Elevated Renal Pelvic Pressures during Percutaneous Nephrolithotomy Risk Higher Postoperative Pain and Longer Hospital Stay

Renal pelvic pressure may vary during percutaneous nephrolithotomy. We sought to determine the relationship of postoperative pain to endoscope caliber, renal pelvic pressure and hospital stay.We reviewed the records of 20 percutaneous nephrolithotomies done under ureteroscopic guidance with renal pelvic pressure monitoring. The ureteroscope working channel was connected to a pressure transducer and used to determine renal pelvic pressure at baseline, when irrigating with a 26Fr rigid nephroscope and a 16Fr flexible nephroscope, and during suction. Patient demographics, operative characteristics, Likert pain scores and length of hospital stay were compared as stratified by average renal pelvic pressure. The Mann-Whitney U and Fisher exact tests were used with p <0.05 considered significant.A total of 220 measurements were recorded in 20 patients undergoing single access percutaneous nephrolithotomy. Mean patient age was 55.2 years (range 20 to 77) and mean body mass index was 32.4 kg/m2 (range 18 to 53.3). Rigid nephroscopy resulted in significantly higher average renal pelvic pressure than flexible nephroscopy (30.3 vs 12.9 mm Hg, p = 0.007). Average renal pelvic pressure was 30 mm Hg or greater in 7 patients (35%) undergoing rigid nephroscopy and in none (0%) undergoing flexible nephroscopy (p <0.01). Patients exposed to an average renal pelvic pressure of 30 mm Hg or greater during rigid nephroscopy had significantly higher average pain scores (p = 0.004) and longer hospital stays (p = 0.04) than patients with renal pelvic pressure less than 30 mm Hg. Average renal pelvic pressure 30 mm Hg or greater during rigid nephroscopy was also associated with a longer skin to calyx distance (105.5 vs 79.7 mm, p = 0.03).Knowledge of the factors that influence renal pelvic pressure and methods to control pressure extremes may improve patient outcomes during percutaneous nephrolithotomy.