LEAK POINT PRESSURE

Authors: Christian Cobreros, Peter Rosier

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INTRODUCTION:
The International Continence Society (ICS) defines Detrusor Leak Point Pressure (DLPP) as the lowest detrusor pressure at which urine leakage occurs in the absence of either a detrusor contraction or increased abdominal pressure.
In contrast: Abdominal Leak point pressure (ALPP) is defined as [cited]: ’…the intravesical pressure at which urine leakage occurs due to increased abdominal pressure in the absence of a detrusor contraction’i. In the comments on this term, newly introduced in 2002, is written that [cited] ‘…the leak pressure point should be qualified according to the site of pressure measurement (rectal, vaginal or intravesical) and the method by which pressure is generated (cough or valsalva). Leak point pressures may be calculated in three ways from the three different baseline values which are in common use: zero (the true zero of intravesical pressure pves), the value of pves measured at zero bladder volume, or the value of pves immediately before the cough or valsalva (usually at 200 or 300 ml bladder volume). The baseline used, and the baseline pressure, should be specified.’ii No comments are given about patient positioning or patient instruction. Standardization of ALPP measurement has not been reported to date and publications reporting ALPP illustrate that the methods used to determine LPP vary and that neither variety has demonstrated superiority .iii

PATHOPHYSIOLOGY
The essence of Stress Urinary Incontinence (SUI) is that that urine leaks out of the bladder because the bladder outlet is not able to cope with abdominal pressure rise(s). The Valsalva manoeuvre is the deliberated elevation of intracorporeal pressure for diagnostic and therapeutic purposes. Popularized by Valsalva (1666-1723), but preceded by Paré (1510-1590).iv- v After Edward McGuire has published his report on the relevance of (detrusor) leak point pressure in patients with spinal dysraphism in 1981,vi he also introduced the term Valsalva Leak Point Pressure (VLPP) related to SUI in 1993vii.
The lack of success in some of those procedures and subsequently the confirmation of severe incontinence in patients with open bladder neck or a non-functional proximal urethra in the absence of any abnormality of the position of the urethra has set a new way of understanding and studying of the mechanisms of continence. McGuire first reported the use of the VLPP as a diagnostic tool and defined type III of incontinence as SUI due to intrinsic sphincter deficiency in the patients where VLPP has been relatively low. He reported that 76% of women with a VLPP less than 60 cmH20 had this type of incontinence without correlation between maximum of urethral closure pressure (measured by UPP) and the VLPP.
While the VLPP was growing as the principal test for diagnosing SUI, it was consecutively initiated as the cut off value test that could determine two distinct types of SUI: Hypermobility of the urethra, treatable with bladder neck support, versus a ‘non coapting’ urethra, in which cases reposition was reported to have lesser success.
The theories of urethral support have been integrated into broader concepts of pelvic muscle function and dynamicsix and this has lead to midurethral support treatment as suitable for most patients with SUI. Sub classification of SUI is not regarded as very relevant by most of the experts now, probably also because of the modest invasiveness of midurethral support treatment. Nevertheless ALPP’s are used in clinical or research practice nowadays and the aim of the teaching module is to present practice that can be regarded as optimal, based on the current evidence.

HOW TO MEASEURE
PREPARATION - TECHNIQUE AND INTERPRETATION
All the requirements and instructions for the measurement of LPP described in this section follow the ICS reports on Good Urodynamic Practicex and urodynamic equipment performancexi. LPP can be obtained during routine cystometry and no specific other equipment or specific patient preparation is required. LPP requires that both vesical and intra abdominal pressure are recorded. As per GUP clinical history and examination -results should be available before urodynamic testing.

STEPS IN PERFORMING LLP
Recording pressure
Contemporary guidelines recommend standard multichannel urodynamics as an option for patients with SUI and urodynamics or videourodynamics in patients with a complicated or recurrent SUI. It is reported that videourodynamics gives less discomfort and more privacy to the patient as leakage does not need to be observed directly by the physician. However there is no evidence that videourodynamics gives significant differences in results. Furthermore the here reported advance must be weighed against the costs, the radiation exposure and the, usually occurring, less comfortable or representative position of the patient, especcially relevant during pressure flow. GUP recommends, and ICI-2013 confirms, that as thin as possible transurethral dual lumen catheter should be used for filling and vesical pressure measurement as well as an intrarectal catheter to monitor intra -abdominal pressure. Both pressures should be referring to atmospheric pressure with external sensors at the level of the pubic symphysis.

Position of the patient
The position of the patient during standard cystometry is, according to GUP and ICI-2014, preferably seated in upright position.

Catheter size and anatomical position
Several monocenter cohort studies have shown that smaller transurethral catheters cause less obstruction during voiding or leakage but the optimal diameter is not determined. (level of evidence 3 B)

Bladder volume at LPP determination
No bladder volume is superior to consider VLPP in all patients. (level of evidence 3)

Pressure generating
The very most frequenly reported method to increase abdominal pressure for LPP is a Valsalva manoeuvre .

Predictive value
VLPP showed weakly or no correlation with the outcomes of surgical procedures for SUI. (level of evidence 2 - 3)
Large prospective cohort observations can show us if the VLPP give us the sensitivity and specify to better predict outcome of management in patients with SUI.

Recommendations for practice
  • We recommend that investigators interpreted the results of the UD procedures as having in all cases an artefact due to the catheter itself independently of the size of it, previous studies as post void residual, free uroflow, the micturition chart should be taken as the most representative parameters of reality. (Recommendation grade B)
  • We do recommend that patient position during the pressure flow study should be reported. We recommend that the testing position correlates with the usual activity of the patient when urinary incontinence is perceived. (Recommendation grade D)
  • On the basis of good urodynamic practice a single double lumen catheter 5-8Fr should be used for cystometry; we recommend this for LPP also. (Recommendation grade D)
  • We do recommend that VLPP should be asked every 100 ml during the filling phase as a standard protocol. We recommend that the VLPP during the smallest bladder volume in which the patient is incontinent is reported. (Recommendation grade D)

CONCLUSION
We recommend that the LPP should be consider as one, but not the only one, of the urodynamic evaluations as well as a procedure to make therapeutically decisions.
The evidence against the LPP as a clinical factor to be taken into account for surgical treatment usually takes the LPP as the unique parameter to be considered, and we do acknowledge the complexity of the pathophysiology of SUI, moreover in the present of prolapse. We recommend the VLPP as another important tool for making diagnosis and prognosis; while using the same standard of procedure: cut off values, sensibility and specificity of the method could more easily be asses.
REFERENCES
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