Hypothesis / aims of study
Detrusor Leak Point Pressure (DLPP) is a relatively established urodynamic parameter to predict the risk to the upper urinary tracts in patients of Neurogenic Bladder Dysfunction.
However the parameter is not sufficiently standardized till date. Besides there are potential technical artefacts in its measurement due to the presence of urodynamic pressure catheter in the urethra during measurement.
We at our centre, have designed a method of measuring the leak point pressure by withdrawing the catheter at the point of leakage and reintroducing it as the leak stops. The pressure measured at this point is the natural bladder pressure to which the upper urinary tracts are exposed to prior to leakage. We called this pressure Detrusor Preleak Point Pressure (DPLPP).
We would like to study the leak point pressure with both the techniques in atleast 40 consecutive cases referred to our department and then correlate our findings with the result of conventional leak point pressure. This will help us to identify if this new parameters offers better accuracy in predicting the risk to upper urinary tract when compared to conventional parameter.
Study design, materials and methods
This is a prospective study of 42 consecutive cases of neurogenic bladder dysfunction, who were referred for Urodynamic evaluation to our Centre between July 2016 and December 2017.
Maximum Voided Volume was estimated from the Frequency / Volume Chart. Where Frequency / Volume Chart was not available, bladder capacity was noted from the latest USG report.
A 6F bilumen catheter was introduced after voiding. Residual urine volume was drained and recorded. Filling rate was calculated as (Maximum voided volume / 10) mls / minute of Normal saline at room temperature in supine position.
Two persons determined the DLPP by watching for leak as the appearance of the fluid drop at the meatus and the recorded pressure simultaneously. This was recorded as the DLPP.
The bilumen catheter was then gently removed without disconnecting it from the pressure transducer. Fluid from the urethra was then allowed to leak freely onto the flow transducer below. As the leak stopped, the bilumen catheter was reintroduced into the bladder and the pressure at that instant was measured and recorded.
We called this point DPLPP (Detrusor Pre-leak Point Pressure) and attempted to correlate its values with the conventional DLPP as well as with the upper tract deterioration.
Results
Measured Detrusor Pre-leak Point Pressures (DPLPP) were found to be consistently lower than the conventional Detrusor Leak Point Pressures (DLPP) in 42 patients, although there was a wide variation of pressure differences between the two vales in individual patients.
Measured DPLPP ranged from 29 cms of H2O to 84 cms. of H2O with a mean pressure of 42 cms. in tese patients, whereas measured DPLPP ranged from 19 cms. of H2O to 51 cms. of H2O in the same group of patients. All these figures were found to be statistically significant (p value < 0.05 using paired t test).
Other risk factors like neurogenic detrusor Overactivity, vu reflux, detrusor compliance and overall bladder capacity have also not been found to have a statistically significant correlation to Upper urinary tract dilatation, although upper tract dilatation was noted in all patients who had DLPP greater than 41 cms. of H2O and DPLPP of 26 cms. of H2O.
Interpretation of results
Reliability of measurement of DLPP needs some special considerations. Theoretically the dynamics of the urethra could be altered by the presence of urethral catheter in two ways.
e. Mechanical occlusion of the urethra and
f. Straightening of the urethra by the presence of a rigid catheter.
Since the results of DPLPP have been found to be consistently lower (and statistically significant), this study suggests that the conventional measurement of DLPP may have multiple artifacts in its measurements.