Biophysical Validation of Intra- Abdominal Pressure and Transurethral Method

Biophysical Validation of Intra- Abdominal Pressure and Transurethral Method

Objective: The increase in intra-abdominal pressure (IAP) is a well-documented phenomenon, directly associated with pathophysiological changes in all organic systems, increasing morbidity and mortality. The gold standard for its determination is the transurethral method (TM), which still today is surrounded by controversy. The purpose of the study is to, through physical principles, demonstrate IAP, validate TM and explain the variables that influence IAP.

Materials and Methods: Development of a biophysical formulation, based on mechanics of fluids, to explain IAP, TM and its variables. Validation of the principles formulated in a non-living animal model, where all components that generate the IAP were determined. Determination of: IAP by TM, intragastric and direct method; gastric, bladder and abdominal areas and volumes; weight of all abdominal structures.

Results: IAP values obtained by the several methods are within the limits described for the species with average values between 2.31 and 7.14 mmHg.

Determination of the areas and strength of all anatomical structures allowed the replacement of values in the biophysical formulation and calculation of IAP. The mathematically calculation of IAP confirms the theoretical definition of IAP.

This value when compared with the direct readings per sensor showed no statistical differences (P<0.05). IAP determination by direct method also showed no differences in the five body positions (P=0.765). Indirect methods revealed statistically significant differences from the direct method only in the Trendelenburg and reverse Trendelenburg. Breathing, muscle contraction, body position and water manometer position influence IAP measurement by indirect methods.

Using digital treatment of images and using pixels analysis algorithms, it is also possible to determine bladder and gastric surface area, in average 6.17*10-3 ± 5.05*103 m2 and 3.55*10-2 ± 1.65*10-2 m2 respectively.

Conclusion: This study improves the knowledge of the application of the direct and indirect methods to accesses IAP. The biophysical principles explain the formation of IAP and prove the accuracy of TM, explaining the variables which affect it.