Attending rounds: a patient with accelerated hypertension and an atrophic kidney

The Role of Hypoxia in Ischemic Chronic Kidney Disease

A gradually developing reduction in renal blood flow from atherosclerotic renovascular disease results in loss of kidney volume and a decrease in glomerular filtration rate that eventually becomes irreversible. Whether this process fundamentally reflects tissue hypoxia has been difficult to establish. Studies of human renovascular disease have indicated that reductions in blood flow of up to 30% to 40% can be tolerated with preservation of normal oxygenation and structural integrity. These observations are consistent with remarkable stability of poststenotic kidney function during sustained medical antihypertensive drug therapy in moderate renovascular disease. With more severe and sustained reductions, however, cortical oxygenation decreases and the magnitude of medullary hypoxia expands. These changes are associated with increasing renal venous levels of inflammatory cytokines, angiogenic markers, and infiltration of inflammatory cells, including tissue macrophages and T cells. Although restoring large-vessel blood flow can improve oxygenation, some of these processes reflect microvascular rarefication, remain activated, and do not depend on hemodynamic factors alone. Elucidation of tissue injury pathways associated with hypoxia opens the possibility of adjunctive therapeutic measures beyond renal revascularization. These include cell-based regeneration, mitochondrial protection, and/or angiogenic cytokine therapy to restore or preserve renal function in ischemic nephropathy.

Renal Arterial Disease and Hypertension

Renal artery disease produces a spectrum of progressive clinical manifestations ranging from minor degrees of hypertension to circulatory congestion and kidney failure. Moderate reductions in renal blood flow do not induce tissue hypoxia or damage, making medical therapy for renovascular hypertension feasible. Several prospective trials indicate that optimized medical therapy using agents that block the renin-angiotensin system should be the initial management. Evidence of progressive disease and/or treatment failure should allow recognition of high-risk subsets that benefit from renal revascularization. Severe reductions in kidney blood flow ultimately activate inflammatory pathways that do not reverse with restoring blood flow alone.

Renal artery stenosis: if and when to intervene

PURPOSE OF REVIEW

Atherosclerotic renovascular disease remains highly prevalent and presents an array of clinical syndromes. Recent prospective trials have dampened enthusiasm for revascularization generally, but clinicians recognize the need to identify patients likely to benefit from vascular intervention.

RECENT FINDINGS

This article highlights the inflammatory nature of vascular occlusive disease and the limits of the kidney to adapt to reduced blood flow. Although moderate reductions can be tolerated, severe impairment of renal perfusion leads to tissue hypoxia and activates inflammatory injury within the kidney. Hence, assessment of kidney viability and potential tools to modify mitochondrial and inflammatory damage may be important to identify patients for whom clinical intervention should be undertaken.

SUMMARY

Clinicians must recognize clinical syndromes that identify 'high-risk' groups and apply revascularization in those likely to benefit. Future efforts to protect the kidney (e.g., mitochondrial protection) or cell-based therapy may amplify clinical recovery when combined with restoring renal blood flow.

Approach to atherosclerotic renovascular disease: 2016

The management of atherosclerotic renal artery stenosis in patients with hypertension or impaired renal function remains a clinical dilemma. The current general consensus, supported by the results of the Angioplasty and Stenting for Renal Atherosclerotic Lesions and Cardiovascular Outcomes for Renal Artery Lesions trials, argues strongly against endovascular intervention in favor of optimal medical management. We discuss the limitations and implications of the contemporary clinical trials and present our approach and formulate clear recommendations to help with the management of patients with atherosclerotic narrowing of the renal artery.

Current approaches to atherosclerotic obstructive renal artery stenosis

Increased lifespan in the last few decades has substantially changed the scenario for renal artery stenosis. Indeed, because older populations show a higher prevalence of atherosclerotic disease, the incidence of atheromatous renal artery stenosis has also increased. Intuitively, one could surmise that stenosis removal should void both the hypertension and the kidney damage resulting from the obstructive stenosis. Surprisingly, a number of important clinical trials have failed to show the reversion seen in experimental models. The reasons for these differences may be linked to chronicity and inflammation associated with the atherosclerotic lesion. However, the failure to obtain a favorable response may also be related to abnormalities in the contralateral kidney. Indeed, this apparently normal kidney should work to compensate the hemodynamic effects of the ipsilateral stenosed kidney. Instead, structure and function in the contralateral kidney can be altered in renal artery stenosis to the point that this nonstenotic kidney may sustain both, hypertension and progressive kidney disease. Certainly, comparing the effects of clip removal in the Goldblatt model to angioplasty in clinical settings with atherosclerotic lesions may be totally inappropriate. Nevertheless, there remain certain clinical situations such as bilateral renal arterial disease, congestive heart failure, and progressive renal failure, where angioplasty may be an alternative. These approaches however are yet to be tested.