Effect of Using Automated Irrigation Systems on the Risk of Infectious Complications after Endoscopic Combined Intrarenal Surgery: A Retrospective Cohort Study

Abstract

Objective:

Endoscopic combined intrarenal surgery (ECIRS) is a treatment option for kidney stones comparable with other standard methods. One reported complication of ECIRS is infection associated with high intrarenal pressure (IRP), and the irrigation system is an important factor affecting the IRP. Therefore, this study aimed to compare the operative outcomes and infectious complications between manual and gravity irrigation and automated irrigation systems for ECIRS.

Materials and Methods:

This single-center, retrospective cohort study enrolled patients who underwent ECIRS between January 2016 and August 2021. We compared operative results and complications between the two irrigation systems, and a multivariate analysis was performed to identify the factors associated with each outcome.

Results:

A total of 294 patients were enrolled in this study. The operative time was significantly longer in the manual and gravity irrigation group than in the automated irrigation group (122 ± 45 vs 108 ± 37 minutes, p = 0.003). Postoperative fever occurred in 25% of the patients in the manual and gravity group compared with 10% in the automated group (p < 0.001). In multivariate analysis, the use of a manual and gravity irrigation system was a significant factor associated with postoperative fever (p = 0.001) and longer operative time (p < 0.001).

Conclusions:

Using an automated irrigation system for flexible ureteroscopy in ECIRS reduces the risk of postoperative fever and the operative time.

Introduction

Endoscopic combined intrarenal surgery (ECIRS) is an alternative choice for the treatment of renal stones.¹ Although ECIRS is a minimally invasive procedure considered as safe as percutaneous nephrolithotomy (PCNL), there are some reports of infectious complications associated with ECIRS, including fever and sepsis, which are related to morbidity and mortality rate.^2
–4 One of the important predictors of fever and sepsis after endourologic procedures is high intrarenal pressure (IRP) above 30 mm Hg.^5,6 High IRP seems to be related to intrarenal backflow from the collecting system to the pyelotubular structure that leads to infection.⁷ Irrigation during the procedure is one of the dominant factors influencing the IRP.⁸ Especially in ECIRS, the simultaneous perfusion of two irrigation systems via the percutaneous and transurethral routes may increase the IRP during surgery.

One of the traditional methods for irrigation in ureteroscopy (URS) is manual and gravity irrigation using the gravity effect and a continuous-flow single-action pumping system (SAPS) for the irrigant fluid. Although a global practice survey showed that the manual pumping irrigation system is the most popular among urologists,⁹ some evidence has revealed that using the manual pumping method results in a higher risk of postoperative infection than a pressure control irrigation system.^8,10 Another recent method is an automated system using a pumping machine that can be adjusted for pressure and ensure adequate fluid irrigation. A high-quality irrigation system is essential for ECIRS to ensure clear visibility and remove stone fragments. Therefore, this study aimed to compare intraoperative and postoperative outcomes, especially infectious complications, of manual and gravity irrigation with those of automated irrigation for flexible URS during ECIRS.

Materials and Methods

Study design and population

This single-center retrospective cohort study was approved by the Institutional Review Board of Nagoya City University (NCU) Hospital (approval number: 60-19-0044), and the requirement for informed consent was waived owing to the retrospective study protocol. All patient data were confidently retained in compliance with the Declaration of Helsinki.

The medical records of all patients who underwent ECIRS at the NCU Hospital from January 2016 to August 2021 were retrospectively reviewed and divided into two groups based on their irrigation system for flexible URS during ECIRS: the manual and gravity irrigation group and the automated irrigation group. From January 2016 to July 2019, we used a manual and gravity irrigation system for flexible URS during ECIRS and switched to an automated irrigation system after August 2019. A one-way valve with an automatic refill syringe SAPS (Boston Scientific) with gravity effect was used as the irrigation system in the manual and gravity irrigation group, whereas the UROMAT® Endoscopic Automatic System (Karl Storz) was used in the automated irrigation group.

All patients were diagnosed with kidney or ureteral stones using CT to evaluate the stones and the degree of hydronephrosis. Patient data were recorded, including demographics, stone characteristics, hydronephrosis, previous ureteral stent or nephrostomy tube status, preoperative urine culture, intraoperative data (surgical duration, PCNL tract size, and access sheath size), and postoperative outcomes (stone-free rate, fever, and sepsis). The stone volume was calculated using the following formula: width × length × height. Stone-free status was categorized based on their maximum length into the following grades: absolute stone-free (Grade A), remnants smaller than 2 mm (Grade B), remnants measuring between 2.1 to 4.0 mm (Grade C), or remnants measuring greater than 4.0 mm (Grade D) on CT scan at 3 months postoperatively. Postoperative infectious complications, including fever and sepsis, were reviewed within 48 hours after ECIRS. Fever was defined as an axillary temperature of >38°C, and sepsis was diagnosed as per the international consensus definition.¹¹

Surgical technique

All ECIRS procedures were performed by at least two urologists. Patients were placed in the modified Galdakao–Valdivia or prone split-leg position under general anesthesia, depending on the surgeon’s discretion. Flexible cystoscopy was performed to identify the ureteral orifice. A 0.035-mm guidewire was passed into the renal pelvis, and then a ureteral access sheath (10/12, 11/13, or 12/14-French [F]) was inserted over the guidewire to the site of the stone. Flexible URS (URF-V2; Olympus) was performed using a manual and gravity or automated irrigation system. In the manual and gravity irrigation group, a 2 L saline bag was suspended 60 cm above the patient and attached to the SAPS. In the automated irrigation group, the automated irrigation system was set to a pressure of 90 mm Hg. Artificial hydronephrosis was induced using a retrograde contrast medium injection. Renal puncture was performed using an ultrasound-guided technique, and a nephrostomy tract (17.5 or 22F) was created and monitored under direct vision from the flexible URS, if possible. The gravity irrigation with a 2 L saline bag suspended 60 cm above the patient was used for PCNL site. Stone fragmentation was conducted by LithoClast lithotripsy (Electro Medical System S.A., Nyon) via a 12F mini-nephroscope and flexible URS using a holmium:yttrium aluminum garnet laser. The stone fragments were removed from the renal puncture site. Finally, a 6F Double-J ureteral stent was placed at the end of the procedure. In the case of active bleeding, a nephrostomy tube was placed. The surgical duration was recorded from the retrograde insertion of the flexible URS until completion of the ureteral stent and/or nephrostomy tube placement.

Antibiotic use

All patients received antibiotics immediately before surgery. Cefazolin was used when there was no preoperative pyuria, and antibiotics were selected according to the urine culture results when pyuria was present. Postoperatively, the patients were hospitalized for 2 days, and antibiotics were administered at approximately 6 and 18 hours after surgery.

Statistical analysis

Demographic data, stone characteristics, intraoperative data, and postoperative data are described as mean ± standard deviation and percentile value. The independent t-test and Pearson chi-square test were used to compare data between the two groups. A binary logistic regression model for multivariate analysis was used to identify factors affecting the perioperative and postoperative outcomes of ECIRS. Statistical analyses were performed using SPSS software (version 28; IBM Corp.), and statistical significance was set at p < 0.05.

Results

A total of 294 patients were enrolled in this study and divided into two groups depending on the type of irrigation device used for flexible URS. In total, 150 (51%) patients were in the manual and gravity irrigation system group (manual and gravity group) and 144 (49%) were in the automated irrigation system group (automated group). The characteristics of the patients and their stones were comparatively analyzed and are presented in Table 1. There were no clinical differences in sex, age, body mass index (BMI), side, stone density, stone volume, or preoperative hydronephrosis between the groups. Although the mean stone volume was slightly larger in the manual and gravity group (15,823 ± 32,597 mm³) than in the automated group (11,311 ± 15,677 mm³), there was no statistically significant difference. There was a significant difference in the stone location, as shown in Table 1 (p = 0.004).

Table 1.

Demographic Data and Stone Characteristics

	Manual and gravity irrigation system group150 (51%)	Automated irrigation system group144 (49%)	p-Value
Age (years)	56 ± 15	58 ± 13	0.462
BMI (kg/m²)	24 ± 4	25 ± 5	0.641
Sex
Male	100 (67)	92 (64)	0.617
Female	50 (33)	52 (36)
Stone laterality
Right	64 (43)	59 (41)	0.768
Left	86 (57)	85 (59)
Stone location
Upper calix	15 (10)	23 (16)	0.004
Middle calix	8 (5)	24 (17)
Lower calix	36 (24)	30 (21)
UPJ	81 (54)	55 (38)
Ureter	10 (7)	12 (8)
Stone density (HU)	1,329 ± 888	1,260 ± 345	0.388
Stone volume (mm³)	15,823 ± 32,597	11,311 ± 15,677	0.134
Preoperative hydronephrosis	77 (51)	65 (45)	0.288
Preoperative PCN or ureteral stent	19 (13)	32 (22)	0.031
Preoperative positive urine culture	52 (35)	26 (18)	0.001

BMI = body mass index; PCN = percutaneous nephrostomy; UPJ = ureteropelvic junction.

Operative outcomes and infectious complications are presented in Table 2. The average surgical duration was significantly longer in the manual and gravity group than in the automated group (122 ± 45 vs 108 ± 37 minutes, p = 0.003). The stone-free rates at 3 months after ECIRS were categorized into Grades A–D and are presented in Table 2 (p = 0.164). Overall, 25% of the patients in the manual and gravity group had postoperative fever compared with 10% in the automated group (p < 0.001). Sepsis was detected in 4% of the patients in both groups (p = 0.942).

Table 2.

Operative Outcomes and Complications

	Manual and gravity irrigation system group150 (51%)	Automated irrigation system group144 (49%)	p-Value
Position
Prone split-leg	103 (69)	87 (60)	0.139
Modified Galdakao–Valdivia	47 (31)	57 (40)
PCNL tract (F)
17.5F	143 (95)	131 (91)	0.138
22F	7 (5)	13 (9)
Ureteral access sheath (F)
10/12F	27 (18)	31 (22)	<0.001
11/13F	44 (29)	86 (60)
12/14F	79 (53)	27 (19)
Surgical duration (minutes)	122 ± 45	108 ± 37	0.003
Stone composition
CaOx	69 (46)	60 (42)	0.219
CaOx+CaP	38 (26)	34 (24)
CaP	16 (11)	14 (10)
UA	9 (6)	5 (3)
MAP	7 (5)	18 (13)
Others	10 (7)	12 (8)
Postoperative fever	38 (25)	15 (10)	<0.001
Postoperative sepsis	6 (4)	6 (4)	0.942
Stone-free status (3 months)
Grade A: Absolute stone-free	71 (52)	67 (51)	0.164
Grade B: Remnants <2 mm	37 (27)	27 (20)
Grade C: Remnants 2.1–4.0 mm	16 (12)	15 (11)
Grade D: Remnants >4.0 mm	12 (9)	23 (17)

CaOx = calcium oxalate; CaP = calcium phosphate; F = French; MAP = magnesium ammonium phosphate; PCNL = percutaneous nephrolithotomy; UA = uric acid.

The multivariate analysis of the operative outcomes showed significant differences between the two types of irrigation, including surgical duration and fever. Use of the manual and gravity irrigation system remained a significant predictor for postoperative fever (3.69, 95% confidence interval [CI]: 1.67–8.15, p = 0.001; Table 3) and longer operative time (22.76, 95% CI: 13.36–32.17, p < 0.001; Table 4) compared with use of the automated irrigation system. In addition, we found that female sex was associated with a higher chance of postoperative fever than male sex (2.21, 95% CI: 1.09–4.47, p = 0.028; Table 3), and positive preoperative urine culture increased the rate of fever after ECIRS (3.12, 95% CI: 1.43–6.81, p = 0.004; Table 3). Using a larger access sheath size such as 12/14F tended to cause less postoperative fever than using a smaller access sheath size such as10/12 or 11/13F (0.28, 95% CI: 0.10–0.72, p = 0.009; Table 3). A higher BMI (1.00, 95% CI: 0.02–1.98, p = 0.045; Table 4), higher stone volume (20.42, 95% CI: 11.08–29.77, p < 0.001; Table 4), and a larger PCNL tract size (25.40, 95% CI: 7.92–42.88, p = 0.005; Table 4) were significantly associated with a longer operative time. The multivariate analysis for postoperative sepsis showed significant associations with female sex (17.34, 95% CI: 2.58–116.52, p = 0.003; Supplementary Table S1) and a positive preoperative urine culture result (8.35, 95% CI: 1.18–59.30, p = 0.034; Supplementary Table S1). In addition, a higher change of absolute stone-free status at 3 months postoperatively was associated with male sex (0.46, 95% CI: 0.26–0.81, p = 0.008) and a shorter operative time (0.31, 95% CI: 0.18–0.56, p < 0.001; Supplementary Table S2). Stone in the upper calix has a lesser chance of being absolute stone free compared with stone in the ureter (0.26, 95% CI: 0.07–0.97, p = 0.044; Supplementary Table S2).

Table 3.

Results of Univariable and Multivariable Analyses of Fever

	Fever N (%)	Univariable models		Multivariable model
	Fever N (%)	OR (95% CI)	p-Value	aOR (95% CI)	p-Value
Age	57 ± 16	1.00 (0.98–1.02)	0.888	1.01 (0.98–1.03)	0.546
BMI	24 ± 5	0.95 (0.88–1.02)	0.150	0.98 (0.90–1.06)	0.585
Sex
Female	28 (53)	2.53 (1.38–4.63)	0.003	2.21 (1.09–4.47)	0.028
Stone location
Upper calix	6 (11)	1.23 (0.35–4.27)	0.744	2.11 (0.49–9.04)	0.313
Middle calix	6 (11)	1.85 (0.66–5.19)	0.242	1.94 (0.58–6.46)	0.279
Lower calix	17 (32)	1.14 (0.43–3.04)	0.789	0.87 (0.27–2.80)	0.810
UPJ	24 (45)	Reference (1)		Reference (1)
Ureter	0 (0)
Stone volume (median)	28 (53)	1.37 (0.75–2.50)	0.302	1.40 (0.66–2.95)	0.383
Preoperative hydronephrosis	30 (57)	1.04 (0.57–1.88)	0.903	1.48 (0.72–3.03)	0.290
Preoperative PCN or ureteral stent	8 (15)	0.82 (0.36–1.86)	0.633	0.84 (0.31–2.26)	0.734
Preoperative positive urine culture	25 (47)	3.17 (1.70–5.88)	<0.001	3.12 (1.43–6.81)	0.004
PCNL tract: 22F	2 (4)	0.49 (0.11–2.16)	0.343	0.34 (0.06–1.84)	0.210
Access sheath (F)
10/12	14 (26)	Reference (1)		Reference (1)
11/13	25 (47)	0.75 (0.36–1.57)	0.444	0.71 (0.29–1.76)	0.466
12/14	14 (26)	0.48 (0.21–1.09)	0.079	0.28 (0.10–0.72)	0.009
Surgical duration (median)	31 (58)	1.01 (1.00–1.01)	0.054	1.45 (0.69–3.08)	0.329
Irrigation: Manual and gravity	38 (72)	2.92 (1.52–5.58)	0.001	3.69 (1.67–8.15)	0.001

aOR = adjusted odds ratio; CI = confidence interval; OR = odds ratio.

Table 4.

Results of Univariable and Multivariable Analyses of Surgical Duration

	Surgical durationmean ± SD	Univariable model		Multivariable model
	Surgical durationmean ± SD	Coeff. (95% CI)	p-Value	aCoeff. (95% CI)	p-Value
Age		−0.65 (−0.99 to −0.32)	<0.001	−0.29 (−0.62 to 0.03)	0.076
BMI		1.41 (0.34–2.48)	0.010	1.00 (0.02–1.98)	0.045
Sex
Female	111.69 ± 38.68	−5.78 (−15.91 to 4.34)	0.262	−3.08 (−12.27 to 6.10)	0.509
Stone location
Upper calix	129.13 ± 49.41	14.77 (−7.07 to 36.61)	0.184	6.66 (−13.89 to 27.22)	0.524
Middle calix	132.09 ± 42.14	17.73 (−4.85 to 40.31)	0.123	12.22 (−8.67 to 33.10)	0.250
Lower calix	111.39 ± 33.99	−2.97 (−23.04 to 17.10)	0.771	−11.52 (−30.14 to 7.09)	0.224
UPJ	109.88 ± 41.30	−4.48 (−23.22 to 14.25)	0.638	−16.26 (−34.16 to 1.64)	0.075
Ureter	114.36 ± 46.43	Reference (1)		Reference (1)
Stone density (median)	116.07 ± 40.04	1.06 (−8.63 to 10.75)	0.830	4.79 (−4.22 to 13.80)	0.297
Stone volume (median)	128.18 ± 43.09	25.37 (16.13–34.61)	<0.001	20.42 (11.08–29.77)	<0.001
Position: Modified Galdakao-Valdivia	114.74 ± 41.46	−1.12 (−11.22 to 8.99)	0.828	3.99 (−5.57 to 13.55)	0.412
Irrigation: Manual and gravity	122.47 ± 44.98	14.31 (4.79–23.84)	0.003	22.76 (13.36–32.17)	<0.001
PCNL tract: 22F	142.15 ± 30.28	28.64 (9.73–47.54)	0.003	25.40 (7.92–42.88)	0.005
Access sheath (F)
10/12	113.98 ± 39.99	Reference (1)		Reference (1)
11/13	116.22 ± 42.94	2.23 (−10.87 to 15.33)	0.738	−5.05 (−16.91 to 6.81)	0.403
12/14	115.35 ± 42.32	1.37 (−12.18 to 14.92)	0.843	−8.65 (−20.98 to 3.69)	0.169

aCoeff. = adjusted coefficient; Coeff. = coefficient; SD = standard deviation.

Discussion

Although ECIRS is a novel technique that is increasingly being discussed, systematic reviews have reported infectious complications after the operation comparable with those of PCNL.^2
–4 According to previous studies, most complications in ECIRS are Grades 1 and 2 according to the Clavien–Dindo classification, for example, fever, sepsis, and bleeding.¹² Our study is the first to analyze the effect of the irrigation system on operative and postoperative outcomes of ECIRS, including infectious complications. We found that the use of a manual and gravity irrigation system was associated with a higher incidence of postoperative fever, aligning with Farag et al.’s study finding.¹⁰

Although the impact of the type of irrigation system on the IRP remains inconclusive, the maximum mean IRP was observed while using the manual irrigation method.^6,8 The manual and gravity irrigation system tended to generate a higher IRP than the automated irrigation group; this can be explained by fluctuation and uncontrollable increases in the IRP caused by the manual and gravity irrigation system.¹³ Another study shows that there is no significant difference in flow rate at the same pressure settings of 150 and 200 mm Hg during flexible URS with the manual and gravity irrigation system and the automated irrigation system.¹⁴ However, most recommendations suggest that the IRP in endourology procedures should not exceed 30 mm Hg.^5,6 Consistent bacteremia via pyelovenous backflow might occur if the IRP value is >90 mm Hg.¹⁵ Still, the IRP can reach up to 350 mm Hg when using manual irrigation.⁸ In addition to the irrigation system, an increasing IRP may be caused by many factors, for example, the scope and sheath ratio, instrument size, suction system, and patient position,^6,8,16 which is consistent with our result that using a larger access sheath size with the same scope is likely to cause less postoperative fever. Our multivariate analysis showed that patient position was not a significant predictor of postoperative fever, which is consistent with findings of previous research showing no association between patient position and IRP change.¹⁷

In addition to the factors affecting the IRP, other factors can cause infectious complications after ECIRS, including female sex, older age, preoperative stent placement, prior urinary tract infection, anatomical abnormality of the collecting system, and prolonged operative time.^18,19 Our multivariate analysis showed that postoperative fever is associated with female sex and a positive preoperative urine culture result, which is consistent with findings of the aforementioned studies. However, we did not find an association between prior ureteral stenting or nephrostomy tube placement and postoperative fever, which may be dependent on the duration of catheter placement.

Operative time in the manual and gravity group was also significantly longer than that in the automated group, which can be explained by the automated irrigation system providing consistent and controlled irrigation flow rates, resulting in better visibility and reduced irrigation-related concerns.²⁰ On the contrary, the manual irrigation cohort had a higher stone volume (not significant), which could also lead to longer overactive time in this cohort. In this study, a longer operative time may have been one of the factors causing a higher chance of fever in the manual and gravity group, which is consistent with findings in previous literature.²¹ However, our results did not find a direct association between the operative time and postoperative fever. The use of a larger PCNL tract size was associated with a longer operative time, which is thought to be because of bias, as the surgeon decided to use a larger tract for complex or large stones. Although some studies have reported the effect of irrigation type on the stone-free rate, there was no considerable difference among irrigation systems, as shown in our study.²⁰

In addition to operative outcomes and complications, the selection of pumping systems also requires consideration of the cost of equipment. At NCU hospital, the cost of an automated irrigation system is divided into two parts as follows: the cost of a single-use UROMAT tube for irrigation is 8000 JPY (70 USD), and the cost of a UROMAT pumping machine is 2,250,000 JPY (20,000 USD). The UROMAT pumping machine can also be used for other endoscopic procedures, such as holmium laser enucleation of the prostate. If a manual and gravity irrigation system is used, a single-use irrigation tube with SAPS costs 3215 JPY (30 USD). Overall, the cost of a manual and gravity irrigation system is cheaper regarding tubes, but not so big. Then, selecting each type of irrigation system still requires considering the equipment’s cost, value, and availability.

This study has some limitations. First, this study may have included bias owing to its retrospective design. Propensity score matching was used to balance the cohorts based on age, sex, BMI, preoperative percutaneous nephrostomy or ureteral stent, preoperative urine culture result, stone location, and access sheath size. There were 95 patients per matched cohort, with an adequate covariate balance. Automated irrigation remained a significant predictor of postoperative fever and shorter surgical duration (Supplementary Table S3). Second, it could not be confirmed whether all cases of postoperative fever were caused by the ECIRS procedure. As the difference in irrigation systems was not correlated with sepsis, postoperative fever can result from not only transient bacteremia but also other causes such as inflammation, drugs, or other sources of infection. Third, although positive stone culture affects infectious outcomes, we had limited data. Further research, including the stone culture data, is warranted. Lastly, there was no accurate IRP measurement in this study, especially during ECIRS because two irrigation systems were required; the automatic settings of the automated irrigation system can result in lower accuracy. Further studies are needed to confirm the correlation between the type of irrigation system, IRP, and postoperative outcomes of ECIRS. Although many factors may help predict postoperative infectious complications, surgeons should make individualized decisions regarding the surgical details for each patient.

Conclusions

Compared with using a manual and gravity irrigation system, using an automated irrigation system for flexible URS in ECIRS was associated with a reduction in the incidence of postoperative fever and a shorter operative time. Although novel technology for irrigation systems is advancing, urologists should be aware of complications because of high IRP during ECIRS.

Footnotes

Authors’ Contributions

Conceptualization: C.B., R.U., K. Taguchi, and S.H. Data curation and investigation: R.U., K. Taguchi, S.N., K. Tori, Y.S., T. Yanase, M.I., R.C., T.O., K.K., and T.S. Formal analysis: R.U., K. Taguchi, R.C., and T.O. Methodology: C.B., R.U., and K. Taguchi. Visualization: C.B., R.U., and K. Taguchi. Writing—original draft: C.B. and R.U. Writing—review and editing: R.U., K. Taguchi, and S.H. Supervision: A.O. and T. Yasui.

Author Disclosure Statement

The authors declare no financial or other conflicts of interest.

Funding Information

No funding was received for this article.

Supplementary Material

Supplementary Table S1

Supplementary Table S2

Supplementary Table S3

Abbreviations Used

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