Safety and outcome of percutaneous nephrolithotomy in patients with solitary kidney: A tertiary care center experience.

INTRODUCTION: Percutaneous nephrolithotomy (PCNL) for stones in solitary kidney poses a significant challenge and potential threat for acute kidney injury or progression of chronic kidney disease (CKD). We present our experience of PCNL in solitary functioning kidney (SFK) to evaluate the safety, efficacy, and postoperative complications and highlight the differences between these outcomes with respect to the stage of CKD.
METHODS: We carried out a retrospective study of patients with SFK, who underwent PCNL at our center from April 2010 to March 2018. Patients who had a minimum of 6 months of follow-up were included. Patients were classified into CKD groups based on the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative. Group 1 included Stages 1, 2, and 3A and Group 2 included Stages 3B, 4, and 5. Postoperative complications and stone-free rate were recorded and graded according to the Clavien-Dindo classification and compared between the two groups.
RESULTS: We had a total of 128 patients (Group 1 - 84 and Group 2 - 44). Stone-free rate after the first PCNL was higher in Group 1 as compared to Group 2 (88.1% [n = 74] vs. 50% [n = 22], P = 0.02). Overall, 48 patients (37.5%) had postoperative complications, but most were minor. Clavien Grade 1 and 2 complications were seen in 34 patients (Group 1, n = 18 and Group 2, n = 16, P = 0.069), whereas Grade 3 and 4 complications were seen in 14 patients (Group 1, n = 2 and Group 2, n = 12, P < 0.001), respectively. Need for postoperative (number of sessions) dialysis was seen with increased frequency in patients with higher chronic kidney stages (Group 1 vs. Group 2; 6 vs. 22 sessions, P < 0.001).
CONCLUSION: PCNL in SFK is safe, with satisfactory outcome, but patients with advanced CKD stage have higher risk of complications including need for dialysis and may require multiple sessions for complete stone clearance. Hence, they should be managed at high output tertiary centers. Copyright:

INTRODUCTION

Percutaneous nephrolithotomy (PCNL) for stones in solitary functioning kidney (SFK) is a seemingly hazardous endeavor, with acute or long-term loss of renal function being a possible complication. Although the procedure incorporates the same surgical steps, the consequences of intraoperative complications are grave. Risks range from the commonly encountered acute renal failure secondary to post-PCNL sepsis to severe hemorrhage[1] requiring embolization[2] or nephrectomy, which may render the patient anephric. Patients with solitary kidney and chronic kidney disease (CKD) have higher American Society of Anesthesiologists scores and are at usually higher risk for anesthesia-related complications.[3] There is a scarcity of evidence regarding the complications of PCNL in solitary functioning kidneys. The success of PCNL in solitary kidneys is lower than in patients with bilateral kidneys with an increased risk of rise in serum creatinine.[3] The long-term success rate of PCNL in this setting is therefore under scrutiny.

Our hospital is a tertiary referral center with considerable experience in managing complicated stone disease. More than 1500 stone-related procedures are performed per year including extracorporeal shock wave lithotripsy (ESWL), ureterorenoscopy, and PCNL. This study reports experience of PCNL in solitary or SFK in terms of safety, efficacy, and perioperative complications and highlights the outcomes with respect to the different stages of CKD.

METHODS

A total of 128 patients who underwent PCNL (four operating surgeons) from April 2010 to March 2018 in a single functioning moiety were identified from our prospectively maintained database. Patients underwent standard PCNL or mini-PCNL (tract size up to 17.5 Fr) as per the preference of the surgeon. Only those patients who had a minimum of 6 months of follow-up were included. Demographics, preoperative SCr, estimated glomerular filtration rate (eGFR), hemoglobin (Hb), and stone size were recorded. Intraoperative variables noted were number of tracts, method of tract dilatation, operative time, and stone clearance. Outcome variables were postoperative day 1 SCr, Hb, eGFR, and duration of hospital stay. SCr was repeated after 6 months and eGFR recalculated. Stone size was taken as the maximum dimension of the calculus on computed tomography (CT) scan. In case of multiple calculi, the cumulative stone diameter calculated as the sum of the largest diameter of each stone in all planes (axial, coronal, and sagittal) was used. Stone clearance was defined as absence of residual calculus or clinically insignificant residual fragment ≤4 mm on follow-up imaging (ultrasonography [USG] kidney, ureter, and bladder [KUB], X-ray KUB, and CT scan) done 6 weeks after the procedure. eGFR was calculated using the CKD-EPI equation. eGFR was estimated after 6 months from PCNL. Major and minor complications were recorded and graded according to the Clavien–Dindo classification. Nephrostomy tube was routinely placed in our patients. Patients were classified into CKD groups based on the National Kidney Foundation's Kidney Disease Outcomes Quality Initiative (NKF K/DOQI). Group 1 included Stages 1, 2, and 3A (GFR ≥45ml/min) and Group 2 included Stages 3B, 4, and 5 (GFR <45 ml/min). Outcomes and complications were analyzed for each group. The cutoff of 45 ml/min was chosen in view of the high risk of progression irrespective of the presence of microalbuminuria as per the NFK/K DOQI 2002 guidelines. Outcomes were also compared between standard PCNL and mini-PCNL.

The data were described in terms of median and range in case of nonparametric continuous data. Mean ± 2 × standard error was used to describe parametric data. Wilcoxon rank-sum test and paired t-test were used for parameters before and after PCNL. Student t-test and Mann–Whitney U-test were used to compare data between Groups 1 and 2. For categorical data, Chi-square test was utilized. IBM SPSS Statistics for Mac, version 23 (IBM Corp., Armonk, N.Y., USA) was used for statistical analysis.

RESULTS

A total of 128 patients were a part of the study, with a median age of 41 years (5–69). The baseline patient characteristics are given in Table 1. Mini-PCNL was done in 40 patients and 88 patients had standard PCNL.

Table 1

Baseline characteristics of our patients

Parameter	Value
Median age, years (range)	41 (5-69)
Median serum creatinine, mg/dL (range)	1.99 (0.9-6.8)
Median eGFR, ml/min (range)	63.9 (20.1-87.5)
Median Hb, g/dl (range)	10.2 (7.7-13.1)
Median BMI, kg/m2 (range)	22.4 (15.1-38.6)
Percentage of patients with prior intervention for stone disease (%)	40.8
Mean stone size (mm)	35 (12-57)
ASA score (mode)	Class 1
CKD 1, 2, and 3A (Group 1) (%)	84 (65.6)
CKD 3B, 4, and 5 (Group 2) (%)	44 (34.4)

eGFR=Estimated glomerular filtration rate, Hb=Hemoglobin, BMI=Body mass index, ASA=American Society of Anesthesiologists, CKD=Chronic kidney disease

Complete clearance was achieved in 96 (75%) patients in a single session with 14 patients requiring second-look PCNL and 4 requiring stented extracorporeal lithotripsy, leading to a final stone clearance rate of 89.1%.

Blood transfusion was required in 14 patients due to Hb falling below 8.0 g/dL. Intercostal drainage for nephropleural fistula was required in 2 patients and postoperative dialysis was required in 12 patients including 3 patients with sepsis requiring ICU care. No incidence of post-PCNL hematuria was recorded after discharge, with a minimum follow-up of 6 months. Comparison of preoperative and postoperative parameters is given in Table 2. Table 2 shows that on average, there was a drop of 1.0 g/dL of Hb that was significant statistically. There was no statistically significant difference in the renal function parameters (SCr and eGFR) postoperatively, and furthermore, the renal function remained stable in most and improved in a few at 6 months after the PCNL. Patient characteristics and outcomes were further compared between low CKD and higher CKD stages or Groups 1 and 2 [Table 3].

Table 2

Pre- and postoperative parameters of our patients

Parameter (median values)	Preoperative	Postoperative	P
Hb, g/dl	10.3	9.3	0.01
Serum creatinine, mg/dl	1.99	1.99	0.43
Serum creatinine, mg/dl (6 months)	1.99	1.92	0.25
eGFR, ml/min (6 months)	63.9	62.5	0.46

eGFR=Estimated glomerular filtration rate, Hb=Hemoglobin

Table 3

Comparison of characteristics of the two groups (based on chronic kidney disease stage)

Characteristic	Group 1 (n=84)	Group 2 (n=44)	P
Median baseline Hb	10.5	9.9	0.05
Cumulative stone diameter, mm (mean)	34	37	0.23
Number of punctures (mean)	1.40	1.77	0.45
Mean operating time (min)	93.5	98.7	0.23
Median fall in Hb, g/dL	0.8	1.0	0.43
Complete stone clearance in single session (%)	74 (87.5)	22 (50)	0.02
Mean hospital stay in days	4.3	6.7	0.04
Complications (Clavien-Dindo Classes 1 and 2)	18	16	0.069
Complications (Clavien-Dindo Classes 3 and 4)	2	12	<0.001
Need for dialysis (patients, number of sessions)	2, 6	10, 22	0.02

Hb=Hemoglobin

The above results reveal that higher CKD stages (Group 2) are associated with lower stone clearance in a single session, prolonged postoperative hospital stay, and increased incidence of higher Clavien grade complications and dialysis. In Group 2, a second procedure was needed in 12 patients to achieve a clearance rate of 77.2%. This was lower than the 95.2% overall clearance achieved in Group 1. Among the ten patients who underwent hemodialysis in Group 2, five patients were already on maintenance hemodialysis. Three were placed on hemodialysis preoperatively after consultation with nephrology preemptively to prevent fluid overload during surgery.

DISCUSSION

Studies on PCNL in patients with solitary kidneys have shown contradictory results. Although most of the studies demonstrate acceptable complication rates and no long-term renal impairment,[245] few studies have reported inferior stone clearance and higher surgical risk.[3] With existing literature, few questions remained unanswered in the setting of PCNL in SFK such as impact on renal function, clearance rates, and complications as a factor of the CKD stage. We have attempted to shed light on these factors in our study.

The stone-free rate in our series was 75% after one session of PCNL, and it improved to 89% after ancillary procedures (4 required stented ESWL and 14 required relook PCNL). This is comparable with other series in the literature reporting 60%–90% clearance rates.[345] This clearance rate was low in patients with higher stage of CKD, which can be explained by the fact that surgeons may have a conservative approach to such patients. We also tend to limit the irrigation time. The limited irrigation time also explains the need of increased number of procedures in Group 2. Although the number of complications in Group 2 seems high (Clavien Grade 3 and 4 complications, 12 of 44 [27.3%]), 8 of these were due to hemodialysis which was either maintenance or preemptive. Two other patients, who needed hemodialysis, only needed it in the postoperative period. We have included these patients in the complication category as per the Clavien–Dindo classification.

Careful preoperative and intraoperative planning may reduce complications associated with PCNL in this special population. Both standard PCNL and mini-PCNL may be acceptable. In our series, forty patients underwent mini-PCNL, whereas 88 patients underwent standard PCNL. The minimum appropriate diameter metallic or Amplatz sheath should be used. Good communication with the anesthesiologist should be maintained throughout the procedure, and threshold for considering a staged procedure should be kept low.

Pneumatic and holmium laser lithotripsies were used for stone fragmentation in our cases. We routinely place double J stent (DJS) after PCNL in solitary kidney except in a few with a single stone, normal renal function, and no intraoperative complications such as pelvicalyceal perforation. The median time to nephrostomy removal was 2 days (range, 1–5), and DJS was removed at 6 weeks. Mahboub and Shakibi reported three cases where tubeless PCNL was performed in solitary kidneys.[2] Tubeless PCNL should only be performed with caution as it may cause an unnecessary increased risk to the patient with SFK.

The transfusion rate in patients with solitary kidneys has been reported to be up to 10%[3] with some suggesting compensatory hypertrophy as an incriminating factor. In our series, 14 patients (10.9%) required transfusion that is similar to transfusion rate in PCNL with both kidneys[67] and also in other series of PCNL in solitary kidney.[589]

We had two cases of PCNL in transplanted kidneys with no complications. The patient was kept supine and access was obtained through an anterior calyx under USG guidance. This is consistent with published literature on acceptable complication rate and improvement in renal function after PCNL in transplanted kidneys.[8]

Kuzgunbay et al. [10] studied stone recurrence and long term renal function after PCNL in patients with renal insufficiency. In 16 patients studied, mean SCr value was 2.30. Creatinine values came down to normal in 6 patients (37.5%) who had stable renal function and increased (>4 mg = dL) in 4 patients (25%) who needed hemodialysis. In a comparable study by Kurien et al.,[11]91 patients with CKD undergoing PCNL were studied for factors predicting further renal deterioration. Deterioration with up-migration of CKD stage was seen in 12 patients (13.2%). Eight patients (8.8%) required RRT in the form of either maintenance hemodialysis or renal transplantation. In our series also, RRT was required in 12 patients, of which 10 (83.3%) were in higher CKD groups. The patients with higher CKD groups also had significantly more complications and blood transfusion. Among our patients in Group 2, ten needed dialysis, of which three were in sepsis and two others had nephropleural fistula. The need for dialysis in 22.7% of patients was seemingly higher than the historic cohort described above, but most of the studies have not subclassified patients and looked into RRT rates in CKD3b and above. Clavien Grade 1 and 2 complications were seen in 16 patients (36.36%) with CKD3b and above. Again, this may seem high, but 11 of these were Clavien Grade 1 including electrolyte disturbances, increased analgesia, and antiemetic requirement. These, especially electrolyte imbalance, can be common in patients with poor renal reserve.

In patients of urolithiasis with bilateral kidneys, PCNL has been shown to preserve long-term renal function. This benefit logically should extend to patients with solitary kidney also. Akman et al.[5] showed that renal function stabilized or improved in 90% of cases at more than 6-month follow-up. Our study results are consistent with this finding, and most of the cases in our series were associated with an improvement or stabilization in eGFR and renal function. Increasing use of smaller diameter sheaths and advances in scope and laser technology has allowed us to increase stone clearance and decrease complications.

Thus, the fear that PCNL will cause long-term deterioration of renal function in patients with solitary kidney or CKD is unfounded. Although PCNL and ESWL have been documented to cause some renal injury,[12] this does not translate into any significant alteration in eGFR.

Limitations of the study include its retrospective nature, and measurements of renal function were based on mathematical formula rather than nuclear renography and GFR estimation; however, this was not practically feasible in all cases, especially with higher stage of CKD. Further, we had a short period of minimum follow-up (6 months). Stone-free rate was not routinely measured using CT scan as it would have been unethical to do so. Further, there was some heterogeneity due to the number of surgeons and the use of both standard PCNL and mini-PCNL.

CONCLUSION

PCNL in SFK is safe, with acceptable stone clearance and adverse events. With increasing stage of CKD, the rate of stone clearance decreases and complications increases. Thus, patients with SFK with compromised renal function should be considered for PCNL in a setting with facilitates handling of untoward complications.