A total of 52 patients (30 men and 22 women; mean age: 43.33 ± 13.78 years) underwent fURS. The mean stone size was 14.44 ± 3.56 mm, and the mean stone density was 1043 ± 335.2 HU. Overall, 31 and 21 patients had left-sided and right-sided stones, respectively. The mean TLT was 26.58 ± 13.44 min, whereas the mean operative time was 41.44 ± 16.67 min; the mean length of hospital stay was 1.08 ± 0.334 day (Table 1).
Table 1. Characteristics of the study population
Variables
|
Frequency N = 52
|
Percentage (%)
|
Sex
Male
Female
|
30
22
|
57.7
42.3
|
Age, years (mean (SD))
|
43.33 (13.78)
|
ASA physical status
1
2
3
4
|
36
10
5
1
|
69.2
19.2
9.6
1.9
|
Lateralization (renal unit)
Right
Left
|
21
31
|
40.4
59.6
|
Stone size (mm)
≤13
>13
|
25
27
|
48.1
51.9
|
Stone density (mean (SD))
|
1043 (335.2)
|
Stone size, mm (mean (SD))
|
14.44 (3.56)
|
Laser time, min (mean (SD))
|
26.58 (13.44)
|
Length of hospital stay, day (mean (SD))
|
1.08 (0.334)
|
Operative time, min (mean (SD))
|
41.44 (16.67)
|
SD standard deviation, ASA American Society of Anesthesiologists
The patients were divided into two groups according to stone density; the low HU group, comprising 24 (46.15%) patients with density ≤1000 HU, and the high HU group, comprising 28 (53.84%) patients with density >1000 HU (Table 2). For statistical analysis, the patients were also classified into the following three laser groups: the first group comprised 24 (46.2%) patients with TLT of 10–24 min; the second group comprised 23 (44.2%) patients with TLT of 25–40 min; and the third group comprised five (9.6%) patients with TLT of >40 min. Our analysis revealed that the overall correlation between stone density and the TLT was not significant (p = 0.486).
Table 2. Relationship between stone density and the TLT
TLT
(min)
|
Frequency (%)
|
Soft stones ≤1000 HU, n (%)
|
Hard stones >1000 HU, n (%)
|
p-value
|
10–24
|
24 (46.2)
|
9
|
15
|
0.486*
|
25–40
|
23 (44.2)
|
12
|
11
|
>40
|
5 (9.6)
|
3
|
2
|
Total
|
52 (100)
|
24 (46.15%)
|
28 (53.84%)
|
|
* Chi-squared test
TLT total laser time, HU Hounsfield units
Table 3 shows the relationship between stone size and the TLT. Among 24 patients in the first TLT group, 17 had stone size ≤13 mm, whereas seven had stone size >13 mm. Among 23 patients in the second TLT group, six had stone size ≤13 mm, whereas 17 had stone size >13 mm. Among five patients in the third TLT group, two had stone size ≤13 mm, whereas three had stone size >13 mm. Stone size showed a significant correlation with the TLT (p = 0.008). In our analysis, we also attempted to determine the impact of stone density on other surgical outcomes.
Table 3. Relationship between stone size and the TLT
TLT
(min)
|
Frequency (%)
|
Stone size ≤13 mm, n (%)
|
Stone size >13 mm, n (%)
|
p-value
|
10–24
|
24 (46.2)
|
17 (68)
|
7 (25.9)
|
0.008*
|
25–40
|
23 (44.2)
|
6 (24)
|
17 (63)
|
>40
|
5 (9.6)
|
2 (8)
|
3 (11.1)
|
Total
|
52 (100)
|
25 (100)
|
27 (100)
|
|
* Chi-squared test
TLT total laser time
Table 4 shows the relationship between stone density and the SFR. The patients were categorized into the following five groups according to the SFR: (i) the immediate group, which presented with stones that completely turned into dust at the time of the procedure; (ii) the 2-week group, which showed no evidence of residual fragment on imaging after 2 weeks; (iii) the 4-week group, which had no fragments at 4 weeks; (iv) the 6-week group; and (v) the residual group, which had fragments that were still present after 3 months. Among 15 (28.8%) patients in the immediate group, six had soft stones, whereas the remaining nine had hard stones. Among 15 (28.8%) patients in the 2-week group, seven had soft stones, whereas eight had hard stones. The 4-week group included only one (1.9%) patient with a hard stone. The 6-week group comprised 11 (21.2%) patients, of whom five and six had soft and hard stones, respectively. Among 10 (19.2%) patients in the residual group, six had soft stones, whereas four had hard stones. Our analysis indicated that stone density had a non-significant effect on the SFR (p = 0.761).
As another surgical outcome of fURS, postoperative complications were analyzed and graded using the Clavien–Dindo classification system. Table 5 shows the relationship between stone density and postoperative complications.
Table 4. Relationship between stone density and the SFR
SFR
|
Frequency (%)
|
Soft stones <1000 HU, n (%)
|
Soft stones <1000 HU, n (%)
|
p-value
|
Immediate
|
15 (28.8)
|
6 (25)
|
9 (32.1)
|
0.761*
|
At 2 weeks
|
15 (28.8)
|
7 (29.2)
|
8 (28.6)
|
At 4 weeks
|
1 (1.9)
|
0 (0)
|
1 (3.6)
|
At 6 weeks
|
11 (21.2)
|
5 (20.8)
|
6 (21.4)
|
Residual (3 months)
|
10 (19.2)
|
6 (25)
|
4 (14.3)
|
Total
|
52 (100)
|
24 (100)
|
28 (100)
|
|
* Chi-squared test
SFR stone-free rate, HU Hounsfield units
Table 5. Relationship between stone density and postoperative complications graded using the Clavien–Dindo classification system
Postoperative complications
|
Frequency (%)
|
Soft stones <1000 HU, n (%)
|
Hard stones >1000 HU, n (%)
|
p-value
|
CDS grade 1
|
9 (17.3)
|
4 (16.7)
|
5 (17.9)
|
0.989*
|
CDS grade 2
|
2 (3.8)
|
1 (4.2)
|
1 (3.6)
|
Nil
|
41 (78.8)
|
19 (79.2)
|
22 (78.6)
|
Total
|
52 (100)
|
24 (100)
|
28 (100)
|
|
* Chi-squared test
CDS Clavien–Dindo score, HU Hounsfield units
Grade 1 complications were observed in nine (17.3%) patients (four with soft stones and five with hard stones). Grade 2 complications were observed in two (3.8%) patients (one with soft stone and one with hard stone). No complications were observed in 41 (78.8%) patients. Our analysis revealed that stone density also had a non-significant effect on postoperative complications (p = 0.989).
Table 6 shows the relationship between stone density and other variables. The operative time was 42.50 min (16.22%) for patients with stone density <1000 HU and 40.54 min (17.29%) for those with stone density >1000 HU; however, there was no statistically significant difference (p = 0.676). Furthermore, the degree of hydronephrosis (p = 0.356), length of hospital stay (p = 0.9), postoperative urea and creatinine levels (p = 0.921 and p = 0.32, respectively), and preoperative stent placement (p = 0.335) were statistically non-significant in relation to stone density. The postoperative hemoglobin levels and the presence of ureteral access sheath were the only two variables found to be positively correlated with stone density (p = 0.01 and p = 0.046, respectively).
Table 6. Relationship between stone density and different variables
Variables
|
Soft stones <1000 HU, n (%)
|
Hard stones >1000 HU, n (%)
|
p-value
|
Operative time, min
|
42.50 (16.22)
|
40.54 (17.29)
|
0.676*
|
Degree of hydronephrosis
0
1
2
3
|
0 (0)
10 (41.7)
13 (54.2)
1 (4.2)
|
3 (10.7)
8 (28.6)
16 (57.1)
1 (3.6)
|
0.356**
|
Length of hospital stay, day
|
1.08 (0.28)
|
1.7 (0.38)
|
0.90*
|
Postoperative urea levels, mg/dL
|
32.63 (12.82)
|
32.93 (9.09)
|
0.921*
|
Postoperative creatinine levels, mg/dL
|
1.014 (0.495)
|
0.904 (0.281)
|
0.320*
|
Postoperative hemoglobin levels, mg/dL
|
13.29 (1.18)
|
14.24 (1.35)
|
0.01*
|
Preoperative stent placement
No
Yes
|
17 (70.8)
7 (29.2)
|
23 (82.1)
5 (17.9)
|
0.335**
|
Presence of ureteral access sheath
No
Yes
|
16 (66.7)
8 (33.3)
|
25 (89.3)
3 (10.7)
|
0.046**
|
Postoperative complications
No
Yes
|
21 (87.5)
3 (12.5)
|
23 (82.1)
5 (17.9)
|
0.594**
|
* Student’s independent t-test
** Chi-squared test
HU Hounsfield units