Intensive care unit admission parameters improve the accuracy of operative mortality predictive models in cardiac surgery

Does severe hyperlactatemia during cardiopulmonary bypass predict a worse outcome?

INTRODUCTION

The aim of the current study was to evaluate the impact of increased blood lactate levels during cardiopulmonary bypass (CPB) on immediate results in patients who underwent open heart surgery.

MATERIALS AND METHODS

We performed a retrospective single-center study on 1290 patients. Adult cardiac surgical patients who underwent valve surgery, coronary artery bypass graft, combined procedure, adult congenital anomalies and aortic surgery were enrolled. Patients with associated comorbidities such as liver dysfunction, hemodynamic instability before surgery were excluded. Arterial blood lactate concentration was measured immediately after weaning from CPB and evaluated together with clinical data and outcomes including in hospital mortality. Patients were classified into 3 groups according to their peak arterial lactate level: group I [normal lactatemia, lactate ˂ 2 mmol/l (n = 749)], group II [mild hyperlactatemia, lactate 2-5 mmol/l (n = 489)], group III [severe hyperlactatemia, lactate ˃ 5 mmol/l (n = 52)].

RESULTS

When comparing outcomes across the 3 groups, severe hyperlactatemia was correlated with worse outcomes including higher in-hospital mortality, low output cardiac syndrome, postoperative renal insufficiency, myocardial infarction, red blood cell transfusion (RBC) transfusion, prolonged mechanical ventilation and longer intensive care unit (ICU) stay hours.

CONCLUSION

Blood lactate level above 5 mmol/l and more during CPB is associated with higher in-hospital mortality rate and postoperative complications. More attention must be given to correct the common abnormalities conditions inherent of CPB in order to conduct adequate tissue perfusion and reduce the risk of hyperlactatemia.

Performance of Sequential Organ Failure Assessment and Simplified Acute Physiology Score II for Post-Cardiac Surgery Patients in Intensive Care Unit

Background: The aim of this study is to assess the performance of Sequential Organ Failure Assessment (SOFA) score and Simplified Acute Physiology Score (SAPS II) on outcomes of patients with cardiac surgery and identify the cutoff values to provide a reference for early intervention.

Methods: All data were extracted from MIMIC-III (Medical Information Mart for Intensive Care-III) database. Cutoff values were calculated by the receiver-operating characteristic curve and Youden indexes. Patients were grouped, respectively, according to the cutoff values of SOFA and SAPS II. A non-adjusted model and adjusted model were established to evaluate the prediction of risk. Comparison of clinical efficacy between two scoring systems was made by decision curve analysis (DCA). The primary outcomes of this study were in-hospital mortality, 28-day mortality, 90-day mortality, and 1-year mortality after cardiac surgery. The secondary outcomes included length of hospital stay and intensive care unit (ICU) stay and the incidence of acute kidney injury (AKI) within 7 days after ICU admission.

Results: A total of 6,122 patients were collected and divided into the H-SOFA group (SOFA ≥ 7) and L-SOFA group (SOFA < 7) or H-SAPS II group (SAPS II ≥ 43) and L-SAPS II group (SAPS II < 43). In-hospital mortality, 28-day mortality, 90-day mortality, and 1-year mortality were higher, the length of hospital and ICU stay were longer in the H-SOFA group than in the L-SOFA group (p < 0.05), while the incidence of AKI was not significantly different. In-hospital mortality, 28-day mortality, 90-day mortality, 1-year mortality, and the incidence of AKI were all significantly higher in the H-SAPS II group than in the L-SAPS II group (p < 0.05). Hospital stay and ICU stay were longer in the H-SAPS II group than in the L-SAPS II group (p < 0.05). According to DCA, the SAPS II scoring system had more net benefits on assessing the long-term mortality compared with the SOFA scoring system.

Conclusion: Exceeding the cutoff values of SOFA and SAPS II scores could lead to increased mortality and extended length of ICU and hospital stay. The SAPS II scoring system had a better discriminative performance of 90-day mortality and 1-year mortality in post-cardiac surgery patients than the SOFA scoring system. Emphasizing the critical value of the scoring system is of significance for timely treatment.

Machine Learning Consensus Clustering Approach for Patients with Lactic Acidosis in Intensive Care Units

BACKGROUND

Lactic acidosis is a heterogeneous condition with multiple underlying causes and associated outcomes. The use of multi-dimensional patient data to subtype lactic acidosis can personalize patient care. Machine learning consensus clustering may identify lactic acidosis subgroups with unique clinical profiles and outcomes.

METHODS

We used the Medical Information Mart for Intensive Care III database to abstract electronic medical record data from patients admitted to intensive care units (ICU) in a tertiary care hospital in the United States. We included patients who developed lactic acidosis (defined as serum lactate ≥ 4 mmol/L) within 48 h of ICU admission. We performed consensus clustering analysis based on patient characteristics, comorbidities, vital signs, organ supports, and laboratory data to identify clinically distinct lactic acidosis subgroups. We calculated standardized mean differences to show key subgroup features. We compared outcomes among subgroups.

RESULTS

We identified 1919 patients with lactic acidosis. The algorithm revealed three best unique lactic acidosis subgroups based on patient variables. Cluster 1 (n = 554) was characterized by old age, elective admission to cardiac surgery ICU, vasopressor use, mechanical ventilation use, and higher pH and serum bicarbonate. Cluster 2 (n = 815) was characterized by young age, admission to trauma/surgical ICU with higher blood pressure, lower comorbidity burden, lower severity index, and less vasopressor use. Cluster 3 (n = 550) was characterized by admission to medical ICU, history of liver disease and coagulopathy, acute kidney injury, lower blood pressure, higher comorbidity burden, higher severity index, higher serum lactate, and lower pH and serum bicarbonate. Cluster 3 had the worst outcomes, while cluster 1 had the most favorable outcomes in terms of persistent lactic acidosis and mortality.

CONCLUSIONS

Consensus clustering analysis synthesized the pattern of clinical and laboratory data to reveal clinically distinct lactic acidosis subgroups with different outcomes.

Machine Learning Prediction Models for Mortality in Intensive Care Unit Patients with Lactic Acidosis

Background: Lactic acidosis is the most common cause of anion gap metabolic acidosis in the intensive care unit (ICU), associated with poor outcomes including mortality. We sought to compare machine learning (ML) approaches versus logistic regression analysis for prediction of mortality in lactic acidosis patients admitted to the ICU. Methods: We used the Medical Information Mart for Intensive Care (MIMIC-III) database to identify ICU adult patients with lactic acidosis (serum lactate ≥4 mmol/L). The outcome of interest was hospital mortality. We developed prediction models using four ML approaches consisting of random forest (RF), decision tree (DT), extreme gradient boosting (XGBoost), artificial neural network (ANN), and statistical modeling with forward stepwise logistic regression using the testing dataset. We then assessed model performance using area under the receiver operating characteristic curve (AUROC), accuracy, precision, error rate, Matthews correlation coefficient (MCC), F1 score, and assessed model calibration using the Brier score, in the independent testing dataset. Results: Of 1919 lactic acidosis ICU patients, 1535 and 384 were included in the training and testing dataset, respectively. Hospital mortality was 30%. RF had the highest AUROC at 0.83, followed by logistic regression 0.81, XGBoost 0.81, ANN 0.79, and DT 0.71. In addition, RF also had the highest accuracy (0.79), MCC (0.45), F1 score (0.56), and lowest error rate (21.4%). The RF model was the most well-calibrated. The Brier score for RF, DT, XGBoost, ANN, and multivariable logistic regression was 0.15, 0.19, 0.18, 0.19, and 0.16, respectively. The RF model outperformed multivariable logistic regression model, SOFA score (AUROC 0.74), SAP II score (AUROC 0.77), and Charlson score (AUROC 0.69). Conclusion: The ML prediction model using RF algorithm provided the highest predictive performance for hospital mortality among ICU patient with lactic acidosis.

Monitoring of the Progression of the Perioperative Serum Lactate Concentration Improves the Accuracy of the Prediction of Acute Mesenteric Ischemia Development After Cardiovascular Surgery

OBJECTIVES

To examine the sensitivity and specificity of perioperative lactate gradients for the prediction of subsequent acute mesenteric ischemia development in patients undergoing cardiovascular surgery.

DESIGN

Retrospective, single-center, case-control study.

SETTING

University hospital.

PARTICIPANTS

The study comprised 108 (1.15%) patients with acute mesenteric ischemia who were selected from 9,385 patients who underwent cardiovascular surgery and were matched to 324 control patients by age and surgery type.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Univariate and logistic regression analyses were used to examine intraoperative and early postoperative lactate levels in patients with and without mesenteric ischemia after cardiac surgery. Late intraoperative lactate concentrations were significantly greater in patients who subsequently developed mesenteric ischemia (p < 0.001). Patients with lactate levels >3 mmol/L had a four-fold increased risk of mesenteric ischemia development (odds ratio [OR] 4.2, 95% confidence interval [CI] 2.4-7.5; area under the curve [AUC] 0.597; p < 0.002). Patients whose lactate levels remained >3 mmol/L on the first postoperative day had a nearly eight-fold increased risk (OR 7.8, 95% CI 4.6-13.3; AUC 0.68; p < 0.001), indicating that mesenteric ischemia developed at an early stage in almost every second patient (p < 0.001). For patients with normal or less elevated lactate levels, similar results were obtained for a >200% increase between the intraoperative and early postoperative periods (OR 4.1, 95% CI 2.4-6.8; AUC 0.62; p < 0.001).

CONCLUSION

Late intraoperative and early postoperative lactate levels >3 mmol/L and increases >200%, even when remaining within the normal range, should raise the suspicion of subsequent mesenteric ischemia development.

Intraoperative initiation of a modified ARDSNet protocol increases survival of septic patients with severe acute respiratory distress syndrome

PURPOSE

To assess the intraoperative initiation and feasibility of a modified NIH-NHLBI ARDS Network Mechanical Ventilation Protocol (mARDSNet protocol) in septic patients with severe ARDS.

MATERIALS AND METHODS

This prospective observational study included consecutive adult septic patients with severe ARDS who underwent emergency abdominal surgery prior to intensive care unit (ICU) admission. The primary outcome was survival to hospital discharge and at 90 days. Secondary outcomes were intraoperative adverse events and ICU length of stay.

RESULTS

Seven patients were included. A statistically significant difference in lung compliance [ε=0.150, F(1.053, 3.158)=31.098, p=0.010] and driving pressure [ε=0.263, F(1.844, 5.532)=7.042, p=0.031] was observed with time, while plateau pressure did not changed significantly during surgery [ε=0.322, F(2.256, 6.769)=1.920, p=0.219]. Also, PEEP values were constantly increased during surgery [ε=0.252, F(1.766, 5.297)=9.994, p=0.017], with the highest values being observed towards to the end of the procedure. No intraoperative adverse events were observed. Mean (±SD) ICU length of stay was 10.43 (±2.64) days, while all patients survived to hospital discharge and at 90 days.

CONCLUSIONS

The intraoperative implementation of our mARDSNet protocol is feasible and may increase the survival of septic patients with severe ARDS if initiated prior to ICU admission.

Lactate Elevation During and After Major Cardiac Surgery in Adults: A Review of Etiology, Prognostic Value, and Management

Elevated lactate is a common occurrence after cardiac surgery. This review summarizes the literature on the complex etiology of lactate elevation during and after cardiac surgery, including considerations of oxygen delivery, oxygen utilization, increased metabolism, lactate clearance, medications and fluids, and postoperative complications. Second, the association between lactate and a variety of outcomes are described, and the prognostic role of lactate is critically assessed. Despite the fact that elevated lactate is strongly associated with many important outcomes, including postoperative complications, length of stay, and mortality, little is known about the optimal management of postoperative patients with lactate elevations. This review ends with an assessment of the limited literature on this subject.

Hyperlactatemia and Cardiac Surgery

The normal blood lactate level is 0-2 mmol/L, and a value above 3-5 mmol/L is variably used to define hyperlactatemia. In cardiac surgical patients, hyperlactatemia can arise from both hypoxic and non-hypoxic mechanisms. The major non-hypoxic mechanism is likely stress-induced accelerated aerobic metabolism, in which elevated lactate results from a mass effect on the lactate/pyruvate equilibrium. The lactate/pyruvate ratio is normal (<20) in this circumstance. Hyperlactatemia can also result from impaired global or regional oxygen delivery, in which case the lactate/pyruvate ratio is typically elevated (>20). Lactate is a strong anion that is virtually fully dissociated at physiological pH. As such, increased lactate concentration reduces the strong ion difference and exerts an acidifying effect on the blood. Hyperlactatemia in cardiac surgery patients has been categorized as either early or late onset. Early-onset hyperlactatemia is that which develops in the operating room or very early following intensive care unit (ICU) admission. Early-onset hyperlactatemia is strongly associated with adverse outcome and probably arises as a consequence of both hypoxic (e.g., microcirculatory shock) and non-hypoxic (accelerated aerobic metabolism) mechanisms. By contrast, late-onset hyperlactatemia is a benign, self-limiting condition that typically arises within 6-12 hours of ICU admission and spontaneously resolves within 24 hours. Late onset hyperlactatemia occurs in the absence of any evidence of global or regional tissue hypoxia. The mechanism of late onset hyperlactatemia is not understood. Hyperlactatemia is a common accompaniment to treatment with β₂-agonists such as epinephrine. Epinephrine-induced hyperlactatemia is thought to be due to accelerated aerobic metabolism and requires no specific intervention. Irrespective of the cause, the presence of hyperlactatemia should trigger a search for remedial causes of impaired tissue oxygenation, bearing in mind that normal-or even supranormal-indices of global oxygen delivery may exist despite regional tissue hypoperfusion.

Retuning mortality risk prediction in paediatric cardiac surgery: the additional role of early postoperative metabolic and respiratory profile

OBJECTIVES

The existing risk stratification scores for paediatric patients undergoing cardiac surgery include the Aristotle Basic Complexity (ABC) Score, the Risk Adjustment in Congenital Heart Surgery-1 (RACHS-1) Score and the Aristotle Comprehensive Complexity (ACC) Score. They are all based on the nature of the surgical operation (ABC and RACHS-1 Scores) with possible adjustment for a number of patient conditions (ACC Score). The present study investigates if the early postoperative parameters may be used to improve the preoperative mortality risk prediction.

METHODS

A retrospective study on 1392 consecutive patients aged ≤12 years old, undergoing cardiac surgery with cardiopulmonary bypass and without a residual right-to-left shunt was conducted. The ABC Score and metabolic and respiratory postoperative parameters at arrival in the intensive care unit were tested for association and discriminative power for operative mortality.

RESULTS

The ABC yielded a c-statistic of 0.746. Additional independent predictors of operative mortality were postoperative hypoxia [Formula: see text] and arterial blood lactates. In a multivariable model including the ABC Score, postoperative hypoxia and arterial blood lactates remained independently associated with operative mortality. A modified ABC Score was created, consisting of the ABC Score plus 1.5 points in case of postoperative hypoxia plus 1 point per each 1 mmol/l of arterial blood lactates. The new model was significantly (P = 0.043) more discriminative than the ABC Score, with a c-statistic of 0.803.

CONCLUSIONS

Early postoperative respiratory and metabolic parameters increased the accuracy and discrimination of the ABC Score. An external validation is needed to confirm our results.

Hemodilution on cardiopulmonary bypass as a determinant of early postoperative hyperlactatemia

Objective

The nadir hematocrit (HCT) on cardiopulmonary bypass (CPB) is a recognized independent risk factor for major morbidity and mortality in cardiac surgery. The main interpretation is that low levels of HCT on CPB result in a poor oxygen delivery and dysoxia of end organs. Hyperlactatemia (HL) is a marker of dysoxic metabolism, and is associated with bad outcomes in cardiac surgery. This study explores the relationship between nadir HCT on CPB and early postoperative HL.

Design

Retrospective study on 3,851 consecutive patients.

Measurements and Main Results

Nadir HCT on CPB and other potential confounders were explored for association with blood lactate levels at the arrival in the Intensive Care Unit (ICU), and with the presence of moderate (2.1 – 6.0 mMol/L) or severe (> 6.0 mMol/L) HL. Nadir HCT on CPB demonstrated a significant negative association with blood lactate levels at the arrival in the ICU. After adjustment for the other confounders, the nadir HCT on CPB remained independently associated with moderate (odds ratio 0.96, 95% confidence interval 0.94-0.99) and severe HL (odds ratio 0.91, 95% confidence interval 0.86-0.97). Moderate and severe HL were significantly associated with increased morbidity and mortality.

Conclusions

Hemodilution on CPB is an independent determinant of HL. This association, more evident for severe HL, strengthens the hypothesis that a poor oxygen delivery on CPB with consequent organ ischemia is the mechanism leading to hemodilution-associated bad outcomes.

Factors affecting on serum lactate after cardiac surgery

BACKGROUND

The relation between elevated blood lactate level and mortality and morbidity rates after coronary bypass surgery is a proven subject. One of the factors that seems to affect directly the blood lactate level is the storage duration of packed red blood cells.

OBJECTIVES

This study aimed to evaluate the effect of storage duration of transfused blood on serum lactate during cardiac surgery and up to 24 hours after that in the ICU.

PATIENTS AND METHODS

In a cross-sectional study, 228 patients referred to three hospitals of Mashhad University of Medical Sciences for open cardiac surgery, was enrolled using systematic random sampling method. Immediately after accessing arterial line, the first sample of arterial blood gas (ABG) was obtained. For evaluation of lactate levels, the next samples were obtained at the end of surgery and after 24 hours of staying ICU.

RESULTS

Among 5 factors which affected lactate level during surgery, diabetes and higher ejection fraction (EF) reduced changes of the lactate level. On the other hand, the number of infused blood units, duration of on-pump time, and the mean storage duration of blood units were associated with elevated serum lactate during surgery. A significant relationship was found between blood storage duration and serum lactate levels 24 hours after surgery.

CONCLUSIONS

Comparing the serum lactate level before operation and 24 hours after the operation showed that the number of received blood units had a significant effect on serum lactate. We found no significant effect for blood storage duration; however, the number of given blood units was more significant.

Development of the Post Cardiac Surgery (POCAS) prognostic score

Introduction

The risk of mortality in cardiac surgery is generally evaluated using preoperative risk-scale models. However, intraoperative factors may change the risk factors of patients, and the organism functionality parameters determined upon ICU admittance could therefore be more relevant in deciding operative mortality. The goals of this study were to find associations between the general parameters of organism functionality upon ICU admission and the operative mortality following cardiac operations, to develop a Post Cardiac Surgery (POCAS) Scale to define operative risk categories and to validate an operative mortality risk score.

Methods

We conducted a prospective study, including 920 patients who had undergone cardiac surgery with cardiopulmonary bypass. Several parameters recorded on their ICU admission were explored, looking for a univariate and multivariate association with in-hospital mortality (90 days). In-hospital mortality was 9%. Four independent factors were included in the POCAS mortality risk model: mean arterial pressure, bicarbonate, lactate and the International Normalized Ratio (INR). The POCAS scale was compared with four other risk scores in the validation series.

Results

In-hospital mortality (90 days) was 9%. Four independent factors were included in the POCAS mortality risk model: mean arterial pressure, bicarbonate ratio, lactate ratio and the INR. The POCAS scale was compared with four other risk scores in the validation series. Discriminatory power (accuracy) was defined with a receiver-operating characteristics (ROC) analysis. The best accuracy in predicting in-hospital mortality (90 days) was achieved by POCAS. The areas under the ROC curves of the different systems analyzed were 0.890 (POCAS), followed by 0.847 (Simplified Acute Physiology Score (SAP II)), 0.825 (Sepsis-related Organ Failure Assessment (SOFA)), 0.768 (Acute Physiology and Chronic Health Evaluation (APACHE II)), 0.754 (logistic EuroSCORE), 0.714 (standard EuroSCORE) and 0.699 (Age, Creatinine, Ejection Fraction (ACEF) score).

Conclusions

Our new system to predict the operative mortality risk of patients undergoing cardiac surgery is better than others used for this purpose (SAP II, SOFA, APACHE II, logistic EuroSCORE, standard EuroSCORE, and ACEF score). Moreover, it is an easy-to-use tool since it only requires four risk factors for its calculation.

The interpretation of perioperative lactate abnormalities in patients undergoing cardiac surgery

Hyperlactataemia and lactic acidosis are commonly encountered during and after cardiac surgery. Perioperative lactate production increases in the myocardium, skeletal muscle, lungs and in the splanchnic circulation during cardiopulmonary bypass. Hyperlactataemia has a bimodal distribution in the perioperative period. An early increase in lactate levels, arising intraoperatively or soon after intensive care unit admission, is a familiar and concerning finding for most clinicians. It is highly suggestive of tissue ischaemia and is associated with a prolonged intensive care unit stay, a prolonged requirement for respiratory and cardiovascular support and increased postoperative mortality. Its presence should prompt a thorough search for potential causes of tissue hypoxia. In contrast, late-onset hyperlactataemia, a less well recognised complication, occurs 4 to 24 hours after completion of surgery and is typically associated with preserved cardiac output and oxygen delivery. Risk factors for late-onset hyperlactataemia include hyperglycaemia, long cardiopulmonary bypass time and elevated endogenous catecholamines. Although patients with this complication may have a longer duration of ventilation and intensive care unit length of stay than those with normolactataemia, an association with increased mortality has not been demonstrated. The discovery of late-onset hyperlactataemia should not delay the postoperative progress of an otherwise stable patient following cardiac surgery.

EuroSCORE and neutrophil adhesion molecules predict outcome post-cardiac surgery

BACKGROUND

This study tested the hypothesis that surgical stress and the host response to this trauma trigger an inflammatory cascade in which the neutrophil plays a central role. We hypothesised that pre-operative neutrophil migratory responses will correlate with post-operative clinical outcome in our shock model of open-heart surgery patients. We also tested the hypothesis that surface expression of adhesion molecules involved in the migratory process - CD11b, CD47 and CD99 - could be used to predict outcome. We believe that combining neutrophil migratory response, CD11b, CD47 and CD99 with the logistic European System for Cardiac Operative Risk Evaluation (EuroSCORE) will strengthen the power of the EuroSCORE not only in predicting post-operative mortality but also other clinical endpoints.

MATERIALS AND METHODS

Neutrophils were isolated pre-operatively from n = 31 patients undergoing open-heart surgery and allowed to migrate across endothelial monolayers in response to N-formyl-methionine-leucine-phenylalanine (fMLP). Isolated neutrophils were also assessed for surface expression of CD11b, CD47 and CD99 in response to fMLP by flow cytometry. Post-operative clinical parameters collected included days 1-5 white cell count and creatinine levels as well as intensive care unit (ICU) and post-operative hospital stay.

RESULTS

Pre-operative surface expression of CD99 and CD47 correlates with post-operative creatinine levels (P < 0·05), a measurement of renal injury. We also show that while the logistic EuroSCORE alone can be used as a predictor of ICU stay, when combined with pre-operative CD99 surface expression, it improves its AUC value (0·794).

CONCLUSION

Immunological markers, specifically the ability of the neutrophil to migrate, combined with the logistic EuroSCORE lead to improved sensitivity and specificity to predict patient outcome.