Endoscopic visual cues of intrarenal pressure during ureteroscopy: in vivo porcine studies

To characterize the endoscopic visual appearance of the collecting system during ureteroscopy in a porcine in vivo model across a range of steady state intrarenal pressures (IRPs).

A flexible ureteroscope with pressure sensor was advanced into the renal pelvis of anaesthetised female porcine subjects. Endoscopic images were captured at IRPs from 8 to 200 cmH₂O, and the collecting system was categorized as follows: insufficiently distended (ID), partially distended (PD), or fully distended (FD). The colour of the urothelium and the prominence of urothelial vessels were also described.

The collecting system was ID at IRP < 12 cmH₂O and FD at IRP > 23 cmH₂O. Between these values, visual cues consistent with PD were apparent. As IRP increased from 23 to 200 cmH₂O, the morphology of the collecting system did not appreciably change. Above 20 cmH₂O, the pink urothelium became pale and the prominence of suburothelial blood vessels diminished.

Prevention of elevated IRP during ureteroscopy has become increasingly important. Although visual cues associated with the changing morphology of PD of the collecting system can provide some guidance during ureteroscopy, they occur in a narrow pressure range (12-23 cmH₂O), which may prove challenging to maintain. Furthermore, the absence of visual cues above 23 cmH₂O precludes visual identification of elevated IRP. Strategies to utilize the full range of safe IRP levels (up to significant pyelovenous backflow) will likely require real-time measurement of IRP.