Abstract
We have read with great interest the article by Cai et al.: In a series of 188 cases, there was no requirement of embolization or blood transfusion. This is a major contribution of miniaturized percutaneous nephrolithotomy (PCNL). They have retrospectively evaluated the safety and efficacy of the new generation super-mini PCNL (new-SMP) for renal stones ≥20 mm in diameter. For this study, the investigators used an 8F miniaturized nephroscope with a 12F/14F newly designed metal irrigation–suction sheath comprising two chambers, both of which are durable and maintain a sufficient intrarenal space to effectively remove fragments with negative pressure aspiration. 1 Clinical outcomes showed that the new-SMP was highly effective at removing 20 to 40 mm stones resulting in a 92.8% stone-free rate (SFR) at 3 months, whereas decreasing to 81.8% for >40 mm stones. Regarding safety, although 9.6% of cases presented with postoperative fever, no patient developed septic shock. In addition, neither blood transfusion nor arterial embolization was required, and no Clavien–Dindo III–IV events was reported.
On the premise that super-mini access tracts might cause longer operating times for large-sized stones and hence increase the risk of infectious complications, a recent prospective study continuously monitored renal pelvic pressures (RPPs) and showed that the irrigation–suction sheath was safe as it was able to maintain RPP <30 mmHg for almost the entire duration of each SMP in the study. 2 RPP ≥30 mm for a limited amount of time (55 seconds) did not correlate with postoperative fever. It is plausible that operative time, as a proxy of cumulative high RPPs, is one of the most important predictors of complications after PCNL. 3 Therefore, rather than tract size, effective drainage of irrigation fluid and time-efficient procedures are of utmost importance to decrease postoperative complication rates. The SFRs are better than the SFRs of retrograde intrarenal surgery (RIRS) and the equipment is less expensive. The median operative time was 35 minutes, much less than the median operative time for a similar size stone by RIRS.
One of the most significant findings of this study was that the median operative time differed slightly (10 minutes) between cases with 20 to 40 mm and >40 mm renal stones, which was also similar to mini-PCNL. 4 The mean postoperative hospital stay between both groups was comparable. These results imply that the indication for SMP may be extended to large-sized renal stones. Nevertheless, the number of cases with renal stones >40 mm was limited. Thus a randomized controlled trial should be performed to reliably compare the clinical application of the new-SMP in medium- and large-sized renal stones. A comparison with larger tract sized PCNL systems would also be of considerable interest to determine the true stance of the new-SMP in the current treatment standards for large renal stones.
Miniaturized PCNL seems to be better for urologists because the reimbursements of PCNL are better than those of RIRS, it is better for the patients because the SFRs seem to be better than RIRS and it is better for the health care system because it is less expensive than RIRS. 5