Doppler ultrasound in kidney diseases: a key parameter in clinical long-term follow-up

Abstract

Doppler ultrasound has been extensively used in detecting reno-vascular diseases, showing to be a noninvasive, safe, low cost and repeatable tool. The Renal Resistive Index (RRI) [(peak systolic velocity -end diastolic velocity)/peak systolic velocity] is a semi-quantitative index derived by Doppler evaluation of renal vascular bed. Normally RRI is in the range of 0.47-0.70, it increases with aging and, usually, it shows a difference between the two kidneys less than 5-8 %. RRI is an important prognostic marker in chronic kidney diseases (CKD), both in diabetic and non-diabetic kidney diseases, because, in longitudinal prospective studies, it significantly correlated with hemodynamic (ABPM, SBP, DBP, pulse pressure) and histopathological parameters (glomerular sclerosis, arteriolosclerosis, interstitial fibrosis/tubular atrophy, interstitial infiltration). In acute kidney injury (AKI) RI is a valid tool in differentiating between pre-renal and renal failure and in predicting renal response to vasoactive agents. In addition a RRI[0.74 can predict the onset of AKI in septic patients. Renal Resistive Index is a useful marker in allograft diseases because it has been widely showed a correlation with histological lesions during worsening of renal function, both in acute rejection and in chronic allograft nephropathy. Recent studies suggest its role in the risk of new onset diabetes after transplantation and it could be one of the parameters to evaluate to shift or withdrawal immunological and/or hypertensive therapy.Keywords Renal resistive index Á Diabetic nephropathy Á Acute kidney injury Á Renal transplantation Á Chronic kidney diseaseRiassunto La Metodica Color Doppler è stata diffusamente utilizzata per evidenziare patologie nefrovascolari in relazione alle caratteristiche di non invasività, sicurezza, basso costo e ripetibilità della stessa. L'indice di resistenza renale (RRI) [(Picco di velocità sistolica -Velocità telediastolica)/ Picco di velocità sistolica] è un indice semiquantitativo derivato dalla valutazione Doppler del letto vascolare renale. Normalmente il valore del RRI è nel range di 0,47-0,70, aumentando con l'età, e usualmente, è presente una differenza tra i due reni inferiore al 5-8%. RRI è un importante marker prognostico nelle patologie renali croniche (CKD), sia diabetiche che non-diabetiche, poichè, in studi prospettici longitudinali, esso correla significativamente con parametri emodinamici (ABPM, Pressione Sistolica, pressione Diastolica, Pressione di Polso) e istopatologici (glomerulosclerosi, arteriolosclerosi, fibrosi interstiziale/ atrofia tubulare e infiltrato interstiziale). Nel Danno Renale Acuto (AKI) RI è un valido strumento nel distinguere l'insufficienza acuta pre-renale da quella renale e nel predire la risposta renale agli agenti vasoattivi. Inoltre un valore di RRI [0,74 può predire la comparsa di AKI nei pazienti affetti da sepsi. RRI è un marker utile nelle patologie del rene trapiantato, perchè è stata ampiamente dimostrata una correlazione con lesioni istologiche...

Longitudinal prospective observational type study about determinants of renal resistive index variations in chronic renal failure patients treated with conventional medical and dietetic therapy

“…In accordance with Hall et al (37) we suppose therefore that a body weight reduction, via caloric restriction and increased physical activity, is an important first step for the management of obesity, hypertension, and chronic kidney disease. Despite its many limitations our study clearly identifies the targets (yet widely known) to act on in order to prevent glomerulosclerosis, arteriosclerosis and tubule interstitial lesions that have shown to be related to RRI more than to others morphologic parameters like renal length and cortex area (3,38). Furthermore it provides further evidence, if any, of the utility of RRI as a key parameter in monitoring patients with chronic renal failure (38) and as a valuable tool to drive the clinical efforts to contrast the kidney disease.…”

Ultrasound of the Kidneys: Application of Doppler and Elastography

“…The normal kidney length is about 11-12 cm (the left kidney is about 3 mm longer than the right kidney) in younger adults and a progressive atrophy with aging. Normal kidney is always as bright as normal liver or spleen tissue [18]. When the kidney cortex became brighter (echogenic) than hepatic tissue or splenic tissue, this reflects inflammatory changes in the kidney tissues.…”

Renal resistive index in non-alcoholic fatty liver disease as an indicator of early renal affection

“…RRI role has been extensively investigated among various kidney diseases as an early test of arterial stiffness and endothelial dysfunction which may lead to severe end-organ disease, due to its known correlations with histological parameters, as tubulointerstitial lesions and glomerulosclerosis [14,15].…”