In the development of FURS, miniaturization is a common trend[12]. Under the working channel of 3.6Fr, the diameter of the latest 7.5Fr disposable FURS is almost 25% smaller than that of the 9Fr (Fig. 1). Theoretically, the effectiveness of lithotomy could potentially be improved by using thinner FURS and lowering IPP[7].
The thinner FURS can be used with the thinner UAS[11]. According to our previous report,, lower IPP and appropriate perfusion fluid flow could be guaranteed under the RESD < 0.75[7]. Our study demonstrated that the combination of 7.5Fr electronic FURS and 10Fr UAS complied to the principle of RESD (unpublished yet). It is possible to meet standards of clinical lithotripsy when the perfusion pressure is 500 H2Ocm, the IPP is only 25.9 H2Ocm, and the perfusion flow is 64.4 ml/min. [13]. The success rate of the UAS insertion increased by reducing its diameter, while simultaneously lessening the pressure the sheath exerted on the ureter, which reduced the risk of ischemia injury[2, 14]. Over 80% of the routine 14Fr UAS placement attempts had been successful[15], causing 46.5% of ureteral mechanical injuries, including 13.3% of lesions to the muscle layer[8]. The success rate of UAS placement in this study was 100%. The sheath was nevertheless able to be introduced at the ureteropelvic junction in two cases despite minor resistance encountered during procedure. After that, the uroscopy examination revealed that two patients who were previously mentioned both had ureteral mucosa injuries (grade-1), however none of patients had any injury to the muscle layer of the ureter.
In order to increase the SFR, this research adopted the strategy of breaking stones into fragments and trapping them out successively. The lithotripsy time was brief due to the small stone diameter (9.6 ± 2.9 mm), the lithotripsy process was completed quickly, whereas operations took roughly 55 minutes to complete, and the most of time was spent netting stones. The stone must first be shattered into tiny pieces before it can be removed because of the narrow channel of the UAS, firstly the stone must be broken into numerous little pieces before being extracted. It is predicted that the operation time can be shortened if the powdered lithotripsy technique combined with the negative pressure suction UAS, respectively[16].
The guidelines suggested that the D-J stent should not be inserted in place if there is no obvious ureteral damage and no residual calculus after the procedure[17]. The recovery period will be more uncomfortable because the D-J stent is generally in left position for 2–4 weeks in the clinic[18]. The symptoms associated to ureteral stent-related occurred frequently, and the main symptoms, which include body discomfort, lower urinary symptoms, and hematuria, and all have a negative impact on the patients' quality of life[19, 20]. In this work, grade-1 ureteral injury required the retention of D-J stents for a month in two cases, and for the second stage operation in one case because no stones identified during the operation. The other patients were discharged without stents with an average stent retention time of 18.3 hours and no severe complications, such as fever. One month after the procedure, the patients’ SFRs were 90% and there was no evidence of ureteral stenosis, indicating a successful clinical outcome. The main drawback of early stent removal was that it caused evident pain, lasting an average duration of 26.4 hours and reaching a maximum VAS score of 9. the majority of patients experienced pain alleviation within eight hours after surgery, which might be due to ureteral edema and spasm. Long-lasting pain in patients exhibited the characteristic symptoms of metastatic pain, which was assumed to be caused by the excretion of small stones. All patients experienced pain relief within 72 hours of their operations, and there was no return of pain after they were discharged. Therefore, a challenge that has to be resolved is how to further reduce the intensity of pain and shorten the duration of pain while using D-J stents or entirely non-stenting after surgery.
The reduction of the UAS channel had no obvious effect on the fluid perfusion of the 7.5Fr UAS and 3.6Fr FURS, ensuring clear vision and a smooth surgical outcome (supplementary video). The electronic FURS employed in this study had a resolution of 40000 pixels, even though it was unable to produce the high-quality images as the thicker electronic FURS, but it was still preferable to the traditional fiber FURS. It might meet the clinical criteria for a lithotripsy tool. Moreover, the introduction of the high-definition cameras significantly improved the picture quality of the most recent generation 7.5Fr disposable electronic FURS.
The decrease in FURS diameter led to a reduction in spare parts and an enhancement in the production process[21]. The single usage of FURS's lowered the criteria for durability, despite that fact that its durability was not as good as that of the FURS with thicker diameter. According to the guidelines, one FURS surgery should be completed within 90 minutes[17]. The study lasted an average duration of 55 minutes, with the shortest and longest duration being 20 and 80 minutes, respectively. The FURS remained undamaged during the whole process and may meet clinical standards.