Renal resistive index as predictor of acute kidney injury after major surgery: A systematic review and meta-analysis

Prediction of Acute Kidney Injury After Cardiac Surgery With Combined Arterial and Venous Intrarenal Doppler

Background

Acute kidney injury (AKI) occurs in up to 50% of cardiac surgical patients and is often hemodynamically mediated. Point-of-care ultrasound is a non-invasive tool that has the potential to characterize intrarenal hemodynamics and predict the risk of AKI.

Objectives

We aimed to determine the predictive characteristics of intrarenal arterial and venous Doppler markers for postoperative AKI in cardiac surgical patients.

Design

This study is the secondary analysis of a prospective cohort study.

Setting

This study is carried out in a care academic cardiac surgical center in Montreal, Quebec, Canada.

Patients

Adult patients undergoing cardiac surgery with the use of cardiopulmonary bypass.

Measurements

Point-of-care ultrasound assessments were performed preoperatively and at intensive care unit admission. Arterial measurements included the renal resistive index (RRI) and intrarenal artery velocity-time integral normalized to peak systolic velocity (VTI/PSV). Venous measurements included intrarenal venous flow (IRVF) pattern and renal venous stasis index (RVSI).

Methods

We used area under the receiving operating characteristic curves (AUCs) with net reclassification index (NRI) and multivariable logistic regression to determine predictive characteristics for postoperative AKI. Furthermore, we used hierarchical clustering to identify potential groups with similar Doppler parameters and performed comparisons of patients' characteristics and outcomes between groups.

Results

We included 136 patients with 47 (34.6%) developing postoperative AKI. At intensive care unit admission, arterial indices showed similar discrimination for the prediction of AKI (RRI: AUC = 0.64; 95% confidence interval (CI) = 0.55 to 0.74; and VTI/PSV: AUC = 0.67; 95% CI = 0.57 to 0.77). Venous Doppler indices including IRVF patterns (AUC = 0.64; 95% CI = 0.53 to 0.74) and RVSI (AUC = 0.60; 95% CI = 0.50 to 0.71) also showed similar performance. The combined model of RRI and IRVF pattern (AUC = 0.69; 95% CI = 0.59 to 0.78) improved the prediction of AKI compared to either RRI (NRI = 0.50; 95% CI = 0.17 to 0.84) or IRVF pattern (NRI = 0.38; 95% CI = 0.04 to 0.70) alone. Through hierarchical clustering, we identified 3 groups (1: low RRI, 2: high RRI/low RVSI, and 3: high RRI/high RVSI) with different patient characteristics and outcomes. The patient in group 3 had a higher risk of AKI and worse clinical outcomes compared with other groups.

Limitations

Single-center design in cardiac surgical patients limits generalizability.

Conclusions

Although more complex indices of intrarenal Doppler indices including the VTI/PSV and RVSI did not improve prediction of postoperative AKI, combining RRI and IRVF pattern improved risk prediction for AKI. Intrarenal arteriovenous Doppler subphenotypes identified patient groups at high risk of postoperative AKI.

Diagnostic value of multi-parameter ultrasound evaluation in sepsis complicated by acute kidney injury

BACKGROUND

This study aimed to discuss the diagnostic value of multi-parameter ultrasound evaluation in sepsis complicated with acute kidney injury (AKI).

METHODS

Patients were divided into an AKI group (n = 50) and a non-injury group (n = 50) based on the presence of AKI. The clinical characteristics were collected, and renal function parameters between the two groups were compared, including 24-h urine volume, serum creatinine, urea, serum cystatin C (CysC), renal parenchymal thickness (RPT), renal artery resistance index (RI), and multi-parameter ultrasound scoring (MPUS). Additionally, logistic regression analysis was conducted to determine the influencing factors of sepsis complicated with AKI. The prediction value was evaluated using a receiver operating characteristic (ROC) curve.

RESULTS

In the AKI group, creatinine, CysC, urea, MPUS score, RPT, and RI values were significantly higher, while the 24-h urine volume was lower than those in the non-injury group (p < 0.01). Moreover, multivariate logistic analysis indicated that high CysC and RI values were independent risk factors, whereas high 24-h urine volume and low MPUS were independent protective factors for sepsis-induced AKI. The ROC curve demonstrated that RI (AUC = 0.906) was more effective than 24-h urine volume (AUC = 0.797), CysC (AUC = 0.730), and MPUS (AUC = 0.794) in identifying sepsis-induced AKI.

CONCLUSION

High RI values increase the risk of sepsis-induced AKI, whereas low MPUS may reduce it. RI showed high diagnosis values for sepsis complicated with AKI.

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.

Prognostic nutritional index as a predictive marker for acute kidney injury in adult critical illness population: a systematic review and diagnostic test accuracy meta-analysis

BACKGROUND

The prognostic nutritional index (PNI), integrating nutrition and inflammation markers, has been increasingly recognized as a prognostic predictor in diverse patient cohorts. Recently, its effectiveness as a predictive marker for acute kidney injury (AKI) in various clinical settings has gained attention. This study aims to assess the predictive accuracy of the PNI for AKI in critically ill populations through systematic review and meta-analysis.

METHODS

A systematic review was conducted using the databases MEDLINE, EMBASE, PubMed, and China National Knowledge Infrastructure up to August 2023. The included trials reported the PNI assessment in adult population with critical illness and its predictive capacity for AKI. Data on study characteristics, subgroup covariates, and diagnostic performance of PNI, including sensitivity, specificity, and event rates, were extracted. A diagnostic test accuracy meta-analysis was performed. Subgroup analyses and meta-regression were utilized to investigate the sources of heterogeneity. The GRADE framework evaluated the confidence in the meta-analysis's evidence.

RESULTS

The analysis encompassed 16 studies with 17 separate cohorts, totaling 21,239 patients. The pooled sensitivity and specificity of PNI for AKI prediction were 0.67 (95% CI 0.58-0.74) and 0.74 (95% CI 0.67-0.80), respectively. The pooled positive likelihood ratio was 2.49 (95% CI 1.99-3.11; low certainty), and the negative likelihood ratio was 0.46 (95% CI 0.37-0.56; low certainty). The pooled diagnostic odds ratio was 5.54 (95% CI 3.80-8.07), with an area under curve of summary receiver operating characteristics of 0.76. Subgroup analysis showed that PNI's sensitivity was higher in medical populations than in surgical populations (0.72 vs. 0.55; p < 0.05) and in studies excluding patients with chronic kidney disease (CKD) than in those including them (0.75 vs. 0.56; p < 0.01). Overall, diagnostic performance was superior in the non-chronic kidney disease group.

CONCLUSION

Our study demonstrated that PNI has practical accuracy for predicting the development of AKI in critically ill populations, with superior diagnostic performance observed in medical and non-CKD populations. However, the diagnostic efficacy of the PNI has significant heterogeneity with different cutoff value, indicating the need for further research.

Elevated Renal-Resistive Index as an Indicator of Acute Kidney Injury Associated With Neonatal Extracorporeal Membrane Oxygenation

OBJECTIVE

The authors aimed to assess the relationship between elevated renal-resistive index (RRI) and acute kidney injury (AKI) related to extracorporeal membrane oxygenation (ECMO) in neonatal patients.

DESIGN

This was a retrospective study.

SETTING

The study was conducted at a teaching hospital.

PARTICIPANTS

Sixteen neonates treated with ECMO at the authors' hospital between June 2021 and December 2022 were included in this study.

INTERVENTIONS

Demographic and clinical data of patients were collected from the computer database. The RRI of patients before and during ECMO treatment was measured by bedside ultrasound. A receiver operating characteristic (ROC) curve was constructed to evaluate the diagnostic value of elevation of RRI as evidence of neonatal ECMO-related AKI. Logistic regression analysis was utilized to calculate the odds ratio (OR) with a 95% CI.

MEASUREMENTS AND MAIN RESULTS

A total of 16 patients met the inclusion criteria. For the primary outcome, the authors observed that the RRI during ECMO therapy was significantly elevated in patients with AKI compared to those without AKI. As for the secondary outcome, ROC curve analysis revealed an optimal RRI cutoff of 0.797, with an area under the curve of 0.855 (95% CI, 0.664-1, p = 0.027). The sensitivity and specificity of RRI values >0.797 for diagnosing AKI were 72.7% and 80%, respectively. Univariate logistic regression analysis indicated an OR of 1.433 (95% CI 1.192-1.873, p < 0.05) for RRI values above 0.797. This association remained statistically significant even after adjusting for serum cystatin C and Sequential Organ Failure Assessment score, with an adjusted OR of 1.352 (95% CI 1.108-1.612, p < 0.05).

CONCLUSION

The elevation of the RRI demonstrated a strong correlation with the onset of neonatal ECMO-related AKI, which may offer valuable support for diagnosing neonatal ECMO-related AKI.

Association of Preoperative Renal-Resistive Index With Long-term Renal and Cardiovascular Outcomes After Cardiac Surgery

OBJECTIVE

To investigate the association of elevated preoperative renal-resistive index (RRI) with persistent renal dysfunction, major adverse kidney events (MAKE), and major adverse cardiovascular events (MACE) after cardiac surgery.

DESIGN

Observational cohort study.

SETTING

University hospital.

PARTICIPANTS

Ninety-six adult patients undergoing cardiac surgery.

INTERVENTIONS

RRI measurement the day before surgery.

MEASUREMENTS AND MAIN RESULTS

Fifty-eight patients (60%) had elevated RRI ≥0.70. Five years after surgery, persistent renal dysfunction (sustained decline in estimated glomerular filtration rate ≥25%) had occurred in 25 patients (26%), MAKE (persistent renal dysfunction, renal replacement therapy, or death) in 34 (35%), and MACE (myocardial infarction, unstable angina, decompensated heart failure, stroke, or cardiovascular death) in 28 (29%). RRI was higher in patients who developed persistent renal dysfunction (median, 0.78 [IQR, 0.74-0.82] v 0.70 [0.66-0.77], p = 0.001), MAKE (0.77 [0.72-0.81] v 0.68 [0.65-0.76], p = 0.002), and MACE (0.77 [0.72-0.81] v 0.70 [0.66-0.77], p = 0.006). Patients with elevated RRI had a significantly higher cumulative incidence of all long-term outcomes. After adjustment for baseline renal function and heart failure, elevated RRI was associated with persistent renal dysfunction (hazard ratio [HR], 5.82 [95% CI, 1.71-19.9]), MAKE (HR, 4.21 [1.59-11.1]), and MACE (HR, 2.81 [1.03-7.65]).

CONCLUSIONS

Elevated preoperative RRI is associated with persistent renal dysfunction, MAKE, and MACE after cardiac surgery. Preoperative RRI may be used for long-term risk assessment in patients undergoing cardiac surgery.

Contrast-Enhanced Ultrasonography for Acute Kidney Injury: A Systematic Review and Meta-Analysis

OBJECTIVE

The aim of the work described here was to provide an evidence-based evaluation of contrast-enhanced ultrasonography (CEUS) in acute kidney injury (AKI) and assess variations in renal microperfusion with CEUS quantitative parameters in patients at a high risk of developing AKI.

METHODS

A meta-analysis and systematic review were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and the Embase, MEDLINE, Web of Science and the Cochrane Library databases were used to search the relevant articles systematically (2000-2022). Studies using CEUS to assess renal cortical microcirculation in AKI were included.

RESULTS

Six prospective studies (374 patients) were included. The overall quality of included studies was moderate to high. CEUS measures, maximum intensity (standard mean difference [SMD]: -1.37, 95% confidence interval [CI]: -1.64 to -1.09) and wash-in rate (SMD: -0.77, 95% CI: -1.09 to -0.45) were lower in the AKI+ group than in the AKI- group, and mean transit time (SMD: 0.76, 95% CI: 0.11-1.40) and time to peak (SMD: 1.63, 95% CI: 0.99-2.27) were higher in the AKI+ group. Moreover, maximum intensity and wash-in rate values changed before creatinine changed in the AKI+ group.

CONCLUSION

Patients with AKI had reduced microcirculatory perfusion, prolonged perfusion time and a reduced rising slope in the renal cortex, which occurred before serum creatinine changes. And they could be measured using CEUS, indicating that CEUS could help in the diagnosis of AKI.

Effects of changes in position, positive end-expiratory pressure and mean arterial pressure on renal, portal and hepatic Doppler ultrasound perfusion indices: a randomized crossover study in cardiac surgery patients

Point-of-care ultrasound perfusion indices can be used for detection of AKI and venous congestion. Patients in the postoperative- and intensive care units are frequently exposed to alternating treatment and loading conditions. We aimed to study the effects of changes in preload (patient positioning), positive end-expiratory pressure (PEEP) and afterload (phenylephrine) on renal, portal and hepatic ultrasound indices. We hypothesized that renal resistive index was not influenced by changes in PEEP and patient positioning. This was a single-site, randomized, crossover study. Patients above 18 years scheduled for elective open-heart surgery at Aarhus University Hospital, Denmark, were available for inclusion. Patients were randomized to a sequence of six combinations of PEEP and position in addition to an increase in mean arterial pressure by phenylephrine. Thirty-one patients participated in the study. Resistive index was influenced by positional change (P = 0.007), but not by change in PEEP (P = 0.50) (Table 1). Renal venous stasis index and portal pulsatility fraction increased in the raised legs position (P ≤ 0.019), but not with increases in PEEP. Renal venous flow pattern and hepatic venous flow pattern were affected by position (P ≤ 0.019), but not by PEEP. None of the ultrasound indices were significantly changed by infusion of phenylephrine. Doppler perfusion indices were significantly affected by changes in preload, but not by changes in PEEP or afterload. Although the changes in the Doppler ultrasound indices were significant, they were small in absolute numbers. Therefore, from a clinical perspective, the ultrasound indices were robust.Trial registration Registered at clinicaltrials.com, first posted online June 5th 2020, identifier: NCT04419662.

The moderate-intensity continuous exercise maintains renal blood flow and does not impair the renal function

Exercise is restricted for individuals with reduced renal function because exercising reduces blood flow to the kidneys. Safe and effective exercise programs for individuals with reduced renal function have not yet been developed. We previously examined the relationship between exercise intensity and renal blood flow (RBF), revealing that moderate-intensity exercise did not reduce RBF. Determining the effects of exercise duration on RBF may have valuable clinical applications. The current study examined the effects of a single bout of continuous exercise at lactate threshold (LT) intensity on renal hemodynamics. Eight adult males participated in this study. Participants underwent 30 min of aerobic exercise at LT intensity using a cycle ergometer. Evaluation of renal hemodynamics was performed before and after exercise, in the recovery phase using ultrasound echo. Furthermore, blood and urine samplings were conducted before and after exercise, in the recovery phase. Compared with resting, RBF was not significantly changed immediately after continuous exercise (319 ± 102 vs. 308 ± 79 ml/min; p = 0.976) and exhibited no significant changes in the recovery phase. Moreover, urinary kidney injury molecule-1 (uKIM-1) level exhibited no significant change immediately after continuous exercise (0.52 ± 0.20 vs. 0.46 ± 0.27 μg/g creatinine; p = 0.447). In addition, the results revealed no significant change in urinary uKIM-1 in 60-min after exercise. Other renal injury biomarkers exhibited a similar pattern. These findings indicate that a single bout of moderate-intensity continuous exercise maintains RBF and does not induce renal injury.

Performance of resistive index and semi-quantitative power doppler ultrasound score in predicting acute kidney injury: A meta-analysis of prospective studies

This study aimed to assess the predictive value of the renal resistive index (RRI) and power Doppler ultrasound (PDU) on subsequent acute kidney injury (AKI) risk using a meta-analytic approach. We searched eligible studies in PubMed, EmBase, and the Cochrane library from inception until August 2021. The parameters included the sensitivity, specificity, positive and negative likelihood ratios (PLR and NLR), diagnostic odds ratio (DOR), and area under the receiver operating characteristic curves (AUC). Twenty-three prospective studies involving 2,400 patients were selected. The pooled sensitivity and specificity of the RRI and PDU were 0.76 and 0.79, and 0.64 and 0.90, respectively. The pooled PLR and NLR were 3.64 and 0.31, and 6.58 and 0.40 for the RRI and PDU, respectively. The DORs of the RRI and PDU for predicting AKI were 11.76, and 16.32, respectively. The AUCs of the RRI and PDU for predicting AKI were 0.83, and 0.86, respectively. There were no significant differences between the RRI and PDU for predicting AKI in terms of sensitivity, PLR, NLR, DOR, and AUC. The specificity of the RRI was lower than that of the PDU for predicting AKI. This study found that the predictive performance of the RRI and PDU from the Doppler ultrasound for AKI was similar, which need to be further verified based on the direct comparison results.

Resistivity and pulsatility indexes in feline kidney disease: a systematic review

Doppler ultrasonography is used in the evaluation of hemodynamics, and the resistivity (RI) and pulsatility (PI) indexes provide information about resistance to blood flow within a vessel. This systematic review was carried out to evaluate renal RI and PI in clinically healthy and nonsedated cats and as well as their usefulness in the evaluation of kidney disease in cats. An electronic search in the PubMed, Scopus, and Web of Science databases was carried out using the terms "resistive index" or "resistivity index" or "pulsatility index;" "Doppler;" "renal" or "kidney;" and "cat" or "feline" in titles, abstracts, and keywords. Variables of interest related to experimental model features, research methods, and technical resources were extracted from the studies. The methodological quality was assessed with SYRCLE's risk of bias tool. Thus, 14 studies involving healthy and sick cats were selected. Interestingly, the upper limits estimated for both RI and PI varied among studies. The upper limits of renal RI for healthy cats varied between 0.64 and 0.72, while for PI, the values varied from 1.06 to 1.29. A limited number of studies evaluated cats with kidney disease. In most studies, RI values of kidneys with different conditions were significantly different from kidneys of healthy animals, indicating that RI values increase with kidney disease. The parameters body weight, heart rate, and age seem to influence the RI values. Standardized studies regarding its realization and description are still necessary to define normal values and analyze its applicability in the clinical diagnostic routine.

Impact of intra-abdominal pressure on early kidney transplant outcomes

Increased intra-abdominal pressure (IAP) is common among post-surgical patients and may cause organ dysfunction. However, its impact after kidney transplantation on early postoperative complications and graft recovery remains unclear. We designed a prospective, observational cohort study to describe the prevalence and determinants of IAP, as well as its effect on delayed graft function, postoperative complications, and graft recovery. IAP was measured in 205 kidney transplant recipients every 8 h during the first 72 h after surgery using the urinary bladder technique. Intra-abdominal hypertension was defined as IAP ≥ 12 mmHg. Patients were followed for 6 months or until graft failure/death. Mean IAP was 12 ± 3.3 mmHg within the first 24 h. 78% of subjects presented with intra-abdominal hypertension during the first 72 h. Increased IAP was associated with higher renal resistive index [r = 0.213; P = 0.003] and lower urine output [r =  - 0.237; P < 0.001]. 72 h mean IAP was an independent risk factor for delayed graft function [OR: 1.31; 95% CI: 1.13-1.51], postoperative complications [OR: 1.17; 95% CI: 1.03-1.33], and absence of graft function recovery [HR for graft function recovery: 0.94; 95% CI: 0.88-0.99]. Increased IAP was highly prevalent after transplantation and was independently associated with delayed graft function, postoperative complications, and absence of graft function recovery. Routine IAP monitoring should be considered post-transplantation to facilitate early recognition of relevant complications.

Renal Resistive Index: Not Only for Kidney Clinics

Renal Resistive Index (RRI) is a measurement of the resistance of the renal blood flow. A value higher than 0.70 is a marker of increased resistance and is correlated with kidney injury and its severity. Additionally, it may be associated with the mortality rate in the post-surgery population. In COVID-19 subjects, we found that high RRI has been associated with high levels of serum C-reactive protein, a marker of systemic inflammatory reaction syndrome. Finally, we propose RRI not only as a marker of kidney injury, but also as a tool to evaluate the course of critical illness.

Renal Resistive Index as A Potential Indicator of Acute Kidney Injury in Horses

Reliable and simple tests are constantly being sought to enable the quick detection of acute kidney injury in humans and animals. Diagnosis of subclinical AKI in horses, mainly in field practice, is difficult. An ultrasound scan is a routine test performed when kidney disease is suspected. The aim of the study was to establish the value of the renal resistive index (RRI) in intrarenal arteries in horses with clinical AKI and compare it to that of healthy horses. The second goal was to determine whether potentially nephrotoxic agents can influence RRI. The kidney ultrasonography examination was performed in 30 healthy horses, 11 horses with AKI and 30 horses at risk for AKI (10 colic horses, 10 horses receiving gentamicin and 10 horses receiving NSAIDs). RRI values were measured using pulsed-wave Doppler. Differences in RRI between groups were observed only in the right kidney. Horses with AKI had significantly higher RRI values compared to healthy horses. In the risk group, there was no effect of potentially nephrotoxic agents on the RRI value. RRI value in horses seem to be lower than in other species. The increase in this parameter in horses with AKI affected only one kidney and these values did not reach values obtained in other species. The clinical application of this method in non-cooperating animals remains questionable, and therefore RRI Doppler ultrasonography of blood flow in the intrarenal arteries may have poor clinical utility as a diagnostic tool in the diagnosis of AKI in horses.

The furosemide stress test, electrolyte response and Renal Index in critically ill patients

BACKGROUND

Acute kidney injury (AKI) is a common syndrome in critically ill patients. The diagnostic ability of traditional markers such as serum creatinine has recently been questioned, and the use of newer tests such as the furosemide stress test or the ultrasound assessment of renal resistive index have been proposed. Aim of the present study was to compare the response to a furosemide stress test, the Renal Index in mechanically ventilated patients with and without acute kidney injury at admission, and who did or did not develop AKI at day three, among those with normal renal function at the CIU admission.

METHODS

Prospective observational study in consecutive mechanically ventilated patients admitted in a general intensive care. Furosemide stress test and ultrasonographical Renal Index were performed at the admission and clinical and laboratory data were collected before and two hours after the furosemide stress text. The urine output after the first and the second hours was recorded.

RESULTS

Forty patients were enrolled, 19 of whom had AKI at admission. The Renal Index was significantly higher in patients with AKI (0.77±0.07 vs. 0.72±0.08, P=0.027); patients with AKI had a significantly lower urine output after the furosemide stress test (400 [340; 1400] vs.1525 [400; 2550] mL; P=0.013). The plasma concentrations of sodium, potassium and chloride were not different before and after the furosemide stress test in patients with and without AKI, whereas in patients with AKI, the total urine output of sodium, potassium and chloride were significantly lower compared to patients without AKI. Similar results were found in patients without AKI at admission and who developed AKI at day three as compared to those who did not develop AKI.

CONCLUSIONS

The response to the furosemide stress test and the Renal Index could be used as additional tools to evaluate the kidney function in critically ill patients.

Potential role of imaging for assessing acute pancreatitis-induced acute kidney injury

Acute kidney injury (AKI) is a common complication of acute pancreatitis (AP) that is associated with increased mortality. Conventional assessment of AKI is based on changes in serum creatinine concentration and urinary output. However, these examinations have limited accuracy and sensitivity for the diagnosis of early-stage AKI. This review summarizes current evidence on the use of advanced imaging approaches and artificial intelligence (AI) for the early prediction and diagnosis of AKI in patients with AP. CT scores, CT post-processing technology, Doppler ultrasound, and AI technology provide increasingly valuable information for the diagnosis of AP-induced AKI. Magnetic resonance imaging (MRI) also has potential for the evaluation of AP-induced AKI. For the accurate diagnosis of early-stage AP-induced AKI, more studies are needed that use these new techniques and that use AI in combination with advanced imaging technologies.

Doppler parameters of renal hemodynamics in women with preeclampsia: A systematic review and meta-analysis

The present meta-analysis aims to compare renal arterial and venous Doppler parameters in women with preeclampsia and healthy pregnant controls. Medline, Scopus, Cochrane Central Register of Controlled Trials, Clinicaltrials.gov, and Google Scholar databases were systematically searched from inception to December 04, 2019. All observational studies reporting renal resistive index, pulsatility index, renal interlobar vein impedance, or pulse transit time among preeclamptic and healthy pregnant women were held eligible. Subgroup analysis was conducted on the basis of disease onset and side of measurement. Both pair-wise and network meta-analysis were performed using Review Manager 5.3 and R-3.4.3 software. Fourteen studies were included, with a total of 1118 women. No difference of renal resistive (MD: 0.00, 95% CI: [-0.03, 0.04]) and pulsatility index (MD: -0.01, 95% CI: [-0.14, 0.12]) was evident between the two groups. Renal interlobar vein impedance was estimated to be significantly higher in preeclampsia (MD: 0.07, 95% CI: [0.06, 0.09]), while venous pulse transit time was significantly lower (MD: -0.10, 95% CI: [-0.14, -0.05]) in women with the disease. Subgroup analysis indicated that early-onset preeclampsia was associated with significantly elevated renal interlobar vein impedance and lower venous pulse transit time than late-onset disease. The outcomes of the present meta-analysis suggest that preeclampsia is characterized by venous hemodynamic dysfunction as it is associated with significantly elevated renal interlobar vein impedance and shorter venous pulse transit time. Future large-scale prospective studies should introduce cutoff values and determine the optimal timing of measurement in order to achieve optimal predictive accuracy.

Feasibility of renal resistive index measurements performed by an intermediate and novice sonographer in a volunteer population

Background

The Doppler-derived renal resistive index (RRI) is emerging as a promising bedside tool for assessing renal perfusion and risk of developing acute kidney injury in critically ill patients. It is not known what level of ultrasonography competence is needed to obtain reliable RRI values.

Objective

The aim of this study was to evaluate the feasibility of RRI measurements by an intermediate and novice sonographer in a volunteer population.

Methods

After a focused teaching session, an intermediate (resident), novice (medical student) and expert sonographer performed RRI measurements in 23 volunteers consecutively and blinded to the results of one another. Intraclass correlation coefficients and Bland–Altman plots were used to evaluate interobserver reliability, bias and precision.

Results

Both non-experts were able to obtain RRI values in all volunteers. Median RRI in the population measured by the expert was 0.58 (interquartile range 0.52–0.62). The intraclass correlation coefficient was 0.96 (95% confidence interval 0.90–0.98) for the intermediate and expert, and 0.85 (95% confidence interval 0.69–0.94) for the novice and expert. In relation to the measurements of the expert, both non-experts showed negligible bias (mean difference 0.002 [95% confidence interval − 0.005 to 0.009, p = 0.597] between intermediate and expert, mean difference 0.002 [95% confidence interval − 0.011 to 0.015, p = 0.752] between novice and expert) and clinically acceptable precision (95% limits of agreement − 0.031 to 0.035 for the intermediate, 95% limits of agreement − 0.056 to 0.060 for the novice).

Conclusions

RRI measurements by both an intermediate and novice sonographer in a volunteer population were reliable, accurate and precise after a brief course. RRI is easy to learn and feasible within the scope of point-of-care ultrasound.

Bedside Renal Doppler Ultrasonography and Acute Kidney Injury after TAVR

Acute kidney injury (AKI) following transcatheter aortic valve replacement (TAVR) is associated with a dismal prognosis. Elevated renal resistive index (RRI), through renal Doppler ultrasound (RDU) evaluation, has been associated with AKI development and increased systemic arterial stiffness. Our pilot study aimed to investigate the performance of Doppler based RRI to predict AKI and outcomes in TAVR patients. From May 2018 to May 2019, 100 patients with severe aortic stenosis were prospectively enrolled for TAVR and concomitant RDU evaluation at our institution (Nouvel Hôpital Civil, Strasbourg University, France). AKI by serum Creatinine (sCr-AKI) was defined according to the VARC-2 definition and AKI by serum Cystatin C (sCyC-AKI) was defined as an sCyC increase of greater than 15% with baseline value. Concomitant RRI measurements as well as renal and systemic hemodynamic parameters were recorded before, one day, and three days after TAVR. It was found that 10% of patients presented with AKI_sCr and AKI_sCyC. The whole cohort showed higher baseline RRI values (0.76 ± 0.7) compared to normal known and accepted values. AKI_sCyC had significant higher post-procedural RRI one day (Day 1) after TAVR (0.83 ± 0.1 vs. 0.77 ± 0.6, CI 95%, p = 0.005). AUC for AKI_sCyC was 0.766 and a RRI cut-off value of ≥ 0.795 had the most optimal sensitivity/specificity (80/62%) combination. By univariate Cox analysis, Mehran Risk Score, higher baseline right atrial pressure at baseline > 0.8 RRI values one day after TAVR (HR 6.5 (95% CI 1.3-32.9; p = 0.021) but not RRI at baseline were significant predictors of AKI_sCyC. Importantly, no significant impact of baseline biological parameters, renal or systemic parameters could be demonstrated. Doppler-based RRI can be helpful for the non-invasive assessment of AKI development after TAVR.

An assessment of the utility and repeatability of the renal resistive index in horses

The aim of this study was to establish the value of the renal resistive index (RI) of intrarenal arteries in healthy warmblood non-racing horses of different ages to assess the influence of physiologic factors and repeatability of measurement. The kidney ultrasonography examination was performed in three age groups: 15 foals, 15 adults and 15 elderly horses. The procedure was performed in unsedated standing animals. RI values were measured using pulsed-wave Doppler at the medial part of each kidney in the intrarenal arteries. To evaluate repeatability, all measurements were repeated two hours after the first examination. Statistical analysis of the relationship between groups was carried out using Fisher’s test. The relationship between the RI value and the physiological parameters was evaluated using linear regression. Repeatability of measurements was determined based on the Bland-Altman plot. The mean RI value in the studied horses was 0.48 ± 0.05 in the left kidney and 0.49 ± 0.05 in the right kidney. There were no statistically significant differences between the RI values in foals and adult horses. The elderly horses had a significantly higher RI value. Pulse pressure was the only physiological parameter affecting the RI value. The repeatability coefficient was 0.089 for the right kidney and 0.09 for the left kidney. The presented result suggest that elderly healthy horses have higher RI values than younger animals, which should be taken into account in clinical practice. The arterial pulse pressure should also be considered when interpreting RI values. The measurements have high repeatability, but in the authors’ opinion, this procedure is time consuming and requires experience.