The value of portable renal hilar Doppler ultrasound screening (RHDUS) for renal artery stenosis in critically-ill patients

Purpose: To evaluate the efficacy and utility of portable Renal Hilar Doppler Ultrasound (RHDUS) screening for Renal Artery Stenosis (RAS) in critically-ill patients. Materials and methods: A retrospective study of adult Intensive Care Unit (ICU) patients receiving RHDUS to rule out RAS spanning a time frame of one year. Patients receiving RHDUS were included with the exclusion of patients under 18 years, and exams of poor diagnostic quality. Patients’ sex, age, serum creatinine and BUN, risk factors for RAS, and primary and secondary indications for the requested Doppler exam were included. Renal Doppler results and confirmatory studies such as Angiography, MRA, CTA, etc. were included when available. Results: 291 (90%) of 325 Doppler studies were included in the study. Twenty-one of the studies met criteria for possible RAS. Sensitivity and specificity was 80% and 98.5% respectively. A significant association between hypertension-related indications and RAS-positive studies was shown (p=.002). Conclusion: RHDUS is a useful screening test in patients with a high suspicion of RAS. In many ICU patients presenting only with AKI or hemodynamic instability, the use of RHDUS screening for RAS is very low yield and should probably not considered an appropriate test. Correspondence to: Mohammad Amarneh, MBBS, Department of Radiology, University of Iowa Hospitals and Clinics, Iowa City, IA 52242, USA, Tel: 337852-8528, Email: [email protected] Received: December 22, 2016; Accepted: January 05, 2017; Published: January 09, 2017 Introduction Renal artery stenosis (RAS) is a common renovascular disease defined by the narrowing of the renal arteries leading to reduced perfusion. This renal ischemia can lead to the overproduction of renin and ultimately renal hypertension. Though not all cases of RAS are clinically significant and its prevalence in the general population is not known, it is considered one the most common causes of secondary hypertension and is estimated to be the main contributor in up to 5% of all hypertensive cases [1,2]. Up to 90% of RAS is caused by atherosclerotic plaques, occurring primarily in the elderly population, and the majority of the remaining cases are due to fibromuscular dysplasia most commonly seen in females under 40. Other rare causes of RAS include vasculitis, thromboembolism, aortic dissection, and renal artery aneurysms. RAS most commonly presents as resistant or uncontrollable hypertension, renal failure secondary to ischemic nephropathy, recurring episodes of congestive heart failure, or flash pulmonary edema [3,4]. Conventional renal Doppler ultrasonography (RDUS) performed in ambulatory patients is often used for the detection of renal artery stenosis due to its noninvasive nature and relatively low cost. It has also been shown by many studies to have high sensitivity and specificity when compared to renal angiography, the gold standard for RAS detection [1,5-10]. This exam includes direct visualization of the renal artery origin and evaluation of the renal poles for accessory and main artery branch stenosis. In the intensive care units where kidney injury can occur as often as 50% of the time [11], patients commonly undergo screening for RAS by Doppler ultrasound. Because of their non-ambulatory state, these critically-ill patients receive a portable and suboptimal form of the Doppler exam, limiting views to the hilar artery only the Doppler evaluation of indirect parameters of acceleration time and index. In this hilar Doppler study (RHDUS) there is no direct assessment of the renal artery origin or accessory arteries. A 2001 study [12-14] looking at using these indirect Doppler parameters as a screening tool for diagnosing RAS found that in a pre-selected group of hypertensive patients, indirect parameters were a useful screening tool. However these indirect parameters have not been studied in the critically-ill population in which they are being employed (Figures 1a and 1b). Even though RDUS is a studied modality of RAS screening and is used in studies looking at the prevalence of RAS [13]. The more limited RHDUS has not been compared to RDUS in its efficacy as a screening tool. However, RHDUS has been shown to have high accuracy when compared to arteriography using the Acceleration Time (AT) and Acceleration Index (AI) [15] (Figure 1c), and is most useful in the setting of a high pre-test probability of RAS and for surveillance following revascularization. But the modality is limited by the presence of multiple arteries, occlusion, and a high incidence of false positives in postoperative and hemodynamically unstable Amarneh M (2017) The value of portable renal hilar Doppler ultrasound screening (RHDUS) for renal artery stenosis in critically-ill patients Vascul Dis Ther, 2017 doi: 10.15761/VDT.1000110 Volume 2(1): 2-7 patients. Doppler generally also does not detect stenosis in mild to moderate disease (<60%) leading to high false negative rates [15]. Given the hemodynamic instability of many critically-ill patients, we will explore the question of whether RHDUS is an effective screening tool when ruling out RAS in the ICU. We have hypothesized the rate of management-altering positive studies to be less than 5%. Materials and methods Reports of all portable RHDUS examinations performed in adult critical care units (i.e., medical, surgical, and cardiovascular) were reviewed retrospectively for the interval of January 1, 2011 to December 31, 2012. Also reviewed was the electronic medical record of those patients. All ultrasounds were performed portably with the acceleration time and index taken from the kidney hilum. The Doppler angle was always targeted for 0 degrees; in cases where the angle was not 0 degrees, the angle was corrected for. All exams were performed by certified sonographer technicians on Acuson Sequoia 512 and Philips IU22 machines. Images were read and interpreted by a board certified radiologist with or without the assistance of a radiology resident. Our Institutional Review Board approved the study. Exclusion criteria included patients under the age of 18 and exams of non-diagnostic quality. Non-diagnostic quality images resulted from issues such as beam attenuation from body habitus or bowel gases, patient position or un-cooperation, inability to hold breath during the exam, wounds or bandages over areas that were required for optimal imaging, irregular Doppler flow caused by a present LVAD or intraaortic balloon pump, or other patient-specific issues making Doppler results unobtainable or unreliable. Patients with both kidneys, but had a Doppler scan with unilateral diagnostic quality were also excluded. This is because renal artery stenosis occurs unilaterally in most patients [12,13] and these exams were not adequate to define the presence or absence of RAS in the patient based on a unilateral renal scan. From the medical record was recorded the following: sex; age; serum creatinine (mg/dL) and blood urea nitrogen concentrations (mg/dL); number of kidneys; principal diagnosis for admission to ICU; documented history of hypertension, chronic kidney disease, diabetes mellitus, and/or cardiovascular disease; and clinical indications for Doppler screening such as acute kidney injury, hypertensive urgency, flash pulmonary edema, aortic dissection, and sepsis. The criterion for acute or acuteon-chronic kidney injury was defined as per the patient medical record. BUN to serum creatinine ratio was also calculated. From the radiology report was recorded the clinical indication for the exam, the presence or absence of renal artery stenosis as reported by the interpreting radiologist based on acceleration time and indices, resistive indices, early systolic peaks, and pertinent grayscale sonographic findings such as kidney length and echogenicity. Criteria for 60% stenosis by indirect parameters included acceleration index of <300 cm/s2, acceleration time of >70 msec, diminished or loss of early systolic peaks and abnormal waveform shape, or resistive index of <0.55. A resistive index of >0.7 was suggestive of microvascular or parenchymal disease. Peak systolic velocity measurements were not collected because, though occasionally available, they are not routinely Figure 1a. 63 year old male with acute kidney injury and uncontrolled hypertension. RDHUS shows classic slow rising systolic peak, so called “Tardus parvus”, with decreased acceleration index or slope. Findings are consistent with renal artery stenosis. Figure 1b. Digital Subtracted Angiogram of the right renal artery shows severe focal stenosis at the proximal right renal artery. This was treated with stent, and post stent angiogram showed no significant residual stenosis (not shown). Figure 1c. Repeat RHDUS showssignificantly improved renal arterial flow, with normal early systolic peak, and normal acceleration index. Amarneh M (2017) The value of portable renal hilar Doppler ultrasound screening (RHDUS) for renal artery stenosis in critically-ill patients Vascul Dis Ther, 2017 doi: 10.15761/VDT.1000110 Volume 2(1): 3-7 evaluated as part of the portable exam. Unobtainable Doppler signal and waveforms due to arterial occlusion were considered abnormal findings if not explained by technical issues. Studies that were normal in all measurements except for the loss of early systolic peaks were not considered as positive findings for significant renal artery stenosis. Studies have shown that loss of early systolic peak alone is not a good indicator of renal artery stenosis [14]. Also noted was the presence or absence of microvascular/medical renal disease by Doppler evidence, renal vein thrombosis, hydronephrosis, stones, and focal lesions excluding simple cysts. Confirmatory tests for RAS-positive Doppler studies were also recorded. These included renal angiography, MRA, and CTA. Also recorded was the patients’ kidney function at discharge from intensive care (Table 1). Dichotomous variables were analyzed by χ2 tests and continuous variables were analyzed with t tests. Sensitivity and specificity were calculated by comparison with angiography, MRA, CTA, or other confirmatory testing available.