Comment on ‘Comparison of safety and efficacy of negative pressure aspiration assisted retrograde intrarenal surgery and traditional percutaneous nephrolithotomy in the treatment of upper urinary tract stones larger than 2 cm: a systematic review and meta-analysis’

Dear Editor,

We read with great interest the recent publication titled “Comparison of safety and efficacy of negative pressure aspiration assisted retrograde intrarenal surgery and traditional percutaneous nephrolithotomy in the treatment of upper urinary tract stones larger than 2 cm: a systematic review and meta-analysis”^[1], which provides a meta-analysis comparing negative pressure assisted retrograde intrarenal surgery (NPAA-RIRS) and percutaneous nephrolithotomy (PCNL). The study under review demonstrates the efficacy of NPAA-RIRS in reducing hemoglobin loss and complications. However, it is imperative to discuss the methodological limitations identified to ensure the robustness of the conclusions. It has been confirmed that the article adheres to the TITAN Guidelines 2025, which govern the declaration and utilization of AI^[2].The following text is intended to provide a comprehensive overview of the subject matter.

First, the included studies exhibit significant heterogeneity in design, with only two randomized controlled trials (RCTs) among ten studies. Additionally, there is an absence of subgroup analysis stratified by study type. Despite the implementation of random-effects models for highly heterogeneous outcomes (e.g., operative time, I² = 93.2%), confounding factors inherent in retrospective studies (e.g., surgeon experience variability) may potentially compromise the reliability of the results. For instance, the complication rates associated with PCNL may be underestimated due to its technical dependence on operator proficiency^[3].

Second, subgroup analysis based on stone location is inadequate. While stones were distributed across renal calyces and ureteropelvic junctions, the impact of anatomical complexity (e.g., lower calyceal stones) on surgical outcomes was not evaluated. The purported advantages of NPAA-RIRS in challenging anatomical regions remain unquantified.

Third, the availability of long-term follow-up data is restricted. The majority of studies documented outcomes within 1–3 months postoperatively, yet they did not include assessments of stone recurrence rates or renal functional deterioration (e.g., hydronephrosis). The possibility of NPAA-RIRS inducing prolonged complications related to pelvic high pressure necessitates prolonged observation^[4].

Moreover, the influence of learning curves on outcomes was not systematically assessed. While PCNL necessitates a more protracted learning curve, the study did not quantify the impact of operator experience on complication rates. For instance, experienced surgeons have been shown to achieve reduced risks of bleeding complications during PCNL. Conversely, the outcomes of retrograde intrarenal surgery are contingent upon the operator’s adeptness in manipulating the flexible ureteroscope.

Furthermore, The evaluation of publication bias is characterized by an absence of objective metrics, representing a significant limitation in the analysis. Although funnel plots were mentioned in the text, the results of Egger’s test were not reported. This omission renders visual inspection insufficient for the detection of small-study effects, which have the potential to skew pooled estimates. The depth of complication classification is limited. Although Clavien–Dindo grading was employed, the review failed to differentiate between intraoperative complications (e.g., ureteral injury) and postoperative management issues (e.g., infection). For instance, the postoperative fever rates documented by the NPAA-RIRS may be associated with the intraoperative irrigation pressure. This is a mechanism that has not yet been explored in the analysis^[5].

In conclusion, while this review enhances our comprehension of NPAA-RIRS’s function in managing substantial renal calculi, the heterogeneous study design, inadequate follow-up duration, and the absence of anatomical and technical subgroup analyses impede its generalizability. The necessity for future multicenter RCTs with standardized operator credentialing and long-term follow-up is evident in order to confirm these findings.

Ethical approval

Not applicable.

Consent

Not applicable.

Sources of funding

No funding was received for this work.

Author contribution

X.L., Z.S., and T.X.: conception, design, and writing – original draft; X.L. and S.H.: writing – review and editing; X.L. and T.X.: investigation, project administration, and resources supervision. All authors were involved in the final approval of the manuscript.

Conflicts of interest disclosure

The authors declare that they have no conflicts of interest.

Guarantor

Sichuan Hou.

Research registration unique identifying number (UIN)

Not applicable.

Provenance and peer review

Not commissioned.

Data availability statement

Not applicable to this article.