Alteration in Resistive Index of Renal Vasculature Following Extracorporeal Shock Wave Lithotripsy for Renal Stones

Introduction: Extracorporeal Shockwave lithotripsy (ESWL) may be associated with both anatomic and functional injuries to the kidney when used in the management of uncomplicated kidney stones. Assessment of the resistive index (RI) is a non invasive diagnostic modality for studying changes in the arterial system. RI, which is measured by color doppler ultrasonography, reflects resistance of intrarenal arteries that indirectly shows the renal blood flow. Aim: To assess changes in intrarenal RI following ESWL in the ipsilateral and contralateral kidneys & to study correlation of alteration in resistive index with age of the patient. Methodology: A total of 38 patients with solitary renal calculus, who underwent extracorporeal shockwave lithotripsy were included in the study. The patients were evaluated for the RI in Clinical Practice Article ipsilateral (diseased) and contralateral kidneys; before, 3 hrs after and 1week after ESWL. Serum creatinine levels & creatinine clearence were measured pre ESWL and 4 weeks after ESWL. Results: RI in ipsilateral kidney pre ESWL was 0.590 and post ESWL (3 hrs after ESWL) was 0.646, it showed a statistical significant increase with a p value of <0.001. 1week post ESWL resistive index values were comparable to pre ESWL value with no significant difference. ESWL had no effect on serum creatinine & creatinine clearance measured pre ESWL & 4 weeks post ESWL. Conclusion: Doppler studies of the kidneys treated with ESWL have shown a transient rise of RI in our study, the long term effect of rise in RI after ESWL still remains to be evaluated.


INTRODUCTION
Patients with uncomplicated kidney stone can be successfully treated with the least invasive modality, i.e., Extracorporeal Shockwave Lithotripsy (ESWL) [1]. ESWL may be associated with injuries to the kidney, both anatomic and functional [2]. Assessment of the resistive index (RI) using color doppler ultrasonography is a non invasive diagnostic modality for studying changes in the arterial system. RI, which is measured by color doppler ultrasonography, shows the renal blood flow which indirectly reflects resistance of intra-renal arteries [3]. RI has proved to be a sensitive tool for monitoring vascular injuries of the kidney. In all these conditions, RI levels greater than 0.7 are considered to indicate pathologic change [4]. In the past, researchers have tried to assess the changes in the RI after ESWL but there are still controversies about the pattern and timeline of RI changes [5].

Aim
The aim of the study is to assess changes in intra-renal RI following ESWL in the ipsilateral and contralateral kidneys & to study correlation of alteration in RI with age of the patient. RI of inter-lobar arteries was measured before ESWL using color doppler ultrasonography. Color doppler machine used for the study was PHILIPS HD 11 using low frequency probe of 3.5 MHz. RI was measured in ipsilateral (within 2cm distance of calculus) and corresponding area in contralateral kidney. Three measurements were taken and the algebric mean of the values was calculated as RI.

MATERIALS AND METHODS
RI is calculated by the equation [6]: Systolic peak velocity -End diastolic peak velocity / Systolic peak velocity ESWL was performed with Dornier-Compact Sigma Lithotriptor without anaesthesia. Patient was injected with an intramuscular injection of diclofenac sodium 50 mg before the start of the procedure. Stone localization was done by fluoroscopy. For study purpose a standard protocol of giving 3000 shocks at 4 KV per session was used in treatment. No pause was taken during the session of 3000 shocks. Post procedure patients were prescribed analgesics such as diclofenac oral twice daily with a proton pump inhibitor & prophylactic antibiotic (ciprofloxacin 500 mg twice daily) for 1 week. Double J stenting was not done in any patient. Tamsulosin was not advised to any patient.
Thereafter at 3 hrs of ESWL color Doppler ultrasonography was repeated and RI was measured in the before mentioned areas. Followup visit for patients having increased RI after ESWL was arranged for 1 week after the procedure and RI of the ipsilateral and contralateral kidney was measured for the third time. Stone Clearance was defined as absence of stone on X-ray KUB/NCCT or residual single stone fragment of size ≤ 4 mm.
Following parameters were evaluated

Satistical Analysis
The values obtained before and after treatment were analyzed statistically using the Paired t-test.
The quantitative data was assessed by student t test, Wilcoxon Mann Whitney rank sum test. A 'p' value less than 0.05 was considered statistically significant.

RESULTS
There were total of 38 patients out of which 13 (34.2%) were female and 25 (65.8%) were male.  Table 3). The difference between the the two groups was not statistically significant with a p value of 0.630.

DISCUSSION
ESWL has a very distinct place in a surgeon's armamentarium for treatment of renal stone disease. Although ESWL has been considered the least invasive procedure for the management of renal calculus, it is also associated with some adverse effects on human tissues. This study was done to assess the effect of ESWL on kidney by evaluating the changes in renal vasculature and functional assessment of the kidney. The study was performed measuring the changes in RI of the ipsilateral and contralateral interlobar renal arteries. The pattern and timeline of RI values are controversial, as is its correlation with age. Change in serum creatinine and creatinine clearance was measured to assess the functional changes.
The doppler study of renal vasculature in ipsilateral kidney showed a significant increase in RI 3 hours post ESWL treatment, indicating vascular compromise in the area where the shock waves were targeted. Y Aoki et al compared the mean of Resistive Index before (0.656 ± 0.053) and after ESWL (0.682 ± 0.052) and showed significant increase in treated kidney with a p value of <0.0001 [8]. In a study by Mohseni et al the resistive index nearby the calculus before and after ESWL (0.594 ± 0.062 and 0.620 ± 0.048) were significantly different with the post ESWL being higher (p value 0.003) [9]. Hiros M et al. [10] studied the change in resistive index of the treated kidney form the baseline value of 0.62 ± 0.05 to 0.67 ± 0.05 post ESWL with a significant difference (p <0.001). Nazaroglu H et al observed a significant increase in resistive index at 30 min and 3 hrs after ESWL in the nearby region [11]. This might occur as a result of tissue damage including blood vessels. Doppler studies performed on patients 1 week after ESWL have shown reduction in RI in ipsilateral kidney reaching almost to the level of preprocedure values. This indicates the reversal of the damage to the renal vasculature and tissue suggesting the temporary nature of the adverse effect. Although few studies have shown the reduction in RI one week after ESWL, [8][9][10]12] there are studies in which RI has not returned to the pretreatment values even after 1 week suggesting there might be cases in which renal damage has not reversed and might require further assessment of the factors leading to delayed or non healing of the damage [5].
Many studies in past have shown the effect of shockwaves on the contralateral kidney in form of increase in RI [8,10,11,13,14]  Assessment of change in function by comparing serum creatinine and creatinine clearance 1 month post ESWL showed no significant difference which suggests that reversible damage to renal tissue and vessels did not exert any long term change in renal function.

LIMITATIONS
Our study had a small sample size of 38 patients. Further follow up of the patients is required to assess the long term effects of ESWL on kidney. More frequent assessment of RI could have been done to know more precise time of changes in RI following EWSL and its return to pre ESWL values.