Author response to comment on: Intrarenal pressure with hand-pump or pressurized-bag irrigation: randomized clinical trial at retrograde intrarenal surgery

BJS, https://doi.org/10.1093/bjs/znae137, published 15 June 2024

Dear Editor

We thank Dr Huang and colleagues for the interest in our paper¹.  The urological community’s understanding of intrarenal pressure is rapidly growing, and certainly will be refined with increased data availability.  In relation to the points made:

1. All patients underwent general anaesthesia, the majority (32 of 34) were ASA grade 1-2, none had pre-existing health conditions that would be expected to exert an influence on intrarenal pressure, and stone sizes were similar between arms (Table 1).  Irrigation fluid was warmed to 37 degrees before hanging; we do acknowledge that the precise temperature at the time of infusion may have varied slightly.  We agree that anatomical structure and renal compliance likely exert an influence on intrarenal pressure, as we have previously discussed².  However, given current limited understanding of these factors, we unfortunately do not feel that it would be feasible to adjust the analysis for them.

• It is very true that mean and peak pressure values do not capture the fluctuance in an intrarenal pressure trace, which may be of clinical significance. In light of this, however, we reported the natural log of variance in addition, which demonstrated a statistically significant difference between the groups (Table 2).

• Postoperative complications are indeed reported in the results section.  Regarding long-term follow-up, this is certainly of interest in any study.  In the case of intrarenal pressure, the current limited evidence would suggest the greatest clinical impact is in relation to urosepsis in the acute postoperative period, which was captured in this RCT.  Postoperative pain is certainly a desirable additional data point, albeit challenging to measure objectively and standardize, meaning that we were unlikely to find any difference between these relatively small groups.  Similarly, the potential for renal fibrosis in the context of elevated intrarenal pressure, as suggested in previous animal studies, merits further exploration, but is challenging to capture.  Whilst we take the suggestions of Dr Huang et al. on board, realistically it is unlikely that significant long-term differences in renal function as measured by serum creatinine, or long-term quality of life, would be detected between our patient groups. 

Accordingly, we feel it would not have been appropriate to withhold the highly relevant data captured in this RCT, in the quest to obtain multiple follow-up points over a protracted period.  We do, of course, look forward to further long-term data relating to intrarenal pressure emerging in the future, from our own work and that of others.