The internist and the renal resistive index: truths and doubts

Decreased renal cortical perfusion post-EGDT is associated with MAKE-30 in sepsis

OBJECTIVE

This study explores alterations in renal cortical perfusion post-Early Goal-Directed Therapy (EGDT) in sepsis patients, to investigate its association with major adverse kidney events within 30 days (MAKE-30) and identify hemodynamic factors associated with renal cortical perfusion.

METHODS

Sepsis patients admitted to the ICU from Jan 2022 to Jul 2023 were prospectively enrolled. Contrast-enhanced ultrasound (CEUS) assessed renal cortical perfusion post-EGDT. Hemodynamic parameters and renal resistive index (RRI) were collected. Patients were categorized into MAKE-30 and non-MAKE-30 groups. The study examined the association between renal cortical perfusion and MAKE-30, explored the hemodynamic factors related to renal cortical perfusion.

RESULTS

Of 94 sepsis patients, 46 (48.9 %) experienced MAKE-30. Distinctions in pulmonary (P = 0.012) and abdominal infection sites (P = 0.001) and significant SOFA (P < 0.001) and APACHE II scores (P = 0.003) differences were observed. No significant differences in baseline characteristics, vasopressor, or diuretic doses were noted (P > 0.05). Hemodynamic parameters in MAKE-30 and non-MAKE-30 patients showed no significant differences. RRI was higher in MAKE-30 patients (0.71 vs 0.66 P = 0.005). Renal microcirculation parameters, including AUC (p = 0.035), rBV (p = 0.021), and PI (p = 0.003), were lower in MAKE-30. Reduced cortical renal perfusion was associated with an increased risk of MAKE-30. Renal cortical perfusion RT was identified as an independent factor associated with this risk (HR 2.278, 95 % CI (1.152-4.507), P = 0.018). RRI correlated with renal cortical perfusion AUC (r = -0.220 p 0.033).

CONCLUSION

Despite normal systemic hemodynamics post-sepsis EGDT, MAKE-30 patients show reduced renal cortical perfusion. CEUS-derived RT is an independent factor associated with this change. RRI correlates with renal cortical perfusion.

Influence of Bridging Stent Graft Implantation into the Renal Artery during Complex Endovascular Aortic Procedures on the Renal Resistance Index

Comparative sonographic examination of the renal resistance index (RRI) can provide evidence of renal artery stenosis. The extent to which the RRI is changed after stent graft implantation is not known. The aim of this study was to investigate the influence of stent graft implantation into non-diseased renal arteries during endovascular treatment of pararenal aortic aneurysms on the RRI. Sonographic examinations of the kidneys were conducted using a GE ultrasound system. The evaluation was performed according to the European Society for Vascular Surgery (ESVS) 2D standard criteria. RRI values were determined in consecutive patients on the day before and after stent graft implantation and compared for each kidney. A total of 32 consecutive patients (73.9 ± 8.2 years, 5 females, 27 males) were treated with a fenestrated or branched aortic stent graft including bridging stent graft implantations into both renal arteries and received pre- and postinterventional examinations. Sonomorphologically, the examined kidneys were inconspicuous. The arborisation of the renal perfusion was preserved pre- and post-implantation. The RRI did not differ (0.66 ± 0.06 versus 0.67 ± 0.07; p = ns). Successful stent graft implantation into non-stenosed renal arteries did not lead to a relevant change in RRI. Therefore, the RRI is a suitable tool for assessing renal perfusion after fenestrated or branched endovascular aortic therapy.

Acute kidney injury in children undergoing cardiac surgery: predictive value of kidney arterial Doppler-based variables

BACKGROUND

Acute kidney injury (AKI) is a common condition in critically ill children and is associated with increased morbidity and mortality. This study aimed to assess the performance of point-of-care ultrasonography to predict AKI in children undergoing cardiac surgery.

METHODS

In this prospective study, consecutive children underwent kidney Doppler ultrasound examination within 24 h following cardiac surgery, and an experienced operator obtained both renal resistive index (RRI) and renal pulsatility index (RPI). AKI was defined by the Kidney Disease Improving Global Outcome (KDIGO) criteria. The primary outcome was the diagnosis of severe AKI (KDIGO stage 2 or 3) on day 3.

RESULTS

A total of 58 patients were included. Median age and weight were 12.9 months (IQR 6.0-37.9) and 7.36 kg (IQR 5.19-11.40), respectively. On day 3, 13 patients were classified as having AKI, of which 11 were severe. RRI could effectively predict AKI (area under the ROC curve [AUC] 0.83, 95% CI 0.71-0.92; p < 0.001) as well as RPI (AUC 0.81, 95% CI 0.69-0.90; p < 0.001). The optimal cutoff value for RRI was 0.85 (sensitivity, 73%; specificity, 83%; positive predictive value [PPV], 50%; and negative predictive value [NPV], 93%), while for RPI was 1.95 (sensitivity, 73%; specificity, 78%; PPV, 44%; and NPV, 92%). Similar results were found in the analysis for prediction on day 5. Significant correlations were found between Doppler-based variables and estimated GFR and furosemide dose on day 3.

CONCLUSIONS

Kidney Doppler ultrasound may be a promising tool for predicting AKI in children undergoing cardiac surgery.

Doppler renal resistivity index in horses: A systematic review

BACKGROUND

The resistivity index (RI) evaluates haemodynamic based on arterial resistance. Alterations in renal blood flow are important for the early detection of kidney damage, as perfusion might be one of the first affected aspects.

OBJECTIVES

To retrieve published studies on equine renal RI to develop a standardised method of renal ultrasonographic examination and to evaluate the current reference range for the renal RI in horses.

STUDY DESIGN

Systematic review.

METHODS

An electronic search in Science Direct, PubMed, Scopus and Web of Science databases was performed in February 2023 using the terms 'RI' OR 'resistivity index' OR 'IP' OR 'pulsatility index' AND (kidney OR renal) AND (equine OR horse) in titles, keywords and abstracts. The studies were screened for inclusion based on pre-determined criteria and data on the variables of interest were collected from included studies. The SYRCLE risk of bias tool was used to assess the methodological quality.

RESULTS

The electronic searches identified 134 studies, of which 5 were eligible for inclusion in this review. The studies had been conducted in healthy non-sedated horses through the transabdominal technique. The upper limit of normality for the renal RI was 0.58 ± 0.06 for the right kidney of untrained horses, which is considerably lower than the value of 0.70 currently used for humans, cats and dogs. There were heterogenous outcomes among the studies: two of the five demonstrated a difference between the right and left renal RI values, and one of the five showed an increased renal RI in elderly horses compared with foals and adult horses.

MAIN LIMITATIONS

Data regarding the RI in horses are still scarce.

CONCLUSIONS

Additional studies that establish a reference range for the renal RI in horses are needed and there is a need to ensure consistency of techniques.

Renal arterial resistive index as a prognostic marker in lupus nephritis patients

INTRODUCTION

Lupus nephritis (LN) is known to be one of the most serious complications of SLE and it is a major predictor of poor prognosis. Despite the improvement in understanding the pathophysiology of lupus nephritis and greater improvement in diagnostic approaches, lupus nephritis patients have poorer outcomes.

OBJECTIVES

Study the relation between renal resistive index (RRI) and renal function and histopathological parameters in lupus nephritis (LN) patients. Also to investigate the usefulness of RRI in predicting response to treatment.

PATIENTS AND METHODS

This study included 126 patients who were split into two groups (group 1: 101 LN patients and group 2: 25 SLE patients without renal affection); and 100 healthy controls (group 3). The RRI was measured for all participants through a colored Doppler ultrasound examination. LN patients underwent renal biopsy and received their therapy and were followed up for 6 months.

RESULTS

The RRI was significantly greater in the LN group (mean±SD; 0.64±0.07) than in SLE patients without nephritis (0.5884±0.04) (P<0.0001). The RRI was greater in LN class IV (P<0.0001). RRI significantly correlated with the chronicity index (r=0.704, P<0.0001), activity index (r=0.310, P=0.002), and serum creatinine (r=0.607, P<0.0001) and negatively correlated with eGFR (r=-0.719, P<0.0001). Almost eighty-five percent (84.8%) of LN patients responded to induction therapy. RRI was significantly greater in the nonresponder group (mean±SD, 0.73±0.02) than that in the responder group (0.63±.07) (P<0.0001). All non-responders to induction therapy while only 29.8% of responders had an RRI of ˃0.7. RRI, according to regression analysis was a significant predictor of response to treatment in LN patients.

CONCLUSION

RRI was significantly greater in the LN group and significantly correlated with kidney function and histopathological parameters. RRI can predict response to induction therapy in LN patients.

Changes in renal microcirculation in patients with nephrotic and nephritic syndrome: The role of resistive index

BACKGROUND

Renal Resistive Index (RRI) is an important and non-invasive parameter of renal damage and it is associated with abnormal microcirculation or to a parenchymal injury. The aim of our study was to compare the RRI in a cohort of patients with renal diseases categorized in three groups: nephrotic syndrome (NS), acute nephritic syndrome (ANS) and patients with urinary abnormalities (UA).

METHODS

Four hundred eighty-two patients with median age of 48 years (IQR 34-62) with indications for kidney disease were included in the study. Biochemical analyses, clinical assessment with detection of NS, ANS and UA and comorbidities were reported. Renal Doppler ultrasound with RRI was evaluated in all patients at the time of enrolment.

RESULTS

NS was present in 81 (16.8 %) patients while ANS in 81 (16.8 %) and UA in 228 (47.3 %) patients. Patients with ANS showed significant higher RRI compared to both patients with NS [0.71 (IQR 0.67-0.78) vs 0.68 (0.63-0.73), p < 0.001] and UA [0.71 (0.67-0.78) vs 0.65 (0.61-0.71), p < 0.001]; RRI was higher in NS patients than in patients with UA [0.68 (0.63-0.73) vs 0.65 (0.61-0.71), p < 0.001]. Patients with ANS had significantly lower median estimated glomerular filtration rate (eGFR) compared respectively to NS and UA patients [19.7 ml/min vs 54.8 ml/min and vs 72.3 ml/min, p < 0.001], while renal length was significantly higher in patients with NS compared to both patients with ANS and UA [111.88 mm vs 101.98 mm and vs 106.15, p < 0.001]. Patients with ANS had more frequently hematuria and RRI ≥ 0.70 (p < 0.001) compared to both patients with NS and patients with UA. The multiple regression analysis, weighted for age, showed that RRI inversely correlates with eGFR (β coefficient = -0.430, p < 0.001).

CONCLUSIONS

Higher and pathological RRI were found in ANS than NS and UA. Renal resistive index in ANS reflects changes in intrarenal perfusion and microvascular dysfunction related to disease characteristics.

Renal Congestion in Heart Failure: Insights in Novel Diagnostic Modalities

Heart failure is increasingly prevalent and is estimated to increase its burden in the following years. A well-reported comorbidity of heart failure is renal dysfunction, where predominantly changes in the patient's volume status, tubular necrosis or other mechanical and neurohormonal mechanisms seem to drive this impairment. Currently, there are established biomarkers evaluating the patient's clinical status solely regarding the cardiovascular or renal system. However, as the coexistence of heart and renal failure is common and related to increased mortality and hospitalization for heart failure, it is of major importance to establish novel diagnostic techniques, which could identify patients with or at risk for cardiorenal syndrome and assist in selecting the appropriate management for these patients. Such techniques include biomarkers and imaging. In regards to biomarkers, several peptides and miRNAs indicative of renal or tubular dysfunction seem to properly identify patients with cardiorenal syndrome early on in the course of the disease, while changes in their serum levels can also be helpful in identifying response to diuretic treatment. Current and novel imaging techniques can also identify heart failure patients with early renal insufficiency and assess the volume status and the effect of treatment of each patient. Furthermore, by assessing the renal morphology, these techniques could also help identify those at risk of kidney impairment. This review aims to present all relevant clinical and trial data available in order to provide an up-to-date summary of the modalities available to properly assess cardiorenal syndrome.

Renal hemodynamic evaluation protocol based on the pathophysiological mechanism of acute kidney injury: Critical Care UltraSound Guided-A(KI)BCDE

The multiple etiological characteristics of acute kidney injury (AKI) have brought great challenges to its clinical diagnosis and treatment. Renal injury in critically ill patients always indicates hemodynamic injury. The Critical Care UltraSound Guided (CCUSG)-A(KI)BCDE protocol developed by the Chinese Critical Ultrasound Study Group (CCUSG), respectively, includes A(KI) diagnosis and risk assessment and uses B-mode ultrasound, Color doppler ultrasound, spectral Doppler ultrasound, and contrast Enhanced ultrasound to obtain the hemodynamic characteristics of the kidney so that the pathophysiological mechanism of the occurrence and progression of AKI can be captured and the prognosis of AKI can be predicted combined with other clinical information; therefore, the corresponding intervention and treatment strategies can be formulated to achieve targeted, protocolized, and individualized therapy.

Research on the correlation between the renal resistive index, renal microvessel density, and fibrosis

BACKGROUND

This study was designed to investigate the relationship between the renal resistive index (RRI), renal microvessel density (RMD), and fibrosis in patients with chronic kidney disease (CKD).

METHODS

A total of 73 CKD patients were included in the study. Prior to kidney biopsy, we recorded the RRI of the interlobar artery and the estimated glomerular filtration rate (eGFR). Immunohistochemical analysis was performed to assess CD34 expression, and Masson staining was used to evaluate histopathological specimens for RMD and the degree of fibrosis. The percentage of the positive area (PPA) was recorded. Subsequently, we investigated the correlation between RRI, RMD, and kidney fibrosis.

RESULTS

RMD (CD34 PPA-total and CD34 PPA-peritubular capillary) showed a slight increase in early CKD stages (1-2) and gradually declined from CKD stages 2 to 5. No correlation was observed between the RRI and RMD or between the RRI and fibrosis across CKD stages 1 to 5. However, across CKD stages 2 to 5, RRI negatively correlated with CD34 PPA-glomerulus (r = -0.353, p = 0.022), but no correlation was found with CD34 PPA-total, CD34 PPA-peritubular capillary, or kidney fibrosis. eGFR showed a positive correlation with RMD (CD34 PPA-total, CD34 PPA-peritubular capillary, and CD34 PPA-glomerulus) across CKD stages 2 to 5, while no correlation was found from CKD stages 1 to 5.

CONCLUSION

There was no correlation between RRI and RMD or between RRI and fibrosis across CKD stages 1 to 5 (RRI ≤ 0.7).

The Relationship of Renal Augmented Velocity Index With Ventricular-Arterial Coupling in Comparison to Renal Resistive Index: Analysis by Means of Arterial and Ventricular Elastances in Hypertensive Patients

OBJECTIVE

It's a well-known scientific statement that the heart and kidney functions are frequently tied together and the impairment of one directly alters the other. However, there exist knowledge gaps about this intricate pathophysiologic link and the exact unifying mechanism is not established. Herein, we aimed to investigate the presence of cardiorenal interaction at subclinical level while the conventional cardiac and renal clinical parameters are not disrupted yet in patients with hypertension.

METHODS

We chose a novel renal Doppler ultrasonographic parameter-augmented velocity index (Avi)-and an echocardiographic measure-ventriculoarterial coupling-which is complex to analyze but increasingly used after its acceptance about being a key determinant of cardiovascular efficiency. We recruited 137 patients without a previous history of antihypertensive medication use (47.4% women; median age, 49 years). Renal Avi, renal resistive index (RI), arterial elastance (Ea ), ventricular elastance (Ees ) and Ea /Ees (ventriculoarterial coupling) parameters were all examined.

RESULTS

Renal Avi, Ea , and Ea /Ees values were higher in females. Correlation analysis revealed that renal Avi was correlated with many hemodynamic variables including Ea and Ea /Ees . On multiple linear regression analysis, Ea and Ea /Ees remained as significant independent predictors of renal Avi but not of renal RI after adjustments for co-variables (β = 0.488, P < .001 for Ea ; β = 0.380, P < .001 for Ea /Ees ).

CONCLUSIONS

In comparison to renal RI, we suggest that renal Avi is a more reliable and promising index that can even measure subclinical changes in the cardiorenal circulation which needs to be elucidated.

Renal perfusion improvement in the perioperative period after unilateral endovascular revascularization in patients with atherosclerotic renal artery stenosis

Background

The clinical benefits of endovascular treatment in renal artery stenosis (RAS) remain controversial. This study used an intraoperative renal perfusion imaging technique, called flat-panel detector parenchymal blood volume imaging (FD-PBV), to observe the change in renal perfusion after endovascular treatment in RAS.

Materials and methods

In a prospective, single-center study, we assigned 30 patients with atherosclerotic RAS who underwent endovascular treatment between March 2016 and March 2021. The preoperative and postoperative results of renal perfusion, blood pressure, and renal function, were compared.

Results

Both median kidney volume (p < 0.001) and median preoperative mean density of contrast medium (MDCM) (p = 0.028) increased significantly after endovascular treatment. The ratio of postoperative and preoperative MDCM differed greatly among the patients. For patients with preoperative MDCM <304.0 HU (Subgroup A, 15 cases), MDCM significantly increased after treatment (p = 0.001) and 12 (80.0%) patients had more than 10% increase in renal perfusion. For patients who had relatively high preoperative renal perfusion (MDCM ≥304.0 HU, Subgroup B, 15 cases), preoperative and postoperative MDCM were similar (p = 0.776). On the other hand, the serum creatinine levels significantly decreased in Subgroup A (p = 0.033) and fewer antihypertensive drugs were used after endovascular revascularization (p = 0.041). The preoperative and postoperative creatinine levels and number of antihypertensive drugs were similar in Subgroup B.

Conclusions

During the perioperative period, RAS patients with relatively low preoperative renal perfusion levels had greater improvement in renal perfusion, renal function, and blood pressure control after endovascular treatment. The improvement of renal function needs to be confirmed by long-term follow-up.

The relationship between renal renal resistive index and hypertensive end-organ damage

Background/Aim: The prevalence of hypertension increases with age and one out of every three adults over the age of 40 has hypertension. Hypertensive end-organ damage is an important predictive factor for patient morbidity and mortality. This study aimed to investigate the role of the renal resistive index (RI) in predicting retinopathy and nephropathy in hypertensive patients. Methods: This study was cross-sectional in design. Sixty hypertensive patients who were followed in Samsun Research and Training Hospital Internal Medicine outpatient clinic were included in the study. In all patients, a routine ophthalmological examination, including visual acuity, anterior segment examination, and dilated ocular fundus examination, was performed. Urinary albumin to creatinine ratio (mg/g) was measured in spot urine samples, and a level ≥30 mg/g was accepted as the presence of proteinuria. Renal Doppler ultrasonography was performed using Esaote mylab x 9 model sonography device vovex probe (C1-8) 3.5 MHz. RI values were measured using Xflow Doppler at the level of interlobular or arcuate arteries of both kidneys. First, the patients were divided into two groups (with or without retinopathy). The patients who had retinopathy were then divided into two groups according to their retinopathy degree. Hypertensive retinopathy was graded according to the Scheie classification. The patients were also divided into two groups according to their proteinuria status (with or without proteinuria). Results: The mean of renal RI was 0.59 (0.04) in patients without retinopathy (n=15), 0.63 (0.05) in patients with grade 1 hypertensive retinopathy (n=29), and 0.66 (0.04) in patients with grade 2 hypertensive retinopathy (n=15). The difference between groups was statistically significant (overall P=0.001). It has been shown that proteinuria develops more frequently in cases in which the renal value is above 0.7, and these results were statistically significant (P=0.034).  Conclusion: This study indicates that renal RI increase is a valuable tool for estimating retinopathy and proteinuria in hypertensive patients.

Evaluating feline lower urinary tract disease: Doppler ultrasound of the kidneys

OBJECTIVES

Ultrasonography is used in the evaluation of urinary disorders, and the resistivity index (RI) and pulsatility index (PI) have been successfully used to detect early hemodynamic changes in the course of kidney diseases in humans and dogs. The aim of this study was to investigate RI and PI in cats with feline lower urinary tract disease (FLUTD).

METHODS

Twenty-nine client-owned cats were selected and divided into a control group (CG; n = 10), a group of animals with obstructive FLUTD (OG; n = 11) and non-obstructive FLUTD (nOG; n = 8). Clinical, laboratory and ultrasound evaluations were performed in all cats.

RESULTS

RI and PI values for cats in the CG were below the upper limit of normal suggested in other studies, while cats with FLUTD showed significantly higher values in the assessment of RI (P = 0.027 and P = 0.034, respectively) and PI (P = 0.044 and P = 0.048, respectively) of the right and left kidneys.

CONCLUSIONS AND RELEVANCE

Alteration in renal blood flow was observed in cats with lower urinary tract disorders, even in the nOG group. To the best of our knowledge, this is the first report of renal blood flow changes related to non-obstructive FLUTD.

Renal Protection and Hemodynamic Improvement by Impella® Microaxial Pump in Patients with Cardiogenic Shock

Acute kidney injury is one of the most frequent and prognostically relevant complications in cardiogenic shock. The purpose of this study was to evaluate the potential effect of the Impella® pump on hemodynamics and renal organ perfusion in patients with myocardial infarction complicating cardiogenic shock. Between January 2020 and February 2022 patients with infarct-related cardiogenic shock supported with the Impella® pump were included in this single-center prospective short-term study. Changes in hemodynamics on different levels of Impella® support were documented with invasive pulmonal arterial catheter. As far as renal function is concerned, renal perfusion was assessed by determining the renal resistive index (RRI) using Doppler sonography. A total of 50 patients were included in the analysis. The increase in the Impella® output by a mean of 1.0 L/min improved the cardiac index (2.7 ± 0.86 to 3.3 ± 1.1 p < 0.001) and increased central venous oxygen saturation (62.6 ± 11.8% to 67.4 ± 10.5% p < 0.001). On the other side, the systemic vascular resistance (1035 ± 514 N·s/m5 to 902 ± 371 N·s/m5p = 0.012) and the RRI were significantly reduced (0.736 ± 0.07 to 0.62 ± 0.07 p < 0.001). Furthermore, in the overall cohort, a baseline RRI ≥ 0.8 was associated with a higher frequency of renal replacement therapy (71% vs. 39% p = 0.04), whereas the consequent reduction of the RRI below 0.7 during Impella® support improved the glomerular filtration rate (GFR) during hospital stay (15 ± 3 days; 53 ± 16 mL/min to 83 ± 16 mL/min p = 0.04). Impella® support in patients with cardiogenic shock seems to improve hemodynamics and renal organ perfusion. The RRI, a well-known parameter for the early detection of acute kidney injury, can be directly influenced by the Impella® flow rate. Thus, a targeted control of the RRI by the Impella® pump could mediate renal organ protection.

Renal replacement therapy for acute kidney injury in burn patients, an international survey and a qualitative review of current controversies

BACKGROUND OF THE STUDY

Acute kidney injury (AKI) is a common complication in critically ill burn patients and is associated with a number of serious adverse outcomes. The clinical decision-making process related to the management of AKI in burn patients is complex and has not been sufficiently standardized. The main aim of this study was to explore the diagnostic approach and clinician's attitudes toward the management of AKI and RRT in burn patients around the world.

METHODS

The questionnaire was widely distributed among the members of International Society for Burn Injury (ISBI), who were invited to complete the survey. Data collection and report was compliant with the the Checklist for Reporting Results of Internet E-Surveys (CHERRIES) Web-survey guidelines. The survey form with multiple-choice questions was divided into 3 parts: a. physician and institutional demographics, b. AKI diagnostic information, c. technical aspects of RRT.

RESULTS

A total of 44 respondents worldwide submitted valuable data in the 2-month period. Of all respondents, 43.2% were from Europe, 30% from North America, 7% from South-East Asia 2.3% from Africa and 18.2% from other regions. 93.1% of participants declare that they use specific definitions to detect AKI, while 11.4% declare the use of renal ultrasonography for AKI diagnosis. CRRT appeared to be the most preferred option by 43.2% of participants, followed by intermittent hemodialysis (25%), and prolonged intermittent RRT (6.8%). The expertise to deliver a modality and the availability of resources were considered important factors when selecting the optimal RRT modality by 20.5% and 29.6% of respondents. The use of specific serum biomarkers for AKI diagnosis are stated by 16% of respondents; 25% of specialists refer to the use of biomarkers of AKI as a criterium for discontinuing the RRT. Femoral vena and right jugular vena were the most frequently used location for RRT temporary catheter placement, 54.6% of respondents declared using ultrasound guidance for catheter placement.

CONCLUSIONS

The majority of burn specialists use specific consensus classifications to detect acute kidney injury. Continuous renal replacement therapy appeared to be the most preferred option, while the expertise to deliver a particular modality and resources availability play a significant role in modality selection. The use of ultrasound and specific biomarkers for AKI evaluation is infrequent in routine clinical practice.

Contrast-Enhanced Ultrasonography Enables the Detection of a Cold Pressor Test-Induced Increase in Renal Microcirculation in Healthy Participants

Background

Renal microcirculation is essential for regulation of the glomerular filtration rate, the reabsorption of salt and water from the interstitium, and hence the blood pressure. Renal ultrasonography coupled to Doppler analysis and contrast-enhanced ultrasound enables the study of renal perfusion. So far, physiologic interventions have rarely been performed to assess the renal perfusion. The objective of our study was to measure the renal perfusion in response to a cold pressor test (CPT).

Methods

Healthy adult participants were exposed to a 2 min CPT or a sham exposure (body temperature). Systemic hemodynamics, renal resistive index (RRI) and renal perfusion index (PI) were measured before and during the CPT or the sham exposure. Renal responses were compared using a paired Student's t-test or Wilcoxon signed rank test. Pearson correlation test was used to test association of variables of interest.

Results

Forty-one normotensive participants (21 women) were included in the study. Mean blood pressure and heart rate both increased with the CPT. The RRI decreased from 0.60 ± 0.05 arbitrary units (AU) to 0.58 ± 0.05 AU (p &lt; 0.05) and the PI increased from 2,074 AU (1,358–3,346) to 3,800 AU (2,118–6,399) (p &lt; 0.05) (+66% (24–106%)). Compared to the sham exposure, the increase in PI with the CPT was more marked. There was a negative association between the increase in heart rate and mean blood pressure with the RRI (r: −0.550, p = 0.002 and r: −0.395, P = 0.016), respectively.

Conclusion

Doppler Ultrasound and CEUS enable the detection of physiological changes within the macro- and microvascular renal circulation. The CPT decreases the RRI and increases the PI. Whether these changes are present in pathological states such as diabetes or hypertension will need additional studies.

Intraoperative evaluation of renal resistive index with transesophageal echocardiography for the assessment of acute renal injury in patients undergoing coronary artery bypass grafting surgery: A prospective observational study

Background

Acute kidney injury (AKI) is a common complication after on pump coronary artery bypass grafting (CABG) surgery and is associated with a poor prognosis. Postoperative AKI is associated with morbidity, mortality, and increase in length of intensive care unit (ICU) stay and increases the financial burden. Identifying individuals at risk for developing AKI in postoperative period is extremely important to optimize outcomes. The aim of the study is to evaluate the association between the intraoperative transesophageal echocardiography (TEE) derived renal resistive index (RRI) and AKI in patients undergoing on-pump CABG surgery.

Methods

This prospective observational study was conducted in patients more than 18 years of age undergoing elective on pump CABG surgery between July 1, 2018, and December 31, 2019, at a tertiary care center. All preoperative, intraoperative, and postoperative parameters were recorded. TEE measurement was performed in hemodynamically stable patients before the sternum was opened. Postoperative AKI was diagnosed based on the serial measurement of serum creatinine and the monitoring of urine output.

Results

A total of 115 patients were included in our study. Thirty-nine (33.91%) patients had RRI >0.7 while remaining seventy-six (66.08%) patients had RRI <0.7. AKI was diagnosed in 26% (30/115) patients. AKI rates were significantly higher in patients with RRI values exceeding 0.7 with 46.15% (18/39) compared to 15.75% (12/76) in RRI values of less than 0.7. Multivariate analysis revealed that AKI was associated with an increase in RRI and diabetes mellitus. The RRI assessed by receiver operating characteristic (ROC) curve and the area under the curve (AUC) to distinguish between non-AKI and AKI groups were 0.705 (95% CI: 0.588-0.826) for preoperative RRI. The most accurate cut-off value to distinguish non-AKI and AKI groups was a preoperative RRI of 0.68 with a sensitivity of 70% and specificity of 67%.

Conclusions

An increased intraoperative RRI is an independent predictor of AKI in the postoperative period in patients undergoing CABG surgery. The cutoff value of TEE-derived RRI in the intraoperative period should be >0.68 to predict AKI in the postoperative period.

Significance of modern diagnostic methods in the early diagnosis of hypertensive nephropathy

The review analyzes modern criteria for early diagnosis of renal damage in hypertensive patients. Based on numerous studies, the role of impaired renal function markers and renal artery Doppler ultrasound in the diagnosis of hypertensive nephropathy is indicated. A search was made for the relationship between laboratory criteria for kidney damage and renal Doppler ultrasound characteristics in hypertensive patients. In addition, the importance of revealing intrarenal hemodynamic disorders in the early diagnosis of hypertensive nephropathy was established.

Non-invasive Early Prediction of Septic Acute Kidney Injury by Doppler-Based Renal Resistive Indexes Combined With Echocardiographic Parameters: An Experimental Study

Non-invasive early prediction of septic acute kidney injury (S-AKI) is still urgent and challenging. Increased Doppler-based renal resistive index (RRI) has been shown to be associated with S-AKI, but its clinical use is limited, which may be explained by the complex effects of systemic circulation. Echocardiogram allows non-invasive assessment of systemic circulation, which may provide an effective supplement to RRI. To find the value of RRI combined with echocardiographic parameters in the non-invasive early prediction of S-AKI, we designed this experiment with repeated measurements of ultrasonographic parameters in the early stage of sepsis (3, 6, 12, and 24 h) in cecum ligation and puncture (CLP) rats (divided into AKI and non-AKI groups at 24 h based on serum creatinine), with sham-operated group serving as controls. Our results found that RRI alone could not effectively predict S-AKI, but when combined with echocardiographic parameters (heart rate, left ventricular end-diastolic internal diameter, and left ventricular end-systolic internal diameter), the predictive value was significantly improved, especially in the early stage of sepsis (3 h, AUC: 0.948, 95% CI 0.839–0.992, P < 0.001), and far earlier than the conventional renal function indicators (serum creatinine and blood urea nitrogen), which only significantly elevated at 24 h. Our method showed novel advances and potential in the early detection of S-AKI.

Evaluation of Intra-Renal Stiffness in Patients with Primary Aldosteronism

INTORDUCTION

Aldosterone is known to play important role in developing cardiovascular, metabolic, renal damage in hypertensive patients.

AIM

Aim of study was to evaluate parameters obtained by eco-color Doppler study, as non-invasive and easly performed method in asyntomatic patients with Essential Hypertension (EH) and Primary Aldosteronism (PA), without overt organ damage.

METHODS

From April 2019 to March 2020 we consecutively enrolled 73 hypertensive subjects (48 males, 25 women), distinguished in two groups: 30 EH patients (mean age 49.5 ± 18.7 years) and 43 PA patients (mean age 53.1 ± 11.6 years)] [23 with aldosterone-secreting adrenal adenoma (APA), 20 with idiopathic aldosteronism (IHA)].

RESULTS

PA group showed higher renal filtration rate and 24-h urinary excretion of albumin respect to EH; moreover, in PA we found higher Pulsatility Index, altered percentage of Renale Resistance Index, Atrophy Index, and reducted parietal thickness than EH. The correlation study showed that plasma aldosterone were positively correlated with pulsatility index in PA group (right r = 0.35; p < 0.05; left r = 0.36; p < 0.05).

CONCLUSION

parameters obtained through the intra-renal eco-color Doppler examination, easly performed and non-invasive, can be useful in the early-stage identification of subclinical microvascular alterations, especially in PA, condition characterized by increased risk of cardio-vascular remodelling and metabolic alterations.

Value of Doppler ultrasound in early detection of diabetic kidney disease: A systematic review and meta-analysis

The diagnosis of diabetic kidney disease can be delayed by limitations of primary biomarkers, which are microalbuminuria and estimated glomerular filtration rate. A number of Doppler ultrasound studies have associated an increase in intrarenal vascular resistance with the disease, which makes ultrasound a potential adjunct tool for early diagnosis. However, there is inadequate evidence to establish the effectiveness of including Doppler ultrasound in the diagnostic process. This systematic review was therefore conducted to determine the value of using Doppler ultrasound in early detection of diabetic kidney disease. Electronic literature searches were carried out in PubMed, CINAHL, Web of Science and EMBASE. All published prospective studies with records of intrarenal Doppler ultrasound, microalbuminuria and estimated glomerular filtration rate were obtained, and their relationship as parameters for diabetic kidney disease assessed. The meta-analysis of Doppler ultrasound versus albuminuria shows insignificant statistical difference between high resistive index of ≥ 0.7 and albuminuria, with the resistive index being the favoured parameter on the forest plot, making Doppler ultrasound highly comparable with albuminuria for the detection of diabetic kidney disease. Again, there was a significant statistical difference between high intrarenal resistive index of ≥ 0.7 and low estimated glomerular filtration rate of < 60 mL/min/1.73 m², with the resistive index being the favoured parameter on the forest plot, making Doppler ultrasound a superior parameter compared with estimated glomerular filtration rate for early detection of diabetic kidney disease.

Renal-Resistive Index for Prediction of Acute Kidney Injury in the Setting of Aortic Insufficiency

Acute kidney injury (AKI) is a common postoperative complication after cardiac surgery with cardiopulmonary bypass (CPB), and leads to significant morbidity, mortality, and cost. Although early recognition and management of AKI may reduce the burden of renal disease, reliance on serum creatinine accumulation to confidently diagnose it leads to a significant and important delay (up to 48 hours). Hence, a search for earlier AKI biomarkers is warranted. The renal-resistive index (RRI) is a promising early AKI biomarker that reflects intrarenal arterial pulsatility as reflected by the peak systolic and end-diastolic blood velocities divided by the peak systolic velocity. During cardiac surgery, post-CPB elevation of RRI is correlated with renal injury. The RRI is influenced by intrarenal and extrarenal factors, as well as different hemodynamic states. Understanding its limitations may increase its usefulness as an early AKI biomarker. For example, tachycardia or aortic stenosis typically results in a lower RRI, whereas bradycardia or increased systemic pulse pressure (as seen with aortic insufficiency) are associated with a higher RRI, unrelated to any intrarenal effects. In this E-Challenge, the authors present two cases in which the RRI was used to evaluate a patient's risk of developing AKI.

Doppler-derived renal resistive index helps predict acute kidney injury in patients undergoing living-related liver transplantation

BACKGROUND

Acute kidney injury (AKI) is commonly associated with increased postoperative morbidity in liver transplant (LT) recipients. The aim of this study was to identify the role of renal resistive index (RRI) in predicting AKI and to study the factors associated with AKI in LT recipients.

PATIENTS AND METHODS

We performed a single-center, prospective study, including adult living donor LT recipients at our center between January 2018 and September 2019 with no preoperative renal dysfunction. RRI was calculated on ultrasound doppler once preoperatively, and once daily in the postoperative period through postoperative day (POD) six. Patients were grouped into AKI and non-AKI groups for comparison.

RESULTS

Fifty patients were included in the study (mean age, 44 years; 20% females). AKI developed in 25 patients (50%). Both groups were similar in baseline characteristics. RRI of ≥ 0.69 on POD 2 predicted AKI (sensitivity 88%; specificity 92%). RRI on the day before AKI diagnosis (0.71 vs. 0.65) and on the day of diagnosis (0.72 vs. 0.65) were significantly increased relative to preoperative baseline.

CONCLUSIONS

Doppler-derived RRI is a rapid, non-invasive, and bedside procedure capable of predicting the occurrence of postoperative AKI in LT recipients.

Renal echography for predicting acute kidney injury in critically ill patients: a prospective observational study

Objective

To investigate the diagnostic performances of renal resistive index (RRI) and semiquantitative power Doppler ultrasound (PDU) scores in predicting acute kidney injury (AKI) stage 3 in critically ill patients.

Methods

This prospective observational study included 148 patients (80 with reduced cardiac index [CI], 68 with maintained CI). RRI and semiquantitative PDU scores were measured within 6 h after intensive care unit admission. AKI was defined according to Kidney Disease Improving Global Outcomes criteria.

Results

A negative correlation between RRI and PDU score (r = −0.517, p < 0.001) and a positive correlation between PDU score and CI (r = 0.193, p = 0.019) were found, whereas RRI was not correlated with CI (r = 0.131, p = 0.121). The predictive value of RRI for AKI stage 3 was similar between CI-reduced (area under the curve [AUC] 0.761, 95% confidence interval 0.650–0.851, p < 0.001) and CI-maintained (AUC 0.786, 95% confidence interval 0.665–0.878, p < 0.001) patients. Conversely, PDU score could effectively predict AKI stage 3 in CI-reduced patients (AUC 0.872, 95% confidence interval 0.778–0.936, p < 0.001) but not in CI-maintained patients (AUC 0.669, 95% confidence interval 0.544–0.778, p = 0.071). The predictive value of PDU score for AKI stage 3 was statistically different between CI-reduced and CI-maintained patients (p = 0.021).

Conclusions

PDU scores could effectively predict AKI stage 3 in CI-reduced patients but not in CI-maintained patients. RRI is a poor predictor of AKI stage 3 in patients with reduced or maintained CI.

Renal resistive index in IgA nephropathy and renal scleroderma vasculopathy

BACKGROUND

Renal Ultra-Sound (US) and Doppler US provide measurements which reflect changes in renal and systemic haemodynamic. The renal resistive index (RRI), obtained through the Doppler spectrum analysis of renal small arteries, is altered in several pathologic conditions. Glomerulonephritis cause minor RRI changes, while renal scleroderma vasculopathy (RSV) leads to significant RRI modifications. The aim of our study was to assess RRI in IgA nephropathy (IgAN) and RSV in a retrospective observational study and to investigate determinants of the RRI in these groups of patients.

METHODS

We enrolled 61 IgAN patients [23 female, median age 41 (33-58) years] and 80 SSc patients [71 female, median age 52 (43-60) years]. RRI was evaluated in all patients at the time of enrolment. Laboratory tests and clinical assessment were evaluated in all patients.

RESULTS

IgAN patients showed lower RRI values than RSV patients [0.70 (0.65-0.73) vs 0.66 (0.62-0.72), p < 0.01], while no significant difference in longitudinal length was observed. Median age was significantly lower in IgAN patients than in RSV patients [41 (33-58) vs 52 (43-60), p < 0.05] while IgAN patients showed a higher prevalence of high blood pressure than RSV patients (39.3% vs 13.8%, p < 0.01). The multiple regression analysis, weighted for age, showed that RRI inversely correlates with estimated glomerular filtration rate (β coefficient = -0.524, p < 0.0001).

CONCLUSION

Higher RRI were found in RSV patients than IgAN patients. IgAN is characterized mainly by glomerular injury, not leading to major RRI changes.

Renal Resistive Index of the Main Renal Arteries and Transmitral Flow in Hypertensive Patients

In hypertensive patients, diastolic dysfunction is related to increased resistive index (RI) of parenchymal renal arteries. To determine the existence of a link between RI of the main renal arteries (RRI) and diastolic dysfunction, a group of 127 hypertensive patients, with glomerular filtration rates >50 mL/min (mean estimated glomerular filtration rate: 88.6 ± 15.2 mL/min) and no comorbidities, was studied. RRI and transmitral flow were evaluated using the deceleration time (DT) and E/A ratio. A statistically significant correlation between RRI and DT (>240 ms) was noted (p < 0.001). The RRI cutoff that best discriminated patients with DT >240 ms was 0.675. For each unitary increment of 10 mm in DT, the log-transformed RRI significantly increased by a mean of 0.006 point (p < 0.001). This study revealed the importance of the link between RRI and transmitral DT in addition to the renowned significance of the increase in RI as a cardiovascular risk factor in hypertensive patients without comorbidities.

Renal doppler changes in patients with acute pancreatitis: A prospective study

BACKGROUND

Renal Doppler to assess renal resistive index (RRI) is an attractive option to prognosticate acute kidney injury (AKI) in acute pancreatitis (AP) as it is feasible within scope of point-of-care ultrasound. However, RRI has been infrequently evaluated in AP.

OBJECTIVE

Prospectively study diagnostic and prognostic performance of RRI in patients with AP.

METHODOLOGY

75 patients with AP were prospectively enrolled and followed till recovery/death. All patients were subjected to renal Doppler and RRI was compared between patients with and without AKI.

RESULTS

Thirty six patients developed AKI and 39 patients did not develop AKI. AKI network stage 1, 2 and 3 AKI was seen in 7(19.4%), 12(33.3%) and 17 (47.2%) patients respectively. Prognostic scoring done at admission by SIRS, modified marshal score, and BISAP scores, as well as duration of hospitalization and mortality rates were significantly higher in patients with AKI. Mean peak systolic velocity and RRI at upper, middle and lower poles of bilateral kidneys were comparable between patients with and without AKI. The RRI was abnormal in 46 (66.6%) patients and it was <0.6 in 35/46 (76%) and >0.7 in 11/46 (24%) patients respectively. RRI <0.6 was observed in 16 (53.3%) and 19 (48.7%) patients with and without AKI respectively (p = 0.80). RRI >0.7 was observed in 4 (53.3%) and 7 (48.7%) patients with and without AKI respectively (p = 0.74).

CONCLUSIONS

AKI is associated with poor prognosis in AP. RRI on renal Doppler at admission seems to have poor diagnostic as well as prognostic performance for AKI in patients with AP.

Differential Impact of the Renal Resistive Index on Future Cardiovascular Events in Hospitalized Atherosclerotic Cardiovascular Patients According to Left Ventricular Ejection Fraction - The Jichi Vascular Hemodynamics in Hospitalized Cardiovascular Patients (J-VAS) Study

BACKGROUND

Determinants of poor outcome in atherosclerotic cardiovascular disease (ASCVD) according to left ventricular ejection fraction (LVEF) are unclear. The renal resistive index (RRI) correlates well with atherosclerotic vascular damage, which, in turn, is correlated with cardiovascular outcomes. This study investigated whether high RRI is associated with poor cardiovascular outcomes in ASCVD patients classified by LVEF.

METHODS AND RESULTS

Records of 1,598 acute coronary syndromes (ACS) and acute decompensated heart failure (ADHF) patients, categorized into preserved (p), mid-range (mr), and reduced (r) ejection fraction (EF) groups (EF ≥50% [n=1,130], 40-50% [n=223], and <40% [n=245], respectively), were analyzed retrospectively. The primary endpoint was any cardiovascular-related event: fatal and non-fatal ACS, ADHF, stroke, and sudden cardiac death. Over 1.9-years follow-up (3,030 person-years), 233 events occurred: 122, 37, and 74 in the pEF, mrEF, and rEF groups, respectively. Adjusted Cox regression analysis revealed RRI ≥0.8 was associated with the primary endpoint in the pEF group (hazard ratio [HR] 1.67; 95% confidence interval [CI] 1.09-2.56), but not in the mrEF or rEF groups. The primary endpoint risk of pEF patients with an RRI ≥0.8 was comparable to that of mrEF patients using the pEF+RRI <0.8 group as the reference (HR 1.89 [95% CI 1.26-2.83] and 1.77 [95% CI 1.19-2.63], respectively).

CONCLUSIONS

RRI was associated with the risk of cardiovascular events in ASCVD patients with pEF.

Renal Resistive Index: Response to Shock and its Determinants in Critically Ill Patients

Introduction:

Shock is characterized by micro- and macrovascular flow impairment contributing to acute kidney injury (AKI). Routine monitoring of the circulation regards the macrocirculation but not the renal circulation which can be assessed with Doppler ultrasound as renal resistive index (RRI). RRI reflects resistance to flow. High RRI predicts persistent AKI. Study aims were to determine whether RRI is elevated in shock and to identify determinants of RRI.

Materials and Methods:

This prospective observational cohort study included two cohorts of patients, with and without shock less than 24-h after intensive care admission. Apart from routine monitoring, three study measurements were performed simultaneously: RRI, sublingual microcirculation, and bioelectral impedance analysis.

Results:

A total of 92 patients were included (40 shock, 52 nonshock), median age was 69 [60–76] vs. 67 [59–76], P = 0.541; APACHE III was 87 [65–119] vs. 57 [45–69], P < 0.001. Shock patients had higher RRI than patients without shock (0.751 [0.692–0.788] vs. 0.654 [0.610–0.686], P < 0.001). Overall, high age, APACHE III score, lactate, vasopressor support, pulse pressure index (PPI), central venous pressure (CVP), fluid balance, and low preadmission estimated glomerular filtration rate, mean arterial pressure (MAP), creatinine clearance, and reactance/m were associated with high RRI at univariable regression (P < 0.01). Microcirculatory markers were not. At multivariable regression, vasopressor support, CVP, PPI and MAP, reactance/m, and preadmission eGFR were independent determinants of RRI (n = 92, adj. R² = 0.587).

Conclusions:

Patients with shock have a higher RRI than patients without shock. Independent determinants of high RRI were pressure indices of the systemic circulation, low membrane capacitance, and preadmission renal dysfunction. Markers of the sublingual microcirculation were not.

Clinical utility of ultrasonographic evaluation in acute kidney injury

Background

This study aimed to evaluate ultrasonography (US) in patients with acute kidney injury (AKI) and the association of US findings with its clinical characteristics.

Methods

This single-center retrospective study evaluated US in AKI patients. A healthy control group was matched by sex and age at a ratio of 2:1 with the AKI group. The US characteristics were compared between the two groups.

Results

The US characteristics of 111 patients with AKI were evaluated. Compared with the control group, AKI patients had greater kidney length and kidney volume (P<0.05). Patients with AKI also displayed thicker parenchyma than those in the control group, but only the difference in the right kidney was found to be significant. Of the 111 AKI patients, 38 had positive US findings including increased parenchymal echogenicity, increased renal resistance index (RRI), and hydronephrosis, while only 5 patients had increased RRI. The cause of AKI was attributed to obstructive nephropathy in eight patients.

Conclusions

Although US evaluation indicated that most of the patients with AKI were “normal ultrasound imaging”, abnormal findings beyond obstructive nephropathy were still detected in some cases. Aside from its ability to exclude obstructive nephropathy, US evaluation might hold further value. It was found that the kidney size of AKI patients is significantly larger than that of healthy controls. Kidney size combined with other ultrasound indicators could hold potential for the evaluation of AKI.

Keywords

Acute kidney injury (AKI); ultrasonography (US); clinical characteristics; parenchymal echogenicity; renal resistance index (RRI)

The Renal Resistive Index: A New Biomarker for the Follow-up of Vascular Modifications in Systemic Sclerosis

Objective.

The aim of the present retrospective observational study was to evaluate the change of Renal Resistive Index (RRI) over time (ΔRRI) and under treatment in patients with systemic sclerosis (SSc) as well as to correlate these changes with disease complications.

Methods.

Two hundred thirty patients [29 male, median age 57 (IQR 48–67) yrs] were enrolled. At baseline and follow-up (3.43, IQR 2.81–4.45 yrs), we collected the following data: disease variables, nailfold videocapillaroscopy (NVC) pattern, forced vital capacity (FVC), diffusing lung capacity for carbon monoxide (DLCO), systolic pulmonary arterial pressure (sPAP), presence of interstitial lung disease, RRI, evaluation of glomerular filtration rate, and new onset of pulmonary arterial hypertension (PAH).

Results.

RRI value is high in SSc patients with digital ulcers and anticentromere antibodies, active and late NVC patterns, and limited cutaneous SSc. A significant correlation was observed between ΔRRI and ΔsPAP (R = 0.17, P = 0.02), with statistically higher ΔRRI (0.08 ± 0.02 vs 0.03 ± 0.05, P = 0.04) in patients complicated by PAH onset. No other new-onset complication was associated with ΔRRI. The receiver-operating characteristic curve analysis confirmed the predictive role of ΔRRI in development of new PAH (area under the curve 0.84, 95% CI 0.75–0.93, P = 0.02). In patients with SSc never exposed to sildenafil, ΔRRI was higher (0.04 ± 0.05) compared to both patients exposed to sildenafil during the study period (0.01 ± 0.05, P = 0.03) or in those exposed at the time of baseline evaluation (0.00 ± 0.05, P = 0.01).

Conclusion.

RRI and its variation in time are a reliable marker of SSc-related vasculopathy, both in renal and extrarenal compartments.

Diagnosis and Treatment of Early Transplant Renal Artery Stenosis: Experience From a Center in Eastern China

Few studies have focused on the clinical characteristics of transplant renal artery stenosis (TRAS) with early onset. Sixteen cases diagnosed with TRAS in our center from January 2014 to August 2018 were retrospectively analyzed. Sixteen transplant patients without TRAS were selected as controls. The median diagnostic time for TRAS was 47.5 days after transplantation. No significant difference was observed between the TRAS group and the control group. The serum creatinine level (Scr), estimated glomerular filtration rate, systolic/diastolic blood pressure, graft artery peak systolic velocity (PSV), and resistive index of intersegmental artery (RI-ISA) between the 2 groups were (5.55 ± 3.49) and (1.89 ± 0.85) mg/dL; (17.83 ± 14.94) and (49.39 ± 19.96) mL/min; (143.50 ± 9.49)/(86.14 ± 7.38) and (130.38 ± 18.86)/(82.81 ± 12.52) mm Hg; (3.39 ± 1.57) and (1.31 ± 0.51) m/s; and (0.51 ± 0.10) and (0.67 ± 0.13), respectively. All showed statistical significance except the diastolic blood pressure. The Scr, estimated glomerular filtration rate, systolic/diastolic blood pressure, graft artery PSV, and RI-ISA in the TRAS group prior and after treatment were (5.55 ± 3.49) and (3.20 ± 1.50) mg/dL; (17.83 ± 14.94) and (25.60 ± 13.29) mL/min; (143.50 ± 9.49)/(86.14 ± 7.38) and (128.07 ± 16.16)/(75.71 ± 7.56) mm Hg; (3.39 ± 1.57) and (2.00 ± 1.04) m/s; and (0.51 ± 0.10) and (0.61 ± 0.10); all showed statistical significance. Receiver operating characteristic analysis showed an area under curve of 0.8616 for PSV and 0.8535 for RI-ISA in diagnosing TRAS. Patients with TRAS in our center showed a unique characteristic of early onset. The most prominent clinical symptom of TRAS is increasing Scr level instead of refractory hypertension. Screening of color Doppler flow imaging with a graft artery PSV >2.5 m/s and RI-ISA <0.5 could yield a preliminary diagnosis of TRAS. Percutaneous transluminal angioplasty/stenting could effectively improve allograft function as well as color Doppler flow imaging indexes.

The Renal Resistive Index in systemic sclerosis: Determinants, prognostic implication and proposal for specific age-adjusted cut-offs

BACKGROUND

Renal Resistive Index (RRI), reflects changes in both renal vascular and tubular-interstitial compartments and in systemic vascular compliance related to age and comorbidities.

OBJECTIVES

a) To investigate determinants of RRI in SSc population, b) its association with SSc-related features and c) to test its prognostic impact on organ specific worsening or death.

METHODS

380 SSc patients ≥18 years were enrolled after giving informed consent. Baseline data on RRI, laboratory, instrumental and therapeutic features were retrospectively collected. Age-SSc adjusted cut-offs were created by dividing the population in age quartiles and considering RRI values >75th percentile as pathologic. Clinical follow-up was performed until last available visit or the development/worsening of specific internal organ involvement or death.

RESULTS

RRI was independently predicted by age and systolic pulmonary arterial pressure on Echo. Therefore, we created Age-SSc adjusted pathologic RRI cut-offs, which were significantly associated with various disease related skin and lung fibrotic manifestations, as well as vasculopathic complications. After a mean follow-up of 3.6 ± 2.6 years, RRI was one of the independent predictors (together with modified Rodnan skin score, interstitial lung disease, presence of dyspnoea and late nailfold-videocapillaroscopy pattern) for mortality, with 0.68 as best cut-off (sensitivity 88.5%, specificity 50.9%).

CONCLUSION

If corroborated, Renal Resistive Index cut-offs might be used to evaluate renal and extrarenal involvement in SSc and could serve as predictors of mortality.

Semiquantitative Power Doppler Ultrasound Score to Predict Acute Kidney Injury in Patients With Sepsis or Cardiac Failure: A Prospective Observational Study

BACKGROUND

Diagnosing acute kidney injury (AKI) stage 3 in critically ill patients may help physicians in making treatment decisions. This diagnosis relies chiefly on urinary output and serum creatinine, which may be of limited value. This study aimed to explore the diagnostic performance of renal resistive index (RRI) and semiquantitative power Doppler ultrasound (PDU) scores in predicting AKI stage 3 in patients with sepsis or cardiac failure.

METHODS

This study is a prospective observational study that included 83 patients (40 with sepsis and 43 with cardiac failure). Renal resistive index and semiquantitative PDU scores were measured within 6 hours following admission to the intensive care unit. Acute kidney injury was defined according to the criteria set by Kidney Disease Improving Global Outcomes.

RESULTS

The predictive values of RRI (area under the curve [AUC] = 0.772, 95% confidence interval [CI] = 0.658-0.886) and PDU score (AUC = 0.780, 95% CI = 0.667-0.892) were similar in all patients. Power Doppler ultrasound score (AUC = 0.910, 95% CI = 0.815-1.000) could effectively predict AKI stage 3 in the cardiac failure subgroup, and the optimal cutoff for this parameter was ≤ 1 (sensitivity = 87.5%, specificity = 92.6%, Youden index = 0.801, accuracy in our population = 90.7%). However, PDU scores (AUC = 0.620, 95% CI = 0.425-0.814) could not predict AKI stage 3 in the sepsis subgroup. The predictive values of RRI for AKI stage 3 in the cardiac failure (AUC = 0.820, 95% CI = 0.666-0.974) and sepsis (AUC = 0.724, 95% CI = 0.538-0.910) subgroups were similar.

CONCLUSIONS

Power Doppler ultrasound scores could effectively predict AKI stage 3 in patients with cardiac failure but not in patients with sepsis. Renal resistive index is a poor predictor of AKI stage 3 in patients with sepsis or cardiac failure.

Comparison of renal arterial resistive index in type 2 diabetic nephropathy stage 0-4

Chronic kidney disease (CKD) is one of world health problems and its prevalence and incidence is increasing. Chronic Kidney Failure involves a range of pathophysiologic processes that are associated with impaired renal function, leading to cardiovascular morbidity and mortality. Renal artery resistive index (RI) is indicator of atherosclerotic change in small vessels. The current study was aimed to assess RI in diabetic nephropathy patients at stage 0-4 and to compare RRI with HbA1c, systolic blood pressure, diastolic blood pressure, albuminuria and glomerular filtration rate (GFR). In this cross sectional study,100 diabetic nephropathy patients who attend to nephrology clinic of Ali-ibn Abi Talib Hospital were entered to the study. Ultrasound Doppler renal resistive index was measured and other information was recorded from their last lab data that was recorded in their medical records. Variable included: systolic blood pressure, diastolic blood pressure, albuminuria, GFR, HbA1c. All data was analyzed by Pearson's Correlation Coefficient. The findings indicated a significant correlation of RI with systolic BP (p=0.04 R=0.75), microalbuminuria (P=0.001 R=0.67), and GFR (P=0.001 R=0.76), while diastolic BP (P=0/45 R=0/32), HbA1c (P=0/56 R=0/43) were not found to be associated with RI. The findings indicated that increased systolic blood pressure, albumin excretion (microalbuminuria) and severity of disease were capable of increasing RI values in diabetic nephropathy patients. In addition, decreased GFR.

Association between 24-hour diastolic blood pressure and renal function in patients receiving treatment for essential hypertension

Objectives

To evaluate the association between diastolic blood pressure (BP), measured by 24-hour ambulatory blood pressure monitoring (ABPM) and renal function in patients receiving treatment for essential hypertension.

Methods

In this cross-sectional study, ABPM, transthoracic echocardiography, estimated glomerular filtration rate (eGFR) on the basis of serum cystatin C (eGFRcyst) and the renal resistive index (RRI) were measured in patients with essential hypertension.

Results

The cohort consisted of 105 patients (39 men, 66 women), with a mean ± SD age of 58 ± 12 years who had been receiving treatment for 11 ± 8 years. 24-hour diastolic BP significantly positively correlated with eGFRcyst and negatively correlated with RRI. No correlation was observed with 24-hour systolic BP values. 24-hour diastolic BP values ≤70 mmHg were associated with eGFRcyst ≤60 ml/min/1.73 m2 (i.e., decreased GFR).

Conclusion

24-hour diastolic BP values were significantly associated with markers of kidney function in patients receiving treatment for essential hypertension and values ≤70 mmHg may be associated with subnormal eGFRcyst.

Lower Systolic Blood Pressure and Cardiovascular Event Risk Stratified by Renal Resistive Index in Hospitalized Cardiovascular Patients: J-VAS Study

BACKGROUND

The threshold of blood pressure (BP) reduction in cardiovascular patients is debatable due to the J-shaped curve phenomenon, which is particularly observed in patients with increased arterial stiffness. The renal resistive index (RRI) correlates well with systemic arterial stiffness; therefore, we aimed to demonstrate the role of RRI in guiding the choice of optimal BP.

METHODS

A retrospective analysis of prospectively collected data of the hospitalized cardiovascular patients at Jichi Medical University Hospital. All patients had the RRI measurement performed and were assigned to a higher (RRI ≥ 0.8) or lower RRI group. Each group was subdivided by quartiles of the BP at discharge. The primary endpoints were fatal and nonfatal cardiovascular events, including heart failure, acute coronary syndrome, acute aortic disease, acute arterial occlusion, and stroke.

RESULTS

The mean follow-up period was 1.9 years (3,365 person-years), n = 1,777 (mean age 64.7 years). There were 252 cardiovascular events occurred, 24.0% and 12.2% in the higher and lower RRI populations, P < 0.001. In the higher RRI group, the lowest systolic BP (SBP) quartile (<105 mm Hg) was a risk factor for cardiovascular events when compared with the highest SBP quartile (≥130 mm Hg; adjusted hazard ratio, 2.42; 95% confidence interval, 1.17-5.03; P = 0.017). A 1 SD decrease of SBP (17.5 mm Hg) was associated with a 25% increase in the risk of cardiovascular events. In the lower RRI group, these associations were not observed.

CONCLUSIONS

Lower SBP at discharge was associated with a risk of cardiovascular events in the hospitalized cardiovascular patients with RRI ≥ 0.8.

Diurnal variation of renal resistive index over 24-hour period in hypertensive patients and healthy controls

PURPOSE

There are no data in the literature to our knowledge related to changes in renal resistive index (RRI) values over 24-h period and the importance of detecting these changes in patients who have hypertension (HT). In this study, we aimed to investigate the variation of RRI values over 24-h period and its usability in hypertensive patients.

METHODS

A total of 118 subjects (80 with HT and 38 healthy controls) were included in the study. Morning, midday, evening, and midnight RRI, renal pulsatility index, and accelerated time were measured by Doppler ultrasonography (US). B-mode US and elastograpic assessment were performed only in the morning.

RESULTS

Temporal RRI varied significantly (p < 0.001). The highest and lowest levels were found in the morning and evening, respectively. All temporal RRI levels were significantly higher in patients with HT (both p < 0.001). The absolute and relative increases in RRI (ΔRRI) levels were similar in two groups. All temporal RRI measurements positively correlated with the patient age, pulse pressure, renal cortical thickness, and cortical stiffness. However, absolute-ΔRRI and relative-ΔRRI positively correlated with the age. Absolute-ΔRRI positively correlated with the pulse pressure and cortical stiffness, and no correlation was observed between relative-ΔRRI and these variables. Of the four temporal measurements, morning RRI were found to be independently associated with cortical stiffness (p < 0.001).

CONCLUSIONS

RRI measurements varied over 24-h period in patients with HT and/or healthy controls. Morning RRI was significantly higher than other day time, and it is also related to renal cortical stiffness.

Factors associated with renal Doppler resistive index in critically ill patients: a prospective cohort study

Background

The renal Doppler resistive index (renal RI) is a noninvasive tool that has been used to assess renal perfusion in the intensive care unit (ICU) setting. However, many parameters have been described as influential on the values of renal RI. Therefore, we proposed this study to evaluate the variables that could impact renal RI in critically ill patients.

Methods

A prospective observational study was performed in a 14-bed medical–surgical adult ICU. All consecutive patients admitted to the ICU during the study period were evaluated for eligibility. Renal RI was performed daily until the third day after ICU admission, death, or renal replacement therapy (RRT) requirement. Clinical and blood test data were collected throughout this period. Acute kidney injury (AKI) reversibility was categorized as transient (normalization of renal function within 3 days of AKI onset) or persistent (non-resolution of AKI within 3 days of onset or need for RRT). A linear mixed model was applied to evaluate the factors that could influence renal RI.

Results

Eighty-three consecutive patients were included. Of these, 65% were male and 50.6% were medical admissions. Mean SAPS 3 was 47 ± 16. Renal RI was significantly different between no-AKI (0.64 ± 0.06), transient AKI (0.64 ± 0.07), and persistent AKI groups (0.70 ± 0.08, p < 0.01). Variables associated with renal RI variations were mean arterial pressure, lactate, age, and persistent AKI (p < 0.05). No association between serum chloride and renal RI was observed (p = 0.868).

Conclusions

Mean arterial pressure, lactate, age, and type of AKI might influence renal RI in critically ill patients.

Renal intraparenchymal resistive index: the ultrasonographic answer to many clinical questions

The use of renal resistive indices (RRIs) for the study of renal microcirculation has in the past been proposed for the identification of renal organ damage or even to specifically identify injury to some areas of the renal parenchyma. Nevertheless, according to the most recent evidences from literature this organ-based conception of RRIs has been proven to be partial and unable to explain the RRIs variations in clinical settings of sepsis or combined organ failure of primitively extrarenal origin or, more generally, the deep connection between RRIs and hemodynamic factors such as compliance and pulsatility of the large vessels. The aim of this review is to explain the physiopathological basis of RRIs determination and the most common interpretative errors in their analysis. Moreover, through a comprehensive vision of these Doppler indices, the traditional and emerging clinical application fields for RRIs are discussed.

Renal resistive index significantly increased in hypertensive children and it is independently related to the pulse pressure and left ventricular mass index

Background: To the best our knowledge there is no data in the literature related to changes in renal resistive index (RRI) values in children who have hypertension (HT). In this study, we aimed to investigate the changes of RRI values and it is usability in children with HT. Methods: A total of 75 children; 48 with newly diagnosed HT and 27 healthy controls were included in the study. Routine history, physical examination, and laboratory examinations were performed. Left ventricular (LV) dimensions and systolic-diastolic functions, septum and posterior wall thickness (IVSd and PWd) and LV mass index (LVMI) were calculated by echocardiography. In addition to routine renal ultrasonography (US), renal pulsatility indexes (RPI), accelerated time and RRI were measured. Increased RRI was accepted as >0.70. Results: Increased RRI was detected in 25 (52%) of HT patients. Systolic and diastolic blood pressure (SBP and DBP), and pulse pressure (PP), low-density lipoprotein cholesterol and triglyceride levels, RRI, RPI, kidney length, IVSd, PWd, and LVMI were significantly higher in patients with HT (both p < 0.05). SBP and PP, PWd, LV ejection fraction, LV fractional shortening, and LVMI were positively correlated with the RRI. High-density lipoprotein cholesterol was negatively correlated with the RRI. Of these measurements, RRI values were found to be independently associated with PP and LVMI (p < 0.05). Conclusions: In hypertensive children, RRI was significantly higher than healthy controls and it is also related with LVMI and PP.

Glycemic control by the SGLT2 inhibitor empagliflozin decreases aortic stiffness, renal resistivity index and kidney injury

Background

Arterial stiffness is emerging as an independent risk factor for the development of chronic kidney disease. The sodium glucose co-transporter 2 (SGLT2) inhibitors, which lower serum glucose by inhibiting SGLT2-mediated glucose reabsorption in renal proximal tubules, have shown promise in reducing arterial stiffness and the risk of cardiovascular and kidney disease in individuals with type 2 diabetes mellitus. Since hyperglycemia contributes to arterial stiffness, we hypothesized that the SGLT2 inhibitor empagliflozin (EMPA) would improve endothelial function, reduce aortic stiffness, and attenuate kidney disease by lowering hyperglycemia in type 2 diabetic female mice (db/db).

Materials/methods

Ten-week-old female wild-type control (C57BLKS/J) and db/db (BKS.Cg-Dock7m+/+Leprdb/J) mice were divided into three groups: lean untreated controls (CkC, n = 17), untreated db/db (DbC, n = 19) and EMPA-treated db/db mice (DbE, n = 19). EMPA was mixed with normal mouse chow at a concentration to deliver 10 mg kg⁻¹ day⁻¹, and fed for 5 weeks, initiated at 11 weeks of age.

Results

Compared to CkC, DbC showed increased glucose levels, blood pressure, aortic and endothelial cell stiffness, and impaired endothelium-dependent vasorelaxation. Furthermore, DbC exhibited impaired activation of endothelial nitric oxide synthase, increased renal resistivity and pulsatility indexes, enhanced renal expression of advanced glycation end products, and periarterial and tubulointerstitial fibrosis. EMPA promoted glycosuria and blunted these vascular and renal impairments, without affecting increases in blood pressure. In addition, expression of “reversion inducing cysteine rich protein with Kazal motifs” (RECK), an anti-fibrotic mediator, was significantly suppressed in DbC kidneys and partially restored by EMPA. Confirming the in vivo data, EMPA reversed high glucose-induced RECK suppression in human proximal tubule cells.

Conclusions

Empagliflozin ameliorates kidney injury in type 2 diabetic female mice by promoting glycosuria, and possibly by reducing systemic and renal artery stiffness, and reversing RECK suppression.

Difference between renal and splenic resistive index as a novel criterion in Doppler evaluation of renal artery stenosis

Detection of renal artery stenosis (RAS) using Doppler is difficult to evaluate, particularly under conditions such as bilateral RAS or difficultly accessible renal arteries (RA). The objective of the present study was to assess the utility of splenic arterial compared to renal flow as an additional parameter in the Doppler evaluation of RAS. The difference between the resistive indices (RI) determined in renal and splenic parenchymal arteries (ΔRI_K-S ) was evaluated in 181 hypertensive subjects without any evidence of RAS. Subsequently 47 RA in 24 patients with suspected RAS were angiographically assessed. A ΔRI_K-S of 0.055 (median) was determined in the population without any evidence of RAS similar to RA with angiographically excluded stenosis (ΔRI_K-S 0.068). In contrast, in angiographic proven RAS, ΔRI_K-S was significantly lower (-0.050; P < .005). The assessment of the ΔRI_K-S , proved to be an easily feasible parameter, which improves the diagnostic accuracy in the detection of RAS.