Navigating Hemolysis, Hemoglobin Toxicity, and Its Renal Implications in Cardiac Surgery

Cardiopulmonary bypass–induced hemolysis is linked to acute kidney injury in cardiac surgery. Emerging therapies targeting cell-free hemoglobin (CFHb), like haptoglobin, nitric oxide (NO), and antioxidants, show promise in reducing kidney injury, highlighting the need for further research.

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.

Impact of Intraoperative Fluid Balance and Norepinephrine on Postoperative Acute Kidney Injury after Cystectomy and Urinary Diversion over Two Decades: A Retrospective Observational Cohort Study

The use of norepinephrine and the restriction of intraoperative hydration have gained increasing acceptance over the last few decades. Recently, there have been concerns regarding the impact of this approach on renal function. The objective of this study was to examine the influence of norepinephrine, intraoperative fluid administration and their interaction on acute kidney injury (AKI) after cystectomy. In our cohort of 1488 consecutive patients scheduled for cystectomies and urinary diversions, the overall incidence of AKI was 21.6% (95%-CI: 19.6% to 23.8%) and increased by an average of 0.6% (95%-CI: 0.1% to 1.1%, p = 0.025) per year since 2000. The fluid and vasopressor regimes were characterized by an annual decrease in fluid balance (-0.24 mL·kg^-1·h^-1, 95%-CI: -0.26 to -0.22, p < 0.001) and an annual increase in the amount of norepinephrine of 0.002 µg·kg^-1·min^-1 (95%-CI: 0.0016 to 0.0024, p < 0.001). The interaction between the fluid balance and norepinephrine levels resulted in a U-shaped association with the risk of AKI; however, the magnitude and shape depended on the reference categories of confounders (age and BMI). We conclude that decreased intraoperative fluid balance combined with increased norepinephrine administration was associated with an increased risk of AKI. However, other potential drivers of the observed increase in AKI incidence need to be further investigated in the future.

Intravenous amino acid therapy for kidney protection in cardiac surgery a protocol for a multi-centre randomized blinded placebo controlled clinical trial. The PROTECTION trial

BACKGROUND

Postoperative acute kidney injury (AKI) is frequent in cardiac surgery patients. Its pathophysiology is complex and involves decreased renal perfusion. Preliminary clinical evidence in critically ill patients shows that amino acids infusion increases renal blood flow and may decrease the incidence and severity of AKI. We designed a study to evaluate the effectiveness of perioperative continuous infusion of amino acids in decreasing AKI.

METHODS

This is a phase III, multi-center, randomized, double-blind, placebo-controlled trial. Adults undergoing cardiac surgery with cardiopulmonary bypass (CPB) are included. Patients are randomly assigned to receive either continuous infusion of a balanced mixture of amino acids in a dose of 2 g/kg ideal body weight/day or placebo (balanced crystalloid solution) from the operating room up to start of renal replacement therapy (RRT), or ICU discharge, or 72 h after the first dose. The primary outcome is the incidence of AKI during hospital stay defined by KDIGO (Kidney Disease: Improving Global Outcomes). Secondary outcomes include the need for, and duration of, RRT, mechanical ventilation; ICU and hospital length of stay; all-cause mortality at ICU, hospital discharge, 30, 90, and 180 days after randomization; quality of life at 180 days. Data will be analyzed in 3500 patients on an intention-to-treat basis.

DISCUSSION

The trial is ongoing and currently recruiting. It will be one of the first randomized controlled studies to assess the relationship between amino acids use and kidney injury in cardiac surgery. If our hypothesis is confirmed, this practice could reduce morbidity in the studied population.

STUDY REGISTRATION

This trial was registered on ClinicalTrials.gov with the trial identification NCT03709264 in October 2018.

Machine learning approach to predict acute kidney injury after liver surgery

BACKGROUND

Acute kidney injury (AKI) after surgery appears to increase the risk of death in patients with liver cancer. In recent years, machine learning algorithms have been shown to offer higher discriminative efficiency than classical statistical analysis.

AIM

To develop prediction models for AKI after liver cancer resection using machine learning techniques.

METHODS

We screened a total of 2450 patients who had undergone primary hepatocellular carcinoma resection at Changzheng Hospital, Shanghai City, China, from January 1, 2015 to August 31, 2020. The AKI definition used was consistent with the Kidney Disease: Improving Global Outcomes. We included in our analysis preoperative data such as demographic characteristics, laboratory findings, comorbidities, and medication, as well as perioperative data such as duration of surgery. Computerized algorithms used for model development included logistic regression (LR), support vector machine (SVM), random forest (RF), extreme gradient boosting (XGboost), and decision tree (DT). Feature importance was also ranked according to its contribution to model development.

RESULTS

AKI events occurred in 296 patients (12.1%) within 7 d after surgery. Among the original models based on machine learning techniques, the RF algorithm had optimal discrimination with an area under the curve value of 0.92, compared to 0.87 for XGBoost, 0.90 for DT, 0.90 for SVM, and 0.85 for LR. The RF algorithm also had the highest concordance-index (0.86) and the lowest Brier score (0.076). The variable that contributed the most in the RF algorithm was age, followed by cholesterol, and surgery time.

CONCLUSION

Machine learning algorithms are highly effective in discriminating patients at high risk of developing AKI. The successful application of machine learning models may help guide clinical decisions and help improve the long-term prognosis of patients.

A comparative study of machine learning algorithms for predicting acute kidney injury after liver cancer resection

Objective

Machine learning methods may have better or comparable predictive ability than traditional analysis. We explore machine learning methods to predict the likelihood of acute kidney injury after liver cancer resection.

Methods

This is a secondary analysis cohort study. We reviewed data from patients who had undergone resection of primary hepatocellular carcinoma between January 2008 and October 2015.

Results

The analysis included 1,173 hepatectomy patients, 77 (6.6%) of whom had AKI and 1,096 (93.4%) who did not. The importance matrix for the Gbdt algorithm model shows that age, cholesterol, tumor size, surgery duration and PLT were the five most important parameters. Figure 1 shows that Age, tumor size and surgery duration had weak positive correlations with AKI. Cholesterol and PLT also had weak negative correlations with AKI. The models constructed by the four machine learning algorithms in the training group were compared. Among the four machine learning algorithms, random forest and gbm had the highest accuracy, 0.989 and 0.970 respectively. The precision of four of the five algorithms was 1, random forest being the exception. Among the test group, gbm had the highest accuracy (0.932). Random forest and gbm had the highest precision, both being 0.333. The AUC values for the four algorithms were: Gbdt (0.772), gbm (0.725), forest (0.662) and DecisionTree (0.628).

Conclusions

Machine learning technology can predict acute kidney injury after hepatectomy. Age, cholesterol, tumor size, surgery duration and PLT influence the likelihood and development of postoperative acute kidney injury.

Acute kidney injury after thoracic surgery: a proposal for a multicentre evaluation (MERITS)

OBJECTIVES

Because the mortality rate is very low in thoracic surgery, its use as a quality discriminator is limited. Acute kidney injury (AKI) is a candidate measure because it is associated with increased rates of morbidity and mortality and is partly preventable. The incidence of AKI after thoracic surgery is not well documented. We conducted an audit to determine the incidence and outcomes of AKI. This audit became a pilot project, and the results indicate the feasibility of a larger study.

METHODS

Retrospective data on renal function post-thoracic surgery were collected at a tertiary cardiothoracic unit over 12 months. Renal impairment was classified according to the Kidney Disease Improving Global Outcomes criteria.

RESULTS

Of 568 patients (mean = 59  ±  SD 18; 38% women), AKI was diagnosed in 86 (15.1%) within 72 h post-thoracic surgery based on the Kidney Disease Improving Global Outcomes staging system (stage 1, n = 55; stage 2, n = 25; stage 3, n = 6). Significant differences were found in postoperative length of stay (3 vs 5 days; P < 0.001) of patients with and without AKI. There was a significant difference between the age groups of patients with and without AKI (P < 0.05) in the open surgical group but not in the group having video-assisted thoracoscopic surgery (VATS). There was no significant difference in the mortality rates between patients with and without AKI.

CONCLUSIONS

The incidence of AKI after thoracic surgery was 15.1%. AKI was associated with longer hospital stays and was more likely in ≥60-year-old patients after open surgery than after VATS. Reducing AKI could improve patient outcomes. We propose that AKI may be a useful quality measure in thoracic surgery. We are developing a multicentre audit based on this approach.

Impact of intra-operative fluid and noradrenaline administration on early postoperative renal function after cystectomy and urinary diversion: A retrospective observational cohort study

BACKGROUND

The use of noradrenaline to enable a restrictive approach to intra-operative fluid therapy to avoid salt and water overload has gained increasing acceptance. However, concerns have been raised about the impact of this approach on renal function.

OBJECTIVES

To identify risk factors for acute kidney injury (AKI) in patients undergoing cystectomy with urinary diversion and determine whether administration of noradrenaline and intra-operative hydration regimens affect early postoperative renal function.

DESIGN

Retrospective observational cohort study.

SETTING

University hospital, from 2007 to 2016.

PATIENTS

A total of 769 consecutive patients scheduled for cystectomy and urinary diversion. Those with incomplete data and having pre-operative haemodialysis were excluded.

MAIN OUTCOME MEASURES

AKI was defined as a serum creatinine increase of more than 50% over 72 postoperative hours. Multiple logistic regression analysis was performed to model the association between risk factors and AKI.

RESULTS

Postoperative AKI was diagnosed in 86/769 patients (11.1%). Independent predictors for AKI were the amount of crystalloid administered (odds ratio (OR) 0.79 [95% confidence interval (CI), 0.68 to 0.91], P = 0.002), antihypertensive medication (OR 2.07 [95% CI, 1.25 to 3.43], P = 0.005), pre-operative haemoglobin value (OR 1.02 [95% CI, 1.01 to 1.03], P = 0.010), duration of surgery (OR 1.01 [95% CI, 1.00 to 1.01], P = 0.002), age (OR 1.32 [95% CI, 1.44 to 1.79], P = 0.002) but not the administration of noradrenaline (OR 1.09 [95% CI, 0.94 to 1.21], P = 0.097). Postoperative AKI was associated with longer hospital stay (18 [15 to 22] vs. 16 [15 to 19] days; P = 0.035) and a higher 90-day major postoperative complication rate (41.9 vs. 27.5%; P = 0.002).

CONCLUSION

Noradrenaline administration did not increase the risk for AKI. A too restrictive approach to administration of crystalloids was associated with an increased risk for AKI, particularly in older patients, those receiving antihypertensive medication, and those whose surgery was prolonged. As AKI was associated with longer hospital stay and increased postoperative morbidity, these observations should be taken into account to improve outcome when addressing peri-operative fluid management.

TRIAL REGISTRATION

Not applicable.

Kidney Tubular Damage and Functional Biomarkers in Acute Kidney Injury Following Cardiac Surgery

Background

Cardiac surgery–associated acute kidney injury (AKI) is associated with increased morbidity and mortality. We examined the utility of combining biomarkers of kidney function loss (serum cystatin C) and kidney tubular damage (urine neutrophil gelatinase-associated lipocalin [NGAL] and Kidney Injury Molecule-1 [KIM-1]) for the prediction of post–cardiac surgery AKI.

Methods

Single-center prospective cohort study of 106 adults undergoing coronary artery bypass grafting and/or valve surgery with cardiopulmonary bypass (CPB). Primary outcome was postoperative in-hospital AKI defined by serum creatinine (SCr)–Kidney Disease: Improving Global Outcomes criteria. Biomarkers were measured preoperatively, 6 hours after CPB and on postoperative days (PODs) 1 to 4.

Results

A total of 23 subjects (21.7%) developed AKI. After adjusting for preoperative left ventricular ejection fraction, body mass index >30 kg/m², and estimated glomerular filtration rate (eGFR) <60 ml/min per 1.73 m², the combination of peak serum cystatin C and peak urine KIM-1/creatinine (Cr) (6 hours post-CPB to POD 1) above optimal cutoff significantly associated with postoperative AKI (odds ratio [OR]: 5.32; 95% confidence interval [CI]: 1.31–21.67; P = 0.020). This biomarker combination significantly improved the performance of the clinical model for the prediction of postoperative AKI (area under the curve [AUC]: 0.77, 95% CI: 0.65–0.90 for the clinical model alone versus 0.83, 95% CI: 0.73–0.93 for the clinical model with the addition of biomarker data, P = 0.049).

Conclusions

Combining biomarkers of postoperative kidney function loss and postoperative kidney tubular damage significantly improved prediction of in-hospital AKI following cardiac surgery. Future large, multicenter studies are warranted to assess whether panels of biomarkers reflecting distinct pathobiology can be used to guide interventions and improve short- and long-term outcomes in patients undergoing cardiac surgery.

Effects of acute kidney injury after liver resection on long-term outcomes

Background

To investigate the effects of acute kidney injury (AKI) after liver resection on the long-term outcome, including mortality and renal dysfunction after hospital discharge.

Methods

We conducted a historical cohort study of patients who underwent liver resection for hepatocellular carcinoma with sevoflurane anesthesia between January 2004 and October 2011, survived the hospital stay, and were followed for at least 3 years or died within 3 years after hospital discharge. AKI was diagnosed based on the Acute Kidney Injury Network classification within 72 hours postoperatively. In addition to the data obtained during hospitalization, serum creatinine concentration data were collected and the glomerular filtration rate (GFR) was estimated after hospital discharge.

Results

AKI patients (63%, P = 0.002) were more likely to reach the threshold of an estimated GFR (eGFR) of 45 ml/min/1.73 m² within 3 years than non-AKI patients (31%) although there was no significant difference in mortality (33% vs. 29%). Cox proportional hazard regression analysis showed that postoperative AKI was significantly associated with the composite outcome of mortality or an eGFR of 45 ml/min/1.73 m² (95% CI of hazard ratio, 1.05–2.96, P = 0.033), but not with mortality (P = 0.699), the composite outcome of mortality or an eGFR of 60 ml/min/1.73 m² (P =0.347).

Conclusions

After liver resection, AKI patients may be at higher risk of mortality or moderate renal dysfunction within 3 years. These findings suggest that even after discharge from the hospital, patients who suffered AKI after liver resection may need to be followed-up regarding renal function in the long term.

Perioperative risk factors for acute kidney injury after liver resection surgery: an historical cohort study

PURPOSE

This study aimed to identify the incidence and risk factors for acute kidney injury (AKI) after liver resection surgery and to clarify the relationship between postoperative AKI and outcome.

METHODS

We conducted a historical cohort study of patients who underwent liver resection surgery with sevoflurane anesthesia from January 2004 to October 2011. Acute kidney injury was diagnosed based on the Acute Kidney Injury Network classification within 72 hr after the surgery. Patient data, surgical and anesthetic data, and laboratory data were extracted manually from the patients' electronic charts. Multivariable logistic regression analysis was used to identify perioperative risk factors for postoperative AKI.

RESULTS

Acute kidney injury was diagnosed in 78 of 642 patients (12.1%; 95% confidence interval [CI]: 9.7 to 14.9). Multivariable analysis showed an independent association between postoperative AKI and preoperative estimated glomerular filtration rate (adjusted odds ratio [aOR] 0.74; 95% CI: 0.64 to 0.85), preoperative hypertension (aOR 2.10; 95% CI: 1.11 to 3.97), and intraoperative red blood cell transfusion (aOR 1.04; 95% CI: 1.01 to 1.07). Development of AKI within 72 hr after liver resection surgery was associated with increased hospital mortality, prolonged length of stay, and increased rates of mechanical ventilation, reintubation, and renal replacement therapy.

CONCLUSION

Perioperative risk factors for AKI after liver resection surgery are similar to those established for other surgical procedures. Further studies are needed to establish causality and to determine whether interventions on modifiable risk factors can reduce the incidence of postoperative AKI and improve patient outcome. This study was registered at the University Hospital Medical Information Network (UMIN) Center (UMIN 000008089).

Does diabetic status in the ICU predict haemofiltration requirement? The haemofiltration in the ICU and diabetic status (HIDS) study

Diabetes is already a major health burden and prevalence is expected to double by 2025. The impact of diabetes and clinical outcomes in the intensive care unit is an evolving area of research. This study seeks to identify whether diabetic status is an independent risk factor for haemofiltration. This is a retrospective cohort study. All unique patients from a seven-year period from 2004 to 2010 at a major intensive care unit in Melbourne, Australia were analysed using multivariate regression to look for an association between diabetic status and haemofiltration. After exclusion criteria there were 7262 patients, 1674 with a history of diabetes (median age of 69, 66.72% male) and 5588 without a history of diabetes (median age 64, 64.13% male). Diabetic status was an independent risk factor (odds ratio 1.401, 95% confidence interval 1.079 to 1.820, P=0.011) for haemofiltration. Further research may identify intensive care unit-based renoprotective measures specifically for patients with diabetes.

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.