Editorial commentary by: Manoj Monga, MD, FACS, Urologist, San Diego, California

Stone disease of the kidneys and urinary tract has been on the rise in recent decades and is estimated to affect about 7% of the world's population and just over 10% of people in the United States.^1-3

Preference for ureteroscopy, which balances the effectiveness of direct treatment with a minimally invasive approach, is reflected in its increasing adoption over shock wave lithotripsy, though shock wave lithotripsy remains an important option in select patients based on stone and anatomical considerations.⁴ Although ureteroscopy is generally safe, serious complications can occur.⁵ A factor contributing to those complications may be intrarenal pressure (IRP), which is influenced by irrigation during the procedure. Unfortunately, there is limited data and, therefore, low awareness about the potential complications that may be associated with elevated IRP or how to control this pressure.⁶

Fluid irrigation and IRP

Fluid irrigationduring flexible ureteroscopy is necessary to improve visibility and distention of the upper urinary tract; however, this can lead to elevated IRP with potential for related complications.⁶ Duration of exposure to elevated IRP, which is related to the length of the procedure, is also believed to be a potentially complicating factor.⁶ As ureteroscopes are increasingly used in more challenging upper urinary tract stone cases,⁷ the procedures tend to be longer, which may be associated with a rise in complications.⁶

Complications from IRP

In one pre-clinical study, higher irrigation pressure was associated with increased depth of absorption of irrigant during ureteroscopy⁸. Higher IRPs have also been hypothesized to be related to significant post-operative complications, including:

• Pyelovenous backflow.^6,8-11 Fluid absorption during retrograde intrarenal surgery is thought to be due to increased intrapelvic pressure.⁹ This may have the potential to lead to pyelovenous backflow, which sends potentially infected urine into the circulation system.¹²

• Sepsis.^6,11-13 According to a recent meta-analysis, patients undergoing ureteroscopy for treatment of kidney stones have a 5% risk of postoperative urosepsis (95% confidence interval 2.4%-8.2%).¹⁴ Another recent study found that among patients with URS, the average all-cause healthcare costs at 1 month in the septic cohort were $49,625 versus $17,782 in the non-septic cohort (p<0.0001).¹⁵

• Systemic inflammatory response syndrome (SIRS).^6,13 During retrograde intrarenal surgery, SIRS occurs in 8.1% of cases, according to one recent study.¹³

• Other potential complications may include pain,^11,16 fever,^6,13 renal damage and pathological changes (animal studies have shown that kidneys subjected to high pressures can be irreversibly damaged),^6,11,17 infection,^6,11-13 subcapsular hematoma during ureteroscopy,¹⁸ and rupture of the collection system.¹⁷

Reducing the risk of elevated IRP

Considerations to reduce the risk of high IRP include:

• Keep the pressure as low as possible while maintaining good visibility.¹⁹ Decreasing IRP is thought to reduce risk of backflow.²⁰

• Consider which type of irrigation allows the most control over – and ability to limit – the amount of pressure. Gravity bag irrigation may reduce IRP compared to other modalities, according to one study.²¹ However, hand-held devices might optimize tailored irrigation to the needs of the patient (ALARA principle; as low as reasonably achievable).

• Consider the use of a ureteral access sheath (UAS), which may improve irrigation flow and visualization while decreasing IRP.²² Literature suggests that the use of a UAS may improve irrigation flow and visualization within the ureter, reduce operative times and overall costs, and improve the effectiveness of surgery.²³

• Ensure that the lumen of the sheath used to access the kidney is larger than the outer diameter of the scope; the space between the two allows fluids to flow out and may decrease the pressure.

• Keep the procedure as short as possible. 

Although monitoring IRP and determining what is a safe pressure level is a developing field, it is important for urologists to be aware of the potential for IRP-related complications during ureteroscopy and to take steps to reduce the associated risks.

References

1. Chewcharat A, Curhan G. Trends in the prevalence of kidney stones in the United States from 2007 to 2016.Urolithiasis. 2021 Feb;49(1):27-39.

2. Chen Z, Prosperi M, Bird VY. Prevalence of kidney stones in the USA: The National Health and Nutrition Evaluation Survey. J Clin Urol. 2019;12(4):296-302.

3. Pawar AS, Thongprayoon C, Cheungpasitporn W, et al. Incidence and characteristics of kidney stones in patients with horseshoe kidney: a systematic review and meta-analysis. Urol Ann. 2018 Jan-Mar;10(1):87-93.

4. Oberlin DT, Flum AS, Bachrach L, et al. Contemporary surgical trends in the management of upper tract calculi. J Urol. 2015 Mar;193(3):880-4.

5. de la Rosette J, Denstedt J, Geavlete P, et al. CROES URS Study Group. The clinical research office of the endourological society ureteroscopy global study: indications, complications, and outcomes in 11,885 patients. J Endourol. 2014 Feb;28(2):131-9.

6. Tokas T, Herrmann TRW, Skolarikos A, et al. Training and Research in Urological Surgery and Technology (T.R.U.S.T.) Group. Pressure matters: intrarenal pressures during normal and pathological conditions, and impact of increased values to renal physiology. World J Urol. 2019 Jan;37(1):125-31.

7. Cohen J, Cohen S, Grasso M. Ureteropyeloscopic treatment of large, complex intrarenal and proximal ureteral calculi. BJU Int. 2013 Mar;111(3 Pt B):E127-31.

8. Loftus C, Byrne M, Monga M. High pressure endoscopic irrigation: impact on renal histology. Int Braz J Urol. 2021 Mar-Apr;47(2):350-6.

9. Guzelburc V, Balasar M, Colakogullari M, et al. Comparison of absorbed irrigation fluid volumes during retrograde intrarenal surgery and percutaneous nephrolithotomy for the treatment of kidney stones larger than 2 cm. Spingerplus. 2016 Oct 4;5(1):1707.

10. Twum-Ampofo JK, Eisner BH. The relationship between renal pelvis pressures and pyelovenous backflow during ureterorenoscopy in alive porcine model. AUA Abstract. 2020.

11. Osther PJS, Pedersen KV, Lildal SK, et al. Pathophysiological aspects of ureterorenoscopic management of upper urinary tract calculi. Curr Opin Urol. 2016 Jan;26(1):63-9.

12. Gutierrez-Aceves J, Negrete-Pulido O, Avila-Herrera P. (2012) Perioperative Antibiotics and Prevention of Sepsis in Genitourinary Surgery. In Smith AD, Badlani GH, Preminger GM, Kavoussi LR (Eds.), Smith’s Textbook of Endourology (pp. 38-52). New York, NY: Blackwell Publishing Ltd.

13. Zhong W, Leto G, Wang L, et al. Systemic inflammatory response syndrome after flexible ureteroscopic lithotripsy: a study of risk factors. J Endourol. 2015 Jan;29(1):25-8.

14. Bhojani NB, Miller LE, Bhattacharyya S, et al. Risk factors for urosepsis after ureteroscopy for stone disease: a systematic review with meta-analysis. J Endourol. 2021 Jul;35(7):991-1000.

15. Bhojani N, Paranjpe R, Cutone B, et al. What is the cost of sepsis after ureteroscopy? Results from the Endourological Society TOWER collaborative. Presentation. 38th World Congress of Endourology. J Endourol. 2021 Oct;35(S1):MP32-03.

16. Pedersen KV, Liao D, Osther SS, et al. Distension of the renal pelvis in kidney stone patients: sensory and biomechanical responses. Urol Res. 2012 Aug;40(4):305-16.

17. Schwalb DM, Eshghi M, Davidian M, et al. Morphological and physiological changes in the urinary tract associated with ureteral dilation and ureteropyeloscopy: an experimental study. J Urol. 1993 Jun;149(6):1576-85.

18. Vaidyanathan S, Samsudin A, Singh G, et al. Large subcapsular hematoma following ureteroscopic laser lithotripsy of renal calculi in a spina bifida patient: lessons we learn. Int Med Case Rep J. 2016 Aug;9:253-9.

19. De Coninck V, Keller EX, Rodriguez-Monsalve M, et al. Systematic review of ureteral access sheaths: facts and myths. BJU Int. 2018 Dec;122(6):959-69.

20. Corrêa Lopes Neto A, Dall’Aqua V, Carrera RV, et al. Intra-renal pressure and temperature during ureteroscopy: does it matter? Int Braz J Urol. 2021 Mar-Apr;47(2):436-42.

21. Wilson WT, Preminger GM. Intrarenal pressures generated during flexible deflectable ureterorenoscopy. J Endourol. 1990 Jan;4(2):135-41.

22. Ng YH, Somani BK, Dennison A, et al. Irrigant flow and intrarenal pressure during flexible ureteroscopy: the effect of different access sheaths, working channel instruments, and hydrostatic pressure. J Endourol. 2010 Dec;24(12):1915-20.

23. Kaplan AG, Lipkin ME, Scales CD Jr, et al. Use of ureteral access sheaths in ureteroscopy. Nat Rev Urol. 2016 Mar;13(3):135-40.