Understanding urine output in critically ill patients

Prognostic Biomarkers and AKI: Potential to Enhance the Identification of Post-Operative Patients at Risk of Loss of Renal Function

Acute kidney injury (AKI) is a common complication after surgery and the more complex the surgery, the greater the risk. During surgery, patients are exposed to a combination of factors all of which are associated with the development of AKI. These include hypotension and hypovolaemia, sepsis, systemic inflammation, the use of nephrotoxic agents, tissue injury, the infusion of blood or blood products, ischaemia, oxidative stress and reperfusion injury. Given the risks of AKI, it would seem logical to conclude that early identification of patients at risk of AKI would translate into benefit. The conventional markers of AKI, namely serum creatinine and urine output are the mainstay of defining chronic kidney disease but are less suited to the acute phase. Such concerns are compounded in surgical patients given they often have significantly reduced mobility, suboptimal levels of nutrition and reduced muscle bulk. Many patients may also have misleadingly low serum creatinine and high urine output due to aggressive fluid resuscitation, particularly in intensive care units. Over the last two decades, considerable information has accrued with regard to the performance of what was termed "novel" biomarkers of AKI, and here, we discuss the most examined molecules and performance in surgical settings. We also discuss the application of biomarkers to guide patients' postoperative care.

Acute kidney injury in patients with burns

Burn injury is associated with a high risk of acute kidney injury (AKI) with a prevalence of AKI among patients with burns of 9-50%. Despite an improvement in burn injury survival in the past decade, AKI in patients with burns is associated with an extremely poor short-term and long-term prognosis, with a mortality of >80% among those with severe AKI. Factors that contribute to the development of AKI in patients with burns include haemodynamic alterations, burn-induced systemic inflammation and apoptosis, haemolysis, rhabdomyolysis, smoke inhalation injury, drug nephrotoxicity and sepsis. Early and late AKI after burn injury differ in their aetiologies and outcomes. Sepsis is the main driver of late AKI in patients with burns and late AKI has been associated with higher mortality than early AKI. Prevention of early AKI involves correction of hypovolaemia and avoidance of nephrotoxic drugs (for example, hydroxocobalamin), whereas prevention of late AKI involves prevention and early recognition of sepsis as well as avoidance of nephrotoxins. Treatment of AKI in patients with burns remains supportive, including prevention of fluid overload, treatment of electrolyte disturbance and use of kidney replacement therapy when indicated.

Early Sepsis-Associated Acute Kidney Injury and Obesity

Importance

The prevalence of obesity is increasing in the intensive care unit (ICU). Although obesity is a known risk factor for chronic kidney disease, its association with early sepsis-associated acute kidney injury (SA-AKI) and their combined association with patient outcomes warrant further investigation.

Objective

To explore the association between obesity, early SA-AKI incidence, and clinical outcomes in patients with sepsis.

Design, Setting, and Participants

This nationwide, prospective cohort study analyzed patients aged 19 years or older who had sepsis and were admitted to 20 tertiary hospital ICUs in Korea between September 1, 2019, and December 31, 2021. Patients with preexisting stage 3A to 5 chronic kidney disease and those with missing body mass index (BMI) values were excluded.

Exposures

Sepsis and hospitalization in the ICU.

Main Outcomes and Measures

The primary outcome was SA-AKI incidence within 48 hours of ICU admission, and secondary outcomes were mortality and clinical recovery (survival to discharge within 30 days). Patients were categorized by BMI (calculated as weight in kilograms divided by height in meters squared), and data were analyzed by logistic regression adjusted for key characteristics and clinical factors. Multivariable fractional polynomial regression models and restricted cubic spline models were used to analyze the clinical outcomes with BMI as a continuous variable.

Results

Of the 4041 patients (median age, 73 years [IQR, 63-81 years]; 2349 [58.1%] male) included in the study, 1367 (33.8%) developed early SA-AKI. Obesity was associated with a higher incidence of SA-AKI compared with normal weight (adjusted odds ratio [AOR], 1.40; 95% CI, 1.15-1.70), as was every increase in BMI of 10 (OR, 1.75; 95% CI, 1.47-2.08). While obesity was associated with lower in-hospital mortality in patients without SA-AKI compared with their counterparts without obesity (ie, underweight, normal weight, overweight) (AOR, 0.72; 95% CI, 0.54-0.94), no difference in mortality was observed in those with SA-AKI (AOR, 0.85; 95% CI, 0.65-1.12). Although patients with obesity without SA-AKI had a greater likelihood of clinical recovery than their counterparts without obesity, clinical recovery was less likely among those with both obesity and SA-AKI.

Conclusions and Relevance

In this cohort study of patients with sepsis, obesity was associated with a higher risk of early SA-AKI and the presence of SA-AKI modified the association of obesity with clinical outcomes.

The addition of Cytosorb in patients on VA-ECMO improves urinary output and ICU survival

INTRODUCTION

The aim of this study was to analyze the efficiency of CytoSorb adsorber in patients presenting with cardiogenic shock and treated with venoarterial extracorporeal membrane oxygenation (VA-ECMO).

METHODS

Sixteen patients put on VA ECMO due to cardiogenic shock were included, stratified according to the use of Cytosorb adsorber in the first 24 h and compared across different clinical outcomes.

RESULTS

Significantly lower vasopressor doses were required among patients treated with Cytosorb at the initiation and before weaning from ECMO. Furthermore, these patients showed significantly higher urine output before weaning and lower lactate levels during the extracorporeal support. Finally, the mortality rate was lower among the Cytosorb therapy group (22.2% vs 57.1%).

CONCLUSION

While a decrease in vasopressor doses was already associated with CytoSorb use, this is the first study showing an increase in urinary output and a trend towards better survival among patients on VA ECMO treated with CytoSorb.

Meaning and Management of Perioperative Oliguria

Perioperative oliguria is an alarm signal. The initial assessment includes closer patient monitoring, evaluation of volemic status, risk-benefit of fluid challenge or furosemide stress test, and investigation of possible perioperative complications.

Kidney Increase Natriuresis but Not Glomerular Filtration Under Veno-venous ECMO, a Retrospective Study

PURPOSE

Acute kidney injury is a frequent complication of acute respiratory distress syndrome (ARDS). We aim to study the evolution of kidney function in patients presenting severe ARDS and requiring veno-venous extracorporeal membrane oxygenation (VV ECMO).

METHODS

We conducted a multicenter retrospective study, including adult patients requiring VV ECMO for ARDS. The primary outcome was the evolution of the serum creatinine level after VV ECMO initiation. Secondary outcomes were change in urine output, and urine biochemical parameters after VV ECMO initiation.

RESULTS

One hundred and two patients were included. VV ECMO was initiated after a median of 6 days of mechanical ventilation, mainly for ARDS caused by COVID-19 (73%). Serum creatinine level did not significantly differ after VV ECMO initiation (P = .20). VV ECMO was associated with a significant increase in daily urine output (+6.6 mL/kg/day, [3.8;9.3] P < .001), even after adjustment for potential confounding factors; with an increase in natriuresis. The increase in urine output under VV ECMO was associated with a reduced risk of receiving kidney replacement therapy (OR 0.4 [0.2;0.8], P = .026).

CONCLUSIONS

VV ECMO initiation in severe ARDS is associated with an increase in daily urine output and natriuresis, without change in glomerular filtration rate.

Design, Synthesis, Evaluation, and Molecular Docking Study of Ascorbic Acid Dual-Coated Omeprazole Pellets and the Antioxidative Effect of Ascorbic Acid on Omeprazole-Induced Renal Injury in an Animal Model

The present study was carried out to investigate the antioxidant effect of ascorbic acid on omeprazole (O.P.)-induced acute kidney infection (AKI). Design of experiment (DoE) was employed to fabricate formulations (P1-P8) by the extrusion spheronization technique, and they were evaluated using various analytical techniques. P1-P8 formulations have % drug loading ranging from 56.34 ± 1.10 to 98.67 ± 1.05%, encapsulation efficiency from 70.98 ± 0.96 to 98.67 ± 1.05%, percentage drug release varying from 36.56 ± 1.34 to 93.45 ± 1.45%, Hausner's ratio ranging from 1.026 ± 0.05 to 1.065 ± 0.02%, and Carr's index varying from 2.3 ± 0.07 to 6.1 ± 0.06 g/mL. The optimized formulation (P6) was dual-coated with Eudragit L-100 (5% w/v) and ascorbic acid (2% w/v). A smooth uniform morphology was found after coating, and particle size nonsignificantly changed from 85.31 ± 77.43 to 101.99 ± 65.56 μm. IR spectra showed omeprazole characteristic peaks confirming drug loading, and peaks at 1747.40 and 1611.51 cm-1 confirmed ascorbic acid and Eudragit L-100 coating. X-ray diffraction (XRD) analysis confirmed the crystalline nature, and thermal degradation studies until 500 °C demonstrated increased stability after coating. Cytotoxicity analysis with 97% cell viability revealed the nontoxic behavior of pellets. In vitro dissolution studies of coated pellets showed <20% drug release at pH 1.2 and 99.54% at pH 6.8. Animal studies showed that pure omeprazole showed a nonsignificant decrease in weight, urine output, and fecal output compared to rodents on ascorbic acid pellets. Increased uric acid and creatinine levels in the group on pure omeprazole indicated AKI. Histopathological studies of renal cells also supported these results. The integration of experimental pellet formulation with molecular docking simulations has unveiled the potential of ascorbic acid and omeprazole as highly promising therapeutic agents for addressing oxidative stress and inflammation.

Urine output for predicting in-hospital mortality of intensive care patients with cardiogenic shock

Background

The role of urine output (UO) in the first 24 h of admission in the clinical management of cardiogenic shock (CS) patients has not been elucidated.

Methods

This study retrospectively analyzed intensive care CS patients in the MIMIC-IV database. Binomial logistic regression analysis was conducted to evaluate whether UO was an independent risk factor for in-hospital mortality in CS patients. The performance of UO in predicting mortality was evaluated by the receiver operating characteristic (ROC) curve and compared with the Oxford Acute Severity of Illness Score (OASIS). The clinical net benefit of UO in predicting mortality was determined using the decision curve analysis (DCA). Survival analysis was performed with Kaplan-Meier curves.

Results

After adjusting for confounding factors including diuretic use and acute kidney injury (AKI), UO remained an independent risk factor for in-hospital mortality in CS patients. The areas under the ROC curves (AUCs) of UO for predicting in-hospital mortality were 0.712 (UO, ml/day) and 0.701 (UO, ml/kg/h), which were comparable to OASIS (AUC = 0.695). In terms of clinical net benefit, UO was comparable to OASIS, with different degrees of benefit at different threshold probabilities. Survival analysis showed that the risk of in-hospital death in the low-UO (≤857 ml/day) group was 3.0143 times that of the high-UO (>857 ml/day) group.

Conclusions

UO in the first 24 h of admission is an independent risk factor for in-hospital mortality in intensive care CS patients and has moderate predictive value in predicting in-hospital mortality.

Does Arterial Blood Gas (ABG) Provide a Safety Net for Extubation in Surgical Patients?

Background Extubation has always been a critical aspect of anaesthesia. Guidelines and recommendations are in place for achieving successful extubation, but the risk of failure always persists. Through this study, we assess whether arterial blood gas (ABG) values taken intraoperatively help predict extubation success in the operation theatre. Materials and methods This was a prospective observational study for one year of extubated patients whose blood gas values were not within the normal range. The patients of age 18 years and above undergoing high-risk elective and emergency surgeries where at least one intraoperative arterial blood sample was taken for blood gas analysis were included. Apart from parameters of ABG demographic data, urgency and duration of surgery, blood loss, urine output, use of intraoperative fluid(s), and blood product(s) were also observed.  Results Of 578 patients enrolled, 116 patients were extubated based on the predefined extubation criteria. Of these, 24 patients were reintubated within 24 hours. ABG parameters such as partial pressure of arterial oxygen (PaO₂) and serum HCO_3- levels were significantly lower in the reintubated patients compared to non-reintubated patients (p-values of 0.045 and 0.003, respectively). Conclusion This study showed that the PaO₂ <100 mm Hg or ratio of arterial oxygen partial pressure to fractional inspired oxygen (P/F ratio) of less than 200 and an HCO_3- value of less than 18 are plausible ABG parameters to decide extubation in post-surgery patients in OT. PaCO₂, base deficit, and lactate were less reliable parameters for planning extubation.

ISCCM Guidelines for Hemodynamic Monitoring in the Critically Ill

Hemodynamic assessment along with continuous monitoring and appropriate therapy forms an integral part of management of critically ill patients with acute circulatory failure. In India, the infrastructure in ICUs varies from very basic facilities in smaller towns and semi-urban areas, to world-class, cutting-edge technology in corporate hospitals, in metropolitan cities. Surveys and studies from India suggest a wide variation in clinical practices due to possible lack of awareness, expertise, high costs, and lack of availability of advanced hemodynamic monitoring devices. We, therefore, on behalf of the Indian Society of Critical Care Medicine (ISCCM), formulated these evidence-based guidelines for optimal use of various hemodynamic monitoring modalities keeping in mind the resource-limited settings and the specific needs of our patients. When enough evidence was not forthcoming, we have made recommendations after achieving consensus amongst members. Careful integration of clinical assessment and critical information obtained from laboratory data and monitoring devices should help in improving outcomes of our patients.

How to cite this article

Kulkarni AP, Govil D, Samavedam S, Srinivasan S, Ramasubban S, Venkataraman R, et al. ISCCM Guidelines for Hemodynamic Monitoring in the Critically Ill. Indian J Crit Care Med 2022;26(S2):S66-S76.

Urine biochemistry assessment in the sequential evaluation of renal function: Time to think outside the box

Urine biochemistry (UB) remains a controversial tool in acute kidney injury (AKI) monitoring, being considered to be of limited value both in terms of AKI diagnosis and prognosis. However, many criticisms can be made to the studies that have established the so called “pre-renal paradigm” (used for decades as the essential physiological basis for UB assessment in AKI) as well as to more recent studies suggesting that UB has no utility in daily clinical practice. The aim of this article is to describe our hypothesis on how to interpret simple and widely recognized urine biochemical parameters from a novel perspective, propose the rationale for their sequential assessment and demonstrate their usefulness in AKI monitoring, especially in the critical care setting.

Survival and recovery modeling of acute kidney injury in critically ill adults

Objectives:

Acute kidney injury is common among the critically ill. However, the incidence, medication use, and outcomes of acute kidney injury have been variably described. We conducted a single-center, retrospective cohort study to examine the risk factors and correlates associated with acute kidney injury in critically ill adults with a particular focus on medication class usage.

Methods:

We reviewed the electronic medical records of all adult patients admitted to an intensive care unit between 1 February and 30 August 2020. Acute kidney injury was defined by the 2012 Kidney Disease: Improving Global Outcomes guidelines. Data included were demographics, comorbidities, symptoms, laboratory parameters, interventions, and outcomes. The primary outcome was acute kidney injury incidence. A Least Absolute Shrinkage and Selection Operator regression model was used to determine risk factors associated with acute kidney injury. Secondary outcomes including acute kidney injury recovery and intensive care unit mortality were analyzed using a Cox regression model.

Results:

Among 226 admitted patients, 108 (47.8%) experienced acute kidney injury. 37 (34.3%), 39 (36.1%), and 32 patients (29.6%) were classified as acute kidney injury stages I–III, respectively. Among the recovery and mortality cohorts, analgesics/sedatives, anti-infectives, and intravenous fluids were significant (p-value < 0.05). The medication classes IV-fluid electrolytes nutrition (96.7%), gastrointestinal (90.2%), and anti-infectives (81.5%) were associated with an increased odds of developing acute kidney injury, odd ratios: 1.27, 1.71, and 1.70, respectively. Cox regression analyses revealed a significantly increased time-varying mortality risk for acute kidney injury-stage III, hazard ratio: 4.72 (95% confidence interval: 1–22.33). In the recovery cohort, time to acute kidney injury recovery was significantly faster in stage I, hazard ratio: 9.14 (95% confidence interval: 2.14–39.06) cohort when compared to the stage III cohort.

Conclusion:

Evaluation of vital signs, laboratory, and medication use data may be useful to determine acute kidney injury risk stratification. The influence of particular medication classes further impacts the risk of developing acute kidney injury, necessitating the importance of examining pharmacotherapeutic regimens for early recognition of renal impairment and prevention.

Comparison of Piperacillin and Tazobactam Pharmacokinetics in Critically Ill Patients with Trauma or with Burn

Critical illness caused by burn and sepsis is associated with pathophysiologic changes that may result in the alteration of pharmacokinetics (PK) of antibiotics. However, it is unclear if one mechanism of critical illness alters PK more significantly than another. We developed a population PK model for piperacillin and tazobactam (pip-tazo) using data from 19 critically ill patients (14 non-burn trauma and 5 burn) treated in the Military Health System. A two-compartment model best described pip-tazo data. There were no significant differences found in the volume of distribution or clearance of pip-tazo in burn and non-burn patients. Although exploratory in nature, our data suggest that after accounting for creatinine clearance (CrCl), doses would not need to be increased for burn patients compared to trauma patients on consideration of PK alone. However, there is a high reported incidence of augmented renal clearance (ARC) in burn patients and pharmacodynamic (PD) considerations may lead clinicians to choose higher doses. For critically ill patients with normal kidney function, continuous infusions of 13.5-18 g pip-tazo per day are preferable. If ARC is suspected or the most stringent PD targets are desired, then continuous infusions of 31.5 g pip-tazo or higher may be required. This approach may be reasonable provided that therapeutic drug monitoring is enacted to ensure pip-tazo levels are not supra-therapeutic.

Molecular Mechanisms and Biomarkers Associated with Chemotherapy-Induced AKI

Acute kidney injury (AKI) is a life-threatening condition characterized by a rapid and transient decrease in kidney function. AKI is part of an array of conditions collectively defined as acute kidney diseases (AKD). In AKD, persistent kidney damage and dysfunction lead to chronic kidney disease (CKD) over time. A variety of insults can trigger AKI; however, chemotherapy-associated nephrotoxicity is increasingly recognized as a significant side effect of chemotherapy. New biomarkers are urgently needed to identify patients at high risk of developing chemotherapy-associated nephrotoxicity and subsequent AKI. However, a lack of understanding of cellular mechanisms that trigger chemotherapy-related nephrotoxicity has hindered the identification of effective biomarkers to date. In this review, we aim to (1) describe the known and potential mechanisms related to chemotherapy-induced AKI; (2) summarize the available biomarkers for early AKI detection, and (3) raise awareness of chemotherapy-induced AKI.

A Retrospective Cohort Study Comparing Outcomes of Pediatric Intensive Care Patients after Changing from Higher to Permissive Blood Pressure Targets

New neurological morbidity post pediatric intensive care (PIC) poses substantial problems, with a need to understand the relationship of outcome to blood pressure (BP) targets. The aim of the study is to see whether a change from a higher BP targeted strategy to a permissive one improved outcomes for development of new neurological morbidity, length of stay (LOS), and PIC-acquired infection. A retrospective cohort analysis was undertaken, comparing outcomes before and after the change. The higher BP cohort targets were set using standardized age-based centiles. In the permissive cohort, lower BPs were allowed, dependent on physiological variables. Targeted treatment continued throughout the critical illness. New neurological morbidity was defined as any deterioration from baseline, attributable to the admission, measured by post discharge clinical and records review over a minimum period of 4 years. Results were analyzed with IBM SPSS Statistics v26. Of 123 admissions in the permissive and 214 admissions in the higher BP target cohorts, 88 (72%) and 188 (88%) survived without new neurological morbidity (permissive vs. higher cohort OR 0.348 [95% CI 0.197–0.613] p <0.001). Median LOS was 2 (interquartile [IQ] range 2–5) and 3 (IQ range 2–6) days for the permissive and higher cohorts, respectively (p = 0.127). Three (2.4%) and 7 (3.3%) admissions in the permissive and higher BP cohorts respectively suffered PIC-acquired infection (p = 0.666). A higher BP targeted strategy was associated with protection from new neurological morbidity as compared with a permissive strategy, supporting the need for prospective studies into BP targets.

Effects of ulinastatin on renal perfusion evaluated by Doppler ultrasonography in a porcine model of septic shock

The present study aimed to evaluate the effect of ulinastatin (UTI) on renal perfusion using Doppler ultrasonography in a porcine model of septic shock induced by smoking inhalation and live methicillin-resistant Staphylococcus aureus instillation. A total of 32 healthy Landrace pigs were randomly assigned into the following four groups: Sham group (SH; n=5), septic shock group (SS; n=9), septic shock treated with vancomycin (15 mg/kg) group (VAN; n=9) and septic shock treated with UTI (50,000 U/kg) + vancomycin (UTI; n=9) group. Renal perfusion was evaluated by contrast-enhanced ultrasound (CEUS) at baseline and at the end of the protocol (24 h). The spectrum of interlobar or arcuate artery was selected to calculate the corrected resistive index (cRI). Sulphur hexafluoride microbubbles were bolus injected via a venous catheter. The peak intensity (Pi) and area under curve (AUC) were calculated using a time-intensity curve. Compared with the baseline group, cRI was increased significantly at the end of the protocol, except for that in the SH group, whereas Pi decreased significantly after injury in all experimental groups but was higher in the UTI group compared with that in the SS and VAN groups (both P<0.001). Linear correlation was found between the cardiac output (CO) and Pi (R²=0.752; P<0.001). The AUC was significantly decreased after injury in the SS and VAN groups compared with the baseline group. All parameters detected by CEUS were improved in the UTI group, and significant differences were found between the UTI and SS or VAN group (all P<0.05). In conclusion, acute renal injury, which occasionally occurs during septic shock, is accompanied with a significantly lower perfusion rate in the renal microcirculation. By contrast, UTI can significantly improve renal perfusion, which can be reliably evaluated using CEUS.

Acute kidney injury detection using refined and physiological-feature augmented urine output

Acute kidney injury (AKI) is common in the intensive care unit, where it is associated with increased mortality. AKI is often defined using creatinine and urine output criteria. The creatinine-based definition is more reliable but less expedient, whereas the urine output based definition is rapid but less reliable. Our goal is to examine the urine output criterion and augment it with physiological features for better agreement with creatinine-based definitions of AKI. The objectives are threefold: (1) to characterize the baseline agreement of urine output and creatinine definitions of AKI; (2) to refine the urine output criteria to identify the thresholds that best agree with the creatinine-based definition; and (3) to build generalized estimating equation (GEE) and generalized linear mixed-effects (GLME) models with static and time-varying features to improve the accuracy of a near-real-time marker for AKI. We performed a retrospective observational study using data from two independent critical care databases, MIMIC-III and eICU, for critically ill patients who developed AKI in intensive care units. We found that the conventional urine output criterion (6 hr, 0.5 ml/kg/h) has specificity and sensitivity of 0.49 and 0.54 for MIMIC-III database; and specificity and sensitivity of 0.38 and 0.56 for eICU. Secondly, urine output thresholds of 12 hours and 0.6 ml/kg/h have specificity and sensitivity of 0.58 and 0.48 for MIMIC-III; and urine output thresholds of 10 hours and 0.6 ml/kg/h have specificity and sensitivity of 0.49 and 0.48 for eICU. Thirdly, the GEE model of four hours duration augmented with static and time-varying features can achieve a specificity and sensitivity of 0.66 and 0.61 for MIMIC-III; and specificity and sensitivity of 0.66 and 0.64 for eICU. The GLME model of four hours duration augmented with static and time-varying features can achieve a specificity and sensitivity of 0.71 and 0.55 for MIMIC-III; and specificity and sensitivity of 0.66 and 0.60 for eICU. The GEE model has greater performance than the GLME model, however, the GLME model is more reflective of the variables as fixed effects or random effects. The significant improvement in performance, relative to current definitions, when augmenting with patient features, suggest the need of incorporating these features when detecting disease onset and modeling at window-level rather than patient-level.

How to monitor cardiovascular function in critical illness in resource-limited settings

PURPOSE OF REVIEW

Hemodynamic monitoring is an essential component in the care for critically ill patients. A range of tools are available and new approaches have been developed. This review summarizes their availability, affordability and feasibility for hospital settings in resource-limited settings.

RECENT FINDINGS

Evidence for the performance of specific hemodynamic monitoring tools or strategies in low-income and middle-income countries (LMICs) is limited. Repeated physical examination and basic observations remain a cornerstone for patient monitoring and have a high sensitivity for detecting organ hypoperfusion, but with a low specificity. Additional feasible approaches for hemodynamic monitoring in LMICs include: for tissue perfusion monitoring: urine output, skin mottling score, capillary refill time, skin temperature gradients, and blood lactate measurements; for cardiovascular monitoring: echocardiography and noninvasive or minimally invasive cardiac output measurements; and for fluid status monitoring: inferior vena cava distensibility index, mini-fluid challenge test, passive leg raising test, end-expiratory occlusion test and lung ultrasound. Tools with currently limited applicability in LMICs include microcirculatory monitoring devices and pulmonary artery catheterization, because of costs and limited added value. Especially ultrasound is a promising and affordable monitoring device for LMICs, and is increasingly available.

SUMMARY

A set of basic tools and approaches is available for adequate hemodynamic monitoring in resource-limited settings. Future research should focus on the development and trialing of robust and context-appropriate monitoring technologies.

Creatinine Assessment in Non-Steady-State Conditions: A Critical Review

OBJECTIVES

To discuss methods for the assessment of creatinine clearance (Cl_cr) when serum creatinine (SCr) is not at steady state in order to estimate kidney function and apply the estimate to kidney function staging for clinical assessment or drug dosing.

DATA SOURCES

A PubMed search was conducted from 1976 to mid-January 2021 with other articles identified through review of bibliographies of retrieved articles and citations in Scopus.

STUDY SELECTION AND DATA EXTRACTION

Articles assessing Cl_cr under non-steady-state conditions and studies evaluating predictive equations were selected.

DATA SYNTHESIS

When SCr is systematically changing (ie, trending up or down), kinetic methods to estimate Cl_cr are appropriate. Estimates from kinetic methods should be individual based and not indexed to body surface area, and careful monitoring is required to confirm predictions as the situation evolves. Standard methods intended for steady-state conditions should not be used to estimate Cl_cr in patients with unstable SCr.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Creatinine continues to be a monitoring parameter of choice and is an important variable in all the commonly used equations for estimating Cl_cr and most important for estimating glomerular filtration rate. However, standard methods of estimating Cl_cr for medication dosing are not accurate under non-steady-state conditions.

CONCLUSION

The methods for kinetic clearance estimation and standards methods for clearance estimation, such as the Cockcroft-Gault equation, are mutually exclusive. There are no benefits of using the kinetic method in patients with stable SCr concentrations, and standard equations are not appropriate with unstable SCr concentrations.

Hemodynamically stable oliguric patients usually do not respond to fluid challenge

Objective

To evaluate renal responsiveness in oliguric critically ill patients after a fluid challenge.

Methods

We conducted a prospective observational study in one university intensive care unit. Patients with urine output < 0.5mL/kg/h for 3 hours with a mean arterial pressure > 60mmHg received a fluid challenge. We examined renal fluid responsiveness (defined as urine output > 0.5mL/kg/h for 3 hours) after fluid challenge.

Results

Forty-two patients (age 67 ± 13 years; APACHE II score 16 ± 6) were evaluated. Patient characteristics were similar between renal responders and renal nonresponders. Thirteen patients (31%) were renal responders. Hemodynamic or perfusion parameters were not different between those who did and those who did not increase urine output before the fluid challenge. The areas under the receiver operating characteristic curves were calculated for mean arterial pressure, heart rate, creatinine, urea, creatinine clearance, urea/creatinine ratio and lactate before the fluid challenge. None of these parameters were sensitive or specific enough to predict reversal of oliguria.

Conclusion

After achieving hemodynamic stability, oliguric patients did not increase urine output after a fluid challenge. Systemic hemodynamic, perfusion or renal parameters were weak predictors of urine responsiveness. Our results suggest that volume replacement to correct oliguria in patients without obvious hypovolemia should be done with caution.

Direct Measurement of Creatinine Clearance over a Short Interval in Intensive Care Settings

Background

The definition of acute kidney injury (AKI), based on serum creatinine and urine output, bears significant limitations in intensive care units (ICUs). Serum creatinine has significant lag-time as it needs to be accumulated and stabilized at a new level whereas urine output is affected by diuresis, antidiuresis, and antinatriuresis. Direct measurement of creatinine clearance (CrCl_direct = urine creatinine × urine flow rate/serum creatinine) over a short interval (3-6 hours) was explored to identify patients with AKI.

Materials and methods

We reanalyzed a previous published dataset. We included 11 patients who had serial daily urine collections over 0 to 3 days of stay in ICU and baseline (day -1) serum creatinine levels.

Result

The ratio of CrCl_direct on day 0 to baseline creatinine clearance predicted the progression of AKI over the subsequent 1 to 3 days of ICU stay [area under receiver operating characteristic curve = 0.933 and 95% confidence interval (CI) = 0.780-1.000].

Discussion

CrCl_direct over a short interval may be an alternative marker of kidney function. Future studies may explore its use to identify patients with AKI who may benefit from early renal replacement therapy.

How to cite this article

Law LSC, Lo EAG, Yeoh SF. Direct Measurement of Creatinine Clearance over a Short Interval in Intensive Care Settings. Indian J Crit Care Med 2021;25(7):800-802.

Positive fluid balance as an early biomarker for acute kidney injury: a prospective study in critically ill adult patients

OBJECTIVES

Positive fluid balance is frequent in critically ill patients and has been considered a potential biomarker for acute kidney injury (AKI). This study aimed to evaluate positive fluid balance as a biomarker for the early detection of AKI in critically ill patients.

METHODS

This was a prospective cohort study. The sample was composed of patients ≥18 years old who stayed ≥3 days in an intensive care unit. Fluid balance, urinary output and serum creatinine were assessed daily. AKI was diagnosed by the Kidney Disease Improving Global Outcome criteria.

RESULTS

The final cohort was composed of 233 patients. AKI occurred in 92 patients (40%) after a median of 3 (2-6) days following ICU admission. When fluid balance was assessed as a continuous variable, a 100-ml increase in fluid balance was independently associated with a 4% increase in the odds of AKI (OR 1.04; 95% CI 1.01-1.08). Positive fluid balance categorized using different thresholds was always significantly associated with subsequent detection of AKI. The mixed effects model showed that increased fluid balance preceded AKI by 4 to 6 days.

CONCLUSION

These results suggest that a positive fluid balance might be an early biomarker for AKI development in critically ill patients.

Immunopathophysiology of trauma-related acute kidney injury

Physical trauma can affect any individual and is globally accountable for more than one in every ten deaths. Although direct severe kidney trauma is relatively infrequent, extrarenal tissue trauma frequently results in the development of acute kidney injury (AKI). Various causes, including haemorrhagic shock, rhabdomyolysis, use of nephrotoxic drugs and infectious complications, can trigger and exacerbate trauma-related AKI (TRAKI), particularly in the presence of pre-existing or trauma-specific risk factors. Injured, hypoxic and ischaemic tissues expose the organism to damage-associated and pathogen-associated molecular patterns, and oxidative stress, all of which initiate a complex immunopathophysiological response that results in macrocirculatory and microcirculatory disturbances in the kidney, and functional impairment. The simultaneous activation of components of innate immunity, including leukocytes, coagulation factors and complement proteins, drives kidney inflammation, glomerular and tubular damage, and breakdown of the blood-urine barrier. This immune response is also an integral part of the intense post-trauma crosstalk between the kidneys, the nervous system and other organs, which aggravates multi-organ dysfunction. Necessary lifesaving procedures used in trauma management might have ambivalent effects as they stabilize injured tissue and organs while simultaneously exacerbating kidney injury. Consequently, only a small number of pathophysiological and immunomodulatory therapeutic targets for TRAKI prevention have been proposed and evaluated.

Regional perfusion monitoring in shock

PURPOSE OF REVIEW

Despite restoration of adequate systemic blood flow in patients with shock, single organs may remain hypoperfused. In this review, we summarize the results of a literature research on methods to monitor single organ perfusion in shock. We focused on methods to measure heart, brain, kidney, and/or visceral organ perfusion. Furthermore, only methods that can be used in real-time and at the bedside were included.

RECENT FINDINGS

We identified studies on physical examination techniques, electrocardiography, echocardiography, contrast-enhanced ultrasound, near-infrared spectroscopy, and Doppler sonography to assess single organ perfusion.

SUMMARY

Physical examination techniques have a reasonable negative predictive value to exclude single organ hypoperfusion but are nonspecific to detect it. Technical methods to indirectly measure myocardial perfusion include ECG and echocardiography. Contrast-enhanced ultrasound can quantify myocardial perfusion but has so far only been used to detect regional myocardial hypoperfusion. Near-infrared spectroscopy and transcranial Doppler sonography can be used to assess cerebral perfusion and determine autoregulation thresholds of the brain. Both Doppler and contrast-enhanced ultrasound techniques are novel methods to evaluate renal and visceral organ perfusion. A key limitation of most techniques is the inability to determine adequacy of organ blood flow to meet the organs' metabolic demands.

Early Recognition of Burn- and Trauma-Related Acute Kidney Injury: A Pilot Comparison of Machine Learning Techniques

Severely burned and non-burned trauma patients are at risk for acute kidney injury (AKI). The study objective was to assess the theoretical performance of artificial intelligence (AI)/machine learning (ML) algorithms to augment AKI recognition using the novel biomarker, neutrophil gelatinase associated lipocalin (NGAL), combined with contemporary biomarkers such as N-terminal pro B-type natriuretic peptide (NT-proBNP), urine output (UOP), and plasma creatinine. Machine learning approaches including logistic regression (LR), k-nearest neighbor (k-NN), support vector machine (SVM), random forest (RF), and deep neural networks (DNN) were used in this study. The AI/ML algorithm helped predict AKI 61.8 (32.5) hours faster than the Kidney Disease and Improving Global Disease Outcomes (KDIGO) criteria for burn and non-burned trauma patients. NGAL was analytically superior to traditional AKI biomarkers such as creatinine and UOP. With ML, the AKI predictive capability of NGAL was further enhanced when combined with NT-proBNP or creatinine. The use of AI/ML could be employed with NGAL to accelerate detection of AKI in at-risk burn and non-burned trauma patients.

Fluid intake-related association between urine output and mortality in acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS), a complex response to various insults, has a high mortality rate. As pulmonary edema resulting from increased vascular permeability is a hallmark of ARDS, management of the fluid status, including the urine output (UO) and fluid intake (FI), is essential. However, the relationships between UO, FI, and mortality in ARDS remain unclear. This retrospective study aimed to investigate the interactive associations among UO, FI, and mortality in ARDS.

Methods

This was a secondary analysis of a prospective randomized controlled trial performed at 10 centers within the ARDS Network of the National Heart, Lung, and Blood Institute research network. The total UO and FI volumes within the 24-h period preceding the trial, the UO to FI ratio (UO/FI), demographic data, biochemical measurements, and other variables from 835 patients with ARDS, 539 survivors, and 296 non-survivors, were analyzed. The associations among UO, FI, the UO/FI, and mortality were assessed using a multivariable logistic regression.

Results

In all 835 patients, an increased UO was significantly associated with decreased mortality when used as a continuous variable (odds ratio [OR]: 0.98, 95% confidence interval [CI]: 0.98–0.99, P = 0.002) and as a quartile variable (OR of Q2 to Q4: 0.69–0.46, with Q1 as reference). To explore the interaction between UO and FI, the UO/FI was calculated, and a cut-off value of 0.5 was detected for the association with mortality. For patients with a UO/FI ≤0.5, an increased UO/FI was significantly associated with decreased mortality (OR: 0.09, 95% CI: 0.03–0.253, P <  0.001); this association was not significant for patients with UO/FI ratios > 0.5 (OR: 1.04, 95% CI: 0.96–1.14, P = 0.281). A significant interaction was observed between UO and the UO/FI. The association between UO and mortality was significant in the subgroup with a UO/FI ≤0.5 (OR: 0.97, 95% CI: 0.96–0.99, P = 0.006), but not in the subgroup with a UO/FI > 0.5.

Conclusions

The association between UO and mortality was mediated by the UO/FI status, as only patients with low UO/FI ratios benefitted from a higher UO.

How can CO2-derived indices guide resuscitation in critically ill patients?

Assessing the adequacy of oxygen delivery with oxygen requirements is one of the key-goal of haemodynamic resuscitation. Clinical examination, lactate and central or mixed venous oxygen saturation (S_vO₂ and S_cvO₂, respectively) all have their limitations. Many of them may be overcome by the use of the carbon dioxide (CO₂)-derived variables. The venoarterial difference in CO₂ tension ("ΔPCO₂" or "PCO₂ gap") is not an indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether blood flow is sufficient to carry CO₂ from the peripheral tissue to the lungs in view of its clearance: it, thus, reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO₂ gap with the arteriovenous difference of oxygen content (PCO₂ gap/C_a-vO₂) might be a marker of anaerobiosis. Conversely to S_vO₂ and S_cvO₂, it remains interpretable if the oxygen extraction is impaired as it is in case of sepsis. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue hypoxia.

Artificial intelligence and machine learning for predicting acute kidney injury in severely burned patients: A proof of concept

BACKGROUND

Burn critical care represents a high impact population that may benefit from artificial intelligence and machine learning (ML). Acute kidney injury (AKI) recognition in burn patients could be enhanced by ML. The goal of this study was to determine the theoretical performance of ML in augmenting AKI recognition.

METHODS

We developed ML models using the k-nearest neighbor (k-NN) algorithm. The ML models were trained-tested with clinical laboratory data for 50 adult burn patients that had neutrophil gelatinase associated lipocalin (NGAL), urine output (UOP), creatinine, and N-terminal B-type natriuretic peptide (NT-proBNP) measured within the first 24 h of admission.

RESULTS

Half of patients (50%) in the dataset experienced AKI within the first week following admission. ML models containing NGAL, creatinine, UOP, and NT-proBNP achieved 90-100% accuracy for identifying AKI. ML models containing only NT-proBNP and creatinine achieved 80-90% accuracy. Mean time-to-AKI recognition using UOP and/or creatinine alone was achieved within 42.7 ± 23.2 h post-admission vs. within 18.8 ± 8.1 h via the ML-algorithm.

CONCLUSIONS

The performance of UOP and creatinine for predicting AKI could be enhanced by with a ML algorithm using a k-NN approach when NGAL is not available. Additional studies are needed to verify performance of ML for burn-related AKI.

Acute kidney injury management using intermittent low efficiency haemodiafiltration in a critical care unit: 39 dogs (2012-2015)

BACKGROUND

Veterinary studies describing acute kidney injury (AKI) management using renal replacement therapy (RRT) are limited and have primarily focused on intermittent haemodialysis in North American populations. European data are lacking, although differences in populations, pathogen and toxin exposure and RRT modalities may exist between Europe and North America. The present study reviewed RRT-managed cases from the intensive care unit (ICU) of VetAgro Sup, Lyon, France, for the period 2012-2015. The aims were to describe a 4-h RRT protocol of intermittent low efficiency haemodiafiltration, population characteristics and outcomes in canine AKI cases requiring RRT and to identify prognostic variables. We defined DeltaCreat/h as the difference between the serum creatinine level after RRT treatment N and that before treatment N + 1 divided by the time between treatments (in hours).

RESULTS

Thirty-nine dogs were included, and 67% were males. The median (range) age, weight, hospitalization length and number of RRT treatments were 4.4 (0.25-15) years, 26.6 (6.7-69) kg, 8 (1-23) days and 3 (1-8) treatments, respectively. The main AKI causes were leptospirosis (74.4%) and nephrotoxins (15.4%). Age (4.0 vs 5.4 years; P = 0.04), admission urine output (0.5 mL/kg/h vs 0 mL/kg/h; P = 0.02) and hospitalization length (10 vs 4 days; P < 0.001) differed between survivors and non-survivors. Hospitalization length [odds ratio (OR) = 0.4], number of treatments (OR = 5.1), serum potassium level on day 2 (OR = 1.9), DeltaCreat/h between the first and second treatments (OR = 1.2), and UOP during hospitalization (OR = 0.2) were correlated with outcome. The main causes of death were euthanasia (44%) and haemorrhagic diatheses (33%). The overall survival rate was 54%, with 55% of survivors discharged with a median creatinine < 240 µmol/L.

CONCLUSIONS

This is the first description in the veterinary literature of a 4-h protocol of intermittent low efficiency haemodiafiltration to provide RRT in a veterinary critical care unit. While this protocol appears promising, the clinical application of this protocol requires further investigation. Among parameters associated with survival, UOP and DeltaCreat/h between the first and second RRT treatments may be prognostic indicators. The applicability of these parameters to other populations is unknown, and further international, multicentre prospective studies are warranted to confirm these preliminary observations.

The Role of Point-of-Care Ultrasound Monitoring in Cardiac Surgical Patients With Acute Kidney Injury

The approach to the patient with acute kidney injury (AKI) after cardiac surgery involves multiple aspects. These include the rapid recognition of reversible causes, the accurate identification of patients who will progress to severe stages of AKI, and the subsequent management of complications resulting from severe renal dysfunction. Unfortunately, the inherent limitations of physical examination and laboratory parameter results are often responsible for suboptimal clinical management. In this review article, the authors explore how point-of-care ultrasound, including renal and extrarenal ultrasound, can be used to complement all aspects of the care of cardiac surgery patients with AKI, from the initial approach of early AKI to fluid balance management during renal replacement therapy. The current evidence is reviewed, including knowledge gaps and future areas of research.

Proenkephalin A 119-159 (Penkid) Is an Early Biomarker of Septic Acute Kidney Injury: The Kidney in Sepsis and Septic Shock (Kid-SSS) Study

Introduction

Sepsis is the leading cause of acute kidney injury (AKI) in critically ill patients. The Kidney in Sepsis and Septic Shock (Kid-SSS) study evaluated the value of proenkephalin A 119-159 (penkid)-a sensitive biomarker of glomerular function, drawn within 24 hours upon intensive care unit (ICU) admission and analyzed using a chemiluminescence immunoassay-for kidney events in sepsis and septic shock.

Methods

The Kid-SSS study was a substudy of Adrenomedullin and Outcome in Severe Sepsis and Septic Shock (AdrenOSS) (NCT02393781), a prospective, observational, multinational study including 583 patients admitted to the intensive care unit with sepsis or septic shock and a validation cohort of 525 patients from the French and euRopean Outcome reGistry in Intensive Care Units (FROG-ICU) study. The primary endpoint was major adverse kidney events (MAKEs) at day 7, composite of death, renal replacement therapy, and persistent renal dysfunction. The secondary endpoints included AKI, transient AKI, worsening renal function (WRF), and 28-day mortality.

Results

Median age was 66 years (interquartile range 55-75), and 28-day mortality was 22% (95% confidence interval [CI] 19%-25%). Of the patients, 293 (50.3%) were in shock upon ICU admission. Penkid was significantly elevated in patients with MAKEs, persistent AKI, and WRF (median = 65 [IQR = 45-106] vs. 179 [114-242]; 53 [39-70] vs. 133 [79-196] pmol/l; and 70 [47-121] vs. 174 [93-242] pmol/l, all P < 0.0001), also after adjustment for confounding factors (adjusted odds ratio = 3.3 [95% CI = 1.8-6.0], 3.9 [95% CI = 2.1-7.2], and 3.4 [95% CI = 1.9-6.2], all P < 0.0001). Penkid increase preceded elevation of serum creatinine with WRF and was low in renal recovery.

Conclusion

Admission penkid concentration was associated with MAKEs, AKI, and WRF in a timely manner in septic patients.

Efficacy of bladder irrigation in preventing urinary tract infections associated with short-term catheterization in comatose patients: A randomized controlled clinical trial

BACKGROUND

Bladder irrigation can be performed to prevent catheter-associated urinary tract infections (CAUTI), but its efficacy has been not reported in short-term indwelling urinary catheterization. This clinical trial aimed to examine the efficacy of bladder irrigation with normal saline solution in preventing CAUTI in comatose patients admitted to intensive care units.

MATERIALS AND METHODS

Eligible patients were randomized to the experimental group or control group. The experimental group received daily bladder irrigation with 450 cc sterile normal saline, in 3 150-mL doses, for 3 consecutive days. Data on signs of CAUTI, including urine culture, axillary body temperature (primary outcomes), and other urine and blood parameters (secondary outcomes) were obtained at baseline and 5 days later.

RESULTS

Results of group comparisons and logistic regression analysis that controlled for fluid intake showed that the risk of CAUTI decreased by 99% in the experimental group compared with the control group (odds ratio, 0.01; P < .001). Additional findings indicated a decrease in axillary body temperature and improvements in urine appearance, urinary red cells and white cells, and erythrocyte sedimentation rates and white-cell counts in the blood following bladder irrigation.

CONCLUSION

Daily bladder irrigation with normal saline during 3 days demonstrated efficacy in preventing CAUTI in comatose patients.

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.

The Role of Oliguria and the Absence of Fluid Administration and Balance Information in Illness Severity Scores

Urinary examination has formed part of patient assessment since the earliest days of medicine. Current definitions of oliguria are essentially arbitrary, but duration and intensity of oliguria have been associated with an increased risk of mortality, and this risk is not completely attributable to the development of concomitant acute kidney injury (AKI) as defined by changes in serum creatinine concentration. The increased risk of death associated with the development of AKI itself may be modified by directly or indirectly by progressive fluid accumulation, due to reduced elimination and increased fluid administration. None of the currently extant major illness severity scoring systems or outcome prediction models use modern definitions of AKI or oliguria, or any values representative of fluid volumes variables. Even if a direct relationship with mortality is not observed, then it is possible that fluid balance or fluid volume variables mediate the relationship between illness severity and mortality in the renal and respiratory physiological domains. Fluid administration and fluid balance may then be an important, easily modifiable therapeutic target for future investigation. These relationships require exploration in large datasets before being prospectively validated in groups of critically ill patients from differing jurisdictions to improve prognostication and mortality prediction.

Value of Kidney Disease Improving Global Outcomes Urine Output Criteria in Critically Ill Patients: A Secondary Analysis of a Multicenter Prospective Cohort Study

BACKGROUND

Urine output (UO) is an essential criterion of the Kidney Disease Improving Global Outcomes (KDIGO) definition and classification system for acute kidney injury (AKI), of which the diagnostic value has not been extensively studied. We aimed to determine whether AKI based on KDIGO UO criteria (KDIGOUO) could improve the diagnostic and prognostic accuracy, compared with KDIGO serum creatinine criteria (KDIGOSCr).

METHODS

We conducted a secondary analysis of the database of a previous study conducted by China Critical Care Clinical Trial Group (CCCCTG), which was a 2-month prospective cohort study (July 1, 2009 to August 31, 2009) involving 3063 patients in 22 tertiary Intensive Care Units in Mainland of China. AKI was diagnosed and classified separately based on KDIGOUOand KDIGOSCr. Hospital mortality of patients with more severe AKI classification based on KDIGOUOwas compared with other patients by univariate and multivariate regression analyses.

RESULTS

The prevalence of AKI increased from 52.4% based on KDIGOSCrto 55.4% based on KDIGOSCrcombined with KDIGOUO. KDIGOUOalso resulted in an upgrade of AKI classification in 7.3% of patients, representing those with more severe AKI classification based on KDIGOUO. Compared with non-AKI patients or those with maximum AKI classification by KDIGOSCr, those with maximum AKI classification by KDIGOUOhad a significantly higher hospital mortality of 58.4% (odds ratio [OR]: 7.580, 95% confidence interval [CI]: 4.141-13.873, P< 0.001). In a multivariate logistic regression analysis, AKI based on KDIGOUO (OR: 2.891, 95% CI: 1.964-4.254, P< 0.001), but not based on KDIGOSCr (OR: 1.322, 95% CI: 0.902-1.939, P = 0.152), was an independent risk factor for hospital mortality.

CONCLUSION

UO was a criterion with additional value beyond creatinine criterion for AKI diagnosis and classification, which can help identify a group of patients with high risk of death.

In situ lactate dehydrogenase activity: a novel renal cortical imaging biomarker of tubular injury?

Renal ischemia-reperfusion injury is the state of which a tissue experiences injury after a phase of restrictive blood supply and recirculation. Ischemia-reperfusion injury (I/R-I) is a leading cause of acute kidney injury (AKI) in several disease states, including kidney transplantation, sepsis, and hypovolemic shock. The most common methods to evaluate AKI are creatinine clearance, plasma creatinine, blood urea nitrogen, or renal histology. However, currently, there are no precise methods to directly assess renal injury state noninvasively. Hyperpolarized 13C-pyruvate MRI enables noninvasive accurate quantification of the in vivo conversion of pyruvate to lactate, alanine, and bicarbonate. In the present study, we investigated the in situ alterations of metabolic conversion of pyruvate to lactate, alanine, and bicarbonate in a unilateral I/R-I rat model with 30 min and 60 min of ischemia followed by 24 h of reperfusion. The pyruvate conversion was unaltered compared with sham in the 30 min I/R-I group, while a significant reduced metabolic conversion was found in the postischemic kidney after 60 min of ischemia. This indicates that after 30 min of ischemia, the kidney maintains normal metabolic function in spite of decreased kidney function, whereas the postischemic kidney after 60 min of ischemia show a generally reduced metabolic enzyme activity concomitant with a reduced kidney function. We have confidence that these findings can have a high prognostic value in prediction of kidney injury and the outcome of renal injury.

Intravenous Fluids in AKI: A Mechanistically Guided Approach

Acute kidney injury (AKI) has been associated with an increased risk of death and morbidity in many clinical scenarios. The prevention and treatment of AKI therefore has been advocated as a high-priority research focus. However, nearly all strategies tested in this setting have failed to prevent or cure AKI and fluid loading remains a cornerstone of preventive and curative treatment of AKI. Concerns have been raised, however, regarding both the efficacy and safety of fluid loading to prevent or reverse AKI. In this review, we address the question of the best use of fluid loading based on current preclinical and clinical data in a mechanistically guided approach. Impacts of fluid resuscitation on renal hemodynamics, from macrocirculation to microcirculation, with physiological end points as well as renal consequences of different fluids available are discussed. Finally, the complex relationship between renal hemodynamics is discussed.

Acute Kidney Injury: Diagnostic Approaches and Controversies

Acute kidney injury (AKI) is a significant independent risk factor for morbidity and mortality. In the last ten years a large number of publications have highlighted the limitations of traditional approaches and the inadequacies of conventional biomarkers to diagnose and monitor renal insufficiency in the acute setting. A great effort was directed not only to the discovery and validation of new biomarkers aimed to detect AKI more accurately but also to standardise the definition of AKI. Despite the advances in both areas, biomarkers have not yet entered into routine clinical practice and the definition of this syndrome has many areas of uncertainty. This review will discuss the controversies in diagnosis and the potential of novel biomarkers to improve the definition of the syndrome.

Veno-arterial extracorporeal membrane oxygenation (VA ECMO) in postcardiotomy cardiogenic shock: how much pump flow is enough?

Post-cardiotomy cardiogenic shock (PCCS) is a complication of heart surgery associated with a poor prognosis: veno-arterial extracorporeal membrane oxygenation (VA ECMO) ensures end-organ perfusion while fully replacing heart and lung function, though it is associated with unsatisfactory results. Few studies have identified reliable predictors of poor prognosis early in the course of extracorporeal support. A recent study showed the strong prognostic power of urine output in the first 24 hours of VA ECMO in predicting early and late mortality of PCCS. Urine output is a commonly collected parameter in all intensive care units (ICU) and has a defined role in the diagnosis of acute kidney injury (AKI) and is inexpensive. These findings offer the possibility to summarize some aspects regarding the adequacy of extracorporeal support early in the course of cardiogenic shock and to shed light about cardio-renal interactions in ECMO patients. Finally, it is our opinion that a timely implantation of mechanical circulatory support in post cardiotomy shock should be considered if systemic perfusion is not ensured by low or medium dose inotropic support and intra-aortic balloon counterpulsation.

Renal ischemia and reperfusion assessment with three-dimensional hyperpolarized 13 C,15 N2-urea

PURPOSE

The aim of this work was to investigate whether hyperpolarized ¹³ C,¹⁵ N₂ -urea can be used as an imaging marker of renal injury in renal unilateral ischemic reperfusion injury (IRI), given that urea is correlated with the renal osmotic gradient, which describes the renal function.

METHODS

Hyperpolarized three-dimensional balanced steady-state ¹³ C magnetic resonance imaging (MRI) experiments alongside kidney function parameters and quantitative polymerase chain reaction measurements were performed in rats subjected to unilateral renal ischemia for 60-minute and 24-hour reperfusion.

RESULTS

We revealed a significant reduction in the intrarenal gradient in the ischemic kidney in agreement with cortical injury markers neutrophil gelatinase-associated lipocalin and kidney injury molecule 1, as well as functional kidney parameters.

CONCLUSION

Hyperpolarized functional ¹³ C,¹⁵ N₂ urea MRI can be used to successfully detect changes in the intrarenal urea gradient post-IRI, thereby enabling in vivo monitoring of the intrarenal functional status in the rat kidney. Magn Reson Med 76:1524-1530, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Early initiation of continuous renal replacement therapy improves survival of elderly patients with acute kidney injury: a multicenter prospective cohort study

Background

Continuous renal replacement therapy (CRRT) is essential in the management of critically ill patients with acute kidney injury (AKI). However, the optimal timing for initiating CRRT remains controversial, especially in elderly patients. Therefore, we investigated the outcomes of early CRRT initiation in elderly patients with AKI.

Methods

A total of 607 patients ≥65 years of age who started CRRT due to AKI between August 2009 and December 2013 were prospectively enrolled. They were divided into two groups based on the median 6-hour urine output immediately before CRRT initiation. Propensity score matching was used to compare the overall survival rate, CRRT duration, and hospitalization duration.

Results

The median age of both groups was 73.0 years, and 60 % of the patients were male. The most common cause of AKI was sepsis. In the early CRRT group, the mean arterial pressure was higher, but the prothrombin time and total bilirubin, aspartate aminotransferase, and alanine aminotransferase levels were lower. The overall cumulative survival rate was higher in the early CRRT group (log-rank P < 0.01). Late CRRT initiation was associated with a higher mortality rate than early initiation after adjusting for age, sex, the Charlson comorbidity index, systolic arterial pressure, prothrombin time, the total bilirubin, aspartate aminotransferase, and alanine aminotransferase levels, cumulative fluid balance and diuretic use (hazard ratio, 1.35; 95 % confidence interval 1.06, 1.71, P = 0.02). Following propensity score matching, patient survival was significantly better in the early CRRT group than in the late CRRT group (P < 0.01). The total duration of hospitalization from the start of CRRT was shorter among the survivors when CRRT was started earlier (26.7 versus 39.1 days, P = 0.04).

Conclusion

A better prognosis can be expected if CRRT is applied early in the course of AKI in critically ill, elderly patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1437-8) contains supplementary material, which is available to authorized users.

Urinary Output Predicts Survival in Patients Undergoing Extracorporeal Membrane Oxygenation Following Cardiovascular Surgery

OBJECTIVES

Extracorporeal membrane oxygenation represents a valuable and rapidly evolving therapeutic option in patients with severe heart or lung failure following cardiovascular surgery. However, survival remains poor and accurate risk stratification challenging. Therefore, we evaluated the predictive value of urinary output within 24 hours after extracorporeal membrane oxygenation initiation on mortality in patients undergoing venoarterial extracorporeal membrane oxygenation support following cardiovascular surgery and aimed to improve established risk prediction models.

DESIGN

Single-center, observational registry.

SETTING

University-affiliated tertiary care center.

PATIENTS

We included 205 patients undergoing veno-arterial extracorporeal membrane oxygenation therapy following cardiovascular surgery at a university-affiliated tertiary-care center into our single-centre registry.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During a median follow-up time of 35 months (interquartile range, 19-69), 64% of patients died. Twenty-four-hour urinary output was the strongest predictor of outcome among renal function variables with an adjusted hazard ratio per 1 SD of 0.55 (95% CI, 0.40-0.76; p < 0.001) for 30-day mortality and of 0.65 (95% CI, 0.53-0.86; p = 0.002) for 2-year long-term mortality. Most remarkably, 24-hour urinary output showed additional prognostic value beyond that achievable with the simplified acute physiology score-3 and sequential organ failure assessment score indicated by improvements in the category-free net reclassification index for 30-day mortality (simplified acute physiology score-3: 36%, p = 0.015; sequential organ failure assessment score: 36%, p = 0.02), as well as for 2-year mortality (simplified acute physiology score-3: 33%, p = 0.02; sequential organ failure assessment score: 43%, p = 0.005).

CONCLUSIONS

We identified 24-hour urinary output as a strong and easily available predictor of mortality in patients undergoing extracorporeal membrane oxygenation therapy following cardiovascular surgery. Implementation of 24-hour urinary output leads to a substantial improvement of established risk prediction models in this vulnerable patient population. These results are particularly compelling because measurement of urinary output is inexpensive and routinely performed in all critical care units.

Urine sodium concentration to predict fluid responsiveness in oliguric ICU patients: a prospective multicenter observational study

Background

Oliguria is one of the leading triggers of fluid loading in patients in the intensive care unit (ICU). The purpose of this study was to assess the predictive value of urine Na⁺ (uNa⁺) and other routine urine biomarkers for cardiac fluid responsiveness in oliguric ICU patients.

Methods

We conducted a prospective multicenter observational study in five university ICUs. Patients with urine output (UO) <0.5 ml/kg/h for 3 consecutive hours with a mean arterial pressure >65 mmHg received a fluid challenge. Cardiac fluid responsiveness was defined by an increase in stroke volume >15 % after fluid challenge. Urine and plasma biochemistry samples were examined before fluid challenge. We examined renal fluid responsiveness (defined as UO >0.5 ml/kg/h for 3 consecutive hours) after fluid challenge as a secondary endpoint.

Results

Fifty-four patients (age 51 ± 37 years, Simplified Acute Physiology Score II score 40 ± 20) were included. Most patients (72 %) were not cardiac responders (CRs), and 50 % were renal responders (RRs) to fluid challenge. Patient characteristics were similar between CRs and cardiac nonresponders. uNa⁺ (37 ± 38 mmol/L vs 25 ± 75 mmol/L, p = 0.44) and fractional excretion of sodium (FENa⁺) (2.27 ± 2.5 % vs 2.15 ± 5.0 %, p = 0.94) were not statistically different between those who did and those who did not respond to the fluid challenge. Areas under the receiver operating characteristic (AUROC) curves were 0.51 (95 % CI 0.35–0.68) and 0.56 (95 % CI 0.39–0.73) for uNa⁺ and FENa⁺, respectively. Fractional excretion of urea had an AUROC curve of 0.70 (95 % CI 0.54–0.86, p = 0.03) for CRs. Baseline UO was higher in RRs than in renal nonresponders (1.07 ± 0.78 ml/kg/3 h vs 0.65 ± 0.53 ml/kg/3 h, p = 0.01). The AUROC curve for RRs was 0.65 (95 % CI 0.53–0.78) for uNa⁺.

Conclusions

In the present study, most oliguric patients were not CRs and half were not renal responders to fluid challenge. Routine urinary biomarkers were not predictive of fluid responsiveness in oliguric normotensive ICU patients.

Acute Kidney Injury Risk Factors For ICU Patients Following Cardiac Surgery: The Application of Joint Modeling

Background

Admission to the ICU (intensive care unit) is frequently complicated by early AKI (acute kidney injury). The development of AKI following cardiac surgery is particularly associated with increased mortality and morbidity. According to AKIN (acute kidney injury network) criteria, UO (urinary output) is a predictor for AKI.

Objectives

The goal of this study was to determine the effects of some AKI risk factors on AKI and also to investigate changes in UO as a predictor of AKI using joint modeling.

Patients and Methods

In a retrospective study, 300 cardiac-operated patients, who had been admitted over a period of three years, were selected according to the consecutive sample selection method, using the ICU at Masih Daneshvari Hospital in Iran as a referral center. The random mixed effect model and the survival model were used to investigate UO changes and estimate the effect of UO and other risk factors on the hazard rate of AKI in a joint analysis.

Results

AKI occurred in 38.0% of patients. A significant decrease of UO occurred more often in female and infected patients, as well as those with a low DBP (diastolic blood pressure). The survival model showed that the risk of AKI in females, older patients and patients with low DBP, lower UO and with infection was higher (P = 0.001). Using joint modeling, the association parameter between the risk of AKI and UO was estimated (-0.3, P = 0.002).

Conclusions

Where there is a relationship between two longitudinal and survival responses, joint modeling can estimate it.