The impact of urolithiasis on renal function is complex and influenced by both the stone disease itself and the interventions employed. Although endourological procedures may not always affect global kidney function, certain factors, such as preoperative renal function, hypertension, diabetes mellitus, and the use of multiple percutaneous tracts, can predispose patients to declines in renal function following the procedure [10]. There exists a lack of epidemiological data on the incidence of AKI in the Indian population with urolithiasis in comparison to Non-Indian population.

Results of our study estimated the incidence of post-PCNL AKI to be 12.4%. This is in accordance with the finding of the previous studies, which estimate the range of incidence of post-PCNL AKI to be between 4.4–16.2% [6, 11]. This suggests that PCNL has a higher incidence of postoperative AKI when compared to other non-cardiac surgery, which have an incidence ranging from 0.8 to 7.5% [12, 13].

There was no statistically significant correlation between age or BMI and post-PCNL AKI, although older age [14] and higher BMI [15] are typically associated with a greater risk of AKI due to factors such as comorbidities and medication-induced renal stress, as well as age-related structural and functional changes, obesity-related glomerular hyperperfusion, oxidative stress and hyperfiltration injury. Although our study revealed a significant association between female sex and postoperative AKI, evidence supporting this finding is lacking. Further validation through larger sample sizes and randomized controlled trials is required to ensure its validity and reliability.

Findings from this study failed to demonstrate a significant correlation between post-PCNL AKI and diabetes, even though AKI is a known complication of uncontrolled diabetes mellitus [16] and is often associated with an increased risk of progression to chronic kidney disease and end-stage renal disease. It should be noted that PCNL is typically performed after achieving adequate diabetic control, which may explain the lack of significant correlation in our findings.

There was a significant correlation between hypertension and AKI post-PCNL in this study, highlighting the increased risk of AKI in hypertensive patients. This can be explained by Hypertension, similar to diabetes, being a systemic condition associated with progressive renal damage [17]. This creates a vicious cycle where hypertension exacerbates renal damage, which in turn worsens hypertension, and so on. Therefore, The importance of adequate blood pressure control in mitigating this risk cannot be overemphasized.

We did not find a significant correlation between preoperative Haemoglobin levels or total leukocyte count and post-PCNL AKI, despite Inflammation [18] and anaemia [19] being established factors that can contribute to AKI due to their capacity to cause renal hypoxia and oxidative stress. However, Notably, PCNL was performed after excluding active UTIs by negative urine cultures and the absence of clinical signs of pyelonephritis. Additionally, PCNL is rarely performed in anaemic patients before preoperative optimization, except in special circumstances such as CKD patients. This may explain the lack of correlation observed in our study.

Hyperuricemia was found to be a significant risk factor for post-PCNL AKI, highlighting the importance of the medical management of hyperuricemia in reducing this risk. Hyperuricemia is associated with a dysfunctional endothelial lining and heightened oxidative stress in the body, contributing to preglomerular arteriolopathy and the transmission of systemic hypertension to the glomerular capillary tuft. Even mild increases in serum uric acid levels can disrupt renal autoregulation and induce vasoconstriction, leading to a reduced glomerular filtration rate (GFR) and renal blood flow, thereby increasing the risk of AKI [20]. A study by Yu et al. similarly demonstrated higher preoperative serum uric acid levels as an independent risk factor for postoperative acute kidney injury (AKI), consistent with the findings of our study [21].

Staghorn calculi, Hounsfield units (mean 1051 HU), and stone volume (mean 5.5 cc) emerged as statistically significant predictors of post-PCNL AKI in this study. These findings are in alignment with existent data on stone factors, including high-volume stones, staghorn stones, and higher Hounsfield units, contributing to procedural complexity, prolonged intraoperative time, and increased risks of bleeding and infective complications, thereby increasing the risk of AKI [22, 23].

Intraoperative factors, particularly increasing tract size, multiple access tracts, and bilateral PCNL were identified as significant predictors of post-PCNL AKI. Multiple access tracts, larger tract sizes, and bilateral PCNL procedures can result in significant renal parenchymal and nephron damage, leading to AKI, as supported by previous studies [22, 24,25,26]. While smaller tracts may predispose patients to greater intrarenal pressures and septic complications, we found that access tracts of 26 Fr or larger were significantly more strongly associated with post-PCNL AKI than smaller tracts were. Additionally, our observations revealed that out of 40 patients who developed AKI, 19 had undergone bilateral PCNL, emphasizing its negative impact on renal function.

We observed that a mean operative time of (97 ± 26.24 min) was associated with an increased risk of postoperative AKI following PNL. A prolonged operative time during PCNL procedures can increase the risk of complications such as haemorrhage and sepsis [27]. Longer procedures often indicate greater surgical complexity, potentially leading to additional insults to the kidney, particularly in the form of septic complications. However, factors such as calyx puncture, number of punctures, intraoperative hypotension, and blood transfusion did not show significant associations with post-PCNL AKI in our study.

Our study underscores the importance of addressing modifiable risk factors such as hypertension (HTN), hyperuricemia, tract size, operative time, and bilateral percutaneous nephrolithotomy (PNL) based on individual patient characteristics. Preoperative control of HTN, management of hyperuricemia, staged bilateral PNL procedures, and minimization of operative time are strategies that can potentially mitigate the risk of AKI following PNL. Furthermore, while certain risk factors, such as Female sex, staghorn calculi, Hounsfield units, and stone volume, are nonmodifiable, they remain crucial considerations in patient management. Endourologists should remain aware of these factors during the treatment of calculi disease to minimize the likelihood of post-PNL AKI.

Based on regression analysis, we developed a nomogram to predict post-PCNL AKI, which demonstrated good efficacy in a validation cohort of 70 patients. Nomograms that have been developed in urolithiasis have predominantly concentrated on the rates of stone clearance and postoperative complications as a whole, but our nomogram specifically targeting the predictive capacity of postoperative AKI in patients undergoing PCNL promises to be a novel tool that has not been extensively explored. However, larger validation studies are warranted to further assess its accuracy and reliability.

The strength of our study lies in its comprehensive characterization of the AKI in a large patient cohort undergoing PCNL, assessing multiple risk factors contributing to the development of AKI. Our study is limited by its single-center design, which restricts the generalizability of findings to other populations undergoing PNL for renal stones. Additionally, due to the short follow-up period of three months, the long-term outcomes of kidney function in patients with post-PNL AKI remain uncertain. A longer follow-up period, extended up to one year, would enable a more comprehensive assessment of overall outcomes and better predict renal function recovery in these patients. To enhance the reliability of our results, future studies could employ a randomized controlled design. The lack of an accurate measurement of intraoperative blood loss, which could influence the development of postoperative AKI, is another limitation of our study. Lastly, AKI was defined based on serum creatinine levels without considering hourly urine output, which is a component of AKI definition. Future studies should also include patient related quality of life and practical considerations in the use of nomograms and scoring systems in these patients [28, 29].