1. A Gammie, C D’Ancona, H-C Kuo & P Rosier.
ICS Teaching Module: Urodynamic Artefacts 1 Common artefacts in water-filled systems
A Gammie, C D’Ancona, H-C Kuo & P Rosier.

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3. Common artefacts in water-filled systems Artefact: ‘Something …that is not naturally present but occurs as a result of …the procedure’ (Oxford)
Movement / tube knock
Patient position change
Expelled vesical catheter
Expelled rectal catheter
Flushed catheter
Line open to syringe
Empty bladder (poor response)
Empty rectal catheter
Poor cough response

4. Movement / tube knock (water)
pves knocked
pabd knocked
Transmission checked
Effect: high frequency, short duration pressure spikes visible in pves, pabd, or both, but with spikes always visible in pdet. (red arrows)
Cause: Knocking of one or both tubes. Note how first the knock is on the pves line, then later on the pabd line. Note also that good pressure transmission is confirmed by the equal rise in pressure on both lines indicated by the blue arrow.
Remedy: Ensure tubes are away from the cause of the knock. Ignore spikes when analysing trace

5. Movement / tube knock (water)
pves knocked
Effect: high frequency, short duration pressure spikes visible in pves, pabd, or both, but with spikes always visible in pdet.
Cause: Knocking of one or both tubes. The knocks in this trace are on the pves line, and can be seen on pdet as well, marked by red arrows.
Remedy: Ensure tubes are away from the cause of the knock. Ignore spikes when analysing trace

6. Patient position change (water filled)B C
Effect: a change in the resting pressures of pves and pabd of equal magnitude on both, usually between 8 and 35 cmH2O. Often accompanied, as in this case, by noisy signals as the lines are knocked.
Cause: change in patient position. In this case, the patient has begun supine (at A), then moved vertically up with respect to the transducers to the standing position (at B). They then sat down on the commode, to a position below the level of the transducer (at C). The level of the transducers was then adjusted (marked by the red arrow) to the level of the symphysis pubis.
Remedy: ensure the transducers are moved to the level of the symphysis pubis after any patient position change. Transmission of pressure should also be checked after patient movement, done here by a cough at the start and live signal at the end being equal on both traces.

7. Patient position change (water filled)
Patient stands up, transducers not adjusted
Effect: a change in the resting pressures of pves and pabd of equal magnitude on both, usually between 8 and 35 cmH2O. (red arrows)
Cause: change in patient position. In this case, the patient has moved vertically up with respect to the transducers, and the transducers have not been adjusted afterwards. Note too the difference in resting pressures that may be caused by poor pressure transmission.
Remedy: ensure the transducers are moved to the level of the symphysis pubis

8. Patient position change (water filled)
Patient stands up
Transducer height adjusted
Effect: a change in the resting pressures of pves and pabd of equal magnitude on both, usually between 8 and 35 cmH2O. (red arrow)
Cause: change in patient position. In this case, the patient has moved from seated to standing position at the red arrow, which raises the abdominal pressure.
Remedy: ensure the transducers are moved to the level of the symphysis pubis. In this case, it entails raising the transducers up vertically, thus lowering the pressure reading (blue arrow).

9. Expelled vesical catheter
vesical catheter expelled
Effect: sudden drop in pves, usually to well below zero, with no response to transmission checks.
Cause: the vesical catheter is expelled from the patient (marked by red arrow), normally by the pressure of voiding (though not in this case)
Remedy: recatheterise and repeat test, if the urodynamic question has not been answered

10. Expelled vesical catheter
vesical catheter voided, giving flow rate spike
Effect: sudden drop in pves, usually to well below zero.
Cause: the vesical catheter is expelled from the patient (marked by red arrow), normally by the pressure of voiding. Note how this can result in an artefactual peak of flow rate, which needs correction.
Remedy: recatheterise and repeat test, if the urodynamic question has not been answered

11. Expelled vesical catheter
vesical catheter voided
Effect: sudden drop in pves, usually to well below zero.
Cause: the vesical catheter is expelled from the patient (marked by red arrow), normally by the pressure of voiding
Remedy: recatheterise and repeat test, if the urodynamic question has not been answered

12. Expelled rectal catheter
rectal catheter voided
Effect: sudden drop in pabd, usually to well below zero.
Cause: the abdominal catheter is expelled from the patient, normally by the pressure of valsalva or straining. Note in the figure how the pabd line drops at the red arrow, and pdet then follows the contour of pves.
Remedy: recatheterise and repeat test, if the urodynamic question has not been answered

13. Expelled rectal catheter
rectal catheter voided
Effect: sudden drop in pabd, usually to well below zero.
Cause: the abdominal catheter is expelled from the patient, normally by the pressure of valsalva or straining. Note in the figure how the pabd line drops at the red arrow, and pdet then follows the contour of pves.
Remedy: recatheterise and repeat test, if the urodynamic question has not been answered

14. Flushed (water) catheter
catheter flushed with water
Effect: a sudden increase in pressure to a value above 200 cmH2O, and maintained for between 2 and 7 sec, followed by a sudden drop in pressure.
Cause: water is pushed through the transducer dome (at the red arrow marker) in order to remove air from the catheter and tubing
Remedy: Check for good pressure transmission after the flush. Ignore the high pressure generated when analysing trace.

15. Line open to syringe (water)
transducer open to syringe, damping signal
tap closed to syringe, artefact removed
Effect: repeated flushes of the line do not restore a good response to a cough signal
Cause: syringe inadvertently remains connected to the water line, and acts as a damper on the signal. Since an air bubble is not the problem, flushing fails to resolve it, as demonstrated at the points marked by red arrows.
Remedy: set taps correctly, so syringe is not connected to dome, marked by blue arrow. Repeat cough test for pressure transmission.

16. Empty bladder (poor response)
No response when bladder is empty,
restored after 50 ml infused
Effect: response of the intravesical catheter to pressure transmission test is poor when bladder volume is low
Cause: When the bladder is empty, the catheter may touch the bladder wall, so pressure changes within the lumen cannot be registered.
Remedy: fill the bladder slightly (e.g. 50ml) and test the pressure transmission again.

17. Empty rectal catheter (water)
rectal catheter loses water and transmission
Effect: deterioration in abdominal pressure transmission, with or without a change in pressure, during filling or voiding.
Cause: reduction of water in the rectal balloon. The balloon fails to connect effectively with the rectal wall as a result - note the loss of transmission at the red arrow marker.
Remedy: refill balloon (refill pressure not shown in above trace, recording had been stopped) and test for good pressure transmission.

18. Poor cough response A B
Effect: One cough spike (here on the pves trace marked A) is visibly smaller than the other, despite a cough affecting pves and pabd equally.
Cause: Usually an air bubble in the water-filled line, reducing the transmission of pressure from patient to transducer, in this case in the vesical line.
Remedy: Flush the line through with water (marked with red arrow), pushing the air bubble from the tube. The next cough (marked B) is registered equally on both traces.

19. Poor cough response
Effect: Here the cough spikes are again unequal on pves and pabd, and the pdet line is thus affected (marked by the red arrow)
Cause: Usually an air bubble in the water-filled line, reducing the transmission of pressure from patient to transducer, in this case in the abdominal line.
Remedy: Flush the line through with water (not visible on this trace), pushing the air bubble from the tube.

20. Poor response to live signal
Effect: Live signal is observed on one trace (in this case pves) and on pdet, despite a cough test being satisfactory.
Cause: Usually an air bubble in the water-filled line, reducing the transmission of pressure from patient to transducer, in this case in the abdominal line. It could also be the pump or patient causing noise on the affected line.
Remedy: Check that there is no interference on the affected line by visual inspection and stopping the pump. If it is still present, flush the line through with water (not visible on this trace), pushing the air bubble from the tube.