7 Ischemic Nephropaty

7/28/2019 7 Ischemic Nephropaty

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ISCHEMICNEPHROPATHY

LIGIA PETRESCU


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DEFINITION

The term "ischemic nephropathy" refersto the reduction in GFR that is caused byhemodynamically significant renal arteryobstruction.The most common cause of ischemic renaldisease in adults is bilateral atheromatous

disease when both kidneys are present orunilateral stenosis in a solitary kidney.


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DEFINITIONThe major clinical questions confronting thenephrologist in considering the diagnosis of ischemic nephropathy include:

1. What is its prevalence in the population with end-stagerenal disease?

2. What is the natural history in patients with less severerenal insufficiency?

3. Which clinical and laboratory features are most usefulin its detection?

4. What are the indications for renal arteryrevascularization?

5. Which method of revascularization is more effective?


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EPIDEMIOLOGY

Hypertension is reportedly a common cause of end-stage renal disease, second only to diabeticnephropathy.During the past decade, the frequency of end-

stage renal disease attributed to hypertension hasincreased fivefold, and during the past 5 years, itsprevalence has increased by more than 10%/y.The median age of this group is 67 years at thetime of the initiation of dialysis, which is among

the oldest for all causes of end-stage renal disease.


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EPIDEMIOLOGY

The median survival for patients with ischemicnephropathy was 27 months, compared with 56 monthsfor the other diagnostic groups. Furthermore, the 5-yearsurvival was 12% compared with 39% for the othergroups.

This poor outcome was attributed to the increasing age of the patients at the time of initiation of dialysis (46 to 60 years) and their advanced systemic atherosclerosis.Compared with a group in whom other causes of chronicrenal disease were found, those with ischemic

nephropathy were older,had more systemic atherosclerosis,had a threefold higher frequency of deterioration of GFR aftertreatment with an ACE inhibitor.


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EPIDEMIOLOGY

These lesions were invariably located at the aorticorifice or within the proximal third of the renal

artery.Renovascular stenosis is often found un-expectedly during the evaluation of occlusivedisease of the aorta and lower extremities.


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NATURAL HISTORY There is compelling evidence that ischemic nephropathy isthe consequence of progressive renal artery stenosis andocclusion.

Angiographic progression of renal artery narrowing wasfound in 49% of 237 patients in five studies in which thefollow-up period ranged from 6 to 180 months. However,there was considerable variability in the rate at which renalartery lesions progressed, ranging from approximately1.5% to 5.0%/y.Progression to complete occlusion has been observed inapproximately 15% of patients with renal artery stenosis.In contrast to these observations in patients withatheromatous lesions, fibromuscular dysplasia did notcommonly progress to complete occlusion.


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DETECTION

Few clinical signs or noninvasive laboratory tests pointto the diagnosis of ischemic nephropathy or signal itsprogression to occlusion.Clinical suspicion should be high in:

elderly patients with progressive renal insufficiency associated with an inactive urine sediment, protein excretion less than 1 g/d, hypertension, and peripheral vascular disease. a reduction in kidney length heralds progressive stenosis and

occlusion, However, the sensitivity of these clinical andlaboratory signs is relatively poor for identifying patients withischemic nephropathy.


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DETECTIONDuplex ultrasonography detected a decrease in length

greater than 1 cm in only 26% of those with progressivestenosis.Excretory urography and renal scintigraphy are inadequatefor identifying patients with ischemic nephropathy.Changes in biochemical measurements are oftenunsatisfactory for detecting progressive disease.Serum creatinine concentration increased more commonly inpatients with ongoing stenosis, this was not the case inother series.PRA, when measured during the captopril test or renal veinrenin sampling, is less reliable for identifying bilateralrenovascular stenosis than for unilaterallesions.


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Characteristic EssentialHypertension (%)

Renovascular Hypertension (%)

Atheroma FibromuscularDysplasia

Race (black) 29 2 10 Family history 67 58 41

Age at onset

50 y 7 39 13

Duration >1 y 10 23 19

Obese 38 17 11

Abdominal bruit 7 41 57

High-renin profile 15 80 80

Hypokalemia (K +


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Pulmonary Edema

We have been impressed by the relatively frequentoccurrence of pulmonary edema in patients withadvanced renovascular hypertension.Successful revascularization of even one of the

ischemic kidneys prevented further occurrence of thepulmonary edema.The occurrence of pulmonary edema was not relatedto the severity of the hypertension or renal failure.

Although it was more common in patients who hadassociated coronary heart disease, it could also occurin patients with normal coronary arteries.


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THERAPEUTIC STRATEGIES FOR PRESERVATION OF RENAL FUNCTION

Medical TherapyMedical treatment does not reliably prevent theprogression of renal artery stenosis, and it isassociated with a high mortality rate after initiationof dialysis. Furthermore, the rate of progression of renal insufficiency often accelerates duringantihypertensive drug treatment in patients withischemic renal disease.This is a well-recognized complication of ACEinhibitor therapy, especially in the setting of Na + depletion when the GFR is especially dependent on

angiotensin II. Accordingly, acute deterioration ismost likely to be provoked by ACE inhibitors duringdiuretic therapy, dietary sodium restriction, orexcessive extrarenallosses (e.g., vomiting,diarrhea).


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THERAPEUTIC STRATEGIES FOR PRESERVATION OF RENAL FUNCTION

Other classes of antihypertensive agents can alsocause acute renal failure: acute blood pressurereduction with nitroprusside (to approximately145/85 mmHg) caused significant decrements in GFR and renal plasma flow.There are individual patients for whom medicaltherapy is selected because more invasive proceduresmay pose unacceptable risks.In this group, renal function should be observedclosely while the patient is receiving antihypertensivemedication, especially when ACE inhibitors are used.Diuretics should not be used routinely in combinationwith ACE inhibitors in patients with ischemicnephropathy because of the increased risk of acuterenal failure.


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RENAL REVASCULARIZATION

Surgery

Reports from uncontrolled retrospective studies

have clearly documented that surgicalrevascularization can improve renal function inpatients with ischemic nephropathy. Postoperativeimprovement, generally defined as a 20% decreasein serum creatinine concentration, was reported inmore than half of the patients in nine studies


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RENAL REVASCULARIZATION

Some features that may predict successfulrestoration of renal function include collateral circulation and nephrogram on angiography,

renal length greater than 9.0 cm, lateralization of renin secretion, differential concentration of urine on split-function

studies, and viable nephrons on biopsy examination.However, these should serve only as generalguidelines because they lack sufficient specificityand sensitivity to determine outcome.


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Renal Angioplasty

Angioplasty is effective for treatingrenovascular hypertension associated withatheromatous lesions.


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SUMMARY

Renovascular disease often causes hypertensionthat can be cured or improved by renalrevascularization.

Another important consequence of renal arterystenosis is ischemic nephropathy. This refers to theprogressive deterioration in GFR that occurs whenrenal blood flow is impaired.Ischemic nephropathy is increasingly recognized asan important cause of end-stage renal disease thathas a high mortality rate when treated

conservatively.

By contrast, clinical improvement is reportedcommonly after renal revascularization.


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SUMMARY

There are few reliable clinical or laboratory markersfor ischemic nephropathy, so that angiography isusually required to confirm the diagnosis.

However, the diagnosis is likely in the elderlypatient with systemic atherosclerosis andhypertension in whom a rapid rise in serumcreatinine concentration is associated withdecreased renal length.Revascularization by either renal angioplasty orsurgery can successfully preserve renal function inselected patients.

7 Ischemic Nephropaty

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