Urodynamics testing is one of the most powerful tools available for diagnosing problems in the lower urinary
tract. However, urodynamics interpretation is as much an art as it is a science. Here, common mistakes that are made during urodynamics interpretation1 will be discussed. Also, check our article on Urodynamics Interpretation: How to do it Right.
Not Flushing Air Bubbles
While use of water charged catheters is the standard practice in urodynamic testing, improper flushing of air bubbles can lead to inaccurate data interpretation. Before testing begins, the system should be primed by flushing sterile water through the lines, ensuring both three way taps are open.
Not Properly Zeroing the Instrument
When measuring abdominal2 and vesicle pressures in the patient, it is important that the instrument is first properly zeroed to atmosphere by selecting the “zero” or “balance” option while the transducer is open to the atmosphere but closed to the patient. If this step is not performed properly, all subsequent pressure readings will be incorrect.
When interpreting a urodynamics tracing, particularly a test that was performed by someone else, it is important to ensure the tracing is properly labeled. For instance, if “permission to void” is not clearly stated on the tracing, regular voiding function can be misidentified as overactive bladder.
One of the most common limitations associated with urodynamics interpretation is the misidentification of artifacts4, which are signals that appear in the urodynamic tracings that are not caused by biological phenomena. For instance, electromyography artifacts in adults are among the most common limitations in urodynamics interpretation.
Electromyography data should only be interpreted if there is good correlation between detrusor pressure, uroflow, and EMG changes. Additionally, spikes in maximum flow rate are typically artificially observed, which can cause significant interpretation errors. It is important to correlate free flow rate studies with the data recorded during catheter voiding in order to make the best interpretation.
Not Recreating Patient’s Symptoms
The symptoms a patient experiences at home may differ from what is observed during urodynamics testing. When interpreting data, it is important to make sure the patient’s symptoms were reproduced during the test. For instance, if interrupted flow is observed during testing, the patient should be asked whether this phenomenon is normal for the individual. If not, the test must be performed again at a later date or else interpretation will be incorrect for the patient’s actual disorder.
Not Making Adjustments During Testing
To make the most accurate readings, pressure transducers should be positioned at the upper edge of the symphysis pubis. When pressure transducers are not in the proper position, artifacts in the pressure measurement are likely, due to the hydrostatic pressure effect. If the patient changes positions during the test, the transducers must be repositioned to the new level of the symphysis pubis.
Misidentifying Rectal Contractions
Detrusor pressure3 can provide a lot of useful information during urodynamics testing. However, a number of occurrences can artificially cause spikes in the recorded detrusor pressure. One such occurrence is spontaneous rectal contractions. When making urodynamics interpretations, make sure changes in detrusor pressure are reproducible.
Not Considering Effect of Catheter on Uroflow
The presence of a catheter in the urethra can affect normal urine flow. For instance, urine flow can appear obstructed in some cases, due to the catheter. Additionally, some patients may find voiding difficult due to the catheter’s presence. If not taken into consideration, a patient can be improperly diagnosed with bladder outlet obstruction.
Not Distinguishing between Low Bladder Compliance and Detrusor Contractions
If an increase in detrusor pressure is observed when the bladder is filled during cystometry, distinguishing between involuntary contractions and low bladder compliance. Before diagnosing the patient with either (or both) problems, stop the water inflow during an observed detrusor pressure increase. If detrusor pressure drops and stabilizes, decreased bladder compliance is likely.
Not Correlating Radiographs with Urodynamic Tracings
When video urodynamics are used during urodynamic testing, a common mistake is to not correlate the urodynamic tracing with the radiographic picture. The urodynamic tracing should be properly labeled to aid in this interpretation. Additionally, extreme care should be taken in properly imaging the urethra such that the x-ray beam is perpendicular to the long axis of the patient. When radiographs are not properly acquired, the bladder will appear improperly positioned in the patient’s body.
- Johnson, K. C., & Rovner, E. S. (2014). The 9 “C’s” of Pressure-Flow Urodynamics. Rapid and Practical Interpretation of Urodynamics, 27-33. doi:10.1007/978-1-4939-1764-8_2 Link
- Kim, K., An, Y., Seo, J., & Song, C. (2008). A non-invasive sensing method to estimate abdominal pressure by electromyography in urodynamics study. 2008 IEEE International Conference on Multisensor Fusion and Integration for Intelligent Systems. doi:10.1109/mfi.2008.4648054 Link
- Vereecken, R. L., & Nuland, T. V. (1998). Detrusor pressure in ambulatory versus standard urodynamics. Neurourology and Urodynamics, 17(2), 129-133. doi:10.1002/(sici)1520-6777(1998)17:2<129::aid-nau6>3.0.co;2-f Link
- Sand, P. K., & Ostergard, D. R. (1995). Filling Catheter Artifacts. Urodynamics and the Evaluation of Female Incontinence, 150-151. doi:10.1007/978-1-4471-2109-1_46 Link