The present article is devoted to the search for the physical factors affecting the intrapelvic pressure in patients with kidney catheters. Based on mathematical prediction and experiment, value of air bubbles, hampering urine outflow and contributing to the development of purulent postoperative complications in urology, was demonstrated. A certain number of air bubbles in catheters leads to the formation of air-urinary impaction, causing a sharp increase of intrapelvic pressure. Correlation analysis showed a direct relationship between the amount of air bubbles in the drainages and resistance force to urinary flow. The study showed that the presence of air bubbles in the catheter and drainage tubes is unacceptable. Compliance with certain rules and standards of work allows to prevent their formation, which in turn reduces the risk of urinary infection and the development of septic complications. This approach will help to predict the possible postoperative complications, accelerate the introduction of modern technologies, and improve the quality of urological care.