Upper ureter or renal stones often were treated with MPCNL and most patients can achieve the purpose of cure. Due to the pressure limit of renal parenchymal reflux is 30 mmHg [
6], when the MPCNL is performed under high pressure perfusion it is easy to cause the intrapelvic pressure over 30 mmHg, and the operation manipulation, the integrity of the pelvic wall epithelium could be injured and thereafter leads to direct exposure of venous and lymphatic system followed by renal parenchyma reflux [
7]; When the stones and infection occur at the same time, tissue edema and congestion are more likely to cause pelvic fluid absorption. A large amount of short-term liquid absorption can cause the perfusion fluid syndrome, and when the bacteria and its toxin reflux into the blood, complications like bacteremia, sepsis, or postoperative fever occur [
8]. MPCNL surgery complication is related to the amount of liquid absorption. It is a positive correlation between the integrity of the epithelial cells, renal pelvic pressure, and the operation time [
6,
9]. Performing MPCNL through irrigation can cause stones shift. When the collection system is connected to the renal abscess pus, due to the blurring of vision, it is not easy to find the pelvic outlet so the surgeon is often forced to abandon stone lithotripsy in which circumstance usually a percutaneous nephrostomy is performed as a first-stage surgery. In the current study, incidence rate of surgical complications in the control group was 51.6%% with 14 cases needing two staged operation. Therefore, how to improve success rate of surgery and reduce postoperative complications for calculus pyonephrosis is always a challenge in the field of Urology [
10].
According to a previous report, when the intra-pelvic pressure is below 20 mmHg, it is feasible to use the EMS LithoClast master for one-phase PCNL of the relatively symptomatically stable patients with calculous pyonephrosis. Nevertheless, this surgical procedure has always carried high risks and its advantages and disadvantages should be validated by further studies of larger sample sizes [
11,
12]. Patented sheath connected during surgery remains 0.01–0.02 MPa negative pressure suction to keep renal pelvis in a negative pressure state, so that the discharge of perfusion fluid and pus went smoothly, avoided lavage, bacteria, toxins reflux and spread to surrounding tissues, reduced fever infection complications after surgery. In the current study, only 10 patients in the observation group were found to have temperature ≥ 38.5 °C, significantly lower than those in the control group; Negative pressure adsorption can remove the effect of blood clots and floc, the vision can be more clear. With negative pressure “adsorption” effect on the gravel, small stones and pus hidden in the calyces can be automatically removed by suction. Due to a big discharge cavity of the sheath which is not easy to be blocked, there is no need of lithotomy forceps or stone basket, without the need for repeated importing a ureteroscope to flush, either. We are thus able to improve the efficacy of lithotripsy and stone clearance, shorten operation time, and reduce the operation complications such as bleeding [
3]. In this study, all patients in the observation group were successfully treated with the MPCNL by one surgery with a stone clearance rate of 96.7%. There were no adjacent organ injury and major bleeding, compared with the control group, with significant difference. With improved success rate of surgery and reduced rate of complication, the hospitalization time was shortened and the cost of hospitalization was reduced. Of course, surgeons may have been more aggressive using the patented sheath and less aggressive with the peel-away sheath due to the aims of this study, therefore getting higher stone-free rates in patients in the observation arm. Other limitation of this study is that we did not measure intrarenal pelvic pressure for every patient during the surgery, even though we have had previous research data revealing that the patented sheath could reduce intrarenal pressure.