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RENAL ARTERY ULTRASONOGRAPHY STUDY By: Randolf Reveral, BBA, Vascular Ultrasonography Student
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ABSTRACT
Great understanding of anatomy and physiology of the kidney is significant in evaluating the renal arteries. Knowledge of pathogies associated with this system should be known to easily recognize what exactly to look for while scanning. The expertise of the technologist in performing the techniques and following the right protocol are required to have a successful examination. Be aware of all the pitfalls that may encounter and be ready to apply the other options available to finish the evaluation. Presentation of proper evaluation and assessment of the study and accuracy in stating the findings will lead to proper treatment and intervention that may save and lengthen the life of the patient.
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KEY WORDS
Renal artery, Kidney, Renal artery stenosis, Fibromuscular dysplasia, Renovascular hypertension, Urinary system
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INTRODUCTION
Patient for Renal Artery Study should be nothing per oral (NPO) from midnight before the examination. This will help visualize the vascular structure in the abdomen. Entire aorta should be evaluated with Doppler and velocity measurement on the midline; this should be use later for Renal Artery Ratio (RAR).Then the orifice of both renal arteries, because most of stenosis is in the proximal portion of renal artery. Also evaluate the mid portion and in the hilum as the distal. Be able to demonstrate both kidneys in long as much as it can and measure the entire length. Significant asymmetry contra laterally indicates possible disease. Renal artery stenosis can lead to further more serious renal disorders. Sometimes this may be asymptomatic due to multiple vessels present in some patients. Hypertension is the most common symptom most Americans complain of and can be devastating disease for millions of people. If left untreated, hypertension can lead to more serious and more fatal condition such as stroke, kidney failure and heart attack. Some people whose suffering for hypertension was diagnose of renal artery stenosis. Through early detection and treatment, hypertension secondary to renal artery stenosis can be cured.
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Anatomy and Physiology
The kidney is retroperitoneal, which means that they positioned behind the parietal peritoneum. The hilum of the kidney is the depression along the medial border through which the renal artery enters, and renal vein and ureter exit. Each kidney is embedded in a fatty fibrous pouch consisting of three layers. The renal capsule-inner most layer, adipose capsule- surrounding the renal capsule is affirm protective mass of adipose tissue.
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The outermost layer is the renal fascia. Arterial blood enters the kidney at the hilum through the renal artery, which divides interlobar arteries that pass between the pyramids through the renal columns. Renal arteries arise from the lateral wall of aorta distal from the Superior Mesenteric Artery (SMA). Normally, Right renal artery (RRA) is longer than the Left Renal Artery (LRA) because RRA courses posterior across the Inferior Vena Cava (IVC). 1
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Pathology
There are enormous numbers of Pathology and disorders involving the kidney. Some of them are in the parenchyma; some are in the intrarenal and extrarenal system of the kidney. Most of the kidney (renal) tumors or neoplasm, involve the kidney cortex. Men and children develop malignant tumors more often than women. Cigarette smoking is considered an important risk factor. Patient with acute renal failure have a sudden deterioration of kidney function that permits water, nitrogen products, and other wastes to accumulate in the body. The condition is a result of injury to renal cells from variety of sources. Any event that interferes with blood flow to the glomeruli may produce acute renal failure. Patients with chronic renal failure or End Stage Renal Disease (ESRD) have progressive irreversible destruction of nephrons that result in accumulation of waste products throughout the body and fluid and electrolyte imbalances.
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The underlying causes of nephron destruction include those that produce acute renal failure: diabetes mellitus, hypertension, sickle cell disease, polyarteritis nodosa, chronic systemic disease, and chronic infection such as tuberculosis or pyelonephritis. Renal vein thrombosis can develop in the renal vein in connection with thrombosis of the inferior vena cava due to external pressure such as neoplasm and renal disease. 2 Hypertension is the most common symptom leading to physician examinations in the United States; it can lead to stroke, kidney failure, aortic dissection, and/or heart attack. Clinical investigations have shown that approximately 6% of hypertensive patients in the United States have elevated blood pressure as a result of renal artery stenosis. Fibromuscular Dysplasia is the second most common cause of renal artery narrowing. This nonatherosclerotic disease entity affects the mid-to-distal segments of the renal artery, predominantly, in young hypertensive women. 3
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Examination Technique
Patient should be scheduled for morning appointment and asked to fast after midnight before examination. Morning is the best time that a person doesn’t accumulate much gas in the stomach and fasting after midnight allows the stomach to digest the food taken that night and makes the stomach free of stuff that can obstruct to abdominal examination. Smoking, chewing tobacco, or gum also introduces air and should be avoided. The patient initially is placed in supine position with the head of the stretcher slightly elevated. Routinely, multiple approaches are use to fully evaluated all segments of the renal arteries and will include midline, flank and posterior views that require the patient to be repositioned from supine to lateral decubitus or even prone positions. The schedule should allow 60-90 min. for a renal duplex scan and its associated patient history and examination worksheet. High resolution duplex technology is required for this challenging type of examination. Both curved linear and phased array transducers will need to be available to accommodate varying depths introduced by various scan approaches and presenting body habitus. Color Doppler is a very important adjunct to successful completion of abdominal vascular testing. Appropriate color Doppler setting can reveal the presence of multiple renal arteries, segmental areas of stenosis in vessels outside or within the renal tissue. The controllable color parameters to consider when optimizing the display during each portion of the examination include wall filter, gain, transmit frequency, pulse repetition frequency (PRF) and size and angulations of the color box.4
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Protocol
As the patient initially supine, evaluate the proximal portion of the aorta in sagittal view in color and spectral Doppler with velocity measurement measuring the systolli. Measure the diameter of the aorta from outer to outer of the vessel in either transverse or longitudinal view. Scan down following the vessel of the aorta to the mid portion viewing where the SMA arise, document in color and measure the velocity just distal to the SMA and get the diameter of the aorta on the same site. Follow the course down of the aorta distally before it bifurcates then acquires a color image and velocity measurement. Go back to the mid portion of the aorta and turn in transverse, use the left renal vein as landmark and scan a little bit down to show the renal arteries bilaterally arise from the lateral wall of the aorta. Document the image in color, then measure the left and right renal arteries in correct angle, start from the orifice or proximal portion of the renal artery then the mid and near the hilum as the distal. Still in supine position, scan the probe a little bit oblique but in longitudinal with regards to the right kidney just inferior to the liver where the upper pole is more medial and the lower pole is more lateral. Acquire a gray-scale image as big as it can and measure the length of the kidney from anterior to posterior. Do the same procedure to view the left kidney using the spleen as the landmark. Left kidney is inferior to spleen in the left lower quadrant of the body.
Ask the patient to turn on his/her side in the lateral decubitus to view if not be able to successfully acquired the image in supine position.4
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Pitfalls
Poor preparation can cause failure in evaluation of abdominal vasculature. Communicate clearly to the patient or the nurse who taking care of the patient prior to the examination. Body habitus sometimes prevent the technologist from getting clear image. Phased array with much lower frequency can give more depth and better images. Inability to control respiratory patterns: work with patient the proper timing of breathing while getting an image or measuring velocities. Tell to the patient when to hold his/her breathe and when to breath again.5
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Treatment or Intervention
Renal artery stenosis may be treated by means of Percuteneous Transluminal Angioplasty (PTA), without stent or with stent placement. The stent is introduced into the renal artery on a balloon catheter. The balloon is inflated within the disease segment of the artery, causing the stent to expand and press against the arterial wall. The interventionalist may choose to further expand the stent with a balloon catheter to ensure that the stent is in full contact with the vessel wall. When the balloon is deflated and withdrawn, the stent remains permanently in place, holding the artery open.6
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CONCLUSION
Start from good communication in preparation of the patient for renal study makes the examination more easy and successful. Great knowledge of abdominal anatomy and physiology and different pathologies required for understanding the concept of the examination. Different techniques and creativity in following the protocol will lead to greater success of the examination. The accuracy and reliability of the findings through a knowledgeable technologist leads to proper interpretation to clinician and beneficial decision of the Physician to perform the right procedure that can cure the patient’s suffering and pro long their life.
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BIBLIOGRAPHY
1. Kent M. Van De Graaff, Stuart Ira Fox, Concepts of Human Anatomy Physiology Fifth Edition, WCB McGraw-Hill, Burr Ridge, IL, 1999.
2. Grace Fleet Bates, RN, MS, Nancy DiMauro, MA, RN, Mason’s Basic Medical-Surgical Nursing, McGraw-Hill, New York, NY, 1997.
3. Marsha M. Neumyer, BS, RVT, Duplex Scanning After Renal Artery Stenting, The Journal to Vascular Ultrasound, 27(3): 177- 183, 2003.
4. Patricia (Tish) A. Poe, BA, RDCS, RVT, Color Duplex Ultrasound Evaluation of Renal and Mesenteric Arteries, The Journal for Vascular Ultrasound, 29(3): 149-155, 2005.
5. Marsha M. Neumyer, BS, RVT, Renal Artery Duplex Study, CME Meeting @ Coosa Valley Technical College, September 1,2005.
6. Tullis MJ. Zierler RE, Glikerman DJ, Bergelin RO, Cantwell-Gab K, StrandnessDE, Result of transluminal angioplasty for atherosclerotic renal artery stenosis: a follow-up study with duplex ultrasonography, Journal for Vascular Surgery, 25: 46-54, 1997.
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Copyright CVTC 2003. All Rights Reserved.