Pressure flow measurement of hydronephrosis in children: A new approach todefinition and quantification of obstruction

Purpose: Hydronephrosis due to obstruction of the ureteropelvic junction is not uncommon in children. The critical level of outflow resistance charact erizing obstruction remains to be established. It was previously found in o ur laboratory that the outflow resistance could be calculated in an animal model by servoregulating the infused flow to preset pressure levels. We det ermine whether this procedure is also feasible in patients with hydronephro sis. Materials and Methods: A total of 46 patients with 48 hydronephrotic kidney s were examined. There were 32 boys and 14 girls with a diagnosis of hydron ephrosis and suspected ureteropelvic, junction obstruction who underwent a pressure flow study under general anesthesia for evaluation before possible surgery. The kidney was punctured percutaneously under ultrasonic guidance , and the study was performed under fluoroscopy. Flow levels were measured when steady state flow was achieved at pressures 5, 10, 15, 20, 25 and 30 m m, Hg greater than the intra-abdominal pressure. A conventional Whitaker te st at an infusion rate of 10 ml. per minute was performed for comparison. T he patient then underwent pyeloplasty if the kidney was considered obstruct ed. Results: There were 2 patients excluded from evaluation because of signific ant leakage of contrast medium. Stable and repeatable recordings were obtai ned in all pressure flow studies but only in 7 of 46 Whitaker tests. A tota l of 41 kidneys were considered obstructed at pressure flow studies and ope rated on. The resistance was pressure dependent. Thus, mean resistance in t he previous range 5 to 15 min. Hg was considered a good overall measure of outflow resistance. Mean resistance less than 0.75 was normal and greater t han 1.25 obstruction. There were 7 patients who had crossing vessels and a high mean resistance (3 or greater). Conclusions: The Whitaker test proved to be of no value for calculating the outflow resistance in ureteropelvic junction obstruction. The pressure flo w study is superior to the Whitaker test for determining the outflow resist ance and also allowing categorization of ureteropelvic junction obstruction .