Renovascular hypertension: the diagnosis and management of renal ischaemia

Optimising renal cancer patients for nephron-sparing surgery: a review of pre-operative considerations and peri-operative techniques for partial nephrectomy

Nonmodifiable factors including pre-operative renal function and amount of healthy renal tissue preserved are the most important predictive factors that determine renal function after partial nephrectomy. Ischaemia time is an important modifiable risk factor and cold ischaemia time should be used if longer ischaemia time is anticipated. New techniques may have a role in maximising postoperative kidney function, but more robust studies are required to understand their potential benefits and risks.

Current Paradigm for Ischemia in Kidney Surgery

PURPOSE

Partial nephrectomy is the accepted standard of care for treatment of patients with small renal masses. The primary goal while performing partial nephrectomy is cancer control with a secondary important goal of maximizing renal function preservation with minimal perioperative morbidity. Recent studies have highlighted the importance of renal parenchymal quality and quantity postoperatively rather than duration of ischemia in determining long-term renal function. We review the available data regarding perioperative renal function optimization with special interest in ischemia during partial nephrectomy, highlighting the controversies and establishing future lines of investigation.

MATERIALS AND METHODS

We performed a comprehensive literature review for the years 1970 to 2014 via MEDLINE(®), PubMed(®) and the Cochrane Library. Review was consistent with the PRISMA (Preferred Reporting Items for Systemic Reviews and Meta-Analyses) criteria. We used MeSH (Medical Subject Headings) terms for the search including "acute kidney injury/failure," "carcinoma, renal cell/carcinoma of kidney/neoplasm of kidney," "kidney failure, chronic/end-stage kidney disease," "ischemia-reperfusion" and "warm ischemia/cold ischemia." Relevant review articles were included. Abstracts from major urological/surgical conferences were reviewed. All studies included were performed in adults, were written in English and had an abstract available.

RESULTS

Our traditional knowledge of renal ischemia is derived from animal studies, ie kidney transplant and retrospective partial nephrectomy series that indicate the risk of renal function impairment for every minute of ischemia. Careful evaluation of historical studies highlights flaws of the use of ischemia duration as a dichotomous marker (25 or 30 minutes) while predicting renal function outcomes. Recent studies have revealed no effect of duration of ischemia on ultimate kidney function in the short or long term. Quality and quantity of parenchyma preserved postoperatively are key predictors of ultimate renal function after partial nephrectomy. Traditionally partial nephrectomy has been performed with hilar occlusion to provide a relatively bloodless surgical field allowing effective oncologic control during tumor excision with secure management of blood vessels, collecting system and renal reconstruction. Selective clamping and nonclamping techniques have been proposed to avoid the perceived harmful effects of ischemia, although they convert a complex surgery into a more challenging procedure, potentially limiting the widespread use of partial nephrectomy for management of renal cancers. Promising urine and blood-based biomarkers (NGAL, KIM-1) in the context of critical care settings and global stress have been observed to predict acute kidney injury. Within the partial nephrectomy environment the usefulness of those markers needs to be further investigated. To date, no study has proved their usefulness in the setting of partial nephrectomy.

CONCLUSIONS

Based on the available evidence, use of a single cutoff for duration of ischemia time as a dichotomous value for renal function outcomes in the setting of partial nephrectomy is flawed. Renal ischemia is a controversial topic with a shifted paradigm within the last decade. Current evidence has shown that patients with 2 kidneys undergoing nephron sparing surgery can tolerate ischemia times of more than 30 minutes without a clinically significant decline in renal function. Biomarkers predictive of renal tubular injury fail to predict acute kidney injury in the context of partial nephrectomy. Indications for partial nephrectomy could be significantly expanded as the safety of limited renal ischemia is now better understood.

Chronic antioxidant treatment improves arterial renovascular hypertension and oxidative stress markers in the kidney in Wistar rats

BACKGROUND

Sympathetic vasomotor hyperactivity and baroreflex dysfunction are involved in the development and maintenance of renovascular arterial hypertension. We hypothesized that angiotensin (Ang) II-dependent oxidative stress contributes to the pathophysiology of the two-kidney, one-clip (2K-1C) model.

METHODS

The mean arterial pressure (MAP), baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated after chronic administration of an antioxidant, vitamin C (vitC 150 mg/kg/day) in male Wistar 2K-1C rats. Additionally, the mRNA levels of Ang II subtype 1 receptor (AT(1)R), NAD(P)H oxidase subunits (p47phox and gp91phox), and major antioxidant enzymes were evaluated in the renal cortex.

RESULTS

After vitC treatment, the MAP (170 +/- 4 vs. 133 +/- 6 mm Hg; P < 0.05) and rSNA (161 +/- 5 vs. 118 +/- 12 spikes/s; P < 0.05) were significantly reduced only in the 2K-1C group. VitC improved the baroreflex control of heart rate (HR) and rSNA. The expression of AT(1)R, p47phox, and gp91phox was elevated (51, 184, and 132%, respectively) in the clipped kidney of 2K-1C group. VitC downregulated AT(1)R in the clipped kidney (31%). Catalase (CAT) expression was reduced in clipped (70%) and nonclipped (83%) kidneys of 2K-1C rats. VitC treatment augmented the expression of glutathione peroxidase (GPx) in both clipped (185%) and nonclipped (212%) kidneys of the 2K-1C group.

CONCLUSIONS

The present study suggests a role for oxidative stress in the cardiovascular and sympathetic alterations in renovascular hypertension, associated with changes in the expression of AT(1)R, NAD(P)H oxidase subunits, and antioxidant enzymes in the kidney.

Assessing the impact of ischaemia time during partial nephrectomy

CONTEXT

The impact of applying renal ischaemia during nephron-sparing surgery to avoid renal damage in the treated kidney has gained importance in different surgical techniques.

OBJECTIVE

The main objective of the present study is to point out the limit of renal ischaemia times for warm and cold ischaemia approaches. Important results of research on renal ischaemia and different surgical techniques as well as results of clinical studies concerning renal function after renal ischaemia in partial nephrectomy are highlighted.

EVIDENCE ACQUISITION

A Medline literature research was performed, combining queries on the keywords nephron-sparing surgery, partial nephrectomy, and ischemia. Links to related articles and cross-reading of citations in related articles were surveyed, as were reviews, letters to editors, and information collected from urologic textbooks. The references formed the basis of this review article, with selection and deletion based on the relevance and importance of the content. In a final step, interactive peer review by the expert panel of coauthors completed the review.

EVIDENCE SYNTHESIS

Renal ischaemia research showed an increasing renal damage proportional to ischemic time. Current clinical data support safe ischaemia times, within 20 min of warm ischaemia and up to 2 h of cold ischaemia, to minimise renal ischemic damage. To date, no ischaemia dose-response curve or algorithm is available to predict the risk of acute kidney injury and chronic kidney disease in patients undergoing intraoperative ischaemia. In general, there seems to be a higher risk for comorbidity caused by renal damage in patients suffering from kidney tumour.

CONCLUSIONS

If ischaemia is required, the tumour should be removed within 20 min of warm ischaemia, regardless of surgical approach. Efforts should be made to start immediately with cold ischaemia, if the feasibility within this span of time seems to be jeopardised. Thus, cold ischaemia times up to 2 h can be tolerated by the kidney, depending on the individual method. Nevertheless, cold ischaemia with ice slush should be kept as short as possible--at best within 35 min. In ischemic nephron-sparing surgery, one of the surgeon's main aims should be to avoid loss of renal function. Only after optimal preoperative appraisal and planning can the best postoperative outcomes for renal function be achieved.

Current management of transplant renal artery stenosis: clinical utility of duplex Doppler ultrasonography

OBJECTIVES

To perform a retrospective study to determine the clinical utility of Doppler ultrasonography (DUS) and to determine its role in the management of transplant renal artery stenosis (TRAS).

METHODS

Patients undergoing DUS between January 1998 and January 2001 for clinical suspicion of TRAS were included in the study. A total of 51 patients were divided into two groups according to the peak systolic velocity. Additional management was based on the clinical and DUS findings and their congruence. Patients were followed up and their outcome was analyzed.

RESULTS

Of the 51 patients who entered the study, 26 were in the low probability group (LPG) and 25 in the high probability group (HPG). Nine patients in the LPG underwent additional investigations; eight underwent magnetic resonance angiography and one angiography. Of these 9 patients, 6 had stenosis, 4 of whom required angiography. In total, 5 patients from the LPG underwent angioplasty, and 4 of them had stenosis (1 with TRAS, 2 with common iliac artery stenosis, and 1 with renal artery ostial stenosis). Three patients underwent angioplasty and 2 of them improved. In the HPG, 20 of 25 patients underwent additional investigations, including magnetic resonance angiography in 12 and angiography in 8, with stenosis in 15 patients. Of the HPG, 13 of 25 patients underwent angiography, with 10 requiring angioplasty--8 for TRAS and 2 for adjacent renal artery stenosis, with improvement in 8 patients. Congruent clinical and DUS findings were highly predictive of significant stenosis more amenable to improvement.

CONCLUSIONS

The results of our study have shown that high-probability DUS and congruent clinical findings are likely to identify a significant stenosis that is amenable to treatment. Low-probability DUS findings do not eliminate the possibility of stenosis, but intervention in this group is less likely to result in improvement.

Endovascular Therapy of Renal Artery Stenosis: Where Do We Stand Today?

Angioplasty and stent therapy for stenoses of the renal artery have long been part of the everyday life of interventional radiologists. Newer studies, however, challenge the clinical significance of the method. A decisive advantage of endovascular techniques for the treatment of arterial hypertension as opposed to therapy with modern antihypertensives could not be proven in individual randomized studies, even though blood pressure control was observed to be facilitated by PTA (percutaneous transluminal angioplasty). Renal function often did not show any sustainable improvement following elimination of the renal artery stenosis. However, progression of kidney insufficiency could be slowed down. There is still no general justification from the existing data for the treatment of incidental stenoses. Many questions remain open regarding the technique. Whereas fibromuscular dysplasia can be treated by balloon angioplasty as a general rule, a metallic endoprosthesis must often be used for atherosclerotic stenoses. The outstanding morphologic results of stent therapy in the short and medium term course are often simply used to justify primary stent implantation in ostial stenoses.

Detection of acute renal ischemia in swine using blood oxygen level-dependent magnetic resonance imaging

PURPOSE

To determine the feasibility and sensitivity of blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) to detect acute renal ischemia, using a swine model, and to present the causes of variability and assess techniques that minimize variability introduced during data analysis.

MATERIALS AND METHODS

BOLD MRI was performed in axial and coronal planes of the kidneys of five swine. Color R2* maps were calculated and mean R2* values and 95% confidence intervals (CIs) for the cortex and medulla were determined for baseline, renal artery occlusion and reperfusion conditions. Paired Student's t-tests were used to determine significance.

RESULTS

Mean R2* measurements increased from baseline during renal artery occlusion in the cortex (axial, 13.8-24.6 second(-1); coronal, 14.4-24.7 second(-1)) and medulla (axial, 19.3-32.2 second(-1); coronal, 20.1-30.7 second(-1)). These differences were significant for both the cortex (axial, P < 0.04; coronal, P < 0.005) and medulla (axial, P < 0.02; coronal, P < 0.0005). No significant change was observed in the contralateral kidney.

CONCLUSION

R2* values were significantly higher than baseline for medulla and cortex during renal artery occlusion. More variability exists in R2* measurements in the medulla than the cortex and in the axial than the coronal plane.