Nadir hematocrit during cardiopulmonary bypass: End-organ dysfunction and mortality

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

Bilateral nephrectomy impairs cardiovascular function and cerebral perfusion in a rat model of acute hemodilutional anemia

Anemia and renal failure are independent risk factors for perioperative stroke, prompting us to assess the combined impact of acute hemodilutional anemia and bilateral nephrectomy (2Nx) on microvascular brain Po2 (PBro2) in a rat model. Changes in PBro2 (phosphorescence quenching) and cardiac output (CO, echocardiography) were measured in different groups of anesthetized Sprague-Dawley rats (1.5% isoflurane, n = 5-8/group) randomized to Sham 2Nx or 2Nx and subsequently exposed to acute hemodilutional anemia (50% estimated blood volume exchange with 6% hydroxyethyl starch) or time-based controls (no hemodilution). Outcomes were assessed by ANOVA with significance assigned at P < 0.05. At baseline, 2Nx rats demonstrated reduced CO (49.9 ± 9.4 vs. 66.3 ± 19.3 mL/min; P = 0.014) and PBro2 (21.1 ± 2.9 vs. 32.4 ± 3.1 mmHg; P < 0.001) relative to Sham 2Nx rats. Following hemodilution, 2Nx rats demonstrated a further decrease in PBro2 (15.0 ± 6.3 mmHg, P = 0.022). Hemodiluted 2Nx rats did not demonstrate a comparable increase in CO after hemodilution compared with Sham 2Nx (74.8 ± 22.4 vs. 108.9 ± 18.8 mL/min, P = 0.003) that likely contributed to the observed reduction in PBro2. This impaired CO response was associated with reduced fractional shortening (33 ± 9 vs. 51 ± 5%) and increased left ventricular end-systolic volume (156 ± 51 vs. 72 ± 15 µL, P < 0.001) suggestive of systolic dysfunction. By contrast, hemodiluted Sham 2Nx animals demonstrated a robust increase in CO and preserved PBro2. These data support the hypothesis that the kidney plays a central role in maintaining cerebral perfusion and initiating the adaptive increase in CO required to optimize PBro2 during acute anemia.NEW & NOTEWORTHY This study has demonstrated that bilateral nephrectomy acutely impaired cardiac output (CO) and microvascular brain Po2 (PBro2), at baseline. Following acute hemodilution, nephrectomy prevented the adaptive increase in CO associated with acute hemodilution leading to a further reduction in PBro2, accentuating the degree of cerebral tissue hypoxia. These data support a role for the kidney in maintaining PBro2 and initiating the increase in CO that optimized brain perfusion during acute anemia.

Impact of Hemoglobin Level in Ex Vivo Heart Perfusion on Donation After Circulatory Death Hearts: A Juvenile Porcine Experimental Model

BACKGROUND

Ex vivo heart perfusion (EVHP) of donation after circulatory death (DCD) hearts has become an effective strategy in adults; however, the small circulating volume in pediatrics poses the challenge of a low-hemoglobin (Hb) perfusate. We aimed to determine the impact of perfusate Hb levels during EVHP on DCD hearts using a juvenile porcine model.

METHODS

Sixteen DCD piglet hearts (11-14 kg) were reperfused for 4 h in unloaded mode followed by working mode. Metabolism, cardiac function, and cell damage were compared between the low-Hb (Hb, 5.0-5.9 g/dL; n = 8) and control (Hb, 7.5-8.4 g/dL; n = 8) groups. Between-group differences were evaluated using 2-sample t-tests or Fisher's Exact tests.

RESULTS

During unloaded mode, the low-Hb group showed lower myocardial oxygen consumption (P < 0.001), a higher arterial lactate level (P = 0.001), and worse systolic ventricular function (P < 0.001). During working mode, the low-Hb group had a lower cardiac output (mean, 71% versus 106% of normal cardiac output, P = 0.010) and a higher arterial lactate level (P = 0.031). Adjusted cardiac troponin-I (P = 0.112) did not differ between the groups. Morphological myocyte injury in the left ventricle was more severe in the low-Hb group (P = 0.028).

CONCLUSIONS

Low-Hb perfusate with inadequate oxygen delivery induced anaerobic metabolism, resulting in suboptimal DCD heart recovery and declined cardiac function. Arranging an optimal perfusate is crucial to organ protection, and further endeavors to refine the priming volume of EVHP or the transfusion strategy are required.

Intraoperative Anemia Mediates Sex Disparity in Operative Mortality After Coronary Artery Bypass Grafting

BACKGROUND

Women undergoing coronary artery bypass grafting (CABG) have higher operative mortality than men.

OBJECTIVES

The purpose of this study was to evaluate the relationship between intraoperative anemia (nadir intraoperative hematocrit), CABG operative mortality, and sex.

METHODS

This was a cohort study of 1,434,225 isolated primary CABG patients (344,357 women) from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (2011-2022). The primary outcome was operative mortality. The attributable risk (AR) (the risk-adjusted strength of the association of female sex with CABG outcomes) for the primary outcome was calculated. Causal mediation analysis derived the total effect of female sex on operative mortality risk and the proportion of that effect mediated by intraoperative anemia.

RESULTS

Women had lower median nadir intraoperative hematocrit (22.0% [Q1-Q3: 20.0%-25.0%] vs 27.0% [Q1-Q3: 24.0%-30.0%], standardized mean difference 97.0%) than men. Women had higher operative mortality than men (2.8% vs 1.7%; P < 0.001; adjusted OR: 1.36; 95% CI: 1.30-1.41). The AR of female sex for operative mortality was 1.21 (95% CI: 1.17-1.24). After adjusting for nadir intraoperative hematocrit, AR was reduced by 43% (1.12; 95% CI: 1.09-1.16). Intraoperative anemia mediated 38.5% of the increased mortality risk associated with female sex (95% CI: 32.3%-44.7%). Spline regression showed a stronger association between operative mortality and nadir intraoperative hematocrit at hematocrit values <22.0% (P < 0.001).

CONCLUSIONS

The association of female sex with increased CABG operative mortality is mediated to a large extent by intraoperative anemia. Avoiding nadir intraoperative hematocrit values below 22.0% may reduce sex differences in CABG operative mortality.

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.

Reno- and cardioprotective molecular mechanisms of SGLT2 inhibitors beyond glycemic control: from bedside to bench

Large placebo-controlled clinical trials have shown that sodium-glucose cotransporter-2 inhibitors (SGLT2i) delay the deterioration of renal function and reduce cardiovascular events in a glucose-independent manner, thereby ultimately reducing mortality in patients with chronic kidney disease (CKD) and/or heart failure. These existing clinical data stimulated preclinical studies aiming to understand the observed clinical effects. In animal models, it was shown that the beneficial effect of SGLT2i on the tubuloglomerular feedback (TGF) improves glomerular pressure and reduces tubular workload by improving renal hemodynamics, which appears to be dependent on salt intake. High salt intake might blunt the SGLT2i effects on the TGF. Beyond the salt-dependent effects of SGLT2i on renal hemodynamics, SGLT2i inhibited several key aspects of macrophage-mediated renal inflammation and fibrosis, including inhibiting the differentiation of monocytes to macrophages, promoting the polarization of macrophages from a proinflammatory M1 phenotype to an anti-inflammatory M2 phenotype, and suppressing the activation of inflammasomes and major proinflammatory factors. As macrophages are also important cells mediating atherosclerosis and myocardial remodeling after injury, the inhibitory effects of SGLT2i on macrophage differentiation and inflammatory responses may also play a role in stabilizing atherosclerotic plaques and ameliorating myocardial inflammation and fibrosis. Recent studies suggest that SGLT2i may also act directly on the Na+/H+ exchanger and Late-INa in cardiomyocytes thus reducing Na+ and Ca2+ overload-mediated myocardial damage. In addition, the renal-cardioprotective mechanisms of SGLT2i include systemic effects on the sympathetic nervous system, blood volume, salt excretion, and energy metabolism.

Clinical evaluation of two adult oxygenator systems in terms of mortality and major adverse events

PURPOSE

The primary aim of this study was to examine the effects of two oxygenator systems on major adverse events and mortality.

METHODS

A total of 181 consecutive patients undergoing coronary artery bypass grafting in our clinic were retrospectively analyzed. The patients were divided into two groups according to the oxygenator used: Group M, in which a Medtronic Affinity (Medtronic Operational Headquarters, Minneapolis, MN, USA) oxygenator was used, and Group S, in which a Sorin Inspire (Sorin Group Italia, Mirandola, Italy) oxygenator was used.

RESULTS

Group S consisted of 89 patients, whereas Group M included 92 patients. No statistically significant differences were found between the two groups in terms of age (p = .112), weight (p = .465), body surface area (p = .956), or gender (p = .484). There was no statistically significant difference in hemorrhage on the first or second postoperative day (p = .318 and p = .455, respectively). No statistically significant differences were observed in terms of red blood cell (p = .468), fresh frozen plasma (p = .116), or platelet concentrate transfusion (p = .212). Infections, wound complications, and delayed sternal closure were significantly more common in Group M (p = .006, p = .023, and p = .019, respectively). Extracorporeal membrane oxygenators and intra-aortic balloon pumps were required significantly more frequently in Group S (p = .025 and p = .013, respectively). Major adverse events occurred in 16 (18%) patients in Group S and 14 (15.2%) patients in Group M (p = .382). Mortality was observed in six (6.7%) patients in Group S and three (3.3%) patients in Group M (p = .232). No statistically significant difference was found between the two groups in terms of length of hospital stay (p = .451).

CONCLUSION

The clinical outcomes of the two oxygenator systems, including mortality, major adverse events, hemorrhage, erythrocyte and platelet transfusions, and length of hospital stay, were similar.

Effect of nadir hematocrit during cardiopulmonary bypass on the early outcomes after surgical repair of acute type A aortic dissection

OBJECTIVE

Although hemodilution during hypothermic cardiopulmonary bypass (CPB) had been thought to improve microcirculation and reduce blood viscosity, there has been no report investigating the effect of low nadir hematocrit (Hct) values caused by severe hemodilution on the surgical outcomes of patients with acute type A aortic dissection (ATAAD).

METHODS

We retrospectively reviewed 112 consecutive patients who emergently underwent emergency surgical repair of ATAAD at our institution. The patients were classified into the high Hct (nadir Hct ≥ 21% during CPB; n = 51) and low Hct (nadir Hct < 21% during CPB; n = 61) groups. After propensity score matching of preoperative characteristics, surgical outcomes were compared between the groups.

RESULTS

Although there was no difference in the surgical procedure, longer CPB time and more blood transfusion during surgery were needed in the low Hct group than in the high Hct group. After surgery, estimated glomerular filtration rate was significantly lower (p = .015), lactaic acid was higher (p = .045), and intubation time was longer (p = .018) in the low Hct group than in the high Hct group, although there was no difference in hospital mortality between the groups. The AUC of the nadir Hct during CPB as a prognostic indicator of prolonged postoperative ventilator support was 0.8, with the highest accuracy at 16.7% (sensitivity 88%, specificity 76.9%). In all cohorts, female sex was an independent risk factor for a lower nadir Hct value of <21% during CPB.

CONCLUSION

A lower nadir Hct value of <21% during CPB may be associated with postoperative renal dysfunction and prolonged ventilator support in patients with ATAAD.

Intraoperative nadir hematocrit as a poor outcome predictor after acute type A aortic dissection surgey

Acute type A aortic dissection is a life-threatening disease associated with high morbidity and mortality that requires urgent surgical intervention. Hemodilution is inevitable in cardiac operations performed with cardiopulmonary bypass, which leads to nadir hematocrit levels. Studies have shown that nadir hematocrit levels are associated with poor postoperative outcomes. The management strategy of intraoperative anemia in these operations is still controversial. Should we follow the patients with intraoperative low hematocrit values or should we transfuse them? In addition to intraoperative nadir hematocrit, cannulation strategies play an important role in early postoperative outcomes after aortic dissection surgery.

Retrograde autologous priming in cardiac surgery: a systematic review and meta-analysis

OBJECTIVES

Guidelines recommend retrograde autologous priming (RAP) of the cardiopulmonary bypass circuit. However, the efficacy and safety of RAP is not well-established. We performed a systematic review and meta-analysis to determine the effects of RAP on transfusion requirements, morbidity and mortality.

METHODS

We searched Cochrane Central Register of Controlled Trials, Medline, ScienceDirect, Cumulative Index to Nursing and Allied Health Literature and Embase for randomized controlled trials (RCTs) and observational studies comparing RAP to no-RAP. We performed title and abstract review, full-text screening, data extraction and risk of bias assessment independently and in duplicate. We pooled data using a random effects model.

RESULTS

Twelve RCTs (n = 1206) and 17 observational studies (n = 3565) were included. Fewer patients required blood transfusions with RAP [RCTs; risk ratio 0.58 [95% confidence interval (CI): 0.51, 0.65], P < 0.001, and observational studies; risk ratio 0.65 [95% CI: 0.53, 0.80], P < 0.001]. The number of units transfused per patient was also lower among patients who underwent RAP (RCTs; mean difference -0.38 unit [95% CI: -0.72, -0.04], P = 0.03, and observational studies; mean difference -1.03 unit [95% CI: -1.76, -0.29], P < 0.006).

CONCLUSIONS

This meta-analysis supports the use of RAP as a blood conservation strategy since its use during cardiopulmonary bypass appears to reduce transfusion requirements.

Development and Validation of a Risk Score for Respiratory Failure After Cardiac Surgery

BACKGROUND

Postoperative respiratory failure, defined as ventilator dependency for more than 48 hours or unplanned reintubation within 30 days, is a costly complication of cardiac surgery that increases mortality and length of stay. Stratification of patients by risk upon intensive care unit admission could identify cases requiring early measures to prevent respiratory failure. This study aimed to develop and validate a risk score for postoperative respiratory failure after cardiac surgery.

METHODS

This retrospective analysis of 4262 patients admitted to the cardiovascular intensive care unit after major cardiac surgery between 01/2013 and 12/2017, used the Society of Thoracic Surgeons database and ventilator data from the respiratory therapy department. Patients were randomly and equally assigned to development and validation cohorts. Covariates used in the multivariable models were assigned weighted points proportional to their β regression coefficient values to create the risk score, which categorized patients into low, medium, and high risk of postoperative respiratory failure.

RESULTS

In both cohorts, postoperative respiratory failure risk was significantly different between risk categories. Compared to low-risk patients, moderate-risk patients had a two times greater risk, and high-risk patients had a four to seven times greater risk. Body mass index, previous cardiac surgery, cardiopulmonary bypass, cardiogenic shock, pulmonary disease presence, baseline functional status, hemodynamic instability, and number of blood products used intraoperatively were significant predictors of respiratory failure.

CONCLUSIONS

This risk score can stratify patients by risk for developing postoperative respiratory failure after major cardiac surgery, which may help in the development of preventive measures.

Anemia in Cardiac Surgery - Can Something Bad Get Worse?

INTRODUCTION

Anemia and blood transfusion are risk factors for morbidity/mortality in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). The objective of this study is to analyze the association of blood transfusion with morbidity/ mortality in patients undergoing coronary artery bypass grafting (CABG) under CPB in the state of São Paulo, Brazil.

METHODS

This is a retrospective analysis using the State of São Paulo Registry of Cardiovascular Surgery from November 2013 to August 2014. Blood transfusion was only considered during surgery or within six hours after surgery. Anemia was defined as hematocrit ≤ 37.5%. Patients < 18 years old were excluded. The sample was divided in four groups - Group I (851, no anemia), Group II (200, anemia without blood transfusion), Group III (181, no anemia and transfusion), and Group IV (258, anemia and transfusion).

RESULTS

A total of 1,490 patients were included; 639 (42.9%) were anemic and 439 (29.5%) underwent blood transfusion. Group II showed lower composite morbidity (odds ratio [OR] -0.05; confidence interval [CI] -0.27-0.17; P=0.81) than Group III (OR 0.41; CI 0.23-0.59; P=0.018) or Group IV (OR 0.54; CI 0.31- 0.77; P=0.016). Group III was at greater risk of mortality (OR 0.73; CI 0.43-1.03; P=0.02) than Group II, which was exposed only to anemia (OR -0.13; CI -0.55-0.29; P=0.75), or Group IV (OR 0.29; CI -0.13-0.71; P=0.539).

CONCLUSION

Anemia in patients undergoing CABG with CPB is bad, but blood transfusion can be worse, increasing at least 50% the risk for mortality and/or morbidity.

Acute Kidney Injury in Cardiac Surgery

Acute kidney injury (AKI) occurs frequently after cardiac surgery and is associated with high morbidity and mortality. Although the number of cardiac surgical procedures is constantly growing worldwide, incidence of cardiac surgery-associated AKI is still around 40% and has a significant impact on global health care costs. Numerous trials attempted to identify strategies to prevent AKI and attenuate its detrimental consequences. Effective options remained elusive. Current evidence supports a multimodal risk-stratification approach with biomarker-guided management of high-risk patients, perioperative administration of dexmedetomidine, and implementation of a care bundle as recommended by the Kidney Disease: Improving Global Outcomes group.

Observational study of pre-operative intravenous iron given to anaemic patients before elective cardiac surgery

Cardiac surgical patients with anaemia experience increased morbidity and mortality. Iron deficiency is the most common cause of pre-operative anaemia in this group. We designed and implemented the Cardiff Pathway, a pre-assessment and treatment pathway to identify cardiac surgical patients with anaemia and iron deficiency. Patients identified with anaemia and/or iron deficiency (Hb < 130 g.l^-1 and ferritin < 100 μg.l^-1 ) were offered intravenous iron infusion 20 mg.kg^-1 pre-operatively. Treatment success was defined as Hb ≥ 130g.l^-1 on the day of surgery. We analysed data from 447 patients: 300 (67%) were not anaemic; 75 (17%) were anaemic and treated with intravenous iron; and 72 (16%) were anaemic and not treated. Haemoglobin concentration increased in successfully treated anaemic patients by a mean (95%CI) of 17 (13-21) g.l^-1 and they received a median (IQR [range]) of 0 (0-2 [0-15]) units of blood peri-operatively. Transfusion was avoided in 54% of the successfully treated anaemic patients, which was significantly more than the unsuccessfully treated anaemic (22%, p = 0.005) and untreated anaemic (28%, p = 0.018) patients and similar to non-anaemic patients who received a median (IQR [range] of 0 (0-1 [0-16])) units of blood and, 63% avoided transfusion). Mean (95%CI) Hb fell between pre-assessment and surgery in the untreated anaemic (-2 (0 to -4) g.l^-1 ) and non-anaemic groups (-2 (-1 to -3) g.l^-1 ). Twenty-one (7%) of the non-anaemic group became newly anaemic waiting for surgery. The Cardiff Pathway reliably identified patients with anaemia and iron deficiency. Anaemic patients who had their Hb restored to normal after treatment required less blood peri-operatively and over half of them required no transfusion at all.

Safety of a Restrictive versus Liberal Approach to Red Blood Cell Transfusion on the Outcome of AKI in Patients Undergoing Cardiac Surgery: A Randomized Clinical Trial

BACKGROUND

Safely reducing red blood cell transfusions can prevent transfusion-related adverse effects, conserve the blood supply, and reduce health care costs. Both anemia and red blood cell transfusion are independently associated with AKI, but observational data are insufficient to determine whether a restrictive approach to transfusion can be used without increasing AKI risk.

METHODS

In a prespecified kidney substudy of a randomized noninferiority trial, we compared a restrictive threshold for red blood cell transfusion (transfuse if hemoglobin<7.5 g/dl, intraoperatively and postoperatively) with a liberal threshold (transfuse if hemoglobin<9.5 g/dl in the operating room or intensive care unit, or if hemoglobin<8.5 g/dl on the nonintensive care ward). We studied 4531 patients undergoing cardiac surgery with cardiopulmonary bypass who had a moderate-to-high risk of perioperative death. The substudy's primary outcome was AKI, defined as a postoperative increase in serum creatinine of ≥0.3 mg/dl within 48 hours of surgery, or ≥50% within 7 days of surgery.

RESULTS

Patients in the restrictive-threshold group received significantly fewer transfusions than patients in the liberal-threshold group (1.8 versus 2.9 on average, or 38% fewer transfusions in the restricted-threshold group compared with the liberal-threshold group; P<0.001). AKI occurred in 27.7% of patients in the restrictive-threshold group (624 of 2251) and in 27.9% of patients in the liberal-threshold group (636 of 2280). Similarly, among patients with preoperative CKD, AKI occurred in 33.6% of patients in the restrictive-threshold group (258 of 767) and in 32.5% of patients in the liberal-threshold group (252 of 775).

CONCLUSIONS

Among patients undergoing cardiac surgery, a restrictive transfusion approach resulted in fewer red blood cell transfusions without increasing the risk of AKI.

Predictors and impact of right heart failure severity following left ventricular assist device implantation

Background

Right heart failure (RHF) is a well-known consequence of left ventricular assist device (LVAD) placement, and has been linked to negative surgical outcomes. However, little is known regarding risk factors associated with RHF. This article delineates pre- and intra-operative risk factors for RHF following LVAD implantation and demonstrates the effect of RHF severity on key surgical outcomes.

Methods

We performed a retrospective analysis of consecutive LVAD patients treated at our center between 2008 and 2016. RHF was categorized using the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) definition of none/mild, moderate, severe, and acute-severe. We constructed a predictive model using multivariable logistic regression and performed a competing risks analysis for survival stratified by RHF severity.

Results

Of 202 subjects, 52 (25.7%) developed moderate or worse RHF. Cardiopulmonary bypass (CPB) time and nadir hematocrit contributed jointly to the model of RHF severity (moderate or worse vs. none/mild; area under the curve =0.77). Postoperative length of stay (LOS) was shortest in the non/mild group and longest in the acute-severe group (median 13 vs. 29.5 days; P<0.001). Stage 2/3 acute kidney injury (range, 26-57%, P=0.002), respiratory failure (13-94%, P<0.001), stroke (0-32%, P=0.02), and 1-year mortality (19-64%, P=0.002) differed by severity. Those with acute-severe RHF had 5.4 [95% confidence interval (CI), 2.5-11.8] times the risk of 1-year mortality compared to those who did not have RHF.

Conclusions

RHF remains a postoperative threat and is associated with worsened surgical outcomes. Ongoing research will reveal further opportunities to mitigate RHF post-LVAD.

Six-Month Outcomes after Restrictive or Liberal Transfusion for Cardiac Surgery

BACKGROUND

We reported previously that, in patients undergoing cardiac surgery who were at moderate-to-high risk for death, a restrictive transfusion strategy was noninferior to a liberal strategy with respect to the composite outcome of death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis by hospital discharge or 28 days after surgery, whichever came first. We now report the clinical outcomes at 6 months after surgery.

METHODS

We randomly assigned 5243 adults undergoing cardiac surgery to a restrictive red-cell transfusion strategy (transfusion if the hemoglobin concentration was <7.5 g per deciliter intraoperatively or postoperatively) or a liberal red-cell transfusion strategy (transfusion if the hemoglobin concentration was <9.5 g per deciliter intraoperatively or postoperatively when the patient was in the intensive care unit [ICU] or was <8.5 g per deciliter when the patient was in the non-ICU ward). The primary composite outcome was death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis occurring within 6 months after the initial surgery. An expanded secondary composite outcome included all the components of the primary outcome as well as emergency department visit, hospital readmission, or coronary revascularization occurring within 6 months after the index surgery. The secondary outcomes included the individual components of the two composite outcomes.

RESULTS

At 6 months after surgery, the primary composite outcome had occurred in 402 of 2317 patients (17.4%) in the restrictive-threshold group and in 402 of 2347 patients (17.1%) in the liberal-threshold group (absolute risk difference before rounding, 0.22 percentage points; 95% confidence interval [CI], -1.95 to 2.39; odds ratio, 1.02; 95% CI, 0.87 to 1.18; P=0.006 for noninferiority). Mortality was 6.2% in the restrictive-threshold group and 6.4% in the liberal-threshold group (odds ratio, 0.95; 95% CI, 0.75 to 1.21). There were no significant between-group differences in the secondary outcomes.

CONCLUSIONS

In patients undergoing cardiac surgery who were at moderate-to-high risk for death, a restrictive strategy for red-cell transfusion was noninferior to a liberal strategy with respect to the composite outcome of death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis at 6 months after surgery. (Funded by the Canadian Institutes of Health Research and others; TRICS III ClinicalTrials.gov number, NCT02042898 .).

Positive impact of retrograde autologous priming in adult patients undergoing cardiac surgery: a randomized clinical trial

BACKGROUND

Adult cardiac surgery with extracorporeal circulation is known to be associated with increased risk of blood transfusion leading to adverse outcomes. Procedures like retrograde autologous priming (RAP) may reduce these negative side effects. This randomized prospective study was initiated to assess whether RAP using specifically designed RAP bag (Terumo) has immediate effects on patient outcome.

METHODS

One hundred eighteen adults undergoing elective CABG or elective aortic valve replacement were randomly assigned by a computer program into two groups: the RAP group (n = 54) in which the retrograde autologous priming was applied and the non-RAP (n = 64) group in which the same setting was used without the possibility to save priming volume. Patient demographics, preoperative characteristics and postoperative outcomes were analyzed for both groups.

RESULTS

The primary endpoint defined as rate of intraoperative blood transfusion was significantly reduced in the RAP-group (p = 0.04). The absolute risk reduction for RAP managed patients was 13.5 percent points. There were no significant differences in operation time and blood loss. No deaths and no myocardial infarctions were observed. The number of patients needed to treat to prevent at least one red blood cell transfusion was around 8 (NNT = 7.42).

CONCLUSIONS

Retrograde autologous priming is a safe and less invasive procedure which achieves clear benefits for adult cardiac surgery patients. In the light of increasing red blood cell transfusion risks and costs and the wish of patients to avoid a transfusion implementation of retrograde autologous priming is an interesting option.

TRIAL REGISTRATION

German Clinical Trials Register ID: DRKS00013512 , registered 04 December 2017.

Preoperative anemia versus blood transfusion: Which is the culprit for worse outcomes in cardiac surgery?

BACKGROUND

Reducing blood product utilization after cardiac surgery has become a focus of perioperative care as studies have suggested improved outcomes. The relative impact of preoperative anemia versus packed red blood cells (PRBC) transfusion on outcomes remains poorly understood, however. In this study, we investigated the relative association between preoperative hematocrit (Hct) level and PRBC transfusion on postoperative outcomes after coronary artery bypass grafting (CABG) surgery.

METHODS

Patient records for primary, isolated CABG operations performed between January 2007 and December 2017 at 19 cardiac surgery centers were evaluated. Hierarchical logistic regression modeling was used to estimate the relationship between baseline preoperative Hct level as well as PRBC transfusion and the likelihoods of postoperative mortality and morbidity, adjusted for baseline patient risk. Variable and model performance characteristics were compared to determine the relative strength of association between Hct level and PRBC transfusion and primary outcomes.

RESULTS

A total of 33,411 patients (median patient age, 65 years; interquartile range [IQR], 57-72 years; 26% females) were evaluated. The median preoperative Hct value was 39% (IQR, 36%-42%), and the mean Society of Thoracic Surgeons (STS) predicted risk of mortality was 1.8 ± 3.1%. Complications included PRBC transfusion in 31% of patients, renal failure in 2.8%, stroke in 1.3%, and operative mortality in 2.0%. A strong association was observed between preoperative Hct value and the likelihood of PRBC transfusion (P < .001). After risk adjustment, PRBC transfusion, but not Hct value, demonstrated stronger associations with postoperative mortality (odds ratio [OR], 4.3; P < .0001), renal failure (OR 6.3; P < .0001), and stroke (OR, 2.4; P < .0001). A 1-point increase in preoperative Hct was associated with decreased probabilities of mortality (OR, 0.97; P = .0001) and renal failure (OR, 0.94; P < .0001). The models with PRBC had superior predictive power, with a larger area under the curve, compared with Hct for all outcomes (all P < .01). Preoperative anemia was associated with up to a 4-fold increase in the probability of PRBC transfusion, a 3-fold increase in renal failure, and almost double the mortality.

CONCLUSIONS

PRBC transfusion appears to be more closely associated with risk-adjusted morbidity and mortality compared with preoperative Hct level alone, supporting efforts to reduce unnecessary PRBC transfusions. Preoperative anemia independently increases the risk of postoperative morbidity and mortality. These data suggest that preoperative Hct should be included in the STS risk calculators. Finally, efforts to optimize preoperative hematocrit should be investigated as a potentially modifiable risk factor for mortality and morbidity.

Measurement of Blood Loss in Cardiac Surgery: Still Too Much

BACKGROUND

Cardiac surgery is associated with a significant decrease in hematocrit. It is unclear whether that occurs from hemodilution, loss of red cells, or both. Hematocrit is a major determinant of transfusion decisions although transfusion is associated with increased morbidity and mortality. Physicians must determine whether this anemia is the result of hemodilution or red blood cell loss as the former would be treated with packed red blood cell transfusions and the latter by diuresis. We hypothesize that the decrease in hematocrit observed in cardiac surgery is due to hemodilution.

METHODS

Blood volume (BV), plasma volume (PV), and red blood cell volume (RBCV) were measured in 54 patients undergoing coronary artery bypass graft surgery, valve surgery, or coronary artery bypass graft/valve surgery. Measurements were made preoperatively, immediately postoperatively, and 2 hours after surgery utilizing a dilution tracer method and hematocrit measurements.

RESULTS

Preoperative average BV was 6,094 mL (SD 1,904 mL), RBCV was 2,024 mL (SD 720 mL), and PV was 4,070 mL (SD 1,339 mL). Postoperative average BV was 4,834 mL (SD 1,432 mL), RBCV 1,226 mL (SD 527 mL), and PV 3,607 mL (SD 993 mL). Blood volume decreased 18% (p < 0.0001), RBCV decreased 38% (p < 0.001), and PV decreased 8% (p < 0.012). There were no significant changes between postoperative values and those 2 hours later in the cardiac surgery intensive care unit.

CONCLUSIONS

Decreases in hematocrit observed in cardiac surgery patients are due to significant red blood cell losses and not to hemodilution. Red blood cell losses averaged 38%. Plasma volume also decreased.

Red blood cell antibody-induced anemia causes differential degrees of tissue hypoxia in kidney and brain

Moderate anemia is associated with increased mortality and morbidity, including acute kidney injury (AKI), in surgical patients. A red blood cell (RBC)-specific antibody model was utilized to determine whether moderate subacute anemia could result in tissue hypoxia as a potential mechanism of injury. Cardiovascular and hypoxic cellular responses were measured in transgenic mice capable of expressing hypoxia-inducible factor-1α (HIF-1α)/luciferase activity in vivo. Antibody-mediated anemia was associated with mild intravascular hemolysis (6 h) and splenic RBC sequestration ( day 4), resulting in a nadir hemoglobin concentration of 89 ± 13 g/l on day 4. At this time point, renal tissue oxygen tension (P_tO₂) was decreased in anemic mice relative to controls (13.1 ± 4.3 vs. 20.8 ± 3.7 mmHg, P < 0.001). Renal tissue hypoxia was associated with an increase in HIF/luciferase expression in vivo ( P = 0.04) and a 20-fold relative increase in renal erythropoietin mRNA transcription ( P < 0.001) but no increase in renal blood flow ( P = 0.67). By contrast, brain P_tO₂ was maintained in anemic mice relative to controls (22.7 ± 5.2 vs. 23.4 ± 9.8 mmHg, P = 0.59) in part because of an increase in internal carotid artery blood flow (80%, P < 0.001) and preserved cerebrovascular reactivity. Despite these adaptive changes, an increase in brain HIF-dependent mRNA levels was observed (erythropoietin: P < 0.001; heme oxygenase-1: P = 0.01), providing evidence for subtle cerebral tissue hypoxia in anemic mice. These data demonstrate that moderate subacute anemia causes significant renal tissue hypoxia, whereas adaptive cerebrovascular responses limit the degree of cerebral tissue hypoxia. Further studies are required to assess whether hypoxia is a mechanism for acute kidney injury associated with anemia.

Restrictive or Liberal Red-Cell Transfusion for Cardiac Surgery

BACKGROUND

The effect of a restrictive versus liberal red-cell transfusion strategy on clinical outcomes in patients undergoing cardiac surgery remains unclear.

METHODS

In this multicenter, open-label, noninferiority trial, we randomly assigned 5243 adults undergoing cardiac surgery who had a European System for Cardiac Operative Risk Evaluation (EuroSCORE) I of 6 or more (on a scale from 0 to 47, with higher scores indicating a higher risk of death after cardiac surgery) to a restrictive red-cell transfusion threshold (transfuse if hemoglobin level was <7.5 g per deciliter, starting from induction of anesthesia) or a liberal red-cell transfusion threshold (transfuse if hemoglobin level was <9.5 g per deciliter in the operating room or intensive care unit [ICU] or was <8.5 g per deciliter in the non-ICU ward). The primary composite outcome was death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis by hospital discharge or by day 28, whichever came first. Secondary outcomes included red-cell transfusion and other clinical outcomes.

RESULTS

The primary outcome occurred in 11.4% of the patients in the restrictive-threshold group, as compared with 12.5% of those in the liberal-threshold group (absolute risk difference, -1.11 percentage points; 95% confidence interval [CI], -2.93 to 0.72; odds ratio, 0.90; 95% CI, 0.76 to 1.07; P<0.001 for noninferiority). Mortality was 3.0% in the restrictive-threshold group and 3.6% in the liberal-threshold group (odds ratio, 0.85; 95% CI, 0.62 to 1.16). Red-cell transfusion occurred in 52.3% of the patients in the restrictive-threshold group, as compared with 72.6% of those in the liberal-threshold group (odds ratio, 0.41; 95% CI, 0.37 to 0.47). There were no significant between-group differences with regard to the other secondary outcomes.

CONCLUSIONS

In patients undergoing cardiac surgery who were at moderate-to-high risk for death, a restrictive strategy regarding red-cell transfusion was noninferior to a liberal strategy with respect to the composite outcome of death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis, with less blood transfused. (Funded by the Canadian Institutes of Health Research and others; TRICS III ClinicalTrials.gov number, NCT02042898 .).

Experimental assessment of oxygen homeostasis during acute hemodilution: the integrated role of hemoglobin concentration and blood pressure

Background

Low hemoglobin concentration (Hb) and low mean arterial blood pressure (MAP) impact outcomes in critically ill patients. We utilized an experimental model of “normotensive” vs. “hypotensive” acute hemodilutional anemia to test whether optimal tissue perfusion is dependent on both Hb and MAP during acute blood loss and fluid resuscitation, and to assess the value of direct measurements of the partial pressure of oxygen in tissue (P_tO₂).

Methods

Twenty-nine anesthetized rats underwent 40% isovolemic hemodilution (1:1) (or sham-hemodilution control, n = 4) with either hydroxyethyl starch (HES) (n = 14, normotensive anemia) or saline (n = 11, hypotensive anemia) to reach a target Hb value near 70 g/L. The partial pressure of oxygen in the brain and skeletal muscle tissue (P_tO₂) were measured by phosphorescence quenching of oxygen using G4 Oxyphor. Mean arterial pressure (MAP), heart rate, temperature, arterial and venous co-oximetry, blood gases, and lactate were assessed at baseline and for 60 min after hemodilution. Cardiac output (CO) was measured at baseline and immediately after hemodilution. Data were analyzed by repeated measures two-way ANOVA.

Results

Following “normotensive” hemodilution with HES, Hb was reduced to 66 ± 6 g/L, CO increased (p < 0.05), and MAP was maintained. These conditions resulted in a reduction in brain P_tO₂ (22.1 ± 5.6 mmHg to 17.5 ± 4.4 mmHg, p < 0.05), unchanged muscle PO₂, and an increase in venous oxygen extraction. Following “hypotensive” hemodilution with saline, Hb was reduced to 79 ± 5 g/L and both CO and MAP were decreased (P < 0.05). These conditions resulted in a more severe reduction in brain P_tO₂ (23.2 ± 8.2 to 10.7 ± 3.6 mmHg (p < 0.05), a reduction in muscle P_tO₂ (44.5 ± 11.0 to 19.9 ± 12.4 mmHg, p < 0.05), a further increase in venous oxygen extraction, and a threefold increase in systemic lactate levels (p < 0.05).

Conclusions

Acute normotensive anemia (HES hemodilution) was associated with a subtle decrease in brain tissue P_tO₂ without clear evidence of global tissue hypoperfusion. By contrast, acute hypotensive anemia (saline hemodilution) resulted in a profound decrease in both brain and muscle tissue P_tO₂ and evidence of inadequate global perfusion (lactic acidosis). These data emphasize the importance of maintaining CO and MAP to ensure adequacy of vital organ oxygen delivery during acute anemia. Improved methods of assessing P_tO₂ may provide an earlier warning signal of vital organ hypoperfusion.

Revisiting blood transfusion and predictors of outcome in cardiac surgery patients: a concise perspective

In the United States, cardiac surgery-related blood transfusion rates reached new highs in 2010, with 34% of patients receiving blood products. Patients undergoing both complex (coronary artery bypass grafting [CABG] plus valve repair or replacement) and non-complex (isolated CABG) cardiac surgeries are likely to have comorbidities such as anemia. Furthermore, the majority of patients undergoing isolated CABG have a history of myocardial infarction. These characteristics may increase the risk of complications and blood transfusion requirement. It becomes difficult to demonstrate the association between transfusions and mortality because of the fact that most patients undergoing cardiac surgery are also critically ill. Transfusion rates remain high despite the advances in perioperative blood conservation, such as the intraoperative use of cell saver in cardiac surgery. Some recent prospective studies have suggested that the use of blood products, even in low-risk patients, may adversely affect clinical outcomes. In light of this information, we reviewed the literature to assess the clinical outcomes in terms of 30-day and 1-year morbidity and mortality in transfused patients who underwent uncomplicated CABG surgery.

Serum TNF-α levels in children with congenital heart disease undergoing cardiopulmonary bypass: A cohort study in China and a meta-analysis of the published literature

OBJECTIVE

To investigate the changes in tumor necrosis factor alpha (TNF-α) serum levels after cardiopulmonary bypass (CPB) in children with congenital heart disease (CHD), followed by a meta-analysis to analyze the clinical value of TNF-α in CPB.

METHODS

Our cohort study enrolled 67 CHD children, assigned into off-pump group (n=32) and CPB group (n=35). The TNF-α serum levels in two groups were detected by ELISA before the operation (T1), at the end of the operation (0 hour, T2), and after 24 hours of the operation (T3). For meta-analysis, literature search was conducted to identify published case-control articles about the changes of TNF-α serum levels with CPB of CHD.

RESULTS

The TNF-α levels in CPB group were lower than that in the off-pump group at T3 (P=.006). TNF-α level at T3 was significantly lower than that at T1 and T2 (all P<.05). Meta-analysis results further confirmed that the TNF-α levels of CHD children were dramatically decreased at T3 as compared to that at T1 and T2 (both P<.001).

CONCLUSION

The TNF-α serum levels showed a transient and dramatic decline after 24 hours of CPB, and it may act as an important biological indicator for monitoring the efficacy of CPB in CHD children.

Fluid filtration and vascular compliance during cardiopulmonary bypass: effects of two volatile anesthetics

BACKGROUND

As intraoperative fluid accumulation may negatively impact post-operative organ function, strategies minimizing edema generation should be sought for. During general anesthesia, isoflurane in contrast to sevoflurane has been associated with increased fluid extravasation and edema generation. In this study, we tested sevoflurane against isoflurane with focus on vascular compliance and fluid shifts in an experimental cardiopulmonary bypass (CPB) model.

METHODS

Sixteen pigs underwent 120 min of cardiopulmonary bypass with isoflurane or sevoflurane anesthesia. Net fluid balance, plasma volume, serum-electrolytes, serum-albumin, serum-protein, colloid osmotic pressures in plasma and interstitial fluid, hematocrit levels, and total tissue water content were recorded. Intra-abdominal and intracranial pressures were measured directly, and fluid extravasation rates were calculated.

RESULTS

Fluid extravasation rate increased dramatically in both groups during initiation of cardiopulmonary bypass, with no group differences. The animals of the sevoflurane group needed significantly more fluid supplementation to maintain a constant reservoir volume in the CPB circuit during bypass. Plasma volumes prior to bypass were 56.5 ± 7.9 ml/kg (mean ± SD) and 58.7 ± 3.8 ml/kg in the isoflurane group and sevoflurane group, respectively. During bypass, plasma volumes in the isoflurane group decreased about 25%, and remained significantly lowered when compared to the sevoflurane group, where the values remained stable.

CONCLUSIONS

No differences in fluid extravasation rates were observed between sevoflurane and isoflurane. The increased net fluid balance in the sevoflurane group during cardiopulmonary bypass was not associated with edema generation. Plasma volume was retained in the sevoflurane group, in contrast to the isoflurane group.

Hematological Changes in Patients Undergoing Coronary Artery Bypass Surgery: a Prospective Study

Objectives:

Removal of pro inflammatory stimuli after CABG, wound closure and the regenerative ability of the bone marrow will ensure a gradual recovery of hematological parameters. The aim of this study was to assess the hematological changes after CABG.

Materials and Methods:

A prospective cohort study included 164 consecutive patients undergoing on pump CABG surgery between January 2012 and January 2013. Patients with primary hematologic disease, emergent or urgent CABG and off-pump CABG were not included. A time line protocol was employed.

Results:

All patients survived surgery. Average values of erythrocytes, hemoglobin and hematocrit declined, to reach lower values on day 3 after surgery (-33.6 %, -33.1 %, -32.6 % versus preoperative value, p<0.001) and then gradually increased to reach normal values after one month and the preoperative values after three months. The average values of leukocytes and neutrophils increased rapidly to achieve the highest value on day 2, while the average value of lymphocytes decreased quickly to achieve lower value on day 1 after surgery (+74.7 %, +127.1 %, -52.4 % respectively from the preoperative value, p<0.001). The average platelet count decreased to the lowest value on day 2 after surgery (-26.4 % from the preoperative value, p<0.001), after which gradually increased up to +100.8 % of preoperative value on day 14 (p<0.001) and then gradually decreased to reach normal values on day 21 and preoperative values after three months.

Conclusions:

Average values of the three peripheral blood cells parameters undergo important changes after CABG, but not life threatening, and regain normal and preoperative values after 1-3 months after surgery.

Does blood transfusion affect intermediate survival after coronary artery bypass surgery?

BACKGROUND

The aim of this study was to investigate the impact of transfusion of blood products on intermediate outcome after coronary artery bypass surgery.

PATIENTS

Complete data on perioperative blood transfusion in patients undergoing coronary artery bypass surgery were available from 2001 patients who were operated at our institution.

RESULTS

Transfusion of any blood product (relative risk = 1.678, 95% confidence interval = 1.087-2.590) was an independent predictor of all-cause mortality. The additive effect of each blood product on all-cause mortality (relative risk = 1.401, 95% confidence interval = 1.203-1.630) and cardiac mortality (relative risk = 1.553, 95% confidence interval = 1.273-1.895) was evident when the sum of each blood product was included in the regression models. However, when single blood products were included in the regression model, transfusion of fresh frozen plasma/Octaplas® was the only blood product associated with increased risk of all-cause mortality (relative risk = 1.692, 95% confidence interval = 1.222-2.344) and cardiac mortality (relative risk = 2.125, 95% confidence interval = 1.414-3.194). The effect of blood product transfusion was particularly evident during the first three postoperative months. Since follow-up was truncated at 3 months, transfusion of any blood product was a significant predictor of all-cause mortality (relative risk = 2.998, 95% confidence interval = 1.053-0.537). Analysis of patients who survived or had at least 3 months of potential follow-up showed that transfusion of any blood product was not associated with a significantly increased risk of intermediate all-cause mortality (relative risk = 1.430, 95% confidence interval = 0.880-2.323).

CONCLUSIONS

Transfusion of any blood product is associated with a significant risk of all-cause and cardiac mortality after coronary artery bypass surgery. Such a risk seems to be limited to the early postoperative period and diminishes later on. Among blood products, perioperative use of fresh frozen plasma or Octaplas seems to be the main determinant of mortality.

Prophylactic intra-aortic balloon counterpulsation in cardiac surgery: it is time for clear evidence

In the previous issue of Critical Care, Yu and colleagues report increased morbidity and mortality in patients after myocardial infarction undergoing prophylactic intra-aortic balloon pump support before coronary artery bypass graft surgery. The impact of prophylactic intra-aortic balloon pump implantation before coronary artery bypass graft therapy still is controversially debated. However, Yu and colleagues emphasize further discussion and substantiate the need for a prospective randomized controlled trial on this subject.