Historical Background
In 1937 Goldblatt demonstrated that renal artery constriction produced atrophy of the kidney and systemic hypertension in a canine model. His elegant experiments defined a causal relationship between renovascular disease and hypertension. Leadbetter and Burkland are credited with the first successful treatment of renovascular hypertension. A 5-year-old child was cured of severe hypertension after removal of an ischemic kidney. After Leadbetter and Burkland’s 1938 report, nephrectomy was performed for patients based on the presence of hypertension associated with a small kidney as demonstrated by intravenous pyelography. In a 1956 review of 575 nephrectomies, Smith found that only 25% of patients were cured of hypertension.
In 1954 Freeman and colleagues performed the first direct surgical repair of renovascular disease—a transaortic bilateral renal artery thromboendarterectomy. His treatment represented the first cure of hypertension by direct surgical repair. This success was accompanied by widespread aortography and direct renovascular repair for presumed blood pressure benefit. However, in the early 1960s it was recognized that repair of renovascular disease in all hypertensive patients benefited less than half of individuals.
Morris, DeBakey, and Cooley reported in 1962 on eight azotemic patients who had improved blood pressure and renal function after direct surgical repair of renovascular disease. This report marked a shift in focus from renovascular hypertension to renovascular renal insufficiency or ischemic nephrectomy. Since that time other groups have found a similar beneficial function response in select patients with global renal ischemia.
Indications
Natural history studies of atherosclerotic renovascular disease among patients with hypertension demonstrated anatomic progression of renal artery stenosis with concomitant decline in kidney size and function. However, more recent studies suggest that anatomic progression is rare in the absence of severe hypertension. After a mean follow-up of 8 years, the rate of progression to more severe renal artery stenosis or occlusion among independent, elderly subjects was estimated at 0.5% per year. Among 434 hypertensive patients, 6% to 9% demonstrated progression of stenosis and 2.3% progressed to occlusion over follow-up of 3.2 years. Progression of disease correlated with renal length but not with renal function. Consequently, in the absence of hypertension, renovascular intervention is not recommended as either isolated repair or renal artery repair in combination with aortic reconstruction.
In the absence of positive physiologic studies, such as select renal vein assays, the most important clinical characteristic of significant renovascular disease is severe hypertension. Severe hypertension is strongly associated with blood pressure benefit and improved renal function when ischemic nephropathy is present. However, severity of hypertension is estimated by untreated blood pressure, not by the number of antihypertensive medications prescribed. The highest recorded blood pressure is a useful surrogate for severity of hypertension.
Preoperative Preparation
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Patients with severe hypertension requiring large doses of multiple medications often have requirements reduced when placed on bed rest. Otherwise, hypertension medications are reduced to the minimum necessary for blood pressure control during the preoperative period. If the blood pressure remains in excess of the 95th percentile for age and length in children or greater than 120 mm Hg diastolic in adults, surgical repair should be postponed until blood pressure is brought under control.
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The combination of an intravenous calcium channel-blocking agent, such as nicardipine, and selective beta-adrenergic blocking agents, such as esmolol or metoprolol, is administered in an intensive care setting.
Pitfalls and Danger Points
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Renal atheroembolism. During renal artery exposure tissues are dissected away from the aorta and renal artery. Systemic heparinization is confirmed by activated clotting time. The distal renal artery or its branches are controlled with atraumatic clamps before proximal aortic or proximal renal artery control. Arterial reconstructions are flushed vigorously with heparinized saline. Renal artery control is released as the final step after reconstruction.
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Criteria for renal endarterectomy. Successful endarterectomy requires that the aortic atheroma end within 1 or 1.5 cm of the renal artery origin. In addition, preaneurysmal degenerative change of the aorta and transmural calcific atheroma must be excluded before endarterectomy.
Operative Strategy for Renovascular Occlusive Disease
Unilateral or Bilateral Renal Artery Repair
The rationale for treatment of renovascular disease is to improve event-free survival. Best evidence suggests that adults cured of severe hypertension and patients with renal insufficiency who demonstrate incremental increase in excretory renal function have improved dialysis-free survival. In the absence of hypertension or renal insufficiency, prophylactic renal artery intervention is not recommended by either direct surgical repair or endovascular intervention.
In contrast to prophylactic intervention, empiric renal artery repair implies that hypertension, excretory renal dysfunction, or both are present even though a causal relationship between renovascular disease and clinical sequelae has not been established. Direct surgical repair of a unilateral renal artery lesion is performed when hypertension remains severe and uncontrollable, despite maximum drug therapy in a young patient without significant risk factors for repair. When a patient has bilateral renovascular disease and hypertension, the decision for direct surgical repair is based on the severity of the hypertension and the severity of the renal artery lesions. When severe stenosis of one renal artery exists with mild to moderate contralateral disease, the patient is treated for a unilateral lesion. When both renal artery lesions are moderately severe (60%-80%), direct repair is undertaking only if the associated hypertension or renal insufficiency is severe. When both renal arteries display severe stenosis (>80%) and are associated with severe hypertension, bilateral renal revascularization is performed.
Renal Artery Anatomy
The renal arteries may vary in location and number. Renal arteries may arise from any portion of the abdominal aorta or iliac system. Single renal arteries to each kidney are found in 80% to 85% of patients. These renal artery origins are usually at the body of the L2 vertebra. The right artery arises from the anterolateral aspect of the aorta, whereas the left artery usually originates from the posterolateral aorta. Between 15% and 20% of patients demonstrate multiple renal arteries. On the right, inferior polar renal arteries frequently course anterior to the inferior vena cava, and all such vessels should be presumed to be renal branches. In the presence of severe occlusive lesions, collateral vessels are prominent, especially in childhood.
Exposure of the Pararenal Aorta
Exposure of the pararenal aorta is facilitated by complete mobilization of the left renal vein from caval origin to renal hilum. The adrenal, gonadal, and renal lumbar branches are identified, ligated, and divided if necessary for exposure. The renal vein may then be retracted superiorly or inferiorly as needed. The right renal artery can be exposed in its entire retrocaval course. This usually does not require division of lumbar veins. Dissection of the neural plexus surrounding the renal arteries is performed with electrocoagulation to minimize blood loss.
Selection of a Method for Direct Surgical Repair
No single direct surgical repair provides optimal reconstruction for all renovascular diseases. Of the three direct techniques—aortorenal bypass, thromboendarterectomy, and renal artery implantation—aortorenal bypass is the most versatile technique. In the atherosclerotic adult, saphenous vein is the preferred conduit, whereas autogenous artery repair is preferred for children. When a conduit is necessary in a child, the hypogastric artery is preferred; however, if the renal artery demonstrates sufficient redundancy, reimplantation is particularly useful in children. In cases of ostial atherosclerotic renovascular disease involving both renal arteries or in the presence of multiple renal arteries, transaortic renal endarterectomy may be preferred. However, successful endarterectomy requires that the aortic atheroma end within 1 or 1.5 cm of the renal artery origin. In addition, preaneurysmal degenerative change of the aorta and transmural calcific atheroma must be excluded before endarterectomy.
Source of Inflow
Direct surgical repair is selected over indirect methods for most patients. Concomitant celiac stenosis occurs in 40% of adult patients, and bilateral renovascular repair is required in half. The infrarenal aorta is the preferred inflow source; however, when patient anatomy precludes this site, the supraceliac aorta is used for inflow. To avoid compromise associated with progressive atherosclerosis, the iliac vessels are avoided as a source of inflow. To minimize renal ischemia during renal artery bypass, the proximal aortorenal anastomosis is performed first, followed by the distal anastomoses.
Intraoperative Assessment of Renovascular Repair
Regardless of the method of direct surgical repair, each reconstruction is evaluated at completion with renal duplex sonography. Images are obtained from sites of arterial exposure, control, and reconstruction with associated Doppler-shifted signals and Doppler spectrum analysis. Major B-scan defects, with a peak systolic velocity of at least 180 cm/sec, have been noted in 12% of all direct repairs. A disproportionate number of major defects occur in association with thromboendarterectomy. When direct surgical repair of renovascular disease is associated with normal completion duplex sonography, a 95% long-term primary patency of reconstruction has been observed.
Operative Strategy for a Renal Artery Aneurysm
Renal Protection
Branch renal artery involvement in association with renal artery aneurysm disease because of atherosclerosis or dissection may be complex, with exposure of branch anatomy often obscured by associated renal veins. When more than 40 minutes of warm renal ischemia are anticipated for direct repair, measures to protect renal function should be used.
Of the methods and techniques purposed for renal protection, the use of hypothermia seems to be most important. Intermittent hypothermic perfusion is preferred, with intracellular electrolyte composition supplemented by topical cooling with ice slush. If exposure is sufficient for branch renal artery repair, the ipsilateral renal vein is left intact and controlled in its caval origin and a small venotomy is made for the drainage of perfusate. If exposure is inadequate, a partial occluding clamp is placed at the origin of the renal vein, and the vein is divided with a cuff of vena cava. In either instance the perfusate is supplemented with topical ice slush, and the kidney is returned to an orthotopic location after repair.
For both in situ and ex vivo perfusion preservation, the ureter is controlled with a doubly passed vessel loop to control periureteric collaterals. Care is taken to mobilize the ureter with an abundant amount of periureteric soft tissue. For ex vivo reconstruction the ureter is mobilized to the level of the pelvic brim, allowing elevation of the kidney.
Selection of a Method for Direct Surgical Repair
A number of techniques have been described for direct surgical repair of renal artery aneurysms. Branch renal reconstruction with syndactyly is preferred to patch angioplasty. In the course of dissection each major and segmental branch of the renal artery is exposed, and the aneurysm is opened at a point remote from the branches. This allows the direct assessment of each branch origin and the elimination of associated stenosis when present.
Operative Technique for Aortorenal Bypass
Incision
For bilateral renovascular repair and combined aortorenal reconstruction, a midline abdominal incision is preferred ( Fig. 36-1 ). With the patient positioned supine and the table break at the level of the umbilicus, the operating table is flexed 10 to 15 degrees. To expose the upper abdominal aorta through a midline incision, it is important that the superior aspect of the wound extend 1 to 2 cm to one side of the xiphoid. Extended flank and subcostal incisions are used for direct unilateral branch reconstruction or for indirect repair. In both instances a fixed mechanical retractor is advantageous.
