Renal resistive index: a new reversible tool for the early diagnosis and evaluation of organ perfusion in critically ill patients: a case report

Assessment of the Utility of Point-of-Care Testing Incorporating Ultrasound and Arterial Blood Gas in Patients with Acute Febrile Illness in the Emergency Department to Determine Disease Severity, Disposition, Need for Ventilation and Renal Replacement Therapy

Introduction

Acute febrile illness (AFI) patients present to the emergency department (ED), with fever to multi-organ dysfunction. There is a lack of early point-of-care-based disposition criteria in AFI patients regarding the need for intensive care unit (ICU) or high dependency unit (HDU) care.

Methods

We enrolled 100 patients with AFI presenting to the ED and evaluated using point-of-care ultrasound with two-dimensional echocardiography (ECHO), lung ultrasound score (LUS), renal arterial resistive index (RRI), and arterial blood gas. The need for ICU/HDU admission, ventilation (either noninvasive or invasive), and renal-replacement therapy (RRT) within 48 h of hospitalization was noted.

Results

Ninety-five patients were included in the analysis. 72 (75.8%) patients required either ICU or HDU admission, 45 (47.4%) required ventilatory support (either noninvasive or invasive), and 32 (33.7%) required RRT. After logistic regression, LUS ≥16, and arterial lactate ≥12 mg/dL were independent predictors of the need for ICU or HDU admission. The respiratory rate (RR) ≥28/minute, LUS ≥16 and RRI ≥61 were the independent predictors of the need for ventilation. The MAP ≤73 mmHg, LUS (≥16), and RRI (≥67) were the predictors of the need for RRT.

Conclusion

In AFI patients presenting to the ED, the MAP, LUS, and lactate are predictors of the need for ICU/HDU admission. The LUS and RRI were predictors of the need for RRT whereas the RR, LUS, and RRI were the predictors of the need for ventilation.

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.

Inferior mesenteric artery embolization ahead of rectal cancer surgery: AMIREMBOL pilot study

Ischaemic conditioning in rectal cancer surgery by preoperative embolization of the inferior mesenteric artery is feasible and safe. It seems to protect from ischaemic stress during the surgical procedure.

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.

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.

Renal resistive index is associated with acute kidney injury in COVID-19 patients treated in the intensive care unit

Background

Renal resistive index (RRI) is a promising tool for the assessment of acute kidney injury (AKI) in critically ill patients in general, but its role and association to AKI among patients with Coronavirus disease 2019 (COVID-19) is not known.

Objective

The aim of this study was to describe the pattern of RRI in relation to AKI in patients with COVID-19 treated in the intensive care unit.

Methods

In this observational cohort study, RRI was measured in COVID-19 patients in six intensive care units at two sites of a Swedish University Hospital. AKI was defined by the creatinine criteria in the Kidney Disease Improving Global Outcomes classification. We investigated the association between RRI and AKI diagnosis, different AKI stages and urine output.

Results

RRI was measured in 51 patients, of which 23 patients (45%) had AKI at the time of measurement. Median RRI in patients with AKI was 0.80 (IQR 0.71–0.85) compared to 0.72 (IQR 0.67–0.78) in patients without AKI (p = 0.004). Compared to patients without AKI, RRI was higher in patients with AKI stage 3 (median 0.83, IQR 0.71–0.85, p = 0.006) but not in patients with AKI stage 1 (median 0.76, IQR 0.71–0.83, p = 0.347) or AKI stage 2 (median 0.79, min/max 0.79/0.80, n = 2, p = 0.134). RRI was higher in patients with an ongoing AKI episode compared to patients who never developed AKI (median 0.72, IQR 0.69–0.78, p = 0.015) or patients who developed AKI but had recovered at the time of measurement (median 0.68, IQR 0.67–0.81, p = 0.021). Oliguric patients had higher RRI (median 0.84, IQR 0.83–0.85) compared to non-oliguric patients (median 0.74, IQR 0.69–0.81) (p = 0.009). After multivariable adjustment, RRI was independently associated with AKI (OR for 0.01 increments of RRI 1.22, 95% CI 1.07–1.41).

Conclusions

Critically ill COVID-19 patients with AKI have higher RRI compared to those without AKI, and elevated RRI may have a role in identifying severe and oliguric AKI at the bedside in these patients.

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.