set up is important to the efficiency of the study. If a child has the ability to void, a toilet should be prepared to allow uroflowmetry. It is often helpful to place the toilet behind a curtain to allow privacy. Preparation of appropriately selected catheters with maintenance of sterility, preparation of EMG electrodes or needles, sterile cups for urine collections, syringes, lubricant, and tape will make catheter placement and urine collection simple and efficient (Fig. 2). All equipment, including computerized urodynamic equipment and fluoroscopy unit, if utilized, should be ready with all connections made and functionality tested prior to patient arrival. A special radiolucent table that can be moved into the sitting position is necessary if fluoroscopy is utilized.

Fig. 2

Set-up for efficient patient preparation for study. (a) Urodynamics tower has been prepared with Pabd and Pves transducers primed with fluid. Note the blue dye added to bottle of radio-opaque contrast. Nearby prep table is readied with necessary supplies. (b) Prep tablet has both pink plastic tape to hold catheters to penis/legs, and cloth tape to cover EMG electrodes, antiseptic and adhesive solution swabs, gauze for drying, urethral dual lumen catheter with lubricant, rectal catheter with priming syringe, sterile gloves, sterile container for urine culture, and large syringe for bladder aspiration

For the sensate child or the child familiar with medical settings, catheter placement often creates the greatest anxiety and barrier to cooperation. Placement of a small amount of lidocaine 2 % jelly to the urethral meatus for a few minutes will provide an anesthetic effect and may reduce both the child’s anxiety and the initial discomfort of the catheter placement. For older boys, instillation of the jelly into the urethra with a nozzle tip can further ease the trauma of catheter insertion. Occasionally, some children are uncooperative regardless of efforts to decrease stress, and sedation or mask anesthesia for catheter and electrode placement may be necessary with urodynamics performed once the child has recovered and is fully awake. Midazolam or low-dose ketamine have been shown to provide satisfactory sedation during pediatric urodynamic studies without impacting urodynamic values [11]. Rarely, if children are combative, urodynamics may be performed under general anesthesia. However, urodynamics performed in a fully anesthetized child may be inaccurate and will not allow any assessment of voiding.

Catheter and EMG Placement

Prior to catheter and EMG placement, uroflowmetry should be performed in patients who are able to volitionally void. This differentiates pediatric urodynamics from adults because many children studied are not able to void volitionally—either because of age or the high proportion with neurogenic bladder. Parents should be instructed to adequately hydrate the child and prevent voiding while waiting for the study to begin. A bladder scan can be utilized to measure the pre-void urinary volume. While the current International Children’s Continence Society recommendations are for examination of PVR after uroflowmetry with ultrasonography [12], in the setting of urodynamics, the PVR may be measured when the urodynamic catheters are placed. Uroflowmetry may only be accurate when the voided volume is greater than 50 % of the maximum bladder volume [13]. The uroflow curve pattern should be noted, and specific types are well described [14].

All children are initially placed in the supine position for catheter and EMG probe placement. Infants, and toddlers remain in the supine position for the study as do some older children with neuropathies that prevent stability in the sitting position. While children should never be restrained, it is sometimes necessary to gently hold the lower extremities while parents help secure the upper body of the child. Children who are large enough and can void volitionally are then moved in the sitting position. This allows the child to void in a more natural position and into the collection funnel during the voiding component of the study. It is rare to conduct a study in the standing position in children. The child and equipment (particularly the C-arm, if fluoroscopy is used) should be positioned so that urinary leakage during detrusor contractions or movement is easily detectable. It is helpful to place a small amount of methylene blue or indigo carmine into the filling solution and a white gauze near the urethral meatus to better detect leakage.

Electromyography (EMG) monitoring of the pelvic floor and external sphincter can be done non-invasively via patch EMG surface electrodes or invasively via needle electrodes. These are typically placed at the 3 and 9 o’clock positions around the anal sphincter since its innervation and function is in parallel with the external urethral sphincter [1]. Patch surface electrodes are more easily and painlessly placed and, therefore, commonly used in children. For these, one should wipe the perineum clean, apply a skin adhesive (such as tincture of benzoin), and cover the patches with tape to prevent EMG artifact if they get wet with voiding, particularly if the child is supine (Fig. 3). Needle EMG is performed using a 24 gauge needle electrodes. Consideration of their use is a trade-off between their more invasive and threatening nature to a child versus their providing more accurate information on sphincter activity during bladder filling and emptying [15].

Fig. 3

Toddler male with catheters in place. Pink plastic tape is placed longitudinally on penis and urethral catheter after application of adhesive solution. This is further secured to lower abdominal wall. Rectal catheter is taped to inner thigh. EMG electrodes are placed peri-anally at 3 and 9 o’clock and covered with cloth tape

Urodynamic catheter size and type should be based on the child’s size and the questions to be answered by the study. In children a 6 Fr, 7 Fr, or 8 Fr dual lumen urethral catheter without a balloon is standard with smaller catheters used in smaller children, especially boys. Since different sized catheters may be used in multiple studies over the course of the day, technical adjustments of the pump may be required. Triple lumen catheters with an occlusion balloon to obstruct the bladder neck may be needed in cases of severe urethral incompetency. This is particularly important when planning bladder outlet surgery because, without occlusion, determination of maximal bladder capacity and pressures and the need for bladder augmentation may be inaccurate.

The bladder must be emptied after the catheter is placed into the bladder. Return of urine confirms proper placement, but no urine may be present if pre-study voiding was complete. A bladder ultrasound (or BladderScan ) may be helpful to determine if the bladder is truly empty. The residual volume is recorded. In patients that do not void, it may be faster to empty the bladder first with a larger single lumen catheter before placing the urodynamic catheter.

Rectal catheters typically measure 6–7 Fr and may be dual lumen with a balloon to detect pressure. The catheters are typically inserted 3–4 cm; however, if anal sphincter laxity is obvious (in children with low spinal lesions or history of imperforate anus surgery), inserting the catheter further may prevent expulsion of the catheter with movement or rectal contraction. In the child with an imperforate or atretic anus, the catheter may need to be placed in the colostomy to detect abdominal pressure. Having the child cough or Valsalva or pressing on the abdomen in those unable to cooperate to insure proper pressure detection in both the bladder (Pves) and rectal (Pabd) catheters is crucial before proceeding further. Special attention is required in children with neurogenic bladder who are often constipated, as mentioned previously.

Securing the catheters is perhaps one of the most critical steps in performing accurate urodynamics in children. For boys, it is most easily accomplished by placing a clear adhesive bandage around or tape along the length of the penis and catheter (Fig. 3). For girls, either can be used to secure the catheter to the upper inner thigh near the perineum to prevent dislodgement with movement. Rectal catheters should be secured similarly to the inner aspect of the gluteal crease. Regardless of the technique utilized, the catheters should double checked to ensure the child is unable to dislodge the catheter with movement or by grabbing and pulling.

If fluoroscopy is utilized, C-arm positioning must be considered so that all catheters and the meatus can be visualized and that the unit be adjusted to image both the upper and lower urinary tract during the study. In infants, this is relatively simple since they are supine and little adjustment is needed to image the entire urinary tract. However, in older children in the sitting position, greater adjustments will be required to allow proper visualization of the bladder neck, especially during voiding, while having the flexibility to image the upper tracts to rule out VUR. It cannot be emphasized enough to limit radiation exposure in children, as gonadal irradiation is unavoidable. No standard recommendations exist for the number of images, but images at the initiation of filling, at half and full capacity and during voiding should be obtained. While the average effective dose of ionizing radiation from videourodynamics is less compared to VCUG, exposure is dependent on fluoroscopy time, body mass index and bladder capacity [16].

The Study

Filling Cystometry

Expected bladder capacity should be determined prior to initiating the study. There are various equations for determining expected bladder capacity. Age + 2 (× 30 ml) is the most widely accepted formula for determining expected bladder capacity; however, for children that are significantly large or small for age, that may need to be adjusted by considering their weight on a standard somatic growth chart. Under the age of 2 years, an alternative formula is weight in kg. × 7 ml. Bladder filling with injection pumps should be performed at a rate of 5–10 % of the expected bladder capacity per minute [17]. Alternatively, fluid can be hung 30–40 cm above the level of the bladder, and a gravity drip can be used [18]. There is little agreement on whether to use solution at room temperature or heated to body temperature via a water bath in efforts to reduce bladder irritability [19]. At the onset of filling, a quick fluoroscopic image is helpful to determine proper positioning of the C-arm and bladder catheter. Faint appearance of the contrast may suggest incomplete bladder emptying during set-up. If fluoroscopy is not utilized, sonography can be used to monitor bladder filling. Periodically, the child should be asked to cough or one should push on the suprapubic area to ensure all monitors are continuing to detect pressure properly. For older children, the initiation of filling may create an unusual sensation, resulting in anxiety with the report of the need to void after minimal volume. Encouragement will usually convince the child to allow additional filling.

Throughout the filling phase, detrusor pressures should be closely monitored. A normal bladder should fill with minimal pressure changes. Intermittent changes in detrusor pressures >15 cm H₂O above baseline are indicative of detrusor overactivity, also referred to as uninhibited bladder contractions, and these contractions may increase in both frequency and magnitude as bladder volume increases [12]. If detrusor overactivity or rapid rise in pressure is noted, the infusion rate should be lowered. Often, decreasing the rate by 50 % or more can alleviate detrusor contractions or demonstrate more realistic compliance and provide a study more representative of natural bladder filling (Fig. 4a, b). In older children, sensation can be monitored by recording the first and additional sensing of filling as well as the urge to void. Abdominal pressure should also be closely watched as some children with neuropathic bowel will have uninhibited rectal contractions during filling, and this will create artifact in the detrusor pressure which is the difference between bladder and rectal (abdominal) pressures.

Fig. 4

Effect of filling rate on pressure curves. (a) Fill rate of 25 ml/min. Pves (magenta) shows steady rise followed by a contraction with peak pressure of 136 cm H₂O at volume of 202 ml (black line on fifth row). Pabd (dark blue) shows rectal contractions near end of filling, and these negatively affect Pdet tracing (green). EMG tracing (red) shows increased activity as detrusor contaction occurs just before volume reaches 188 ml, reflective of detrusor sphincter dyssynergia. (b) A second infusion at 10 ml/min is performed immediately following the previous study. Similar capacity is noted with detrusor contraction at 228 ml. Rise in pressure is diminished at this fill rate. Increased sphincter EMG activity is seen with increasing volume and detrusor pressure; dyssynergia is then noted with detrusor contraction. The increase in Pabd (dark blue) near capacity is not associated with patient movement and again represents rectal contraction and is subtracted from Pdet (green)

Bladder capacity is one of the key parameters to evaluate bladder function, so the child should be encouraged to allow filling to occur as long as possible. Distraction tools mentioned previously may take the child’s mind off of the bladder and allow higher volumes to be achieved. Filling should continue until the child has a strong urge to void, micturition occurs, or the child is uncomfortable [14]. For children that cannot communicate verbally, one must closely observe the child for signs of restlessness or abdominal distension. In children with poor sensation, severe VUR, or inability to void, filling should be stopped at 150–200 % of expected bladder capacity, with prolonged detrusor pressure >40 cm H₂O, or the child is uncomfortable or agitated [1]. Children with neurogenic bladder may have absent or altered sensation in which bladder fullness is manifested as abdominal fullness or back pain. In those with incontinence due to high detrusor pressure and/or incompetent outlet, filling may be stopped when the rate of leakage appears to equal the infusion rate.

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