Rapid oral hydration results in hydronephrosis as demonstrated by bedside ultrasound

Study objective: To determine whether vigorous oral hydration (20 mL/kg) ca uses hydronephrosis as determined by bedside ultrasound. Methods: We conducted a prospective laboratory trial in 35 healthy voluntee rs weighing less than 90 kg and between the ages of 18 and 50 years. The ri ght kidney of the volunteers was scanned by emergency physicians at time 0 both before and after voiding, and the volunteers then drank 20 mL/kg of bo ttled water. The kidney was scanned in the transverse and sagittal planes b oth before and after voiding at 60 and 90 minutes after completion of the w ater load. The scans were interpreted by a physician trained and credential ed in emergency ultrasound, blinded to the volunteers' identity, the time o f the scan, and the volume of urine voided by the subject. Images were rate d as to the degree of hydronephrosis according to literature-established cr iteria, as follows: grade 0=no hydronephrosis, grade 1=mild, grade 2=modera te, and grade 3=severe hydronephrosis. Results: Hydronephrosis was present in 3 (8.6%) of the 35 subjects at time 0 (prehydration), 24 (68.6%) at 60 minutes, and 20 (57.1%) at 90 minutes. O verall, hydronephrosis occurred at least once in 28 (80%) of the 35 subject s after oral hydration compared with 3 (8.6%) of the 35 subjects before hyd ration. Hydronephrosis was found to be significantly related to forced hydr ation for all posthydration times (60 minutes, 90 minutes, and 60+90 minute s combined) versus prehydration time 0 (P<.001). Conclusion: Without prior fluid intake, even mild degrees of hydronephrosis were relatively uncommon, and seen in only 8.6% of study patients. In the presence of vigorous oral hydration, however, mild or moderate hydronephros is is a frequent occurrence seen at least once in 80% of our study of healt hy volunteers after hydration. Caution is warranted in this setting when in terpreting mild or moderate hydronephrosis found on bedside ultrasound by e mergency physicians.