The renal compartment: a hydraulic view. Intensive Care Med Exp. 2014;2:26. [PMID: 26266923 PMCID: PMC4512983 DOI: 10.1186/s40635-014-0026-x]

Venous Congestion Assessed by Venous Excess Ultrasound (VExUS) and Acute Kidney Injury in Children with Right Ventricular Dysfunction

Background

Right ventricular dysfunction (RVD) is a complication following congenital cardiac surgery in children and can lead to systemic venous congestion, low cardiac output, and organ dysfunction. Venous congestion can be transmitted backwards and adversely affect encapsulated organs such as the kidneys.

Primary objective

To investigate the association between systemic venous congestion, as estimated by Venous Excess Ultrasound (VExUS), and the occurrence of acute kidney injury (AKI) in children with RVD following congenital heart surgery. Secondary objectives included comparing changes in VExUS scores after initiating treatment for RVD and venous congestion.

Methods and results

This was a prospective observational study in children with RVD. The VExUS study was performed on day 1, day 2, and day 3 and categorized as VExUS-1, VExUS-2, and VExUS-3. Among 43 patients with RVD and dilated inferior vena cava, 19/43 (44%), 10/43 (23%), and 12/43 (28%) were VExUS-2 and VExUS-3, respectively. There was an association between severe RVD and elevated pulmonary artery systolic pressures and a VExUS score >2. A significant association was observed between central venous pressure (CVP) measurements and VExUS. Among 31 patients with a high VExUS score >2, 18 (58%) had AKI. Additionally, improvement in CVP and fluid balance was associated with improving VExUS scores following targeted treatment for RVD.

Conclusion

VExUS serves as a valuable bedside tool for diagnosing and grading venous congestion through ultrasound Doppler. An elevated VExUS score was associated with the occurrence of AKI, and among the components of VExUS, portal vein pulsatility may be useful as a predictor of AKI.

How to cite this article

Natraj R, Bhaskaran AK, Rola P, Haycock K, Siuba MTT, Ranjit S. Venous Congestion Assessed by Venous Excess Ultrasound (VExUS) and Acute Kidney Injury in Children with Right Ventricular Dysfunction. Indian J Crit Care Med 2024;28(5):447-452.

Controlled Mechanical Ventilation in Critically Ill Patients and the Potential Role of Venous Bagging in Acute Kidney Injury

A very low incidence of acute kidney injury (AKI) has been observed in COVID-19 patients purposefully treated with early pressure support ventilation (PSV) compared to those receiving mainly controlled ventilation. The prevention of subdiaphragmatic venous congestion through limited fluid intake and the lowering of intrathoracic pressure is a possible and attractive explanation for this observed phenomenon. Both venous congestion, or "venous bagging", and a positive fluid balance correlate with the occurrence of AKI. The impact of PSV on venous return, in addition to the effects of limiting intravenous fluids, may, at least in part, explain this even more clearly when there is no primary kidney disease or the presence of nephrotoxins. Optimizing the patient-ventilator interaction in PSV is challenging, in part because of the need for the ongoing titration of sedatives and opioids. The known benefits include improved ventilation/perfusion matching and reduced ventilator time. Furthermore, conservative fluid management positively influences cognitive and psychiatric morbidities in ICU patients and survivors. Here, it is hypothesized that cranial lymphatic congestion in relation to a more positive intrathoracic pressure, i.e., in patients predominantly treated with controlled mechanical ventilation (CMV), is a contributing risk factor for ICU delirium. No studies have addressed the question of how PSV can limit AKI, nor are there studies providing high-level evidence relating controlled mechanical ventilation to AKI. For this perspective article, we discuss studies in the literature demonstrating the effects of venous congestion leading to AKI. We aim to shed light on early PSV as a preventive measure, especially for the development of AKI and ICU delirium and emphasize the need for further research in this domain.

Acute Kidney Injury: Definition, Management, and Promising Therapeutic Target

Acute kidney injury (AKI) is caused by a sudden loss of renal function, resulting in the build-up of waste products and a significant increase in mortality and morbidity. It is commonly diagnosed in critically ill patients, with its occurrence estimated at up to 50% in patients hospitalized in the intensive critical unit. Despite ongoing efforts, the death rate associated with AKI has remained high over the past half-century. Thus, it is critical to investigate novel therapy options for preventing the epidemic. Many studies have found that inflammation and Toll-like receptor-4 (TLR-4) activation have a significant role in the pathogenesis of AKI. Noteworthy, challenges in the search for efficient pharmacological therapy for AKI have arisen due to the multifaceted origin and complexity of the clinical history of people with the disease. This article focuses on kidney injury's epidemiology, risk factors, and pathophysiological processes. Specifically, it focuses on the role of TLRs especially type 4 in disease development.

A Critical Reassessment of the Kidney Risk Caused by Tetrastarch Products in the Perioperative and Intensive Care Environments

Purpose: To reassess the results of former meta-analyses focusing on the relationship between novel HES preparations (130/0.4 and 130/0.42) and acute kidney injury. Previous meta-analyses are based on studies referring to partially or fully unpublished data or data from abstracts only. Methods: The studies included in the former meta-analyses were scrutinized by the authors independently. We completed a critical analysis of the literature, including the strengths, weaknesses and modifiers of the studies when assessing products, formulations and outcomes. Results: Both the published large studies and meta-analyses show significant bias in the context of the deleterious effect of 6% 130/0.4-0.42 HES. Without (1) detailed hemodynamic data, (2) the exclusion of other nephrotoxic events and (3) a properly performed evaluation of the dose-effect relationship, the AKI-inducing property of 6% HES 130/0.4 or 0.42 should not be considered as evidence. The administration of HES is safe and effective if the recommended dose is respected. Conclusions: Our review suggests that there is questionable evidence for the deteriorating renal effect of these products. Further well-designed, randomized and controlled trials are needed. Additionally, conclusions formulated for resource-rich environments should not be extended to more resource-scarce environments without proper qualifiers provided.

Association between intrarenal venous flow from Doppler ultrasonography and acute kidney injury in patients with sepsis in critical care: a prospective, exploratory observational study

BACKGROUND

Intrarenal venous flow (IRVF) patterns assessed using Doppler renal ultrasonography are real-time bedside visualizations of renal vein hemodynamics. Although this technique has the potential to detect renal congestion during sepsis resuscitation, there have been few studies on this method. We aimed to examine the relationship between IRVF patterns, clinical parameters, and outcomes in critically ill adult patients with sepsis. We hypothesized that discontinuous IRVF was associated with elevated central venous pressure (CVP) and subsequent acute kidney injury (AKI) or death.

METHODS

We conducted a prospective observational study in two tertiary-care hospitals, enrolling adult patients with sepsis who stayed in the intensive care unit for at least 24 h, had central venous catheters placed, and received invasive mechanical ventilation. Renal ultrasonography was performed at a single time point at the bedside after sepsis resuscitation, and IRVF patterns (discontinuous vs. continuous) were confirmed by a blinded assessor. The primary outcome was CVP obtained at the time of renal ultrasonography. We also repeatedly assessed a composite of Kidney Disease Improving Global Outcomes of Stage 3 AKI or death over the course of a week as a secondary outcome. The association of IRVF patterns with CVP was examined using Student's t-test (primary analysis) and that with composite outcomes was assessed using a generalized estimating equation analysis, to account for intra-individual correlations. A sample size of 32 was set in order to detect a 5-mmHg difference in CVP between IRVF patterns.

RESULTS

Of the 38 patients who met the eligibility criteria, 22 (57.9%) showed discontinuous IRVF patterns that suggested blunted renal venous flow. IRVF patterns were not associated with CVP (discontinuous flow group: mean 9.24 cm H2O [standard deviation: 3.19], continuous flow group: 10.65 cm H2O [standard deviation: 2.53], p = 0.154). By contrast, the composite outcome incidence was significantly higher in the discontinuous IRVF pattern group (odds ratio: 9.67; 95% confidence interval: 2.13-44.03, p = 0.003).

CONCLUSIONS

IRVF patterns were not associated with CVP but were associated with subsequent AKI in critically ill adult patients with sepsis. IRVF may be useful for capturing renal congestion at the bedside that is related to clinical patient outcomes.

Association of Volume Status During Veno-Venous Extracorporeal Membrane Oxygenation with Outcome

Fluid overload in acute respiratory distress syndrome is associated with increased mortality. The purpose of this study was to investigate the association of cumulative fluid balance (CFB) during the first 7 days of veno-venous extracorporeal membrane oxygenation (VV ECMO) and mortality. Adult patients on VV ECMO for greater than 168 hours, between November 2015 and October 2019, were included. CFB during the first 7 ECMO days was compared between survivors and nonsurvivors, and survival was analyzed using Kaplan-Meier analysis and cox proportional hazards modeling. One hundred forty-six patients were included. Median age was 45 years [32, 55], respiratory ECMO survival prediction score was 3 [0, 5], and P/F ratio was 70 [55, 85]. CFB for ECMO days 1-3 was +2,350 cc [-540, 5,941], days 4-7 -3,070 cc [-6,545, 437], and days 1-7 -341 cc [-4,579, 5,290]. One hundred seventeen patients (80%) survived to hospital discharge. Survivors were younger (41 years [31, 53] vs. 53 years [45, 60], p < 0.001) and had a higher respiratory ECMO survival prediction score, (3 [1, 5] vs. 1.5 [-1, 3], p = 0.002). VV ECMO survivors had a significantly more negative CFB during the first 7 days of VV ECMO (-1,311 cc [-4,755, 4,217] vs. 3,617 cc [-2,764, 9,413], p = 0.02), and CFB was an independent predictor of 90 day mortality (HR = 1.07 [1.01, 1.14], p = 0.02). Further studies are needed to determine the causal relationship between fluid balance and survival during VV ECMO.

Pathophysiology of Acute Kidney Injury in Critical Illness: A Narrative Review

Acute kidney injury (AKI) is a syndrome that entails a rapid decline in kidney function with or without injury. The consequences of AKI among acutely ill patients are dire and lead to higher mortality, morbidity, and healthcare cost. To prevent AKI and its short and long-term repercussions, understanding its pathophysiology is essential. Depending on the baseline kidney histology and function reserves, the number of kidney insults, and the intensity of each insult, the clinical presentation of AKI may differ. While many factors are capable of inducing renal injury, they can be categorized into a few processes. The three primary processes reported in the literature are hemodynamic changes, inflammatory reactions, and nephrotoxicity. The majority of patients with AKI will suffer from more than one during their development and/or progression of AKI. Moreover, the development of one usually leads to the instigation of another. Thus, the interactions and progression between these mechanisms may determine the severity and duration of the AKI. Other factors such as organ crosstalk and how our concurrent therapies interact with these mechanisms complicate the pathophysiology of the progression of the AKI even further. In this narrative review article, we describe these three main pathophysiological processes that lead to the development and progression of AKI. © 2022 American Physiological Society. Compr Physiol 12: 1-14, 2022.

Fluid accumulation and major adverse kidney events in sepsis: a multicenter observational study

Background

Whether early fluid accumulation is a risk factor for adverse renal outcomes in septic intensive care unit (ICU) patients remains uncertain. We assessed the association between cumulative fluid balance and major adverse kidney events within 30 days (MAKE30), a composite of death, dialysis, or sustained renal dysfunction, in such patients.

Methods

We performed a multicenter, retrospective observational study in 1834 septic patients admitted to five ICUs in three hospitals in Stockholm, Sweden. We used logistic regression analysis to assess the association between cumulative fluid balance during the first two days in ICU and subsequent risk of MAKE30, adjusted for demographic factors, comorbidities, baseline creatinine, illness severity variables, haemodynamic characteristics, chloride exposure and nephrotoxic drug exposure. We assessed the strength of significant exposure variables using a relative importance analysis.

Results

Overall, 519 (28.3%) patients developed MAKE30. Median (IQR) cumulative fluid balance was 5.3 (2.8–8.1) l in the MAKE30 group and 4.1 (1.9–6.8) l in the no MAKE30 group, with non-resuscitation fluids contributing to approximately half of total fluid input in each group. The adjusted odds ratio for MAKE30 was 1.05 (95% CI 1.02–1.09) per litre cumulative fluid balance. On relative importance analysis, the strongest factors regarding MAKE30 were, in decreasing order, baseline creatinine, cumulative fluid balance, and age. In the secondary outcome analysis, the adjusted odds ratio for dialysis or sustained renal dysfunction was 1.06 (95% CI 1.01–1.11) per litre cumulative fluid balance. On separate sensitivity analyses, lower urine output and early acute kidney injury, respectively, were independently associated with MAKE30, whereas higher fluid input was not.

Conclusions

In ICU patients with sepsis, a higher cumulative fluid balance after 2 days in ICU was associated with subsequent development of major adverse kidney events within 30 days, including death, renal replacement requirement, or persistent renal dysfunction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01040-6.

The Intensivist's Perspective of Shock, Volume Management, and Hemodynamic Monitoring

One of the primary reasons for intensive care admission is shock. Identifying the underlying cause of shock (hypovolemic, distributive, cardiogenic, and obstructive) may lead to entirely different clinical pathways for management. Among patients with hypovolemic and distributive shock, fluid therapy is one of the leading management strategies. Although an appropriate amount of fluid administration might save a patient's life, inadequate (or excessive) fluid use could lead to more complications, including organ failure and mortality due to either hypovolemia or volume overload. Currently, intensivists have access to a wide variety of information sources and tools to monitor the underlying hemodynamic status, including medical history, physical examination, and specific hemodynamic monitoring devices. Although appropriate and timely assessment and interpretation of this information can promote adequate fluid resuscitation, misinterpretation of these data can also lead to additional mortality and morbidity. This article provides a narrative review of the most commonly used hemodynamic monitoring approaches to assessing fluid responsiveness and fluid tolerance. In addition, we describe the benefits and disadvantages of these tools.

Utility of bedside ultrasound derived hepatic and renal parenchymal flow patterns to guide management of acute kidney injury

PURPOSE OF REVIEW

Ideal fluid management of critically ill patients is maintaining an adequate perfusion pressure but avoiding venous congestion. Venous excess ultrasound score (VExUS) quantifies venous congestion to guide the management of fluid balance.

RECENT FINDINGS

VExUS of abdominal veins measures fluid tolerance and helps clinicians avoid congestion. VExUS scoring predicts the development of acute kidney injury (AKI) that is a common hospital problem resulting in higher mortality and morbidity. VExUS can predict patients at risk of developing AKI post cardiac surgery. VExUS has been associated with an increase in adverse outcomes in a general intensive care population. Hepatic vein ultrasound can manifest as a sequela of right heart failure and pulmonary hypertension. Intrarenal congestion suggests poorer prognosis in heart failure patients. VExUS score has been used in decision-making to remove fluid in patients with cardiorenal syndrome. VExUS scoring may help curtail overly aggressive fluid resuscitation for patients with septic shock and help avoid iatrogenic 'salt water drowning'.

SUMMARY

We summarize the technique and clinical practice of VExUS to help guide fluid balance across different populations of critically ill patients.

Renal negative pressure treatment as a novel therapy for heart failure-induced renal dysfunction

Congestion is the primary pathophysiological lesion in most heart failure (HF) hospitalizations. Renal congestion increases renal tubular pressure, reducing glomerular filtration rate (GFR) and diuresis. Because each nephron is a fluid-filled column, renal negative pressure therapy (rNPT) applied to the urinary collecting system should reduce tubular pressure, potentially improving kidney function. We evaluated the renal response to rNPT in congestive HF. Ten anesthetized ∼80-kg pigs underwent instrumentation with bilateral renal pelvic JuxtaFlow catheters. GFR was determined by iothalamate clearance (mGFR) and renal plasma flow (RPF) by para-aminohippurate clearance. Each animal served as its own control with randomization of left versus right kidney to -30 mmHg rNPT or no rNPT. mGFR and RPF were measured simultaneously from the rNPT and no rNPT kidney. Congestive HF was induced via cardiac tamponade maintaining central venous pressure at 20-22.5 mmHg throughout the experiment. Before HF induction, rNPT increased natriuresis, diuresis, and mGFR compared with the control kidney (P < 0.001 for all). Natriuresis, diuresis, and mGFR decreased following HF (P < 0.001 for all) but were higher in rNPT kidney versus control (P < 0.001 for all). RPF decreased during HF (P < 0.001) without significant differences between rNPT treatments. During HF, the rNPT kidney had similar diuresis and natriuresis (P > 0.5 for both) and higher fractional excretion of sodium (P = 0.001) compared with the non-rNPT kidney in the no HF period. In conclusion, rNPT resulted in significantly increased diuresis, natriuresis, and mGFR, with or without experimental HF. rNPT improved key renal parameters of the congested cardiorenal phenotype.

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.

Use of Ultrasound to Assess Hemodynamics in Acutely Ill Patients

Early diagnosis of AKI and preventive measures can likely decrease the severity of the injury and improve patient outcomes. Current hemodynamic monitoring variables, including BP, heart and respiratory rates, temperature, and oxygenation status, have been used to identify patients at high risk for AKI. Despite the widespread use of such variables, their ability to accurately and timely detect patients who are high risk has been questioned. Therefore, there is a critical need to develop and validate tools that can measure new and more kidney-specific hemodynamic and laboratory variables, potentially assisting with AKI risk stratification, implementing appropriate and timely preventive measures, and hopefully improved outcomes. The new ultrasonography techniques provide novel insights into kidney hemodynamics and potential management and/or therapeutic targets. Contrast-enhanced ultrasonography; Doppler flow patterns of hepatic veins, portal vein, and intrakidney veins; and ultrasound elastography are among approaches that may provide such information, particularly related to vascular changes in AKI, venous volume excess or congestion, and fluid tolerance. This review summarizes the current state of these techniques and their relevance to kidney hemodynamic management.

Fluid balance management during continuous renal replacement therapy

In critically ill patients, particularly in the setting of shock and sepsis volume management frequently results in a fluid overloaded state, requiring diuresis or intervention with renal replacement therapy. Achieving appropriate volume management requires knowledge of the underlying cardiovascular pathophysiology and careful evaluation of intravascular and extravascular volume status. In the presence of a failing kidney, fluid removal is often a challenge. Continuous renal replacement therapy (CRRT) techniques offer a significant advantage over intermittent dialysis for fluid control, however, any form of RRT in the critically ill patient requires careful attention to prescription and monitoring to avoid complications. In order to utilize these therapies for their maximum potential it is necessary to understand which factors influence fluid balance and have an understanding of the principles and kinetics of fluid removal with extra-corporeal techniques.

VEXUS-The Third Eye for the Intensivist?

How to cite this article: Gupta S, Tomar DS. VEXUS-The Third Eye for the Intensivist? Indian J Crit Care Med 2020;24(9):746-747.

Quantifying systemic congestion with Point-Of-Care ultrasound: development of the venous excess ultrasound grading system

Background

Organ congestion is a mediator of adverse outcomes in critically ill patients. Point-Of-Care ultrasound (POCUS) is widely available and could enable clinicians to detect signs of venous congestion at the bedside. The aim of this study was to develop several grading system prototypes using POCUS and to determine their respective ability to predict acute kidney injury (AKI) after cardiac surgery. This is a post-hoc analysis of a single-center prospective study in 145 patients undergoing cardiac surgery for which repeated daily measurements of hepatic, portal, intra-renal vein Doppler and inferior vena cava (IVC) ultrasound were performed during the first 72 h after surgery. Five prototypes of venous excess ultrasound (VExUS) grading system combining multiple ultrasound markers were developed.

Results

The association between each score and AKI was assessed using time-dependant Cox models as well as conventional performance measures of diagnostic testing. A total of 706 ultrasound assessments were analyzed. We found that defining severe venous congestion as the presence of severe flow abnormalities in multiple Doppler patterns with a dilated IVC (≥ 2 cm) showed the strongest association with the development of subsequent AKI compared with other combinations (HR: 3.69 CI 1.65–8.24 p = 0.001). The association remained significant after adjustment for baseline risk of AKI and vasopressor/inotropic support (HR: 2.82 CI 1.21–6.55 p = 0.02). Furthermore, this severe VExUS grade offered a useful positive likelihood ratio (+LR: 6.37 CI 2.19–18.50) when detected at ICU admission, which outperformed central venous pressure measurements.

Conclusions

The combination of multiple POCUS markers may identify clinically significant venous congestion.

Reinterpreting Renal Hemodynamics: The Importance of Venous Congestion and Effective Organ Perfusion in Acute Kidney Injury

The significance of effective renal perfusion is relatively underemphasized in the current literature. From a renal standpoint, besides optimizing cardiac output, renal perfusion should be maximized as well. Among the several additional variables of the critically ill, such as intra-abdominal pressure, the presence of venous congestion and elevated central venous pressures, airway pressures generated by mechanical ventilation do affect net renal perfusion. These forces represent both a potential danger and an ongoing opportunity to improve renal outcomes in the critically ill and an opportunity to move beyond the simplified viewpoint of optimizing volume status. Therefore, to optimize nephron-protective therapies, nephrologists and intensive care physicians should be familiar with the concept of net renal perfusion pressure. This review appraises the background literature on renal perfusion pressure, including the initial animal data and historical human studies up to the most current developments in the field, exploring potential avenues to assess and improve renal blood supply.

Intraoperative renal resistive index threshold as an acute kidney injury biomarker

STUDY OBJECTIVE

The lag in creatinine-mediated diagnosis of cardiac surgery-associated acute kidney injury (AKI) may be impeding the development of renoprotection therapies. Postoperative renal resistive index (RRI) measured by transabdominal Doppler ultrasound is a promising early AKI biomarker. RRI measured intraoperatively by transesophageal echocardiography (TEE) is available even earlier but is less evaluated. Therefore, we conducted an assessment of intraoperative RRI as an AKI biomarker using previously reported post-renal insult thresholds.

DESIGN

Retrospective convenience sample.

SETTING

Intraoperative.

PATIENTS

180 adult cardiac surgical patients between July 2013 and July 2014.

INTERVENTION

None.

MEASUREMENTS

Pre- and post-cardiopulmonary bypass (CPB) RRI thresholds, measured using intraoperative TEE, exceeding 0.74 or 0.79 were used to evaluate for an association with KDIGO AKI risk using the Chi-square test. Other consensus AKI criteria (AKIN, RIFLE) were similarly evaluated. Additional t-test analyses examined the relationship of pre- and pre-to-post (delta) CPB RRI with AKI.

MAIN RESULTS

Post-CPB RRI for 99 patients included 36 and 23 with values exceeding 0.74 and 0.79, respectively. Analyses confirmed associations of both RRI thresholds with all consensus AKI definitions (0.74; KDIGO: p = 0.05, AKIN: p = 0.03, RIFLE: p = 0.03, 0.79; KDIGO: p = 0.002, AKIN: p = 0.001, RIFLE: p = 0.004). In contrast, pre-CPB and pre-to post-CPB RRI were not associated with AKI.

CONCLUSIONS

RRI obtained intraoperatively in cardiac surgery patients, assessed using previously reported thresholds, is highly associated with AKI and warrants further evaluation as a promising "earliest" AKI biomarker. These significant findings suggest that RRI assessment should be included in the standard intraoperative TEE exam.

Fluid balance after continuous renal replacement therapy initiation and outcome in paediatric multiple organ failure

BACKGROUND

Patients with multiple organ failure (MOF) often receive large amounts of resuscitation fluid, making them at high risk of fluid overload (FO). Our main objective was to investigate if the ability to achieve a negative fluid balance during the first 3 continuous renal replacement therapy (CRRT) days was associated with mortality in children with MOF.

METHODS

Retrospective cohort study in a tertiary multidisciplinary academic paediatric hospital. The study included 63 patients (age 0-18 years) with 3 or more failing organs receiving CRRT due to acute kidney injury and/or fluid overload.

RESULTS

The median age was 4 months, and PICU mortality was 29%. Survivors had significantly lower degree of FO at CRRT initiation, (median 15% (Interquartile range 9-22)) than non-survivors (24% (17%-37%), P = 0.002). On PICU admission, PIM-3 score was significantly higher in non-survivors (P = 0.01), but at CRRT initiation there was no difference in PELOD-2 score (P = 0.98). Mortality in patients achieving a cumulative net negative fluid balance during the first 3 days after CRRT initiation was 12%, compared to 86% in those not achieving this (P < 0.0001). In multivariate analysis, the inability to achieve a net negative fluid balance during 3 days after CRRT initiation (P < 0.0001) and FO >20% at CRRT initiation (P = 0.0019) remained associated with mortality.

CONCLUSION

Our results suggest that early fluid removal is associated with improved patient outcome in critically ill children receiving CRRT, and that prompt measures should be taken to prevent fluid overload in critical illness. These results need to be verified in further, prospective studies.

Renal Decapsulation Prevents Intrinsic Renal Compartment Syndrome in Ischemia-Reperfusion-Induced Acute Kidney Injury: A Physiologic Approach

OBJECTIVES

Acute kidney injury is a serious complication with unacceptably high mortality that lacks of specific curative treatment. Therapies focusing on the hydraulic behavior have shown promising results in preventing structural and functional renal impairment, but the underlying mechanisms remain understudied. Our goal is to assess the effects of renal decapsulation on regional hemodynamics, oxygenation, and perfusion in an ischemic acute kidney injury experimental model.

METHODS

In piglets, intra renal pressure, renal tissue oxygen pressure, and dysoxia markers were measured in an ischemia-reperfusion group with intact kidney, an ischemia-reperfusion group where the kidney capsule was removed, and in a sham group.

RESULTS

Decapsulated kidneys displayed an effective reduction of intra renal pressure, an increment of renal tissue oxygen pressure, and a better performance in the regional delivery, consumption, and extraction of oxygen after reperfusion, resulting in a marked attenuation of acute kidney injury progression due to reduced structural damage and improved renal function.

CONCLUSIONS

Our results strongly suggest that renal decapsulation prevents the onset of an intrinsic renal compartment syndrome after ischemic acute kidney injury.

Does fluid management affect the occurrence of acute kidney injury?

PURPOSE OF REVIEW

To describe the potential impact of different fluid management strategies on renal outcomes in critically ill and postoperative patients.

RECENT FINDINGS

Uncritical fluid administration may induce renal compartment syndrome and renal venous congestion, which contribute to kidney dysfunction. In more than 5000 randomized surgical or septic patients, goal-directed therapy did not reduce fluid accumulation, acute kidney injury (AKI) development or need for renal replacement therapy. In contrast to synthetic colloids, which increase the risk of AKI, albumin solutions and balanced crystalloids appear well tolerated from a renal standpoint in medical and surgical patients requiring intensive care. However, any clinical benefits compared with 0.9% sodium chloride have not yet been demonstrated.

SUMMARY

Although synthetic colloids should be avoided in patients with or at risk of AKI, the renal efficacy of using albumin solutions and/or balanced crystalloids as alternatives to 0.9% sodium chloride in high-risk patients is yet to be confirmed or refuted. Improved goal-directed protocols, which minimize unnecessary fluid administration and reduce potentially harmful effects of fluid overload, need to be developed and tested.

Acute kidney injury in trauma patients

PURPOSE OF REVIEW

To review epidemiology and pathophysiology of acute kidney injury (AKI) in trauma patients and propose strategies that aim at preventing AKI after trauma.

RECENT FINDINGS

AKI in trauma patients has been reported to be as frequent as 50% with an association to a prolonged length of stay and a raise in mortality. Among the specific risk factors encountered in trauma patients, hemorrhagic shock, rhabdomyolysis severity, age, and comorbidities are independently associated with AKI occurrence. Resuscitation with balanced solutes seems to have beneficial effects on renal outcome compared with NaCl 0.9%, particularly in the context of rhabdomyolysis. However, randomized clinical studies are needed to confirm this signal. Abdominal compartment syndrome (ACS) is rare but has to be diagnosed to initiate a dedicated therapy.

SUMMARY

The high incidence of AKI in trauma patients should lead to early identification of those at risk of AKI to establish a resuscitation strategy that aims at preventing AKI.

Sepsis-induced acute kidney injury

PURPOSE OF REVIEW

Sepsis is a common and frequently fatal condition in which mortality has been consistently linked to increasing organ dysfunction. For example, acute kidney injury (AKI) occurs in 40-50% of septic patients and increases mortality six to eight-fold. However, the mechanisms by which sepsis causes organ dysfunction are not well understood and hence current therapy remains reactive and nonspecific.

RECENT FINDINGS

Recent studies have challenged the previous notion that organ dysfunction is solely secondary to hypoperfusion, by showing, for example, that AKI occurs in the setting of normal or increased renal blood flow; and that it is characterized not by acute tubular necrosis or apoptosis, but rather by heterogeneous areas of colocalized sluggish peritubular blood flow and tubular epithelial cell oxidative stress. Evidence has also shown that microvascular dysfunction, inflammation, and the metabolic response to inflammatory injury are fundamental pathophysiologic mechanisms that may explain the development of sepsis-induced AKI.

SUMMARY

The implications of these findings are significant because in the context of decades of negative clinical trials in the field, the recognition that other mechanisms are at play opens the possibility to better understand the processes of injury and repair, and provides an invaluable opportunity to design mechanism-targeted therapeutic interventions.

Intraoperative Renal Resistive Index as an Acute Kidney Injury Biomarker: Development and Validation of an Automated Analysis Algorithm

OBJECTIVE

Intraoperative Doppler-determined renal resistive index (RRI) is a promising early acute kidney injury (AKI) biomarker. As RRI continues to be studied, its clinical usefulness and robustness in research settings will be linked to the ease, efficiency, and precision with which it can be interpreted. Therefore, the authors assessed the usefulness of computer vision technology as an approach to developing an automated RRI-estimating algorithm with equivalent reliability and reproducibility to human experts.

DESIGN

Retrospective.

SETTING

Single-center, university hospital.

PARTICIPANTS

Adult cardiac surgery patients from 7/1/2013 to 7/10/2014 with intraoperative transesophageal echocardiography-determined renal blood flow measurements.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Renal Doppler waveforms were obtained retrospectively and assessed by blinded human expert raters. Images (430) were divided evenly into development and validation cohorts. An algorithm for automated RRI analysis was built using computer vision techniques and tuned for alignment with experts using bootstrap resampling in the development cohort. This algorithm then was applied to the validation cohort for an unbiased assessment of agreement with human experts. Waveform analysis time per image averaged 0.144 seconds. Agreement was excellent by intraclass correlation coefficient (0.939; 95% confidence interval [CI] 0.921 to 0.953) and in Bland-Altman analysis (mean difference [human-algorithm] -0.0015; 95% CI -0.0054 to 0.0024), without evidence of systematic bias.

CONCLUSION

The authors confirmed the value of computer vision technology to develop an algorithm for RRI estimation from automatically processed intraoperative renal Doppler waveforms. This simple-to-use and efficient tool further adds to the clinical and research value of RRI, already the "earliest" among several early AKI biomarkers being assessed.

The Association of Aortic Valve Pathology With Renal Resistive Index as a Kidney Injury Biomarker

BACKGROUND

Acute kidney injury (AKI) is a common serious complication after cardiac surgery. Doppler-determined renal resistive index (RRI) is a promising early AKI biomarker in this population. However, the relationship between aortic valve pathology (insufficiency and/or stenosis) and RRI is unknown. This study aimed to investigate RRI variability related to aortic valve pathology.

METHODS

In a retrospective review of cardiac surgery patients, RRI and aortic valve pathology were assessed prior to cardiopulmonary bypass using transesophageal echocardiography. Aortic valve status was categorized into four subgroups: normal (insufficiency and stenosis, none/trace/mild), insufficiency (insufficiency, moderate/severe; stenosis, none/trace/mild), combined insufficiency/stenosis (insufficiency and stenosis, moderate/severe), or stenosis (insufficiency, none/trace/mild; stenosis, moderate/severe). RRI and time-matched hemodynamic and Doppler measurements were compared among subgroups.

RESULTS

Of 175 patients, 60 had aortic valve pathology (16 insufficiency, 18 insufficiency/stenosis, 26 stenosis). Compared with the normal subgroup, patients with aortic insufficiency had lower diastolic blood pressure and trough renal Doppler velocities, and higher RRI (0.77 versus 0.69; p < 0.001); patients with combined insufficiency/stenosis also had higher RRI (0.72 versus 0.69, p = 0.042).

CONCLUSIONS

Patients with aortic insufficiency and combined insufficiency/stenosis had higher median RRI values compared with normal patients. For these individuals, diastolic flow differences related to aortic insufficiency may explain why their presurgery RRI values often exceeded postoperative thresholds typically associated with AKI. Strategies to account for the potentially confounding effects of aortic insufficiency on renal flow patterns, independent of renal injury, may add to the value of RRI as an early AKI biomarker.

Does Fluid Type and Amount Affect Kidney Function in Critical Illness?

Acute kidney injury (AKI) is common, although commonly used clinical diagnostic markers are imperfect. Intravenous fluid administration remains a cornerstone of therapy worldwide, but there is minimal evidence of efficacy for the use of fluid bolus therapy outside of specific circumstances, and emerging evidence associates fluid accumulation with worse renal outcomes and even increased mortality among critically ill patients. Artificial colloid solutions have been associated with harm, and chloride-rich solutions may adversely affect renal function. Large trials to provide guidance regarding the optimal fluid choices to prevent or ameliorate AKI, and promote renal recovery, are urgently required.

Tissue Edema, Fluid Balance, and Patient Outcomes in Severe Sepsis: An Organ Systems Review

Severe sepsis and septic shock remain among the deadliest diseases managed in the intensive care unit. Fluid resuscitation has been a mainstay of early treatment, but the deleterious effects of excessive fluid administration leading to tissue edema are becoming clearer. A positive fluid balance at 72 hours is associated with significantly increased mortality, yet ongoing fluid administration beyond a durable increase in cardiac output is common. We review the pathophysiologic and clinical data showing the negative effects of edema on pulmonary, renal, central nervous, hepatic, and cardiovascular systems. We discuss data showing increased morbidity and mortality following nonjudicious fluid administration and challenge the assumption that patients who are fluid responsive are also likely to benefit from that fluid. The distinctions between fluid requirement, responsiveness, and tolerance are central to newer concepts of resuscitation. We summarize data in each organ system showing a predictable increase in morbidity and mortality with nonbeneficial fluid administration, providing a better framework for precision in volume management of the patient with severe sepsis.

Forced fluid removal versus usual care in intensive care patients with high-risk acute kidney injury and severe fluid overload (FFAKI): study protocol for a randomised controlled pilot trial

Background

Intravenous administration of fluids is an essential part of critical care. While some fluid administration is likely beneficial, there is increasing observational evidence that the development of fluid overload is associated with increased mortality. There are no randomised trials to confirm this association in patients with acute kidney injury. We aim to perform a pilot trial to test the feasibility of forced fluid removal compared to standard care in patients with acute kidney injury and severe fluid overload, the FFAKI trial.

Methods

Then FFAKI trial is a pilot, multicentre, randomised clinical trial recruiting adult intensive care patients with acute kidney injury and fluid overload, defined as more than 10% of ideal bodyweight. Patients are randomised with concealed allocation to either standard care or forced fluid removal with a therapeutic target of negative net fluid balance ≥1 mL/kg/h. The safety of fluid removal is continually evaluated according to predefined criteria of hypoperfusion: lactate ≥4 mmol/L, mean arterial pressure <50 mmHg or mottling beyond the edge of the kneecaps. If patients fulfil one of these criteria, fluid removal is suspended until hypoperfusion has resolved. The primary outcome measure is fluid balance at 5 days after randomisation and secondary outcomes include mean daily fluid balance, fluid balance at discharge from the intensive care unit, time to neutral fluid balance, number of serious adverse reactions and number of protocol violations. All patients are followed for 90 days.

Discussion

The FFAKI trial started in October 2015 and, when completed, will provide data to evaluate whether a large trial of forced fluid removal in critically ill patients is feasible. Our primary outcome will show if the experimental intervention leads to a clinically relevant difference in fluid balance, which could prove beneficial in intensive care patients with acute kidney injury.

Trial registration

EudraCT, identifier: 2015-001701-13. Registered on 19 September 2015;

ClinicalTrials.gov, identifier: NCT02458157. Registered on 21 May 2015;

Danish Ethics Committee, identifier: H-15009589H. Registered on 22 September 2015; Danish Health and Medicines Authority, identifier: 2015070013. Registered on 11 August 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1935-2) contains supplementary material, which is available to authorized users.

Are all fluids bad for the kidney?

PURPOSE OF REVIEW

To describe the harmful effects of intravenous fluids on kidney structure and function and summarize recent comparisons between different fluids and their effect on kidney outcome.

RECENT FINDINGS

Administration of intravenous fluids may contribute to the development and sustention of acute kidney injury. In excess, fluids cause kidney interstitial edema and venous congestion, which prevents renal blood flow and glomerular filtration rate. In contrast to balanced crystalloids, chloride-rich solutions impair renal blood flow via autoregulatory mechanisms. Synthetic colloids, such as hydroxyethyl starches, gelatins, and dextrans are potentially nephrotoxic because they can cause osmotic nephrosis, which, in susceptible patients, might precede permanent kidney damage. Albumin solutions appear well tolerated to use in septic patients, although their renal efficacy over balanced crystalloids is not established. In contrast, administration of albumin solutions to patients with decompensated liver failure effectively prevents and ameliorates hepatorenal syndrome.

SUMMARY

Being nephrotoxic, synthetic colloids should be avoided in patients with reduced renal reserve, such as in critically ill patients and in patients with preexisting renal dysfunction. Suggested adverse effects with chloride-rich solutions need confirmation from ongoing trials. Albumin solutions are well tolerated in patients with sepsis and/or liver failure and improve outcomes in the latter.

Sepsis-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a serious yet potentially reversible complication of sepsis. Several molecular mechanisms involved in the development of septic AKI have been identified. These mechanisms may be important targets in the development of future therapies. This review highlights the role of the innate immune response to sepsis and its downstream effects on kidney structure and function with special reference to the adaptive cellular response and glomerular hemodynamic changes. In addition, current evidence surrounding the management of patients with septic AKI is summarized. Finally, potential novel therapies for septic AKI are presented.

Fluid and electrolyte overload in critically ill patients: An overview

Fluids are considered the cornerstone of therapy for many shock states, particularly states that are associated with relative or absolute hypovolemia. Fluids are also commonly used for many other purposes, such as renal protection from endogenous and exogenous substances, for the safe dilution of medications and as “maintenance” fluids. However, a large amount of evidence from the last decade has shown that fluids can have deleterious effects on several organ functions, both from excessive amounts of fluids and from their non-physiological electrolyte composition. Additionally, fluid prescription is more common in patients with systemic inflammatory response syndrome whose kidneys may have impaired mechanisms of electrolyte and free water excretion. These processes have been studied as separate entities (hypernatremia, hyperchloremic acidosis and progressive fluid accumulation) leading to worse outcomes in many clinical scenarios, including but not limited to acute kidney injury, worsening respiratory function, higher mortality and higher hospital and intensive care unit length-of-stays. In this review, we synthesize this evidence and describe this phenomenon as fluid and electrolyte overload with potentially deleterious effects. Finally, we propose a strategy to safely use fluids and thereafter wean patients from fluids, along with other caveats to be considered when dealing with fluids in the intensive care unit.