Percutaneous nephrolitholapaxy (PCNL) is currently a standard method of treatment for kidney stones. This low invasive treatment method for patients with large and staghorn kidney stones showed its effectiveness and a low rate of complications [1-10].

Percutaneous low invasive surgeries on kidneys have specific complications that include inflammation, hemorrhage, pleural and abdominal cavity lesion, and the need for repeated operation [9-19]. PCNL does not always provide complete stone elimination in patients with large and multiple kidney stones, especially staghorn stones. In such cases, surgeons must perform several surgical interventions, which increase the risks of perioperative complications [19-21].

Percutaneous interventions currently require radiograph guidance [7][22-24]. X-ray guidance has certain drawbacks that include radiological exposure of medical personnel and patients and the need for a specialized surgical ward with expensive equipment. Although medical personnel use special protection during such surgeries, percutaneous interventions with radioscopy can often lead to complications in them [24-28]. Long-term radioscopy during percutaneous surgeries can lead to the development of a cataract [27]. The maximum radiation dose to the surgeon’s eyes is observed after 1200 PCNL surgeries within one year, with a total full-body radiation dose of 150 mSv [28]. Besides, medical personnel must wear special protection, the weight of which significantly disrupts surgeon thermoregulation and complicates manipulation during surgery.

PCNL technique is continually evolving with the development of new safer technologies [29]. Lately, ultrasonic scanning methods have been implemented in clinical practice as an alternative to X-ray guidance during PCNL [30-37]. Thus, a complex clinical evaluation of the efficiency of new PCNL technology is relevant.

The study aimed to identify the most significant factors that affect the rate of complete elimination of kidney stones and the development of complications in patients after PCNL performed under ultrasound (US) and endovisual guidance.

A total of 515 patients (81.0%) patients who underwent PCNL under an original method of US and endovisual guidance (Patent for Invention of the Russian Federation No. 2755226 dated March 15, 2021) were studied [38]. The patients were operated in the urological clinic of the Privolzhskiy Regional Medical Center of the Nizhny Novgorod Russian Federal Clinical Research Center. The analysis and stratification of complications after PCNL were made using the modified classification of surgical complications of Clavien-Dindo [39-44].

Percutaneous nephrolitholapaxy under ultrasound and endovisual guidance. Specialists from the urological clinic of the Privolzhskiy Regional Medical Center in 2007 developed and advanced an original method of PCNL performed under US and endovisual control [38]. By now, over 4,000 PCNL surgeries were performed using this method. There are several technical peculiarities in this type of surgery. The patient is positioned on the “healthy” side in the dorsal-lateral position so that the kidney to be operated on would be on top. The costovertebral angle is increased by lowering the head and leg ends of the surgical table relative to the axis at the level of L4-L5 (Fig. 1).

An ultrasonic scanner Phillips HD7 (Koninklijke Philips N.V., Philips Medical Systems Nederland B.V., Heerlen, The Netherlands) is set in the puncture mode. US investigation of the kidney and surrounding organs is performed, and US landmarks are differentiated (kidney shape and dimensions, type of the pyelocalyceal system (PCS), the number, configuration, and dimensions of kidneys). Further, the optimal direction for puncture is identified. The puncture channel should not cross neighboring organs (liver, spleen, lung sinus, intestine, peritoneal reflection, and large vessels). The lack of PCS dilation does not prevent its puncture. In this case, the final puncture point will be at the outer edge of the stone in the pelvis or calix. The needle is inserted toward the chosen point, considering the puncture landmarks on the screen. The needle is gradually inserted according to the respiratory movements of the patient, i.e. during the pauses at the height of inhalation or expiration. During the manipulation, the puncture needle end should be visible as a bright light point. When the needle penetrates the cavity, the internal part of the needle is extracted. A syringe is connected to the needle to create a vacuum effect and get urine. Further, a super-stiff guidewire is introduced, which must be controlled by US visualization. When the guidewire end is moved over the needle end, it rolls in a coil because of its construction and prevents damage to distal tissues. The guidewire is left inside, and the needle is removed from the guidewire and extracted.

The next stage includes dilation of the puncture channel to 12 Ch using a plastic dilator, which is placed on the guidewire and moved to the guidewire coil (natural obstacle) by rotational movements. Further, the dilator should be extracted and a 10 Ch ureteroscope should be placed on the guidewire (Karl Storz SE GmbH & Co. KG., Tuttlingen, Germany). The ureteroscope is inserted in the nephrostomy channel over the guidewire under irrigation. The punctured tissues are visualized. Surgeons can see and diagnose damage to the intestine and pleural cavity and other accidental injuries before installing the Amplatz tube (Boston Scientific Corp., San Jose, CA, USA) and before the beginning of the main stage of surgery. If there are any technical obstacles that prevent surgical intervention, the prepared channel should be left.

When the puncture is successful, the ureteroscope passes through the layers of the abdominal wall, the retroperitoneum, and the kidney parenchyma in the kidney cavity. Further, nephroscopy is performed (Karl Storz SE GmbH & Co. KG., Tuttlingen, Germany). A safety guidewire is introduced in the ureteropelvic junction and ureter (Fig. 2). A safety guidewire remains introduced and the ureteroscope should be removed. After that, the ureteroscope is introduced again in the puncture channel along the safety wire and the channel is examined again. When the tool is inserted into the renal cavitary system, all cavities should be re-examined. The stone and the possibility of its removal should be evaluated. Under visualization, an optimal place is chosen in the renal system for further channel dilation and the introduction of an Amplatz tube. A super-stiff guidewire is inserted again in this place; its coil is placed in the PCS area. The ureteroscope is removed from the guidewire. The channel is dilated to 26 Ch using Alken dilators (Karl Storz SE GmbH & Co. KG., Tuttlingen, Germany).

For safe channel dilation with simultaneous insertion to the final point, it is necessary to fix the external nephroscope tube equipped with an Amplatz tube, which prevents their disposition when moving into the kidney and accidental injury by the external nephroscope tube. The authors used an original advanced construction of the fixing element (Karl Storz SE GmbH & Co. KG., Tuttlingen, Germany), which was taken from a nephroscope obturator. It was welded to the last tube of the dilator. To dilate the channel, it is necessary to introduce the first tube with an olive tip to the guidewire coil, which is a natural obstacle to further insertion. This stage should be performed without forced movements. The tube should slide along the wire until some resistance is obtained. The initial direction and the depth of the channel are visually controlled during the movement. Each next tube is placed on this tube and introduced to the obstacle. At the same time, the external part of the tube with an olive tip should be fixed in place to prevent uncontrolled movement forward from the chosen point. Palpation is used to control the location of the tubes in the cavity. When all tubes are introduced one by one to the obstacle on the olive tip, the external tube is moved 3 – 4 mm, and the olive tube can be freely moved from the end of the dilator tubes to the distal end. This can be a stone, a calix wall, or a pelvis. The Amplatz tube is not introduced; it is left on the nephroscope tube. When the last dilator with a fixed external nephroscope tube 26 Ch is introduced (Fig. 3), the fixing thread is cut and removed, or the original fixing mechanism is unlocked. The dilators are removed, and the guidewire remains inside the kidney.

A ureteroscope with a connected irrigation system is introduced into an external nephroscope tube that is hold. It is necessary to examine and visually evaluate the dilated channel with the help of an assistant who can help hold either a ureteroscope or nephroscope tube. At the same time, the Amplatz tube should be moved further until it appears on the screen of the video system. The ureteroscope is replaced with a nephroscope. The final positioning of the tubes is performed under visual guidance.

Lithotripsy can be performed with pneumatic, ultrasonic, and/or laser lithotriptors. Stone fragments are removed with forceps or evacuated by suction. The assistant holds an external tube to prevent its migration. Visually and under US guidance, surgeons check the completeness of stone fragment removal. If there are fragments revealed, it is necessary to evaluate the possibility of stones removal from this access or a need for an additional channel. After lithotripsy, a ureteral stent is installed via the Amplatz tube. The stent is associated with nephrostomy drainage under endovisual guidance without X-ray technology (Fig. 4).

Statistical analysis. Statistical data processing was performed using the licensed software package IBM SPSS Statistics ver. 14.0.1 (SPSS: An IBM Company, IBM SPSS Corp., Armonk, NY, USA) and electronic tables Microsoft Word 2016 and Excel 2016 (Microsoft Corp., Redmond, WA, USA). In the groups, the authors calculated the descriptive statistics parameters (mean values, mean errors, mode, median, maximal, and minimal values). The statistical analysis of qualitative features included the method of calculation of the Spearman’s correlation coefficient and 95% confidential intervals (CI). To check the hypothesis on the statistical significance of differences in qualitative features, the authors analyzed the contingency tables with the calculation of the Pearson χ2 test and χ2 test with Yates’ correction for four-fold tables (the number of observations in separate cells ≥10). The groups were compared by the qualitative features using Student’s t-test when applicable and the Mann-Whitney test in the other cases. The odds ratio (OR) was estimated using regression analysis (logit regression). The data were significant at 0.05 (p < 0.05).

The initial demographics of patients before PCNL are presented in Table 1. The mean duration of surgery was 77.2 ± 1.9 minutes. Most surgeries were performed via one puncture (95.1%) and in one stage (91.8%) with the complete elimination of stones in 80.6% of cases. The level of hemoglobin decreased by 12.18 ± 0.6 g/L in the postoperative period. The postoperative complications rate was 29.3%. In most cases, complications were Clavien-Dindo I – II degrees of severity (Table 2).

Clavien-Dindo IIIa complication was registered in one case (pneumothorax and pleural puncture). Clavien-Dindo IIIb complications were observed in eight (1.6%) patients: one (0.58%) had intraabdominal bleeding (laparoscopy), one (0.19%) — colon perforation (laparotomy and suturing of colon defect), three (0.58%) — renal bleeding (selective embolization of the vessel), and one (0.19%) – retroperitoneal bleeding (kidney revision, hemostasis). Most of these complications (six out of eight) were registered within the first year of the development and implementation of the PCNL technique. Clavien-Dindo IVa complication was observed in one patient (0.19%) — angina pectoris. Clavien-Dindo IVb complication was registered in one patient (0.19%) – urosepsis and septic shock that resolved after intensive therapy. Clavien-Dindo V complication was registered in one patient (0.19%) — massive pulmonary artery thromboembolia (PATE) with a lethal outcome.

Univariate regression analysis was performed to establish independent predictors of complete stone elimination (Table 3). Independent predictors that affect the rate of complete stone elimination included body mass index (BMI), stone dimension, the number of stones, the number of surgery stages and accesses, the presence of staghorn stone, X-ray-negative stones, and the duration of the operation.

Multivariate regression analysis was performed to study the character of independent predictors of stone elimination (Table 4). Independent predictors that affect the rate of complete stone eradication included the number of stones (p = 0.012), the presence of a staghorn (p = 0.016), and the number of stages of surgical intervention (p = 0.001).

The results of correlation analysis showed a statistically significant weak negative correlation between BMI and complications (Spearman’s = -0.187; p = 0.005) and a weak positive correlation between the presence of urinary tract infection and complications (Spearman’s = 0.13; p = 0.048). Additionally, correlation analysis revealed a weak statistically significant positive correlation between bleeding severity and complications (Spearman’s = 0.263; p < 0.001).

PCNL is one of the most effective methods of treatment for large and staghorn kidney stones [1-6]. Due to the improvement in technology, PCNL replaced open surgery in patients with complicated kidney stones. However, regardless of the method, PCNL is associated with the development of complications of different types and severities [9][10][16][19][43]. A literature review conducted by Taylor et al. (2012) included 5,803 patients who underwent PCNL performed by traditional methods. The rate of complications was 21.5% [42]. A pleural injury was observed in 0.30 – 1.58% of cases, blood transfusion was performed in 2.0 – 6.9% of cases, repeated surgeries for complications were required in 2.0% of patients, and lethal outcomes were registered in two (0.03%) of patients with Clavien-Dindo V complication (PATE, myocardial infarction associated with severe sepsis). Another literature review that included over 12,000 patients showed that the rate of complications after PCNL was 23.3% (16.2 – 60.3%): fever — 10.8%, blood transfusion — 7.0%, thoracic complications — 1.5%, sepsis — 0.5%, abdominal organ injury — 0.4%, renal artery embolization — 0.4%, urinoma — 0.2%, and lethality — 0.05% (0.04 –0.10%) [44]. The rate, structure, and severity of complications after PCNL, shown in the present study, agreed with modern published data. An important parameter of PCNL effectiveness is the complete stone-free rate (78.0% according to the published data). The complete stone-free rate depends on the stone dimensions and varies depending on the stone size (<1 cm — 100.0%, 1 – 2 cm — 93.0%, >2 cm — 86.0%) [21]. Osman et al. (2005) reported that after primary US-guided PCNL, additional interventions were needed in 33.0% of patients (extracorporeal shock wave lithotripsy, repeated PCNL, ureteroscopy) who primarily had staghorn stones [32]. In the present study, the complete stone-free rate was 80.6%. The results in the present study were comparable to other PCNL published results.

PCNL performed under US and endovisual guidance without the application of radiological technology is an efficient surgical intervention method for most patients with stone kidneys. The complete stone-free rate of kidney stones with PCNL performed under US and endovisual guidance was 80.6%. The complete sone-free rate significantly depends on the number of stones, the presence of staghorn stone, and the number of stages of surgical intervention. The rate of early complications after PCNL was 29.3%. Primarily, they were I – II degrees of severity by Clavien-Dindo. The rate of complications was affected by BMI, the presence of urinary infection, and the degree of decrease in hemoglobin during surgery.