Cardioprotective Effects of Acute Normovolemic Hemodilution in Patients Undergoing Coronary Artery bypass Surgery

Management of severe peri-operative bleeding: Guidelines from the European Society of Anaesthesiology and Intensive Care: Second update 2022

BACKGROUND

Management of peri-operative bleeding is complex and involves multiple assessment tools and strategies to ensure optimal patient care with the goal of reducing morbidity and mortality. These updated guidelines from the European Society of Anaesthesiology and Intensive Care (ESAIC) aim to provide an evidence-based set of recommendations for healthcare professionals to help ensure improved clinical management.

DESIGN

A systematic literature search from 2015 to 2021 of several electronic databases was performed without language restrictions. Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used to assess the methodological quality of the included studies and to formulate recommendations. A Delphi methodology was used to prepare a clinical practice guideline.

RESULTS

These searches identified 137 999 articles. All articles were assessed, and the existing 2017 guidelines were revised to incorporate new evidence. Sixteen recommendations derived from the systematic literature search, and four clinical guidances retained from previous ESAIC guidelines were formulated. Using the Delphi process on 253 sentences of guidance, strong consensus (>90% agreement) was achieved in 97% and consensus (75 to 90% agreement) in 3%.

DISCUSSION

Peri-operative bleeding management encompasses the patient's journey from the pre-operative state through the postoperative period. Along this journey, many features of the patient's pre-operative coagulation status, underlying comorbidities, general health and the procedures that they are undergoing need to be taken into account. Due to the many important aspects in peri-operative nontrauma bleeding management, guidance as to how best approach and treat each individual patient are key. Understanding which therapeutic approaches are most valuable at each timepoint can only enhance patient care, ensuring the best outcomes by reducing blood loss and, therefore, overall morbidity and mortality.

CONCLUSION

All healthcare professionals involved in the management of patients at risk for surgical bleeding should be aware of the current therapeutic options and approaches that are available to them. These guidelines aim to provide specific guidance for bleeding management in a variety of clinical situations.

Hemodilution on microvascular oxygen delivery potential of the blood during coronary bypass surgery

PURPOSE

The hematocrit-to-whole blood viscosity ratio (Hct/WBV) reflects the blood O₂ delivery potential (O₂-DP). WBV is variable to the dynamic vascular shear rate (SR), 1-5/s at microcirculation and 300/s at larger vessels. To estimate the impact of hemodilution on the blood O₂-DP to the myocardium, we analyzed the hemodilution-induced change of Hct/WBV at SR 5/s (Hct/WBV₅) during off-pump coronary bypass (OPCAB) surgery.

METHODS

During OPCAB surgery (n = 21), 10% acute normovolemic hemodilution (HD 10%) was applied. Arterial blood samples were taken: one before and two after HD 10%. One of which after HD 10% underwent an additional 33% in vitro hemodilution (reaching 40% hemodilution in total, HD 40%). WBV of all blood samples was determined using a scan-capillary tube viscometer (Hemovister^™). The changes of Hct/WBV₅ were analyzed as a primary measure of the study and compared with those of Hct/WBV at SR 300/s (Hct/WBV₃₀₀).

RESULTS

Median[IQR] of Hct/WBV₅ [3.5 (2.8-4.2)%/cPoise] was significantly increased by HD 10 and HD 40% [3.6 (3.2-4.6)%/cPoise and 4.2 (3.3-5.2)%/cPoise, respectively, all P < 0.001], but the degrees of changes after HD 10 and HD 40% were not different. Median[IQR] of Hct/WBV₃₀₀ [10.3(8.6‒10.8)%/cPoise] was not changed by HD 10% [10.3(9.1-11.1)%/cPoise], but it was significantly decreased by HD 40% [8.4(7.4‒9.2)%/cPoise, P < 0.001].

CONCLUSION

The increased Hct/WBV₅ suggests that 10-40% hemodilution improves the blood O₂-DP to the myocardium during OPCAB surgery. The SR-specific discrepancy in Hct/WBV changes advocates using microvascular WBV and Hct/WBV to evaluate the blood O₂-DP changes to the myocardium. Further study is warranted to assess the actual changes in myocardial O₂ delivery.

Effect of acute normovolemic hemodilution on coronary artery bypass grafting: A systematic review and meta-analysis of 22 randomized trials

BACKGROUND

Efficacy of minimal acute normovolemic hemodilution (ANH) in avoiding homologous blood transfusion during cardiovascular surgery remains controversial. Postoperative bleeding and transfusion remain a source of morbidity and cost after open heart operations. To better understand the role of acute normovolemic hemodilution (ANH) in coronary artery bypass grafting (CABG), we compared ANH with standard intraoperative care in a systematic review including a standard pairwise meta-analysis of randomized controlled trials (RCTs).

METHODS

We searched the Cochrane Library, PubMed, EMBASE, Web of Science and Chinese National Knowledge Infrastructure (CNKI) up to April 1, 2020. The primary outcome was to assess the incidence of ANH-related number of allogeneic red blood cell units (ARBCu) transfused. Secondary outcomes included the rate of allogeneic blood transfusion and estimated total blood loss.

RESULTS

A total of 22 RCTs including 1688 patients were identified for the present meta-analysis. Of these studies, 19 were about CABG with on-pump and three with off-pump. Our pooled result indicated that patients received ANH experienced fewer ARBCu transfusions, with a standardized mean difference (SMD) of -0.60 (95%CI -0.96 to -0.24; P = 0.001). The rate of allogeneic blood transfusion in ANH group was significant reduced when compared with controls, with a relative risk (RR) of 0.65 (95%CI 0.52 to 0.82; P = 0.0002). In addition, less postoperative estimated total blood loss was present, with a SMD of -0.53 (95%CI -0.88 to -0.17; P = 0.004).

CONCLUSIONS

The present meta-analysis indicated that ANH could reduce the number of ARBCu transfused in the CABG surgery setting. In addition, ANH could also reduce the rate of ARBCu transfusion and estimated total blood loss for CABG patients.

Proceedings From the Society for Advancement of Blood Management Annual Meeting 2017: Management Dilemmas of the Surgical Patient-When Blood Is Not an Option

Vigilance is essential in the perioperative period. When blood is not an option for the patient, especially in a procedure/surgery that normally holds a risk for blood transfusion, complexity is added to the management. Current technology and knowledge has made avoidance of blood transfusion a realistic option but it does require a concerted patient-centered effort from the perioperative team. In this article, we provide suggestions for a successful, safe, and bloodless journey for patients. The approaches include preoperative optimization as well as intraoperative and postoperative techniques to reduce blood loss, and also introduces current innovative substitutes for transfusions. This article also assists in considering and maneuvering through the legal and ethical systems to respect patients' beliefs and ensuring their safety.

A feasibility and safety study of intracoronary hemodilution during primary coronary angioplasty in order to reduce reperfusion injury in myocardial infarction

OBJECTIVES

We designed a pilot study to evaluate safety and feasibility of an inexpensive and simple approach to intracoronary hemodilution during primary angioplasty (PPCI) to reduce reperfusion injury.

INTRODUCTION

Early revascularization in acute myocardial infarction decreases infarct size and improves outcomes. However, abrupt restoration of coronary flow results in myocardial reperfusion injury and increased final infarct size. Dilution of coronary blood during revascularization may help reduce this damage. If proved effective, such an approach would need to be simple and suitable for widespread adoption.

METHODS

Ten patients presenting with STEMI underwent intracoronary dilution with room temperature Hartmann's solution delivered through the guiding catheter during primary angioplasty (PPCI). Infusion of perfusate began prior to crossing the occluded artery with the guidewire, continuing until 10 min after completion of the balloon and stenting procedure. Infusion was briefly interrupted for contrast injection and pressure monitoring. The outcome measures were safety, including intracoronary temperature reduction and volume of intracoronary perfusate infused, and technical feasibility.

RESULTS

There were no significant symptomatic, hemodynamic, ECG ST/T segment or rhythm changes observed during perfusate administration. The median (interquartile range) volume of perfusate administered was 550 mL (350-725 mL) and the median intracoronary temperature reduction observed was 3.4°Celsius. Myocardial salvage was 0.54 (0.43-0.65).

CONCLUSIONS

Transcatheter intracoronary hemodilution with room temperature perfusate during PPCI is feasible and appears safe. Such a strategy is simple and inexpensive, with potential to be widely applied. Further mechanistic and subsequent outcome powered studies are required to evaluate whether this strategy can reduce reperfusion injury in STEMI.

Mild volume acute normovolemic hemodilution is associated with lower intraoperative transfusion and postoperative pulmonary infection in patients undergoing cardiac surgery -- a retrospective, propensity matching study

Background

Perioperative allogenic transfusion is required in almost 50% of patients undergoing cardiac surgery and is associated with higher risk of mortality and morbidity (Xue et al., Lancet 387:1905, 2016; Ferraris et al., Ann Thorac Surg 91:944–82, 2011). Acute normovolemic hemodilution (ANH) is recommended as a potential strategy during cardiac surgery, but the blood conservation effect and the degree of ANH was still controversial. There is also an increasing concern about the improved outcomes associated with ANH. Therefore, a better understanding of the effect of mild volume ANH during cardiac surgery is urgently needed.

Methods

This retrospective study included 2058 patients who underwent cardiac surgery between 2010 and 2015. The study population was split into two groups (with and without mild volume ANH). Propensity score adjustment analysis was applied. We reported the association between the use of mild volume ANH and perioperative outcomes.

Results

A total of 1289 patients were identified. ANH was performed in 358 patients, and the remaining 931 patients did not receive any ANH. Five hundred of the total patients (38.8%) received perioperative RBC transfusions, 10% (129/1289) of patients received platelet, and 56.4% (727/1289) of patients received fresh frozen plasma transfusions. Mild volume ANH administration was significantly associated with decreased intraoperative RBC transfuse rate (8.5% vs. 14.4%; p = 0.013), number of RBC units (p = 0.019), and decreased postoperative pulmonary infection (6.8 vs. 11.3%; p = 0.036) during cardiac surgery. However, there was no significant difference regarding intraoperative fresh frozen plasma (FFP) and platelet concentrate transfusions, as well as postoperative and total perioperative allogeneic transfusions. Furthermore, there was no significant difference regarding postoperative outcomes including mortality, prolonged wound healing, stroke, atrial fibrillation, reoperation for postoperative bleeding and acute kidney injury. There was also no difference in postoperative ventilation time, length of ICU and hospital stay.

Conclusion

Based on the 5-year experience of mild volume ANH in cardiac surgeries with CPB in our large retrospective cohort, mild volume ANH was associated with decreased intraoperative RBC transfusion and postoperative pulmonary infection in Chinese patients undergoing cardiac surgery. However, there was no significant difference regarding postoperative and total perioperative allogeneic transfusions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12871-017-0305-7) contains supplementary material, which is available to authorized users.

Anesthetic management of a patient with polycythemia vera undergoing emergency repair of a type-A aortic dissection and concomitant coronary artery bypass grafting: a case report

Polycythemia vera is a chronic progressive myeloproliferative disease characterized by increased circulating red blood cells, and the hyperviscosity of the blood can lead to an increased risk of arterial thrombosis. In a previous survey regarding postoperative outcomes in polycythemia vera patients, an increased risk of both vascular occlusive and hemorrhagic complications have been reported. Aortic surgery involving cardiopulmonary bypass may be associated with the development of a coagulopathy, and as a result, the occurrence of thrombotic complications should be avoided after coronary anastomosis. Thus, optimizing the hemostatic balance is an important concern for anesthesiologists. However, only a few cases of anesthetic management in polycythemia vera patients undergoing concomitant aorta and coronary arterial bypass surgery have ever been reported. Here, we experience a polycythemia vera patient who underwent an emergency repair of a type-A aortic dissection and concomitant coronary artery bypass grafting, and report this case with a review of the relevant literature.

Greater Volume of Acute Normovolemic Hemodilution May Aid in Reducing Blood Transfusions After Cardiac Surgery

BACKGROUND

Perioperative red blood cell transfusions (RBC) are associated with increased morbidity and mortality after cardiac surgery. Acute normovolemic hemodilution (ANH) is recommended to reduce perioperative transfusions; however, supporting data are limited and conflicting. We describe the relationship between ANH and RBC transfusions after cardiac surgery using a multi-center registry.

METHODS

We analyzed 13,534 patients undergoing cardiac surgery between 2010 and 2014 at any of the 26 hospitals participating in a prospective cardiovascular perfusion database. The volume of ANH (no ANH, <400 mL, 400 to 799 mL, ≥ 800 mL) was recorded and linked to each center's surgical data. We report adjusted relative risks reflecting the association between the use and amount of ANH and the risk of perioperative RBC transfusion. Results were adjusted for preoperative risk factors, procedure, body surface area, preoperative hematocrit, and center.

RESULTS

The ANH was used in 17% of the patients. ANH was associated with a reduction in RBC transfusions (RRadj [adjusted risk ratio] 0.74, p < 0.001). Patients having 800 mL or greater of ANH had the most profound reduction in RBC transfusions (RRadj 0.57, p < 0.001). Platelet and plasma transfusions were also significantly lower with ANH. The ANH population had superior postoperative morbidity and mortality compared with the no ANH population.

CONCLUSIONS

There is a significant association between ANH and reduced perioperative RBC transfusion in cardiac surgery. Transfusion reduction is most profound with larger volumes of ANH. Our findings suggest the volume of ANH, rather than just its use, may be an important feature of a center's blood conservation strategy.

Transfusion triggers for guiding RBC transfusion for cardiovascular surgery: a systematic review and meta-analysis*

OBJECTIVE

Restrictive red cell transfusion is recommended to minimize risk associated with exposure to allogeneic blood. However, perioperative anemia is an independent risk factor for adverse outcomes after cardiovascular surgery. The purpose of this systematic review and meta-analysis is to determine whether perioperative restrictive transfusion thresholds are associated with inferior clinical outcomes in randomized trials of cardiovascular surgery patients.

DATA SOURCES

The Cochrane Central Register of Controlled Trials, MEDLINE, and EMBASE from inception to October 2013; reference lists of published guidelines, reviews, and associated articles, as well as conference proceedings. No language restrictions were applied.

STUDY SELECTION

We included controlled trials in which adult patients undergoing cardiac or vascular surgery were randomized to different transfusion thresholds, described as a hemoglobin or hematocrit level below which RBCs were transfused.

DATA EXTRACTION

Two authors independently extracted data from included trials. We pooled risk ratios of dichotomous outcomes and mean differences of continuous outcomes across trials using random-effects models.

DATA SYNTHESIS

Seven studies (enrolling 1,262 participants) met inclusion criteria with restrictive and liberal transfusion thresholds most commonly differing by a hemoglobin of 1 g/dL or hematocrit of 6-7%, resulting in decreased transfusions by 0.71 units of RBCs (95% CI, 0.31-1.09, p = 0.0002) without an associated change in adverse events: mortality (risk ratio, 1.12; 95% CI, 0.65-1.95; p = 0.60), myocardial infarction (risk ratio, 0.94; 95% CI, 0.30-2.99; p = 0.92), stroke (risk ratio, 1.15; 95% CI, 0.57-2.32; p = 0.70), acute renal failure (risk ratio, 0.98; 95% CI, 0.64-1.49; p = 0.91), infections (risk ratio, 1.23; 95% CI, 0.85-1.78; p = 0.27), or length of stay. There was no between-trial heterogeneity for any pooled analysis. Including four pediatric trials (456 participants) and 10 trials utilizing only intraoperative acute normovolemic hemodilution (872 participants) did not substantially change the results except that unlike the transfusion threshold trials, the hemodilution trials did not reduce the proportion of patients transfused (interaction p = 0.01).

CONCLUSIONS

Further randomized controlled trials are necessary to determine the optimal transfusion strategy for patients undergoing cardiovascular surgery.

Therapeutic options to minimize allogeneic blood transfusions and their adverse effects in cardiac surgery: a systematic review

INTRODUCTION

Allogeneic blood is an exhaustible therapeutic resource. New evidence indicates that blood consumption is excessive and that donations have decreased, resulting in reduced blood supplies worldwide. Blood transfusions are associated with increased morbidity and mortality, as well as higher hospital costs. This makes it necessary to seek out new treatment options. Such options exist but are still virtually unknown and are rarely utilized.

OBJECTIVE

To gather and describe in a systematic, objective, and practical way all clinical and surgical strategies as effective therapeutic options to minimize or avoid allogeneic blood transfusions and their adverse effects in surgical cardiac patients.

METHODS

A bibliographic search was conducted using the MeSH term "Blood Transfusion" and the terms "Cardiac Surgery" and "Blood Management." Studies with titles not directly related to this research or that did not contain information related to it in their abstracts as well as older studies reporting on the same strategies were not included.

RESULTS

Treating anemia and thrombocytopenia, suspending anticoagulants and antiplatelet agents, reducing routine phlebotomies, utilizing less traumatic surgical techniques with moderate hypothermia and hypotension, meticulous hemostasis, use of topical and systemic hemostatic agents, acute normovolemic hemodilution, cell salvage, anemia tolerance (supplementary oxygen and normothermia), as well as various other therapeutic options have proved to be effective strategies for reducing allogeneic blood transfusions.

CONCLUSION

There are a number of clinical and surgical strategies that can be used to optimize erythrocyte mass and coagulation status, minimize blood loss, and improve anemia tolerance. In order to decrease the consumption of blood components, diminish morbidity and mortality, and reduce hospital costs, these treatment strategies should be incorporated into medical practice worldwide.

Acute Normovolemic Hemodilution in the Pig Is Associated with Renal Tissue Edema, Impaired Renal Microvascular Oxygenation, and Functional Loss

Background:

The authors investigated the impact of acute normovolemic hemodilution (ANH) on intrarenal oxygenation and its functional short-term consequences in pigs.

Methods:

Renal microvascular oxygenation (µPo2) was measured in cortex, outer and inner medulla via three implanted optical fibers by oxygen-dependent quenching of phosphorescence. Besides systemic hemodynamics, renal function, histopathology, and hypoxia-inducible factor-1α expression were determined. ANH was performed in n = 18 pigs with either colloids (hydroxyethyl starch 6% 130/0.4) or crystalloids (full electrolyte solution), in three steps from a hematocrit of 30% at baseline to a hematocrit of 15% (H3).

Results:

ANH with crystalloids decreased µPo2 in cortex and outer medulla approximately by 65% (P &lt; 0.05) and in inner medulla by 30% (P &lt; 0.05) from baseline to H3. In contrast, µPo2 remained unaltered during ANH with colloids. Furthermore, renal function decreased by approximately 45% from baseline to H3 (P &lt; 0.05) only in the crystalloid group. Three times more volume of crystalloids was administered compared with the colloid group. Alterations in systemic and renal regional hemodynamics, oxygen delivery and oxygen consumption during ANH, gave no obvious explanation for the deterioration of µPo2 in the crystalloid group. However, ANH with crystalloids was associated with the highest formation of renal tissue edema and the highest expression of hypoxia-inducible factor-1α, which was mainly localized in distal convoluted tubules.

Conclusions:

ANH to a hematocrit of 15% statistically significantly impaired µPo2 and renal function in the crystalloid group. Less tissue edema formation and an unimpaired renal µPo2 in the colloid group might account for a preserved renal function.

Aortic arch replacement and elephant trunk procedure: an interdisciplinary approach to surgical reconstruction, perfusion strategies and blood management

Surgical treatment of patients who present with large aneurysms of the ascending aorta, transverse arch and descending aorta, including the thoracic and abdominal aorta typically consists of a two-staged elephant trunk procedure. Typically, these operations are lengthy, requiring long cardiopulmonary bypass times, deep hypothermic circulatory arrest and multiple anastamotic suture lines, which increases the risks for coagulopathic bleeding and the need for massive transfusions. The purpose of this report is to describe our approach, involving advanced surgical techniques and the innovative perfusion considerations as well as modified blood management strategies to minimize perioperative blood loss and the need for transfusions. All of the above will highlight critical cardiac team communications. An ever-evolving case requires forward thinking, revised judgments, open discussion and the continued involvement of all team members. In turn, this ensures evidence-based medical and perfusion practices that lead to achieving a positive peri-operative course, with optimal blood conservation.

Safety of cardiac surgery without blood transfusion: a retrospective study in Jehovah's Witness patients

The aim of this retrospective study was to compare the utilisation of blood products and outcomes following cardiac surgery for 123 Jehovah's Witnesses and 4219 non-Jehovah's Witness patient controls. The study took place over a 7-year period at the Amphia Hospital in Breda, the Netherlands. A specific protocol was used in the management of Jehovah's Witness patients, while the control group received blood without restriction according to their needs. Patients' characteristics were comparable in both groups. Pre-operatively, the mean (SD) Euro Score was higher in the Jehovah's Witness group (3.2 (2.6) vs 2.7 (2.5), respectively; p < 0.02). Pre-operative haemoglobin concentration was higher in the Jehovah's Witness group (8.9 (0.7) vs 8.6 (0.9) g.dl(-1), respectively; p < 0.001). The total cardiopulmonary bypass time did not differ between groups. The requirement for allogenic blood transfusion was 0% in the Jehovah's Witness group compared to 65% in the control group. Postoperatively, there was a lower incidence of Q-wave myocardial infarction (2 (1.8%) vs 323 (7.7%), respectively; p < 0.02), and non Q-wave infarction (11 (9.8%) vs 559 (13.2%), respectively; p < 0.02) in the Jehovah's Witness group compared with controls. Mean (SD) length of stay in the intensive care unit (2.3 (3.2) vs 2.6 (4.2) days; p = 0.26), re-admission rate to the intensive care unit (5 (4.5%) vs 114 (2.7%); p = 0.163), and mortality (3 (2.7%) vs 65 (1.5%); p = 0.59), did not differ between the Jehovah's Witness and control groups, respectively.

Cerebral oximetry monitoring during aortic arch aneurysm replacement surgery in Jehovah's Witness patient -A case report-

Anesthetic management for aortic arch aneurysm (AAA) surgery employing deep hypothermic circulatory arrest in a Jehovah's Witness (JW) patient is a challenge to anesthesiologist due to its complexity of procedures and their refusal of allogeneic transfusion. Even in the strict application of intraoperative acute normovolemic hemodilution (ANH) and intraopertive cell salvage (ICS) technique, prompt timing of re-administration of salvaged blood is essential for successful operation without allogeneic transfusion or ischemic complication of major organs. Cerebral oximetery (rSO(2)) monitoring using near infrared spectroscopy is a useful modality for detecting cerebral ischemia during the AAA surgery requiring direct interruption of cerebral flow. The present case showed that rSO(2) can be used as a trigger facilitating to find a better timing for the re-administration of salvaged blood acquired during the AAA surgery for JW patient.

Red blood cell transfusion in the treatment and management of anaemia: the search for the elusive transfusion trigger

Therapeutic red blood cell (RBC) transfusion is widely utilized in the management of anaemia. Critically ill intensive care unit (ICU) patients in particular, as well as medical and haematology-oncology patients, are among the largest groups of users of RBC products. While anaemia is common in these patients, its treatment and management, including appropriate thresholds for RBC transfusion, remain controversial. We review here the function of RBCs in oxygen transport and physiology, with a view to their role in supporting and maintaining systemic tissue oxygenation. Adaptive and physiological compensatory mechanisms in the setting of anaemia are discussed, along with the limits of compensation. Finally, data from clinical studies will be examined in search of evidence for, or against, a clinically relevant transfusion trigger.

Allogeneic red blood cell transfusion: Physiology of oxygen transport

Allogeneic red blood cell (RBC) transfusions have been shown to be associated with considerable risks. While their efficiency in many clinical situations has not been proven, the number of studies finding adverse outcomes in terms of morbidity (e.g. postoperative infections) and mortality continues to rise. In view of these facts, physicians involved in transfusion medicine have to be as restrictive as possible with RBC transfusions. Only a thorough knowledge of the physiology and pathophysiology of oxygen transport can be a solid base for meaningful transfusion decisions. Therefore, the goal of this article is to review the basics of oxygen transport and normovolaemic anaemia.

Cardioprotective effects of acute normovolemic hemodilution in patients with severe aortic stenosis undergoing valve replacement

BACKGROUND

After acute normovolemic hemodilution (ANH), improvement of the rheologic conditions may contribute to optimize tissue oxygen delivery and attenuate ischemia-reperfusion injuries. It was hypothesized that ANH would confer additional cardioprotection in patients with ventricular hypertrophy undergoing open heart surgery.

STUDY DESIGN AND METHODS

This study was a randomized controlled trial. Forty patients scheduled for elective aortic valve replacement were randomly assigned to a control group (standard care) or an ANH group (target hematocrit level of 28%). All patients were managed with standard myocardial preservation techniques (cold blood cardioplegia, anesthetic preconditioning). The outcome measures included the release of myocardial enzymes, perioperative hemodynamic changes, the need for pharmacologic cardiovascular support, and cardiac complications.

RESULTS

In the ANH group, the postoperative release of troponin I (mean peak plasma concentrations, 1.7 ng/mL; 95% confidence interval, 1.4-2.1 ng/mL) and myocardial fraction of creatine kinase (22 U/L; range, 18-24 U/L) was significantly lower than in the control group (3.6 [range, 3.0-4.2] ng/mL and 45 [range, 39-51] U/L, respectively). In addition, requirement for inotropic support was significantly lower and fewer hemodiluted patients presented adverse cardiac events. After ANH, there was a significant decrease in heart rate (-11 +/- 6%) and rate-pressure product (-16 +/- 8%) until the aortic cross-clamping time and, at the end of surgery, the circulating levels of erythropoietin (EPO) were higher than in control patients (13.6 +/- 4.2 mUI/mL vs. 7.3 +/- 2.4 mUI/mL; p < 0.05).

CONCLUSIONS

Besides conventional cardiac preservation techniques, preoperative ANH further attenuates myocardial injuries. Optimization of preischemic myocardial oxygen delivery and/or consumption and the postconditioning effects of endogenous EPO are potential mechanisms for ANH-induced cardioprotection.

Indications for Blood Transfusion in Cardiac Surgery

In addition to its life-saving effect in hemorrhagic shock, transfusion of allogenic packed red blood cells can be beneficial in situations where a critically low hematocrit is contributing to a state of oxygen-supply dependency. These benefits are countered by the risks of transfusion-associated lung injury, transfusion-associated immunomodulation, and cellular hypoxia after RBC transfusion. The critical hematocrit is patient and organ specific, and varies intraoperatively according to the duration and temperature of bypass, as well as for a variable postoperative period. Future randomized studies must prospectively evaluate regional indicators of tissue oxygenation in transfusion algorithms.

Acute decrease in renal microvascular PO2 during acute normovolemic hemodilution

Large differences in the tolerance of organ systems to conditions of decreased O(2) delivery such as hemodilution exist. The kidney receives approximately 25% of the cardiac output and O(2) delivery is in excess of the oxygen demand under normal circumstances. In a rat model of acute normovolemic hemodilution (ANH), we studied the effect of reduced hematocrit on renal regional and microvascular oxygenation. Experiments were performed in 12 anesthetized male Wistar rats. Six animals underwent four steps of ANH (hematocrit 25, 15, 10, and <10%). Six animals served as time-matched controls. Systemic and renal hemodynamic and oxygenation parameters were monitored. Renal cortical (c) and outer medullary (m) microvascular PO(2) (microPO(2)) and the renal venous PO(2) (P(rv)O(2)) were continuously measured by oxygen-dependent quenching of phosphorescence. Despite a significant increase in renal blood flow in the first two steps of ANH, cmicroPO(2) and mmicroPO(2) dropped immediately. From the first step onward oxygen consumption (VO(2(ren))) became dependent on oxygen delivery (DO(2(ren))). With a progressive decrease in hematocrit, a significant correlation between microPO(2) and VO(2(ren)) could be observed, as well as a PO(2) gap between microPO(2) and P(rv)O(2). Furthermore, there was a high correlation between VO(2(ren)) and RBF over a wide range of flows. In conclusion, the oxygen supply to the renal tissue is becoming critical already in an early stage of ANH due to the combination of increased VO(2(ren)), decreased DO(2(ren)), and intrarenal O(2) shunt. This has clinical relevance as recent publications reporting that hemodilution during surgery forms a risk factor for postoperative renal dysfunction.

Anemia and perioperative red blood cell transfusion: a matter of tolerance

In the past, anemia in the perioperative period has been treated by red blood cell (RBC) transfusions relatively uncritically. RBC transfusions were believed to increase oxygen delivery by increasing hemoglobin concentration. Arbitrary transfusion triggers such as the "10/30 rule" (i.e., RBC transfusion indicated below a hemoglobin concentration of 10 g/dL or a hematocrit of 30%) were applied. However, there is now increasing evidence that RBC transfusions are associated with adverse outcomes and should be avoided whenever possible. Restraining from RBC transfusions and maintaining normovolemia in patients suffering from surgical blood loss results in acute anemia. Therefore, knowing the compensatory mechanisms during acute anemia is crucial. This review focuses on acute anemia tolerance, its limits, and physiologic transfusion triggers in the perioperative period.

Cardioprotective effects of acute isovolemic hemodilution in a rat model of transient coronary occlusion*

OBJECTIVES

Following isovolemic hemodilution (AIH), lowering blood viscosity induces acceleration of erythrocyte velocity resulting in improved tissue oxygen delivery. Using a rat model of myocardial infarct, we tested the hypothesis that AIH would attenuate myocardial damage due to transient coronary occlusion.

DESIGN

Prospective, randomized, and controlled animal study.

SETTING

Animal research laboratory in a university hospital.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

All rats were subjected to 30 mins of left coronary artery occlusion followed by 48 hrs of reperfusion. Before the ischemic period, the anesthetized rats were randomly allocated to undergo either 15 mins of waiting (controls) or AIH to achieve a hematocrit of 30% (AIH-CO) by stepwise blood withdrawal and isovolemic compensation with 6% hydroxyethylstarch 200-0.5.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic variables were comparable in the two groups, except for higher indexes of stroke volume in the AIH-CO group. During coronary occlusion and the reperfusion period, AIH resulted in a lower incidence of fatal ventricular tachyarrhythmia (17% vs. 50% in control group, p < .05) and higher survival at 48 hrs of postreperfusion (83% vs. 42%, p < .05).Preischemic hemodilution significantly attenuated myocardial damage as shown by lower release of cardiac troponin I and reduction in myocardial infarct size as measured by tetrazolin staining. Histologic examination revealed no difference regarding peri-ischemic infiltration with neutrophil granulocytes.

CONCLUSIONS

Our data provide the first experimental demonstration that preischemic moderate AIH confers cardioprotection and improves survival in a rat model of myocardial infarct.