Cell-Free Plasma Hemoglobin and Male Gender Are Risk Factors for Acute Kidney Injury in Low Risk Children Undergoing Cardiopulmonary Bypass

Female sex hormones inversely regulate acute kidney disease susceptibility throughout life

While epidemiological and experimental studies have demonstrated kidney-protective effects of estrogen and female sex in adulthood, some epidemiological data showed deterioration of kidney function during puberty when estrogen production increases. However, molecular mechanisms explaining these conflicting phenomena remain unknown. Here, we showed that the pubertal sex hormone surge in female mice increases susceptibility to kidney ischemia reperfusion injury partly via downregulation of insulin-like growth factor 1 receptor (IGF-1R) expression in proximal tubules. Adult mice ovariectomized pre-pubertally (at postnatal day 21) showed strong tolerance to kidney ischemia, which was partly reversed by the administration of 17β-estradiol, while adult mice ovariectomized post-pubertally (at 8 weeks of age) were vulnerable to kidney ischemia. Kidney tubular IGF-1R protein expression decreased during postnatal growth but was highly expressed in adult mice ovariectomized pre-pubertally and in infant mice, which might be partly explained by different expression of an E3 ligase (MDM2) of IGF-1R. Mice deficient of Igf-1r in proximal tubules (iIGF-1RKO mice) during postnatal kidney growth showed increased susceptibility to ischemic injury. RNA-seq and western blotting analysis using proximal tubular cells from pre-pubertally ovariectomized iIGF-1RKO and control mice revealed altered expression of cell cycle-associated molecules such as cyclin D1. These results suggest that Igf-1r deletion during postnatal growth renders proximal tubular cells susceptible to ischemia possibly via altered cell cycle regulation. Thus, our findings provide evidence that exposure to pubertal sex hormones leads to increased susceptibility to kidney ischemia, which is partly mediated by modulation of IGF-1R signaling.

A Machine Learning-Based Prediction Model for Acute Kidney Injury in Patients With Community-Acquired Pneumonia: Multicenter Validation Study

BACKGROUND

Acute kidney injury (AKI) is common in patients with community-acquired pneumonia (CAP) and is associated with increased morbidity and mortality.

OBJECTIVE

This study aimed to establish and validate predictive models for AKI in hospitalized patients with CAP based on machine learning algorithms.

METHODS

We trained and externally validated 5 machine learning algorithms, including logistic regression, support vector machine, random forest, extreme gradient boosting, and deep forest (DF). Feature selection was conducted using the sliding window forward feature selection technique. Shapley additive explanations and local interpretable model-agnostic explanation techniques were applied to the optimal model for visual interpretation.

RESULTS

A total of 6371 patients with CAP met the inclusion criteria. The development of CAP-associated AKI (CAP-AKI) was recognized in 1006 (15.8%) patients. The 11 selected indicators were sex, temperature, breathing rate, diastolic blood pressure, C-reactive protein, albumin, white blood cell, hemoglobin, platelet, blood urea nitrogen, and neutrophil count. The DF model achieved the best area under the receiver operating characteristic curve (AUC) and accuracy in the internal (AUC=0.89, accuracy=0.90) and external validation sets (AUC=0.87, accuracy=0.83). Furthermore, the DF model had the best calibration among all models. In addition, a web-based prediction platform was developed to predict CAP-AKI.

CONCLUSIONS

The model described in this study is the first multicenter-validated AKI prediction model that accurately predicts CAP-AKI during hospitalization. The web-based prediction platform embedded with the DF model serves as a user-friendly tool for early identification of high-risk patients.

Navigating Hemolysis and the Renal Implications of Hemoglobin Toxicity in Cardiac Surgery

Acute kidney injury (AKI) affects 20% to 30% of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). This review synthesizes clinical evidence indicating that CPB-induced hemolysis plays a pivotal role in the development of AKI. The pathogenesis involves cell-free hemoglobin, which triggers oxidative stress, depletes nitric oxide, and incites inflammation, culminating in renal damage. We highlight emerging interventions, including haptoglobin administration, nitric oxide supplementation, and antioxidants, which are promising in reducing the toxicity of cell-free hemoglobin and the incidence of AKI. Current clinical data support the potential efficacy of these treatments. Our analysis concludes that sufficient proof of concept exists to further develop and test these targeted therapies for preventing hemoglobin-induced AKI in patients undergoing CPB.

Cardiopulmonary bypass-induced hemolysis is linked to acute kidney injury in cardiac surgery. Emerging therapies targeting cell-free hemoglobin, like haptoglobin, nitric oxide, and antioxidants, show promise in reducing kidney injury, highlighting the need for further research.

Association between plasma-free haemoglobin and postoperative acute kidney injury in paediatric cardiac surgery: a prospective observational study

Background

Acute kidney injury (AKI) is a common complication among patients requiring cardiopulmonary bypass (CPB) during paediatric cardiac surgery. Plasma-free haemoglobin (PFH) produced by haemolysis during CPB contributes to AKI. This study aimed to determine the association between PFH and postoperative AKI during paediatric cardiac surgery requiring CPB.

Methods

This prospective, single-centre, observational study included children aged <5 yr who underwent cardiac surgery requiring CPB. PFH was measured pre-CPB, every 30 min during CPB, after modified ultrafiltration, on ICU admission, and once a day at 1-3 days after surgery. The study outcome included the relationship between peak PFH concentrations and the development of postoperative AKI up to 3 days after surgery. Additionally, multivariable analysis was performed to determine the risk factors for AKI.

Results

Of 179 patients, 74 (41%) developed postoperative AKI. Patients who developed AKI had significantly higher peak PFH concentrations (80 mg dl-1 [inter-quartile range, 50-132.5] vs 60 mg dl-1 [40-100]; P=0.006). Multivariable analysis did not identify peak PFH concentrations as an independent risk factor for postoperative AKI (odds ratio [OR] 1.00; 95% confidence interval [CI]: 0.99-1.00; P=0.268). Factors associated with postoperative AKI were age in months (OR 0.96; 95% CI: 0.94-0.99; P=0.007) and CPB duration (OR 1.02; 95% CI: 1.01-1.02; P<0.001).

Conclusions

There was an association between postoperative AKI and CPB time rather than PFH. Perioperative peak PFH concentrations were significantly higher in patients with postoperative AKI after paediatric cardiac surgery requiring CPB.

Urine dipstick blood and acute kidney injury in infants undergoing cardiopulmonary bypass

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with hemolysis and acute kidney injury (AKI). The study aim was to determine if urine dipstick blood in infants after CPB was associated with AKI and urine neutrophil gelatinase-associated lipocalin (NGAL).

METHODS

Infants who underwent CPB at a single center were enrolled prospectively between October 2017 and June 2019. Urine samples prior to CPB and 6 h after CPB cessation were analyzed in batch for NGAL and dipstick blood. AKI was defined using creatinine-based KDIGO criteria within 72 h of CPB. Spearman correlation examined associations between urine dipstick blood and NGAL at each time point. Linear regression estimated the associations between urine dipstick blood and log-transformed NGAL 6 h after CPB. Logistic regression estimated associations and compared discrimination between urine dipstick blood and NGAL for predicting AKI.

RESULTS

At baseline, 7/63 samples (11%) had > trace blood. Six hours after CPB, 62/98 samples (63%) had > trace blood and 26% had 3 + (large) blood. In total, 18/98 (18%) with a 6-h post-CPB sample had postoperative AKI. Urine dipstick blood values correlated with urine NGAL 6 h after CPB (r = 0.52, p < 0.01), but not at baseline (r = 0.06, p = 0.66). Those with 3 + (large) blood on urine dipstick had 6 times higher mean NGAL values compared to those with negative/trace blood (mean ratio 6.6, 95%CI 3.1-14.4, p < 0.01). Those with 3 + (large) blood had 8 times higher odds of AKI (OR 7.99, 95%CI 1.5-41.9, p = 0.01).

CONCLUSIONS

Urine dipstick blood post CPB may be a simple and inexpensive tool to help predict AKI in infants.

Hemolysis Index, Carboxyhemoglobin, and Methemoglobin for the Early Identification of Patients at Risk for Cardiac Surgery-Associated Acute Kidney Injury

OBJECTIVES

Hemolysis is a contributor to CS-AKI. Biochemistry analyzers provide a hemolysis index to quantify in vitro hemolysis, a condition that can, for example, affect the accuracy of potassium concentration measurements. We aimed to assess whether the postoperative plasma level of the hemolysis index (HIpostoperative) could aid the early recognition of patients at risk for cardiac surgery-associated acute kidney injury (CS-AKI) and also to evaluate other hemolysis indicators: plasma carboxyhemoglobin (COHbpostoperative) and methemoglobin (MetHbpostoperative).

DESIGN

One-year retrospective study.

SETTING

University hospital.

PARTICIPANTS

Patients undergoing elective cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In 1090 patients, the median HIpostoperative was higher in patients who developed CS-AKI compared to patients who did not (11 mg/dL [interquartile range (IQR), 5-38 mg/dL] v 7 mg/dL [IQR, 3-16 mg/dL]; p < 0.001). HIpostoperative refined the early recognition of CS-AKI: the area under the precision-recall curve (AUPRC) for HIpostoperative was 37% (95% confidence interval [CI], 31%-42%), whereas the AUPRC associated with no discriminative power, equal to the prevalence of CS-AKI in the whole population, was 21%. Among the 611 patients with measurements for all 3 biomarkers, the AUPRC of HIpostoperative was higher than that of COHbpostoperative or MetHbpostoperative (+6.6% and +7.4% respectively; p < 0.0001 for both). Unlike COHbpostoperative or MetHbpostoperative, the incorporation of HIpostoperative into a model (trained on a sample then validated in another sample) of CS-AKI early recognition significantly enhanced its performance, with a +1.9% (95% CI, 1.6%-2.1%) increase in AUPRC (p < 0.0001).

CONCLUSIONS

Elevated HIpostoperative represents an early alert signal for the development of CS-AKI. Our findings support the incorporation of HIpostoperative, a readily available biomarker, into predictive scores of CS-AKI.

Cardiopulmonary bypass associated acute kidney injury: better understanding and better prevention

Cardiopulmonary bypass (CPB) is a common technique in cardiac surgery but is associated with acute kidney injury (AKI), which carries considerable morbidity and mortality. In this review, we explore the range and definition of CPB-associated AKI and discuss the possible impact of different disease recognition methods on research outcomes. Furthermore, we introduce the specialized equipment and procedural intricacies associated with CPB surgeries. Based on recent research, we discuss the potential pathogenesis of AKI that may result from CPB, including compromised perfusion and oxygenation, inflammatory activation, oxidative stress, coagulopathy, hemolysis, and endothelial damage. Finally, we explore current interventions aimed at preventing and attenuating renal impairment related to CPB, and presenting these measures from three perspectives: (1) avoiding CPB to eliminate the fundamental impact on renal function; (2) optimizing CPB by adjusting equipment parameters, optimizing surgical procedures, or using improved materials to mitigate kidney damage; (3) employing pharmacological or interventional measures targeting pathogenic factors.

Accuracy of the HemoCue® to measure cell-free plasma hemoglobin and detect clinically significant hemolysis

INTRODUCTION

Monitoring cell-free plasma hemoglobin (PHb) during extracorporeal therapies allows early intervention of significant hemolysis, but timely measurements are often challenging. We thus present an analysis of a rapid benchtop device's ability to detect clinically significant hemolysis (PHb ≥50 mg/dL).

METHODS

PHb was measured in 419 plasma samples from 88 pediatric patients undergoing cardiopulmonary bypass via both the benchtop device (HemoCue® Plasma/Low Hb system) and the clinical laboratory at the Children's Hospital of Pittsburgh (reference standards). Values of PHb ≥50 mg/dL as measured by the reference standard was defined as the binary outcome of clinically significant hemolysis. Analyses included Pearson correlations, logistic regression, receiver operating characteristic curves, and Bland-Altman. Because the manufacturer specifications identify the measurement range of the HemoCue® system as 30-3000 mg/dL, a secondary analysis was completed using PHb ≥30 mg/dL.

RESULTS

Using reference measurements, 66/88 subjects had at least one PHb level that fell within the range of detection (≥30 mg/dL) of the benchtop device and 46/88 had significant hemolysis as defined by PHb ≥50 mg/dL. PHb levels ≥30 mg/dL largely correlated with measurements made with the benchtop device (r = 0.82, p < .001). The device was able to predict PHb values ≥30 mg/dL (AUROC 0.9582) and ≥50 mg/dL (AUROC 0.9637). The Bland-Altman demonstrated a mean difference of 7.0 mg/dL with <5% outside the 95% limits of agreement.

CONCLUSIONS

The HemoCue® system is an effective surrogate for more robust laboratory testing to identify clinically significant hemolysis during cardiopulmonary bypass.

Perioperative acetaminophen is associated with reduced acute kidney injury after cardiac surgery

BACKGROUND

Cardiac surgery-associated acute kidney injury (AKI) is associated with increased postoperative morbidity and mortality. Evidence suggests an association between perioperative acetaminophen administration and decreased incidence of postoperative AKI in pediatric cardiac surgery patients; however, an effect in adults is unknown.

METHODS

All patients (n = 6192) undergoing coronary and/or valve surgery with a recorded Society of Thoracic Surgeons (STS) risk score at our institution between 2010 and 2018 were stratified by acetaminophen exposure on the day of surgery using institutional pharmacy records. AKI was determined using the Kidney Disease: Improving Global Outcomes (KDIGO) staging criteria. Logistic regression was used to analyze the association between perioperative acetaminophen and postoperative kidney injury or STS major morbidity. A sensitivity analysis using propensity score matching on the STS predicted risk of renal failure and cardiopulmonary bypass time was performed to account for time bias.

RESULTS

Perioperative acetaminophen exposure was associated with lower odds of stage 1 to 3 acute kidney injury (odds ratio [OR], 0.68; 95% CI, 0.56-0.83; P < .001) and decreased prolonged postoperative ventilation (OR, 0.53; 95% CI, 0.37-0.76; P < .001). A sensitivity analysis provided well-balanced (standard mean difference <0.10) groups of 401 pairs, in which acetaminophen was associated with a decreased incidence of postoperative AKI (OR, 0.7; 95% CI, 0.52-0.94; P = .016).

CONCLUSIONS

Exposure to acetaminophen on the day of surgery was associated with a decreased incidence of AKI in our patients undergoing cardiac surgery. These data serve as a measure of effect size to further explore the therapeutic potential of acetaminophen to reduce postoperative AKI after cardiac surgery and to elucidate the mechanisms involved.

Acute Kidney Injury after Cardiac Surgery: Prediction, Prevention, and Management

Acute kidney injury (AKI) is a common complication in cardiac surgery patients, with a reported incidence of 20 to 30%. The development of AKI is associated with worse short- and long-term mortality, and longer hospital length of stay. The pathogenesis of cardiac surgery-associated AKI is poorly understood but likely involves an interplay between preoperative comorbidities and perioperative stressors. AKI is commonly diagnosed by using increases in serum creatinine or decreased urine output and staged using a standardized definition such as the Kidney Disease Improving Global Outcomes classification. Novel biomarkers under investigation may provide earlier detection and better prediction of AKI, enabling mitigating therapies early in the perioperative period. Recent clinical trials of cardiac surgery patients have demonstrated the benefit of goal-directed oxygen delivery, avoidance of hyperthermic perfusion and specific fluid and medication strategies. This review article highlights both advances and limitations regarding the prevention, prediction, and treatment of cardiac surgery-associated AKI.

Predicting acute kidney injury with an artificial intelligence-driven model in a pediatric cardiac intensive care unit

BACKGROUND

Acute kidney injury (AKI) is among the most common complications following cardiac surgery in adult and pediatric patients, significantly affecting morbidity and mortality. Artificial Intelligence (AI) with Machine Learning (ML) can be used to predict outcomes. AKI diagnosis anticipation may be an ideal target of these methods. The scope of the study is building a Machine Learning (ML) train model with Random Forest (RF) algorithm, based on electronic health record (EHR) data, able to forecast AKI continuously after 48 h in post-cardiac surgery children, and to test its performance. Four hundred nineteen consecutive patients out of 1115 hospital admissions were enrolled in a single-center retrospective study. Patients were younger than 18 years and admitted from August 2018 to February 2020 in a pediatric cardiac intensive care unit (PCICU) undergoing cardiac surgery, invasive procedure (hemodynamic studies), and medical conditions with complete EHR records and discharged after 48 h or more.

RESULTS

Thirty-six variables were selected to build the algorithm according to commonly described cardiac surgery-associated AKI clinical predictors. We evaluated different models for different outcomes: binary AKI (no AKI vs. AKI), severe AKI (no-mild vs severe AKI), and multiclass classification (maximum AKI and the most frequent level of AKI, mode AKI). The algorithm performance was assessed with the area under the curve receiver operating characteristics (AUC ROC) for binary classification, with accuracy and K for multiclass classification. AUC ROC for binary AKI was 0.93 (95% CI 0.92-0.94), and for severe AKI was 0.99 (95% CI 0.98-1). Mode AKI accuracy was 0.95, and K was 0.80 (95% CI 0.94-0.96); maximum AKI accuracy was 0.92, and K was 0.71 (95% CI 0.91-0.93). The importance matrix plot demonstrated creatinine, basal creatinine, platelets count, adrenaline support, and lactate dehydrogenase for binary AKI with the addition of cardiopulmonary bypass duration for severe AKI as the most relevant variables of the model.

CONCLUSIONS

We validated a ML model to detect AKI occurring after 48 h in a retrospective observational study that could help clinicians in individuating patients at risk of AKI, in which a preventive strategy can be determinant to improve the occurrence of renal dysfunction.

The impact of oxygen supply and erythrocytes during normothermic kidney perfusion

The influence of erythrocytes and oxygen concentration on kidneys during long-term normothermic kidney perfusion is under debate. This study compares acellular and erythrocyte-based NMP with focus on oxygen delivery to the tissue as well as the effects of high oxygenation on tissue integrity. Pig kidneys were connected to NMP for six hours. The first group (n = 6; AC500) was perfused without addition of oxygen carriers, arterial perfusate pO2 was maintained at 500 mmHg. In the second group (n = 6; RBC500) washed erythrocytes were added to the perfusate at pO2 of 500 mmHg. Third group (n = 6; RBC200) was perfused with erythrocyte containing perfusate at more physiological pO2 of 200 mmHg. Addition of RBC did not relevantly increase oxygen consumption of the kidneys during perfusion. Likewise, there were no differences in kidney functional and injury parameters between AC500 and RBC500 group. Expression of erythropoietin as indicator of tissue hypoxia was comparable in all three groups. Cell free NMP at supraphysiological oxygen partial pressure seems to be a safe alternative to erythrocyte based perfusion without adverse effect on kidney integrity and provides a less cumbersome application of NMP in clinical practice.

Investigating non-immune haemolytic transfusion reactions in surgical patients

OBJECTIVE

To perform a Root Cause Analysis (RCA) to identify the cause for Acute Haemolytic Transfusion Reaction (AHTR) in five patients who received red cell transfusions.

BACKGROUND

The occurrence of red coloured urine following blood transfusion carries the possibility of an immune or non-immune mediated haemolytic transfusion reaction (HTR). Non-immune haemolysis can be due to thermal, osmotic, or mechanical injury to red blood cells. The authors report five cases of non-immune HTR that occurred in surgical patients in the peri-operative period.

METHODS

AHTR was reported to the Transfusion Medicine Department, in five patients who underwent surgery and received a blood transfusion in the peri-operative period. Transfusion reaction workup and RCA were performed to identify the cause for AHTR.

RESULTS

The initial presentation was red coloured urine and suspicion of an immune HTR. Immunohaematology workup ruled out an immune mediated haemolysis and further analysis revealed the possibility of mechanical red cell destruction in all these cases.

CONCLUSION

Multiple factors can result in non-immune destruction of red cells. Possibility of non-immune haemolysis should be considered while evaluating haemolytic transfusion reactions.

Cell-Free Hemoglobin Concentration in Blood Prime Solution Is a Major Determinant of Cell-Free Hemoglobin Exposure during Cardiopulmonary Bypass Circulation in the Newborn

Exposure to circulating cell-free hemoglobin is a ubiquitous feature of open-heart surgery on cardiopulmonary bypass circulation. This study aims to determine the origins and dynamics of circulating cell-free hemoglobin and its major scavenger proteins haptoglobin and hemopexin during neonatal cardiopulmonary bypass. Forty neonates with an isolated critical congenital heart defect were included in a single-center prospective observational study. Blood samples were obtained preoperatively, hourly during bypass circulation, after bypass separation, at admission to the pediatric intensive care unit, and at postoperative days 1–3. Concentrations of cell-free hemoglobin, haptoglobin and hemopexin were determined using ELISA. Neonates were exposed to significantly elevated plasma concentrations of cell-free hemoglobin and a concomitant depletion of scavenger protein supplies during open-heart surgery. The main predictor of cell-free hemoglobin exposure was the concentration of cell-free hemoglobin in blood prime solution. Concentrations of haptoglobin and hemopexin in prime solution were important determinants for intra- and postoperative circulating scavenger protein resources.

Plasma haemolysis index and interleukine-6 for the early prediction of cardiac surgery-associated acute kidney injury. A proof-of-concept study

Introduction

Haemolysis and inflammation contribute to cardiac surgery-associated acute kidney injury (CS-AKI). We aimed to assess the performance of plasma haemolysis index (HI) and interleukine-6 (IL-6) for the prediction of all-stage CS-AKI. We also assessed their ability to predict moderate-to-severe CS-AKI and to discriminate persistent from transient CS-AKI.

Methods

Adult patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) were prospectively included. Haemolysis index and IL-6 were measured immediately after the end of CPB and 6 hours later. Correction for haemodilution relied upon changes in albuminaemia. Persistent CS-AKI was defined as a steady/increasing CS-AKI stage between the 48th and the 60th postoperative hour as compared with the worst stage observed within the 48 first hours.

Results

Among 82 patients, CS-AKI occurred in 37 (45%) patients. Postoperative HI and IL-6 were positively correlated to the duration of CPB (r ≤ 0.51, p ≤ 0.0003). Whether we considered isolated measurements of HI or IL-6, their indexation to haemodilution or not, their kinetics and/or their combination, the prediction of all stage CS-AKI was inaccurate (area under the receiver operating characteristic curve [AUCROC]≤ 0.68) whereas moderate-to-severe CS-AKI (6 patients only) was predicted with an honourable performance (AUCROC = 0.77 [95%CI 0.67;0.86] and 0.87 [95%CI 0.77;0.93] for HI and IL-6, respectively). The persistent/transient nature of CS-AKI was inaccurately predicted (AUCROC ≤ 0.68).

Conclusions

In a population in which most CS-AKI cases were mild, although they frequently (41%) persisted >48 hours, CS-AKI was inaccurately predicted by HI and/or IL-6. A better performance for moderate-to-severe CS-AKI prediction is likely. These preliminary findings are yet to be validated.

Association Between Hyperoxemia and Increased Cell-Free Plasma Hemoglobin During Cardiopulmonary Bypass in Infants and Children

OBJECTIVES

To determine potential risk factors for severe hemolysis during pediatric cardiopulmonary bypass and examine whether supraphysiologic levels of oxygen and cardiopulmonary bypass duration are associated with hemolysis.

DESIGN

Prospective observational study.

SETTING

Cardiac ICU in a university-affiliated children's hospital.

PATIENTS

Greater than 1 month to less than 18 years old patients undergoing cardiopulmonary bypass for cardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma samples from 100 patients to assess cell-free plasma hemoglobin levels were obtained at start cardiopulmonary bypass, at the end of cardiopulmonary bypass, and 2 and 24 hours after reperfusion. Arterial blood gas samples were obtained before and every 30 minutes during cardiopulmonary bypass. Patient demographics and laboratory data were collected from the electronic medical record. Plasma hemoglobin levels peaked at the end of cardiopulmonary bypass and haptoglobin levels continued to fall throughout all time points. There were 44 patients with severe hemolysis (change in cell-free plasma hemoglobin > 50 mg/dL). Younger age (odds ratio/sd 0.45 [95% CI, 0.25-0.81]) and higher mean Pao2 × cardiopulmonary bypass duration (31.11 [1.46-664.64]) were identified as risk factors for severe hemolysis in multivariable analysis. Severe hemolysis was associated with longer hospital and ICU lengths of stay as well as acute kidney injury.

CONCLUSIONS

We observed younger age and the exposure to both oxygen and duration of cardiopulmonary bypass as risk factors for hemolysis. Oxygen delivery through the cardiopulmonary bypass circuit is an easily modifiable risk factor. Its role in the production of reactive oxygen species that could alter the erythrocyte membrane deserves further examination in larger prospective studies.

Free Hemoglobin Ratio as a Novel Biomarker of Acute Kidney Injury After On-Pump Cardiac Surgery: Secondary Analysis of a Randomized Controlled Trial

BACKGROUND

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with a high risk of postoperative acute kidney injury (AKI). Due to limitations of current diagnostic strategies, we sought to determine whether free hemoglobin (fHb) ratio (ie, levels of fHb at the end of CPB divided by baseline fHb) could predict AKI after on-pump cardiac surgery.

METHODS

This is a secondary analysis of a randomized controlled trial comparing the effect of nitric oxide (intervention) versus nitrogen (control) on AKI after cardiac surgery (NCT01802619). A total of 110 adult patients in the control arm were included. First, we determined whether fHb ratio was associated with AKI via multivariable analysis. Second, we verified whether fHb ratio could predict AKI and incorporation of fHb ratio could improve predictive performance at an early stage, compared with prediction using urinary biomarkers alone. We conducted restricted cubic spline in logistic regression for model development. We determined the predictive performance, including area under the receiver-operating-characteristics curve (AUC) and calibration (calibration plot and accuracy, ie, number of correct predictions divided by total number of predictions). We also used AUC test, likelihood ratio test, and net reclassification index (NRI) to compare the predictive performance between competing models (ie, fHb ratio versus neutrophil gelatinase-associated lipocalin [NGAL], N-acetyl-β-d-glucosaminidase [NAG], and kidney injury molecule-1 [KIM-1], respectively, and incorporation of fHb ratio with NGAL, NAG, and KIM-1 versus urinary biomarkers alone), if applicable.

RESULTS

Data stratified by median fHb ratio showed that subjects with an fHb ratio >2.23 presented higher incidence of AKI (80.0% vs 49.1%; P = .001), more need of renal replacement therapy (10.9% vs 0%; P = .036), and higher in-hospital mortality (10.9% vs 0%; P = .036) than subjects with an fHb ratio ≤2.23. fHb ratio was associated with AKI after adjustment for preestablished factors. fHb ratio outperformed urinary biomarkers with the highest AUC of 0.704 (95% confidence interval [CI], 0.592-0.804) and accuracy of 0.714 (95% CI, 0.579-0.804). Incorporation of fHb ratio achieved better discrimination (AUC test, P = .012), calibration (likelihood ratio test, P < .001; accuracy, 0.740 [95% CI, 0.617-0.832] vs 0.632 [95% CI, 0.477-0.748]), and significant prediction increment (NRI, 0.638; 95% CI, 0.269-1.008; P < .001) at an early stage, compared with prediction using urinary biomarkers alone.

CONCLUSIONS

Results from this exploratory, hypothesis-generating retrospective, observational study shows that fHb ratio at the end of CPB might be used as a novel, widely applicable biomarker for AKI. The use of fHb ratio might help for an early detection of AKI, compared with prediction based only on urinary biomarkers.

Toxic effects of cell-free hemoglobin on the microvascular endothelium: implications for pulmonary and nonpulmonary organ dysfunction

Levels of circulating cell-free hemoglobin are elevated during hemolytic and inflammatory diseases and contribute to organ dysfunction and severity of illness. Though several studies have investigated the contribution of hemoglobin to tissue injury, the precise signaling mechanisms of hemoglobin-mediated endothelial dysfunction in the lung and other organs are not yet completely understood. The purpose of this review is to highlight the knowledge gained thus far and the need for further investigation regarding hemoglobin-mediated endothelial inflammation and injury to develop novel therapeutic strategies targeting the damaging effects of cell-free hemoglobin.

Plasma hemoglobin: A method comparison of six assays for hemoglobin and hemolysis index measurement

INTRODUCTION

Plasma hemoglobin (Hb) is measured for assessment of in vivo and in vitro hemolysis. The objective of the present investigation was to conduct a method comparison of five quantitative and one semi-quantitative Hb and H-index (hemolysis index) assays to evaluate their performance measuring plasma Hb in clinical specimens.

METHODS

One hundred and fourteen clinical specimens previously tested for plasma Hb using a laboratory-developed spectrophotometric assay were also tested for Hb using a HemoCue Plasma/Low Hb assay (azide methemoglobin), a laboratory-modified Pointe Scientific Hb assay (cyanmethemoglobin), tested for H-index measurements using a Roche cobas c501, an Abbott Architect c8000, and a semi-quantitative (binned) H-index measurement on a Beckman AU5800. The reference result was defined as the median Hb score (median of all Hb or H-index results).

RESULTS

The laboratory-developed spectrophotometric Hb assay and Roche H-index methods mostly closely matched the median Hb score across all data, as well as for lower range median Hb score results ≤2.0 g/L. Two-way frequency table analysis using an Hb (or H-index) cutoff of 0.5 g/L (or 0.5 H-index units) was then performed to compare methods to the median Hb score cutoff. The Beckman method had the highest accuracy at this cutoff, the Roche and Abbott methods had the highest positive predictive value (PPV), and the Beckman, HemoCue, and Pointe methods had the highest negative predictive value (NPV).

CONCLUSIONS

Plasma Hb and H-index results vary by method. Laboratories should evaluate the performance characteristics of their respective assays when considering adoption of spectrophotometric or chemical methods for plasma Hb assessment.

Risk factors for acute kidney injury in neonates with congenital diaphragmatic hernia

OBJECTIVE

To examine incidence of acute kidney injury (AKI), antenatal and postnatal predictors, and impact of AKI on outcomes in infants with congenital diaphragmatic hernia (CDH).

STUDY DESIGN

Single center retrospective study of 90 CDH infants from 2009-2017. Baseline characteristics, CDH severity, possible AKI predictors, and clinical outcomes were compared between infants with and without AKI.

RESULT

In total, 38% of infants developed AKI, 44% stage 1, 29% stage 2, 27% stage 3. Lower antenatal lung volumes and liver herniation were associated with AKI. Extracorporeal life support (ECLS), diuretics, abdominal closure surgery, hypotension, and elevated plasma free hemoglobin were associated with AKI. Overall survival was 79%, 47% with AKI, and 35% with AKI on ECLS. AKI is associated with increased mechanical ventilation duration and length of stay.

CONCLUSION

AKI is common among CDH infants and associated with adverse outcomes. Standardized care bundles addressing AKI risk factors may reduce AKI incidence and severity.

The Effect of Optimized Ultrafiltration on Perioperative Pulmonary Function During Cardiopulmonary Bypass in Infants Under 10 kg

Objective: This study aims to investigate the effect of optimized ultrafiltration on perioperative electrolytes, acid-base balance, and pulmonary function during cardiopulmonary bypass (CPB) in infants with low body weight (under 10 kg), using traditional balanced ultrafiltration and modified ultrafiltration. Methods: A total of 30 children who underwent surgical correction for congenital heart disease in Changzhou Children's Hospital between January 2018 and December 2019 were randomly divided into two groups. In the treatment group, ultrafiltration pre-treatment was carried out with blood-containing priming fluid prior to CPB. Balanced ultrafiltration was performed during the operation, and optimized and modified ultrafiltration were conducted before closing and extubation. In the control group, traditional balanced ultrafiltration was used during the operation, and a modified ultrafiltration combination was used before closing and extubation. Indexes such as blood gas analysis and electrolytes were measured perioperatively, and pulmonary function was observed. Results: No deaths were reported in either group. The ventilator-assisted breathing time was shorter in the treatment group than in the control group (P < 0.05). The indexes of the treatment group were closer than those of the control group to the optimal physiological values. The concentrations of potassium ion (K⁺), lactate (Lac), and blood glucose (Glu) decreased, and there was significant difference between the two groups (P < 0.05) at the end of CPB. Hemoglobin (Hb) and hematocrit (HCT) in the treatment group increased (P < 0.01). Alveolar-arterial differences for oxygen (A-aDO₂) and respiratory index (RI) increased significantly in both groups after operation. Children in the treatment group began to recover lung function earlier than children in the control group. Both A-aDO₂ and RI were lower in the treatment group than in the control group at each time point after operation (P < 0.05). Conclusion: Optimizing and modifying the traditional ultrafiltration combination method can effectively shorten the ultrafiltration time, reduce the adverse impacts of the ultrafiltration technique, and improve the lung function of infants after operation.

The Role of Circulating Cell-Free Hemoglobin in Sepsis-Associated Acute Kidney Injury

Sepsis is a heterogeneous clinical syndrome that is complicated commonly by acute kidney injury (sepsis-AKI). Currently, no approved pharmacologic therapies exist to either prevent sepsis-AKI or to treat sepsis-AKI once it occurs. A growing body of evidence supports a connection between red blood cell biology and sepsis-AKI. Increased levels of circulating cell-free hemoglobin (CFH) released from red blood cells during hemolysis are common during sepsis and can contribute to sepsis-AKI through several mechanisms including tubular obstruction, nitric oxide depletion, oxidative injury, and proinflammatory signaling. A number of potential pharmacologic therapies targeting CFH in sepsis have been identified including haptoglobin, hemopexin, and acetaminophen, and early phase clinical trials have suggested that acetaminophen may have beneficial effects on lipid peroxidation and kidney function in patients with sepsis. Bedside measurement of CFH levels may facilitate predictive enrichment for future clinical trials of CFH-targeted therapeutics. However, rapid and reliable bedside tests for plasma CFH will be required for such trials to move forward.

Bioactive Oxylipins in Infants and Children With Congenital Heart Disease Undergoing Pediatric Cardiopulmonary Bypass

OBJECTIVES

To determine the production of 9-hydroxyoctadecadienoic acid and 13-hydroxyoctadecadienoic acid during cardiopulmonary bypass in infants and children undergoing cardiac surgery, evaluate their relationship with increase in cell-free plasma hemoglobin, provide evidence of bioactivity through markers of inflammation and vasoactivity (WBC count, milrinone use, vasoactive-inotropic score), and examine their association with overall clinical burden (ICU/hospital length of stay and mechanical ventilation duration).

DESIGN

Prospective observational study.

SETTING

Twelve-bed cardiac ICU in a university-affiliated children's hospital.

PATIENTS

Children were prospectively enrolled during their preoperative clinic appointments with the following criteria: greater than 1 month to less than 18 years old, procedures requiring cardiopulmonary bypass INTERVENTIONS:: None.

MEASUREMENTS AND MAIN RESULTS

Plasma was collected at the start and end of cardiopulmonary bypass in 34 patients. 9-hydroxyoctadecadienoic acid, 13-hydroxyoctadecadienoic acid, plasma hemoglobin, and WBC increased. 9:13-hydroxyoctadecadienoic acid at the start of cardiopulmonary bypass was associated with vasoactive-inotropic score at 2-24 hours postcardiopulmonary bypass (R = 0.25; p < 0.01), milrinone use (R = 0.17; p < 0.05), and WBC (R = 0.12; p < 0.05). 9:13-hydroxyoctadecadienoic acid at the end of cardiopulmonary bypass was associated with vasoactive-inotropic score at 2-24 hours (R = 0.17; p < 0.05), 24-48 hours postcardiopulmonary bypass (R = 0.12; p < 0.05), and milrinone use (R = 0.19; p < 0.05). 9:13-hydroxyoctadecadienoic acid at the start and end of cardiopulmonary bypass were associated with the changes in plasma hemoglobin (R = 0.21 and R = 0.23; p < 0.01). The changes in plasma hemoglobin was associated with milrinone use (R = 0.36; p < 0.001) and vasoactive-inotropic score less than 2 hours (R = 0.22; p < 0.01), 2-24 hours (R = 0.24; p < 0.01), and 24-48 hours (R = 0.48; p < 0.001) postcardiopulmonary bypass. Cardiopulmonary bypass duration, 9:13-hydroxyoctadecadienoic acid at start of cardiopulmonary bypass, and plasma hemoglobin may be risk factors for high vasoactive-inotropic score. Cardiopulmonary bypass duration, changes in plasma hemoglobin, 9:13-hydroxyoctadecadienoic acid, and vasoactive-inotropic score correlate with ICU and hospital length of stay and/mechanical ventilation days.

CONCLUSIONS

In low-risk pediatric patients undergoing cardiopulmonary bypass, 9:13-hydroxyoctadecadienoic acid was associated with changes in plasma hemoglobin, vasoactive-inotropic score, and WBC count, and may be a risk factor for high vasoactive-inotropic score, indicating possible inflammatory and vasoactive effects. Further studies are warranted to delineate the role of hydroxyoctadecadienoic acids and plasma hemoglobin in cardiopulmonary bypass-related dysfunction and to explore hydroxyoctadecadienoic acid production as a potential therapeutic target.

Nitric Oxide Decreases Acute Kidney Injury and Stage 3 Chronic Kidney Disease after Cardiac Surgery

RATIONALE

No medical intervention has been identified that decreases acute kidney injury and improves renal outcome at 1 year after cardiac surgery.

OBJECTIVES

To determine whether administration of nitric oxide reduces the incidence of postoperative acute kidney injury and improves long-term kidney outcomes after multiple cardiac valve replacement requiring prolonged cardiopulmonary bypass.

METHODS

Two hundred and forty-four patients undergoing elective, multiple valve replacement surgery, mostly due to rheumatic fever, were randomized to receive either nitric oxide (treatment) or nitrogen (control). Nitric oxide and nitrogen were administered via the gas exchanger during cardiopulmonary bypass and by inhalation for 24 hours postoperatively.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was as follows: oxidation of ferrous plasma oxyhemoglobin to ferric methemoglobin was associated with reduced postoperative acute kidney injury from 64% (control group) to 50% (nitric oxide group) (relative risk [RR], 0.78; 95% confidence interval [CI], 0.62-0.97; P = 0.014). Secondary outcomes were as follows: at 90 days, transition to stage 3 chronic kidney disease was reduced from 33% in the control group to 21% in the treatment group (RR, 0.64; 95% CI, 0.41-0.99; P = 0.024) and at 1 year, from 31% to 18% (RR, 0.59; 95% CI, 0.36-0.96; P = 0.017). Nitric oxide treatment reduced the overall major adverse kidney events at 30 days (RR, 0.40; 95% CI, 0.18-0.92; P = 0.016), 90 days (RR, 0.40; 95% CI, 0.17-0.92; P = 0.015), and 1 year (RR, 0.47; 95% CI, 0.20-1.10; P = 0.041).

CONCLUSIONS

In patients undergoing multiple valve replacement and prolonged cardiopulmonary bypass, administration of nitric oxide decreased the incidence of acute kidney injury, transition to stage 3 chronic kidney disease, and major adverse kidney events at 30 days, 90 days, and 1 year. Clinical trial registered with ClinicalTrials.gov (NCT01802619).

Association Between Early Postoperative Acetaminophen Exposure and Acute Kidney Injury in Pediatric Patients Undergoing Cardiac Surgery

IMPORTANCE

Acute kidney injury (AKI) is a common and serious complication for pediatric cardiac surgery patients associated with increased morbidity, mortality, and length of stay. Current strategies focus on risk reduction and early identification because there are no known preventive or therapeutic agents. Cardiac surgery and cardiopulmonary bypass lyse erythrocytes, releasing free hemoglobin and contributing to oxidative injury. Acetaminophen may prevent AKI by reducing the oxidation state of free hemoglobin.

OBJECTIVE

To test the hypothesis that early postoperative acetaminophen exposure is associated with reduced risk of AKI in pediatric patients undergoing cardiac surgery.

DESIGN, SETTING, AND PARTICIPANTS

In this retrospective cohort study, the setting was 2 tertiary referral children's hospitals. The primary and validation cohorts included children older than 28 days admitted for cardiac surgery between July 1, 2008, and June 1, 2016. Exclusion criteria were postoperative extracorporeal membrane oxygenation and inadequate serum creatinine measurements to determine AKI status.

EXPOSURES

Acetaminophen exposure in the first 48 postoperative hours.

MAIN OUTCOMES AND MEASURES

Acute kidney injury based on Kidney Disease: Improving Global Outcomes serum creatinine criteria (increase by ≥0.3 mg/dL from baseline or at least 1.5-fold more than the baseline [to convert to micromoles per liter, multiply by 88.4]) in the first postoperative week.

RESULTS

The primary cohort (n = 666) had a median age of 6.5 (interquartile range [IQR], 3.9-44.7) months, and 341 (51.2%) had AKI. In unadjusted analyses, those with AKI had lower median acetaminophen doses than those without AKI (47 [IQR, 16-88] vs 78 [IQR, 43-104] mg/kg, P < .001). In logistic regression analysis adjusting for age, cardiopulmonary bypass time, red blood cell distribution width, postoperative hypotension, nephrotoxin exposure, and Risk Adjustment for Congenital Heart Surgery score, acetaminophen exposure was protective against postoperative AKI (odds ratio, 0.86 [95% CI, 0.82-0.90] per each additional 10 mg/kg). Findings were replicated in the validation cohort (n = 333), who had a median age of 14.1 (IQR, 3.9-158.2) months, and 162 (48.6%) had AKI. Acetaminophen doses were 60 (95% CI, 40-87) mg/kg in those with AKI vs 70 (95% CI, 45-94) mg/kg in those without AKI (P = .03), with an adjusted odds ratio of 0.91 (95% CI, 0.84-0.99) for each additional 10 mg/kg.

CONCLUSIONS AND RELEVANCE

These results indicate that early postoperative acetaminophen exposure may be associated with a lower rate of AKI in pediatric patients who undergo cardiac surgery. Further analysis to validate these findings, potentially through a prospective, randomized trial, may establish acetaminophen as a preventive agent for AKI.