Performing UDT

and Apichana Kovindha²

(1)

University of Antwerp, Antwerp, Belgium

(2)

Rehabilitation Medicine, Chiang Mai University, Chiang Mai, Thailand

5.1 Positioning of the Patient

Choice between supine and sitting position depends on availability of a special table for UDT, and the mobility of the patient. Bedside UDT is possible but less practical when a multichannel electronic device is used.

Pressure development changes with a different position. In any case, a patient should be comfortable, well protected against pressure ulcer development, with material to collect out flow of urine and faeces. The mean duration of a UDT is, transfers included, around 30–45 min, depending on the filling rate.

Neurologic examination and specific manipulation in the lumbosacral area may be needed in some cases, which needs easy access to the genital area and perineum.

5.2 Placing the Measurement Catheters

A bladder pressure catheter must be introduced gently through the urethra so that its openings are well inside the bladder. Preferably a non-anaesthetic lubricant is used to preserve the evaluation of local sensation. Mostly used are small calibre catheters, either special UDT catheters (4–8 Fr) or an ordinary non-hydrophilic catheter Fr 8–10. The choice of material of the catheter will depend on availability, budget, allergy for latex. If spasticity at the sphincter blocks the further insertion of the catheter, extra gel, anaesthetic gel, or rarely stretching of the spastic anal sphincter can help. Difficulty to introduce due to kinking in the bulbar urethra in men, can be overcome with digital support/stretching of the urethra through the rectum, vagina or perineal surface. When no imaging is available, the position of the catheter can be indicated by the outflow of urine, and guided by the length of catheter introduced. In women 7–10 cm and in men 20 cm or more must have passed the external meatus. The catheter connected to the pressure gauge, is securely fixed at the meatus, the perineal area or the thigh. The entire pressure measuring tube should, before introduction of the catheter, be filled with filling solution. The pressure measured is “Pves”.

A bowel pressure catheter is used to measure the rectal/abdominal pressure “Pabd”. A catheter with a balloon at the top is inserted through the anal sphincter with lubricant and eventually on a penetrating finger if the anal sphincter is spastic. If a special UDT catheter is not available, a urinary catheter can be used with open end or broad side holes in the proximal part. A balloon is made with a finger cut from a glove or a condom and fixed, covering the proximal holes, around the catheter with a string. When introduced in the rectum its top is protected by a condom. The catheter should be introduced 5–8 cm (if possible) through the anus. If the rectum is filled with stool, the bowel should preferably be emptied. The rectal catheter and its balloon are filled with water and connected to the pressure gauge.

If one chooses to prepare the patient for UDT with an enema, it should be applied early enough beforehand (day before) to avoid defecation on the urodynamic table during the test.

A urethral pressure catheter with side holes is used to measure the pressure at the urethral sphincter “Pura”. This tube may, together with a filling tube and a bladder pressure measuring tube, be part of a 3 channel catheter.

The catheter is introduced till the side holes are in the bladder, filled with saline and then slowly retracted until the urethral pressure tracing shows a clear pressure rise. This indicates that the holes are at the level of the urethral sphincter. The catheter is fixed to the skin in this position.

5.3 Calibration and Controlling of the Pressure Lines

Zeroing of the transducers can be done with the catheters outside the body, positioned at the level of the bladder, or after introduction and fixation. If done before introduction, Pves and Pabd will show pressures above zero. If done after positioning in the body both traces should start at zero. In both cases Pdet should always start at zero.

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