Risk Factors Associated With The Adverse Outcome Of Residual Stones After PCNL For Upper Urinary Tract Calculi

doi:10.21203/rs.3.rs-1458634/v1

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Risk Factors Associated With The Adverse Outcome Of Residual Stones After PCNL For Upper Urinary Tract Calculi

https://doi.org/10.21203/rs.3.rs-1458634/v1

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posted 18 Mar, 2022

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The study aims to investigate the risk factors associated with the adverse outcome of residual stones after percutaneous nephrolithotomy (PCNL) for upper urinary tract calculi. 233 patients who underwent PCNL for upper urinary tract calculi and had postoperative residual stones were included. The adverse outcome of residual stones was defined as an increase in postoperative residual stone diameter or the recurrence of stone-related symptoms. The risk factors were analyzed from the patients’ records and the presence or absence of the adverse outcome. The factors examined were gender, age, location of the stone, the maximum diameter of stone, serum creatinine, calcium in blood, urine PH, size of residual stone, urine culture, hypertension, and diabetes. In addition, the difference was examined for stone composition and the type of bacteria in the urine culture. An adverse outcome of residual stones developed in 125 of 233 patients. Univariate analysis showed that the size of postoperative residual stones and positive urine culture were the risk factors for the adverse outcome. The probability of adverse outcome increased by about 1.694 times, when the diameter of residual stones increased by 1mm. The probability of adverse outcome in patients with positive urine culture was about 2.111 times higher than those with negative urine culture. However, other factors analyzed were not related to the adverse outcome of residual stone. In conclusion, longer diameter of residual stones and positive urine culture are risk factors associated with the adverse outcome of residual stones after PCNL for upper urinary tract calculi.

Urolithiasis

Kidney Calculi

Ureteral Calculi

Percutaneous Nephrolithotomy

Fragments

Postoperative outcome

Although PCNL is one of the main methods for the treatment of upper urinary tract calculi, with a high success rate[1, 2], it can’t completely avoid the residue of stone fragments. Residual stones less than 4 mm, without urinary tract infection and obstruction, are usually referred to as clinically insignificant residual fragments (CIRF) and usually do not require special treatment[3]. Previous studies have also shown that stones can be eliminated naturally through lifestyle changes or medication for patients with residual stones less than 6 mm in diameter[4].

However, the latest studies show that in some patients, postoperative small residual stones fragments are not expelled and may lead to stone-related symptoms such as infection, hematuria, back pain, and even require surgical treatment[5–8]. In addition, the probability of stone growth in patients with upper urinary tract stones after surgery is 10% within 1 year, 35% within 5 years, and up to 50% within 10 years[9, 10]. And yet to now, there is no clear evidence of risk factors for developing these adverse outcomes.

Therefore, this study aimed to investigate the risk factors related to adverse outcomes in patients with residual stones after PCNL for upper urinary tract stones and attempt to explore the theoretical basis for preventing the adverse outcomes of postoperative residual stones.

Study design

We collected the clinical data of all patients who underwent PCNL for kidney stones or upper ureteral stones at The First Affiliated Hospital Of University Of South China from 2013 to 2020. The inclusion criteria were as follows: (1) all patients with upper urinary tract calculi who underwent PCNL and had residual stones after the operation. (2) the diameter of the postoperative residual stone must be less than 7mm. If the postoperative residual stone diameter is larger than 7mm, it was regarded as a treatment failure. Exclusion criteria: (1) patients with incomplete clinical data; (2) patients who were missed during follow-up; (3) patients who had previous operations for renal or upper ureteral calculi; (4) patients with malignant tumors; (5) patients who had factors affecting the results of the experiment. 233 cases were finally included according to the inclusion and exclusion criteria. The adverse outcome of residual stones was defined as an increase in the diameter of postoperative stones, or the occurrence of stone-related symptoms such as ipsilateral low back pain, fever, and gross hematuria, demanding re-hospitalization[11]. According to the presence or absence of adverse outcome of postoperative residual stones, the patients were divided into the adverse outcome group (n = 125) and control group (n = 108). Factors as gender, age, stone location (left and right), maximum stone diameter, serum creatinine, calcium in blood, urine PH value, the maximum diameter of residual stones, urine bacterial and fungal culture, hypertension, and diabetes were compared between the two groups. In addition, the difference was examined for stone composition and the type of bacteria in the urine culture. The study was retrospectively designed and approved by The First Affiliated Hospital Of University Of South China Review Board.

Data Collection

All patients were diagnosed as renal or upper ureteral calculi by the plain film of kidney-ureter-bladder (KUB) or urinary computed tomography (CT) before the operation, and all patients were reexamined by KUB or urinary CT examination after the operation. The maximum length diameter of the stone was measured by KUB or CT, respectively, by two professional doctors of the imaging department. The average value of the two measurements was taken if the difference was within 1 mm; if the difference was greater than 1 mm, the third professional would then re-measure and took the average value of the two closest measurements. For the patients who did not come to our hospital regularly for re-examination, they were followed up at least once within 1 year after the operation, and confirmed whether they had undergone stone-related re-examination and whether they had any residual stone volume growth or stone-related symptoms after discharge. The stone composition was analyzed by an automatic infrared spectroscopic instrument, model LⅡR-20A/20B (Tianjin Lanmode Scientific Instrument Co., Ltd.). The rest of the clinical data are from the archived data of the medical records department of our institution.

Statistical analysis

Data were analyzed using the software Statistical Pack-age for Social Science version 25.0 (IBM, USA). The continuous variables were calculated by Mean ± SD and analyzed by a two-sample t-test. The Chi-square test was used to analyze the classified variables. In multivariate analysis, binary or multiple Logistic regression analysis was used, and P values < 0.05 were considered statistically significant. The statistically significant factors in multivariate analysis were tested by Hosmer-Lemeshow test and calibration curve to test the superiority of the prediction model, and the effectiveness of the prediction model was further evaluated by the area under the ROC curve.

Of the 233 patients with residual stones after PCNL for upper urinary tract calculi, adverse outcomes occurred in 125 patients (53.6%), including 64 males (51.2%) and 61 females (48.8%), with a mean age of 50.58 ± 11.39 years. And there were 108 patients with no adverse outcome (46.4%), including 70 male patients (64.8%) and 38 female patients (35.2%), with an average age of 53.01 ± 13.24 years.

Table 1 shows the comparison of measurement data between patients with adverse outcomes and those without adverse outcomes. The results of the independent samples t-test showed that the differences between the two groups were statistically significant (P < 0.05) in terms of residual stone size, while the differences were not statistically significant (P > 0.05) in terms of age, maximum stone diameter, Serum creatinine, calcium in blood, and urine pH value. Table 2 shows a comparison of the counting data between patients with adverse outcomes and those without adverse outcomes. The results of the chi-square test showed that there were significant differences in gender, positive urine culture between the two groups (P < 0.05). However, no significant differences were observed between both groups in hypertension, diabetes, side of stone occurrence (P > 0.05). The factors with statistically significant differences in the above results were further introduced into the binary logistics regression model for multivariate analysis (Table 3). The results showed that there were significant differences between the two groups in the size of residual stones and the positive culture of bacteria and fungi in urine. And it can be considered that they are the risk factors related to the adverse outcome of residual stones after upper urinary tract calculi operation. The probability of adverse outcome increased by about 1.694 times, when the diameter of residual stones increased by 1mm. The risk of adverse outcome of residual stones in patients with positive urine bacterial and fungal culture is about 2.111 times higher than that in patients with a negative urine culture. However, it can’t prove that gender is an independent risk factor for the adverse outcome of residual stones after PCNL for upper urinary tract calculi (P > 0.05). We finally obtain the prediction probability of the risk prediction model as P = 1/ [1 + e ^{(−1.995 + 0.527×Residual stone size (mm) + 0.747×Urine culture (positive=1, negative=0))}]. Table 4 showed 67% accuracy of this model to predict the adverse outcome of postoperative residual stones in upper urinary tract calculi. After the establishment of the prediction model, the superiority of the prediction model was tested by Hosmer-Lemeshow test (χ 2 = 9.451, P > 0.05) and calibration curve (Fig. 1). Results indicated that the difference was not statistically significant, which verified the fine superiority and clinical value of the prediction model. The effectiveness of the prediction model is further evaluated by the area under the ROC curve (Fig. 2). The area under the ROC curve is 0.7488 (95% CI: 0.6871–0.8105), indicating that the model has high accuracy in predicting the adverse outcome of residual stones after PCNL.

Table 1

Comparison of measurement data between the two groups of patients
Factors	Adverse outcome group (n = 125)	Control group (n = 108)	Statistical value	P values
Age (years)	50.58 ± 11.39	53.08 ± 13.24	t = 1.554	.122
Maximum stone diameter (cm)	2.03 ± 0.91	1.95 ± 0.88	t = -0.668	.505
Serum creatinine (µmol/L)	97.14 ± 39.47	104.81 ± 53.31	t = 1.258	.210
Calcium in blood (mol/L)	2.23 ± 1.96	2.21 ± 1.12	t = -0.689	.386
Urine pH value	6.07 ± 0.70	6.09 ± 0.74	t = 0.031	.736
Residual stone size (mm)*	3.42 ± 1.61	2.12 ± 1.41	t = 6.475	< 0.001
* Residual stone size refers to its maximum diameter

Table 2

Comparison of measurement data between the two groups of patients
Factors	Adverse outcome group (n = 125)	Control group (n = 108)	Statistical value	P values
Hypertension (with/without)	90/35	79/29	Χ² = 0.038	.845
Diabetes (with/without)	110/15	99/9	Χ² = 0.843	.359
Side of stone (left/right)	66/59	49/59	Χ² = 1.283	.258
Gender (male/female)	76/49	92/16	Χ² = 17.128	< 0.001
Urine culture (positive/ negative)	64/61	70/38	Χ² = 4.395	.036

Table 3

Multivariate analysis of the adverse outcomes
Components	β	SE	Wald	OR (95%CI)	P value
Residual stone size (mm)	0.527	0.110	23.064	1.694 (1.366–2.100)	< 0.001
Urine culture (positive/ negative)	0.747	0.362	4.255	2.111 (1.038–4.295)	.039
Gender (male/female)	0.385	0.300	1.645	1.470 (0.816–2.649)	.200
Constant	-1.995	0.530	14.182	0.013(-)	< 0.001

Table 4

Accuracy of model prediction
		Predicted value		Correct percentage
		No adverse outcomes	Have an adverse outcome	Correct percentage
Measured value	No adverse outcomes	78	30	(78/108) 72.2%
Measured value	Have an adverse outcome	47	78	(78/125) 62.4%
Overall percentage				67%

This study also analyzed the stone composition of 159 patients with upper urinary tract stones, including 88 in the adverse outcome group and 71 in the control group. In both the adverse outcome group and the control group, the main stone components were calcium oxalate monohydrate, followed by carbonated apatite, uric acid stones, magnesium ammonium phosphate hexahydrate, and calcium oxalate dihydrate, respectively (Fig. 3). The main pathogenic species in the urine of patients with positive urine bacterial and fungal culture results were investigated. Escherichia coli was found to be the leading pathogenic organism of urinary tract infection in both groups, with 28 (57.1%) cases cultured in the adverse outcome group and 10 (62.5%) cases cultured in the control group. In addition, 1 case of Acinetobacter baumannii, 1 case of Staphylococcus epidermidis, 1 case of Enterobacter aerogenes, 1 case of E. faecalis, 1 case of Proteus mirabilis and 1 case of Fungi were cultured in the control group. 1 case of E. asburiae, 1 case of Staphylococcus epidermidis, 1 case of E. fergusonii, 1 case of Saprophytic staphylococci, 1 case of E. agglomerans, 1 case of E. casseliflavus, 1 case of Staphylococcus haemolyticus, 1 case of Streptococcus agalactiae, 1 case of Acinetobacter baumannii, 1 case of candida albicans, 1 case of Pesudomonas pyocyaneum, 2 cases of E. faecalis, 2 cases of Candida, 3 cases of E. faecium and 3 cases of Klebsiella pneumoniae pneumonia were cultured in the adverse outcome group.

Upper urinary tract calculi is one of the most common diseases worldwide, which has caused serious harm to the safety of life and property of people all over the world. In the past 30 years, the incidence of upper urinary tract calculi has been increasing continuously. The overall incidence of upper urinary tract stones in China is 6.4%, among which the incidence of upper urinary tract stones in men is 6.5% and in women is 5.1%, with a male to female ratio being 1.27[12]. The harm of upper urinary tract calculi to the human body is huge[13]. Therefore, it is very important to understand the risk factors related to the adverse outcome of postoperative residual calculi in upper urinary tract calculi and to select appropriate clinical treatment and prevention methods, which can reduce the physical burden and the medical expenses of patients.

In previous studies, we have concluded that postoperative residual stones may have the following hazards: (1) Postoperative residual stones may cause and perpetuate the urinary tract infection; (2) New stones may form with residual stones as the core; (3) The movement of residual stones after surgery may cause obstruction and trigger new symptoms. Although postoperative residual stones have many hidden dangers, it is still difficult to completely remove all stones due to the limitations of surgical equipment, medical technology, and surgeon experience in actual clinical work. In the past, in conditions of normal upper urinary tract anatomy, no urinary tract infection or other symptoms, stones with postoperative diameter less than 4mm were called meaningless residual stones. Moreover, it was considered that these stones had a high pass rate. However, at present, the significance of these meaningless residual stones is becoming controversial. In recent studies, the probability of adverse outcomes for what were previously considered nonsignificant residual stones has also increased[8]. In the 2020 edition of the EAU Guidelines on Urolithiasis, postoperative residual calculi greater than 2mm increase the risk of recurrence of calculi-related symptoms and require appropriate clinical management[14]. Stones smaller than 2mm also require close clinical observation. Therefore, in the future treatment of upper urinary tract stones, removing residual stone fragments as far as possible may become a new issue to urologists. In our study, we found that there was a strong correlation between the size of postoperative residual stones and the postoperative adverse outcome. The larger the size of postoperative residual stones are, the greater the possibility of adverse outcomes is. The adverse outcome rate of upper urinary tract calculi increases nearly 1.5 times with the increase by 1mm in the diameter of postoperative residual stones, which indicates the necessity of clinical intervention for postoperative residual stones.

Although there is still controversy on the treatment of postoperative residual stones, we believed it is important for urologist to help every stone patient remove the stones completely in the future. Many researchers have done a lot of researches and developed novel techniques on the treatment of postoperative residual stones. Friedlander et al developed a novel device that captures stones in a sealed polyethylene bag in vivo to prevent dispersion of stone fragments during PCNL and found in their study that the use of this device significantly reduced the median time for stone fragmentation [15]. Tracy et al developed a magnetic tool to improve the efficiency of lithotripsy under a ureteroscope. Compared with the traditional Ni-Ti alloy stone extraction basket, the time for magnetic stone extraction tools to extract residual stone fragments is reduced by 53%. Although the visual field of magnetic stone extraction tools is worse than that of traditional stone extraction tools, and it is more difficult to deal with residual stones larger than 3mm, this design is still under further development and improvement[16, 17]. Heinet et al proposed a new type of biocompatible adhesive. In the experiment of pig kidneys, the time of chasing stones in the experimental group was significantly less than that in the control group, and no obvious adverse reactions were found in the experiment. With the emergence, innovation and use of new technologies, the treatment of residual stones after upper urinary tract stone surgery will become much easier in the future of urology.

In the study, we found that bacterial or fungal infection in urine is an independent risk factor for the adverse outcome of residual stones after PCNL. Patients with a positive urine culture were nearly twice as likely to have an adverse outcome of postoperative residual stones as those who were negative. Among the bacterial species cultured, Escherichia coli was the most common, with 27 (55.1%) cases in the adverse outcome group and 10 (58.8%) cases in the control group. Previous studies have shown that in Escherichia coli-infected kidneys, the expression of osteopontin (OPN) is elevated in renal tubular epithelial cells, which leads to tubular epithelial cell damage and induces a renal inflammatory response that activates multiple immune response signaling pathways, thereby promoting stone formation[18].

Component analysis of calculi in some patients revealed that infectious stones accounted for 28.9% of all stones, with a 60.9% prevalence of infectious stones in women, similar to previous epidemiological studies. In our study, we also cultured the urine of all patients, in which a small amount of Klebsiella and Proteus were cultured. But due to the limited number of positive cases of culture, it is hard to prove whether a special bacterial infection increases the probability of an adverse outcome in patients with residual stones after the operation. The low detection rate of these urease-producing bacteria may be explained that they usually produce biofilms adhering to the urothelial tissue, thus reducing the bacterial count in the urine and making it more difficult for clinical testing. Whether there is a direct relationship between the formation of infectious stones and urease-producing bacteria may require further experiments and data analysis of stone culture, molecular analysis, or other detection methods[19].

In previous epidemiological studies, the incidence of upper urinary tract stones was generally higher in men than in female patients[12]. However, studies in recent years have found that the incidence of upper urinary tract stones in female patients is also increasing with the increase in the incidence of upper urinary tract stones worldwide[20]. It has been reported that for women between the ages of 15 and 44, their lifetime risk of developing urinary calculi increased by 45% or more [21]. This study found that the incidence of the adverse outcome of postoperative residual stones in female patients was significantly higher than that in male patients. In the adverse outcome group, the ratio of female to male patients reached 1:1, while in the control group, the proportion of female to male patients was just 1:2. It seemed that female patients with upper urinary tract calculi have a higher probability of adverse outcome after operation. However, after binary logistics analysis, it can’t be considered that gender is an independent risk factor for adverse outcome of postoperative residual stones in patients with upper urinary tract calculi. Therefore, whether female is a risk factor associated with the adverse outcome of residual stones after PCNL deserved further study.

There is a positive correlation between the size of residual stones after PCNL and the adverse outcome of postoperative residual stones. The larger the residual stones are, the higher the rate of adverse resolution of postoperative residual stones is. In addition, patients with bacterial or fungal cultured in urine after PCNL for upper urinary tract stones also have an increased rate of adverse outcomes with postoperative residual stones.

Acknowledgments

This study was supported by the Research and Reform Project of Hospital Administration of University of South China (No. 2021YYGL10) and Clinical research Project of University of South China (No. USCKF201902K01).

Compliance with ethical standards

Conflict of interest The authors declare that they have no conflict of interest.

Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional committee and the 1964 Declaration of Helsinki.

Informed consent Informed consent was given by all patients included in this study.

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No competing interests reported.

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posted 18 Mar, 2022

You are reading this latest preprint version

Risk Factors Associated With The Adverse Outcome Of Residual Stones After PCNL For Upper Urinary Tract Calculi

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Version 1

Abstract

Figures

Introduction

Materials And Methods

Study design

Data Collection

Statistical analysis

Results

Discussion

Conclusions

Declarations

References

Competing Interests

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