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

Impact of positive end-expiratory pressure on renal resistive index in mechanical ventilated patients

PURPOSE

Growing evidence shows the complex interaction between lung and kidney in critically ill patients. The renal resistive index (RRI) is a bedside measurement of the resistance of the renal blood flow and it is correlated with kidney injury. The positive end-expiratory pressure (PEEP) level could affect the resistance of renal blood flow, so we assumed that RRI could help to monitoring the changes in renal hemodynamics at different PEEP levels. Our hypothesis was that the RRI at ICU admission could predict the risk of acute kidney injury in mechanical ventilated critically ill patients.

METHODS

We performed a prospective study including 92 patients requiring mechanical ventilation for ≥ 48 h. A RRI ≥ 0.70, was deemed as pathological. RRI was measured within 24 h from ICU admission while applying 5,10 and 15 cmH2O of PEEP in random order (PEEP trial).

RESULTS

Overall, RRI increased from 0.62 ± 0.09 at PEEP 5 to 0.66 ± 0.09 at PEEP 15 (p < 0.001). The mean RRI value during the PEEP trial was able to predict the occurrence of AKI with AUROC = 0.834 [95%CI 0.742-0.927]. Patients exhibiting a RRI ≥ 0.70 were 17/92(18%) at PEEP 5, 28/92(30%) at PEEP 10, 38/92(41%) at PEEP 15, respectively. Thirty-eight patients (41%) exhibited RRI ≥ 0.70 at least once during the PEEP trial. In these patients, AKI occurred in 55% of the cases, versus 13% remaining patients, p < 0.001.

CONCLUSIONS

RRI seems able to predict the risk of AKI in mechanical ventilated patients; further, RRI values are influenced by the PEEP level applied.

TRIAL REGISTRATION

Clinical gov NCT03969914 Registered 31 May 2019.

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.

Influence of arterial blood gases on the renal arterial resistive index in intensive care unit

BACKGROUND

Renal artery Doppler sonography with resistive index (RI) determination is a noninvasive, fast, and reliable diagnostic tool increasingly used in the intensive care unit (ICU) to predict and assess the reversibility of acute kidney injury (AKI). However, interpreting the RI can be challenging due to numerous influencing factors. While some studies have explored various confounding factors, arterial blood gases have received limited attention. Therefore, our study aims to evaluate the impact of arterial blood gases on the RI in the ICU setting.

METHODS

This prospective observational study enrolled ICU patients who required blood gas analysis and had not experienced significant hemodynamic changes recently. The RI was measured using standardized Doppler ultrasound within an hour of the arterial blood gases sampling and analysis.

RESULTS

A total of sixty-four patients were included in the analysis. Univariate analysis revealed a correlation between the RI and several variables, including PaCO2 (R = 0.270, p = 0.03), age (R = 0.574, p < 0.0001), diastolic arterial pressure (DAP) (R = - 0.368, p = 0.0028), and SaO2 (R = - 0.284, p = 0.0231). Multivariate analysis confirmed that age > 58 years and PaCO2 were significant factors influencing the RI, with respective odds ratios of 18.67 (p = 0.0003) and 1.132 (p = 0.0267).

CONCLUSION

The interpretation of renal arterial RI should take into account thresholds for PaCO2, age, and diastolic arterial pressure. Further studies are needed to develop a comprehensive scoring system that incorporates all these cofactors for a reliable analysis of RI levels. Trial registration This observational study, registered under number 70-0914, received approval from local Ethical Committee of Toulouse University Hospital.

The clinical significance of renal resistance index (RRI) and renal oxygen saturation (RrSO2) in critically ill children with AKI: a prospective cohort study

OBJECTIVE

The purpose of this study was to look into the clinical significance of the renal resistance index (RRI) and renal oxygen saturation (RrSO2) in predicting the development of acute kidney injury (AKI) in critically ill children. A new non-invasive method for the early detection and prediction of AKI needs to develop.

METHODS

Patients admitted to the pediatric intensive care unit (PICU) affiliated with the capital institute of pediatrics from December 2020 to March 2021 were enrolled consecutively. Data of clinical information, renal Doppler ultrasound, RrSO2, and hemodynamic index within 24 h of admission were prospectively collected. Patients were divided into two groups: the study group was AKI occurred within 72 h, while the control group did not. SPSS (version 25.0) was used to analyze the data, and P < 0.05 was considered a statistical difference.

RESULTS

1) A total of 66 patients were included in this study, and the incidence of AKI was 19.70% (13/66). The presence of risk factors (shock, tumor, severe infection) increased the incidence of AKI by three times. 2) Univariate analysis showed significant differences in length of hospitalization, white blood cells (WBC), C-reactive protein (CRP), renal resistance index (RRI), and ejection fraction (EF) between the study and control groups (P < 0.05). There were no significant differences in renal perfusion semi-quantitative score (P = 0.053), pulsatility index (P = 0.051), pediatric critical illness score (PCIS), and peripheral vascular resistance index (P > 0.05). 3) Receiver operating characteristic (ROC) curve showed that if RRI > 0.635, the sensitivity, specificity, and AUC for predicting AKI were 0.889, 0.552, and 0.751, respectively; if RrSO2 < 43.95%, the values were 0.615, 0.719 and 0.609, respectively; if RRI and RrSO2 were united, they were 0.889, 0.552, and 0.766, respectively.

CONCLUSIONS

The incidence of AKI is high in PICU patients. And infection, RRI, and EF are risk factors for AKI in PICU patients. RRI and RrSO2 have certain clinical significance in the early prediction of AKI and may provide a new non-invasive method for early diagnosis and prediction of AKI.

Renal toxicity and biokinetics models after repeated uranium instillation

During nuclear fuel processing, workers can potentially be exposed to repeated inhalations of uranium compounds. Uranium nephrotoxicity is well documented after acute uranium intake, but it is controversial after long-term or protracted exposure. This study aims to analyze the nephrotoxicity threshold after repeated uranium exposure through upper airways and to investigate the resulting uranium biokinetics in comparison to reference models. Mice (C57BL/6J) were exposed to uranyl nitrate (0.03-3 mg/kg/day) via intranasal instillation four times a week for two weeks. Concentrations of uranium in urines and tissues were measured at regular time points (from day 1 to 91 post-exposure). At each exposure level, the amount of uranium retained in organs/tissues (kidney, lung, bone, nasal compartment, carcass) and excreta (urine, feces) reflected the two consecutive weeks of instillation except for renal uranium retention for the highest uranium dose. Nephrotoxicity biomarkers, KIM-1, clusterin and osteopontin, are induced from day 4 to day 21 and associated with changes in renal function (arterial fluxes) measured using non-invasive functional imaging (Doppler-ultrasonography) and confirmed by renal histopathological analysis. These results suggest that specific biokinetic models should be developed to consider altered uranium excretion and retention in kidney due to nephrotoxicity. The threshold is between 0.25 and 1 mg/kg/day after repeated exposure to uranium via upper airways.

Ultrasound Doppler Flow Parameters Are Independently Associated with Renal Cortex Contrast-Enhanced Multidetector Computed Tomography Perfusion and Kidney Function

BACKGROUND

The assessment of kidney perfusion has an emerging significance in many diagnostic applications. However, whether and which of the ultrasound Doppler parameters better express renal cortical perfusion (RCP) was not shown. The study aimed to prove the usefulness of Doppler ultrasound parameters in the assessment of RCP regarding low-dose contrast-enhanced multidetector computer tomography (CE-MDCT) blood flow.

METHODS

Thirty non-stenotic kidneys in twenty-five hypertensive patients (age 58.9 ± 19.0) with mild-to-severe renal dysfunction were included in the study. Resistive index (RI) and end-diastolic velocity (EDV) in segmental arteries, color Doppler dynamic RCP intensity (dRCP), RI (dRI), pulsatility index (dPI), and CE-MDCT blood flow (CBF) in the renal cortex were estimated.

RESULTS

CBF correlated significantly with age, estimated glomerular filtration rate (eGFR), RI, EDV, dRI, dPI, and dRCP. In separate multivariable backward regression analyses, RI (R² = 0.290, p = 0.003) and dRCP (R² = 0.320, p = 0.001) were independently associated with CBF. However, in the common ultrasound model, only dRCP was independently related to CBF (R² = 0.317, p = 0.001). Only CBF and EDV were independently associated with eGFR (R² = 0.510, p < 0.001).

CONCLUSIONS

Renal cortical perfusion intensity is the best ultrasound marker expressing renal cortical perfusion. In patients with hypertension and kidney dysfunction, renal resistive index and end-diastolic velocity express renal cortical perfusion and kidney function, respectively.

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.

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.

Intrarenal Doppler approaches in hemodynamics: A major application in critical care

The treatment of severe cases usually requires multimodality hemodynamic monitoring approaches, particularly for tissue and organ perfusion tracking. Currently, only a few studies have investigated renal perfusion status at the bedside. Ultrasound has become increasingly utilized to guide the hemodynamic management of severe patients. Similarly, intrarenal Doppler (IRD) is widely used to assess renal perfusion from both the intrarenal artery and vein perspectives. The renal resistive index (RRI), which reflects the renal arterial blood flow profile, is often applied to predict the reversibility of renal dysfunction and to titrate hemodynamic support. Intrarenal venous flow (IRVF) patterns and the renal venous stasis index (RVSI), which reflects the intrarenal vein blood flow profile, are now being used to assess intravenous congestion. They may also be useful in predicting the risk of acute kidney injury and avoiding fluid overload. IRD can provide diverse and supplemental information on renal perfusion and may help to establish the early diagnosis in severe patients. This review focused on the specific operational methods, influencing factors, and applications of IRD in hemodynamics.

Renal Resistive Index on Intensive Care Unit Admission Correlates With Tissue Hypoperfusion Indices and Predicts Clinical Outcome

BACKGROUND

Renal resistive index (RRI) has been used to evaluate renal blood flow. Our aim was to investigate the relation between RRI and global tissue hypoperfusion indices and their association with clinical outcome, in intensive care unit (ICU) patients.

METHODS

RRI was measured within 24 h of ICU admission. Gas exchange and routine hemodynamic variables at the time of RRI assessment were recorded. An elevated RRI was defined as >0.7. The ratio of central venous-to-arterial carbon dioxide partial pressure difference by arterial-to-central venous oxygen content difference (P(cv-a)CO2/C(a-cv)O2) and lactate were used as global tissue hypoperfusion indices.

RESULTS

A total of 126 patients were included [median age 61 (IQR 28) years, 74% males]. P(cv-a)CO2/C(a-cv)O2 ratio and arterial lactate were significantly higher in patients with RRI >0.7 compared with those with RRI ≤0.7 [2.88 (3.39) vs. 0.62 (0.57) mmol/L and 2.4 (2.2) vs. 1.2 (0.6)] respectively, both P < 0.001)]. RRI was significantly correlated with P(cv-a)CO2/C(a-cv)O2 ratio and arterial lactate for the whole patient population (rho = 0.64, both P < 0.0001) and for the subset of patients with shock (rho = 0.47, P = 0.001; and r = 0.64, P < 0.0001 respectively). Logistic regression models showed a significant association between RRI and P(cv-a)CO2/C(a-cv)O2 ratio with clinical outcome. The combination of RRI with P(cv-a)CO2)/(C(a-cv)O2 ratio and lactate better predicted mortality than RRI alone [AUC 84.8% (95% CI 5.1% -94.4%)] vs. [AUC 74.9% (95% CI 61%-88.8%)] respectively, P < 0.001.

CONCLUSIONS

Renal blood flow assessed by RRI, on ICU admission, correlates with global tissue hypoperfusion indices. In addition, RRI in combination with tissue perfusion estimation better predicts clinical outcome than RRI alone.

Shock Resuscitation - the Necessity and Priority of Renal Blood Perfusion Assessment

Improving organ perfusion is the aim of shock resuscitation; therefore, improving organ blood perfusion is a direct indicator for shock resuscitation. During shock, different organs have different capacities for blood flow autoregulation. The kidney is an important organ with excellent ability to autoregulate the blood flow and with vulnerability to poor organ perfusion, which places kidney perfusion in a position of necessity and priority relative to that of other organs in shock. Critical-care ultrasonography provides the best evaluation of renal perfusion.

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.

Renal resistive index in chronic kidney disease patients: Possible determinants and risk profile

BACKGROUND

High ultrasound renal resistive index (RI) predicts poor cardiorenal outcomes in chronic kidney disease (CKD) and has recently emerged as a marker of nephroprotective drugs response. Thus, having a risk profile of CKD patients with abnormal RI may be relevant for the clinicians.

METHODS

Consecutive patients referred to our non-dialysis CKD clinic from 01/01/2016 to 01/12/2016, were evaluated by clinical and ultrasound analysis. Inclusion criteria were age >18 years and presence of CKD defined as estimated glomerular filtration rate (eGFR)<60 mL/min/1.73m2 and/or proteinuria>0.150g/24h. Renal artery stenosis, solitary kidney, acute kidney injury were the main exclusion criteria. RI value was the mean of three measures in segmental arteries in each kidney. Univariate analysis was performed to evaluate associations between continuous RI and clinical variables. Multivariate linear regression analysis, based on stepwise method with an elimination criterion of p<0.10, was used to assess the independent correlates of RI as continuous variable.

RESULTS

We studied 73 patients (69.9% men). Mean RI was 0.67±0.09. Frequencies of diabetes and cardiovascular disease (CVD) were 19.2% and 20.6% and median eGFR 54.1 [30.0-84.6] mL/min/1.73m2. From low (<0.65) to intermediate (0.65-0.70) to high (>0.70) RI categories, eGFR and haemoglobin levels were decreased while diabetes, cardiovascular disease (CVD), phosphate and smokers were higher. At univariate analysis, RI was significantly associated with age, presence of diabetes, CVD, serum phosphorus, eGFR, Urea and haemoglobin. Multi-adjusted stepwise regression analysis showed that lower eGFR levels (p<0.001), diabetes (p = 0.042), CVD (p = 0.009), smoking habit (p = 0.021) and higher serum phosphorus levels (p = 0.001) were associated with higher continuous RI. Serum phosphorus showed Area Under the Curves (AUC) values of 0.714 and 0.664 for discriminating RI cut-offs of 0.70 and 0.65.

CONCLUSIONS

This analysis suggests that RI is higher in CKD patients with CVD, diabetes, smoking habit and higher serum phosphorus, regardless of eGFR. Further studies are needed to verify whether higher RI indicates more complex pathway of intrarenal damage, besides and beyond kidney function.

[Diagnosing acute organ ischemia : A practical guide for the emergency and intensive care physician]

Ischemia refers to a reduction or interruption of the blood flow to one or more organs. Early recognition of shock, a global ischemic state of the body, is of key importance in emergency and intensive care medicine. The physical examination and point-of-care laboratory diagnostics (i.e. lactate, base deficit, central/mixed venous oxygen saturation, venous-arterial carbon dioxide partial tension) are the methods of choice to diagnose shock in clinical practice. Importantly, a state of shock can also be present in patients with normo- or hypertensive arterial blood pressures. In shock, hypoperfusion of vital and visceral organs occurs. In the second part of this article, physical examination techniques, laboratory and diagnostic methods to detect shock-related hypoperfusion of the brain, heart, kidney and gastrointestinal tract are reviewed.

Impact of microaxillar mechanical left ventricular support on renal resistive index in patients with cardiogenic shock after myocardial infarction: a pilot trial to predict renal organ dysfunction in cardiogenic shock

OBJECTIVES

To evaluate the effects of left ventricular support with the microaxial left ventricular pump using the Impella device on the renal resistive index assessed by Doppler ultrasonography in haemodynamically stable patients with cardiogenic shock following myocardial infarction.

METHODS

A non-randomised interventional single-centre study. Consecutive patients with cardiogenic shock supported with an Impella were included during May 2018 and October 2018. The renal resistive index determined as a quotient of (peak systolic velocity - end diastolic velocity)/ peak systolic velocity was obtained using Doppler ultrasound; invasive blood pressure was determined in radial artery simultaneously for safety reasons.

RESULTS

A total of 15 patients were measured. The renal resistive index was determined in both kidneys in 13 patients and for one kidney in two patients, respectively. The mean difference between right and left renal resistive index was 0.026 ± 0.023 (P=0.72). When increasing the Impella microaxillar mechanical support by a mean of 0.44 L/min (±0.2 L/min), the renal resistive index decreased significantly from 0.66 ± 0.08 to 0.62 ± 0.06 (P<0.001) consistently in all patients, whereas systolic or diastolic blood pressure remained unchanged.

CONCLUSIONS

Microaxillar mechanical support by the Impella device in haemodynamically stable patients with cardiogenic shock led to a significant reduction of the renal resistive index without affecting systolic or diastolic blood pressure. This observation is consistent with the notion that Impella support may promote renal organ protection by enhancing renal perfusion.

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.