Myocardial metabolism and adaptation during extreme hemodilution in humans after coronary revascularization

Transfusion of Blood Products Affects Outcome in Cardiac Surgery

There remains controversy as to when patients undergoing cardiac surgery should receive a transfusion and whether a low hematocrit and its treatment with a transfusion of red cells influences outcome. The data related to this controversy are reviewed. Although the risk of known viral transmission is currently low, stored red cells do not function normally, and each unit contains activated inflammatory cells and mediators. These changes cause limited oxygen release, impaired microcirculatory flow, and immune suppression. A number of studies have observed decreased survival associated with transfusions in trauma, coronary artery bypass grafting, and intensive care unit patients. Studies that show an adverse outcome associated with low hematocrit are not definitive, because they fail to distinguish between the impact of low hematocrit per se and the possible adverse effects of transfusion, for what the low hematocrit may simply be a surrogate. The observation that a low hematocrit is associated with an adverse outcome does not necessarily prove that “treatment” of the anemia with a red cell transfusion will improve the outcome. Stored platelets contain a highly activated mixture of platelets with storage lesions and inflammatory mediators. Two retrospective post hoc multifactorial analyses suggest that platelet transfusions are associated with substantial increased morbidity and mortality. Clearly, large prospective studies are required to define the proper trigger for blood product transfusion to balance the adverse effects of anemia and platelet deficiency or dysfunction with the adverse effects of transfusion of blood products on morbidity and mortality associated with cardiac surgery and anesthesia.

The silent risks of blood transfusion

PURPOSE OF REVIEW

Clinical research has identified blood transfusion as an independent risk factor for immediate and long-term adverse outcomes, including an increased risk of death, myocardial infarction, stroke, renal failure, infection and malignancy. New findings have called into question the traditional assumptions clinicians utilize in evaluating the risks and benefits of blood transfusion. Appreciation of newly recognized risks is important for conserving scarce resources and optimizing patient outcomes.

RECENT FINDINGS

Recent clinical outcomes research has examined the impact of blood transfusion on critically ill patients, trauma patients, patients undergoing cardiac surgery, patients experiencing acute coronary syndromes, oncology patients and others. These studies provide additional evidence of adverse outcomes associated with blood transfusion in a wide variety of clinical contexts.

SUMMARY

The benefits of blood transfusion have never been conclusively demonstrated, but evidence of transfusion-related harm continues to accumulate. Given the transfusion triggers that currently predominate in clinical practice it appears that clinical outcomes could improve significantly with more widespread adoption of restrictive transfusion strategies.

Usefulness of low prime perfusion pediatric circuit in decreasing blood transfusion

We tested the efficiency of small prime volume in decreasing the blood requirement during pediatric cardiac surgery. This is a retrospective analysis of transfusion in 259 consecutive patients weighing <15 kg. We downsized the bypass circuit and avoided noncritical components to obtain a cardiopulmonary bypass prime volume, including a cardioplegia circuit of 140 ml for patients up to 6 kg, and of 170 ml for those weighing 6-15 kg. For intra- and postoperative care, transfusions were limited to 1 unit of packed red blood cells and 1 unit of fresh frozen plasma in 129 of the 134 patients weighing <6 kg. Seventy-six of 125 (61%) patients who were between 6 kg and 15 kg had bloodless surgery. None of the 259 patients had platelets infusion. In transfused cases, only eight patients (3%) needed more than two different donor products. In bloodless cases, hemoglobin values were 11.5 +/- 1.8 g/dl before, 9.4 +/- 1.7 g/dl during, and 10.5 +/- 1.8 g/dl after surgery. No adverse effects of this procedure were encountered. Small prime volume is efficient and safe in decreasing blood use in pediatric surgery.

The impact of an hematocrit of 20% during normothermic cardiopulmonary bypass for elective low risk coronary artery bypass graft surgery on oxygen delivery and clinical outcome--a randomized controlled study [ISRCTN35655335]

Introduction

Cardiopulmonary bypass (CPB) induces hemodilutional anemia, which frequently requires the transfusion of blood products. The objective of this study was to evaluate oxygen delivery and consumption and clinical outcome in low risk patients who were allocated to an hematocrit (Hct) of 20% versus 25% during normothermic CPB for elective coronary artery bypass graft (CABG) surgery.

Methods

This study was a prospective, randomized and controlled trial. Patients were subjected to normothermic CPB (35 to 36°C) and were observed until discharge from the intensive care unit (ICU). Outcome measures were calculated whole body oxygen delivery, oxygen consumption and clinical outcome. A nonparametric multivariate analysis of variance for repeated measurements and small sample sizes was performed.

Results

In a total of 54 patients (25% Hct, n = 28; 20% Hct, n = 26), calculated oxygen delivery (p = 0.11), oxygen consumption (p = 0.06) and blood lactate (p = 0.60) were not significantly different between groups. Clinical outcomes were not different between groups.

Conclusion

These data indicate that an Hct of 20% during normothermic CPB maintained calculated whole body oxygen delivery above a critical level after elective CABG surgery in low risk patients. The question of whether a transfusion trigger in excess of 20% Hct during normothermic CPB is still supported requires a larger prospective and randomized trial.

Open Heart Surgery for Small Children Without Homologous Blood Transfusion by Using Remote Pump Head System

BACKGROUND

To avoid excessive hemodilution, the transfusion of a large amount of homologous blood may be required in open heart surgery for small children, which in turn, can cause a significant immunologic response.

METHODS

Cardiopulmonary bypass systems with remote pump heads were used for patients weighing 5 kg or less that were undergoing ventricular septal defect repair. The procedures took place from January 1997 to August 2002. The surgery was started with bloodless prime in 122 out of 158 (77.2%) consecutive patients. Exclusion criteria were a predicted hematocrit after the initiation of bypass of less than 15%, respiratory failure or heart failure (or both), and pulmonary vascular obstructive disease.

RESULTS

The mean age and body weight were 3.8 +/- 1.8 months and 4.3 +/- 0.5 kg, respectively. The priming volume was 181.0 +/- 32.5 (minimum: 130) mL. The hematocrit after cardiopulmonary bypass was initiated was 16.7% +/- 2.3%. Six patients required subsequent blood transfusion owing to postoperative complications that resulted in compromised hematopoiesis. In the rest, the hematocrit before discharge was 30.6% +/- 3.0%. Renal and liver function tests were maintained within the normal range. Patients were extubated at 5.6 +/- 2.8 hours after operation with proper oxygenation. Neurodevelopment was apparently normal. The Japanese psychomotor developmental scale assessment was given to patients without chromosomal abnormality between the ages of 1 and 3 years; the resulting score was 102.2 +/- 15.4 (mean = 100 for normal population).

CONCLUSIONS

Open heart surgery was achieved without blood transfusion in the selected group of small children. The use of remote pump heads reduced the overall need for blood transfusions and possibly inflammatory reactions.

The Hemodynamic and Metabolic Effects of Shivering During Acute Normovolemic Hemodilution

To assess the hemodynamic and metabolic effects of shivering during extreme normovolemic hemodilution, we anesthetized 16 pigs with fentanyl-midazolam-pancuronium. Mild hypothermia (36.5 degrees +/- 0.1 degrees C) was induced by surface cooling, and the animals were randomized to either a control group (hemoglobin 118 +/- 3 g/L) or a hemodilution group (hemoglobin 52 +/- 2 g/L). In the latter group, blood was replaced with an isotonic Ringer's acetate/dextran 70 solution. Shivering was allowed to occur by a controlled decrease in the infusion rate of pancuronium. Shivering increased oxygen consumption (VO(2)) in both groups (P < 0.001). Initially, this was predominantly compensated for by an increased oxygen extraction ratio (ER), but when VO(2) was 2.3 +/- 0.2 times baseline, critical levels of mixed venous oxygenation (SVO(2) = 18% +/- 2%; PVO(2) = 22.5 +/- 1.5 mm Hg) and ER (82% +/- 3%) were recorded in anemic animals. Control animals did not reach critical levels until VO(2) was maximal (3.7 +/- 0.3 times baseline). Maximal attained VO(2) was less (2.9 +/- 0.1 times baseline) in the anemic animals (P = 0.01), and at this stage two of these pigs had myocardial lactate production, one of which died in ventricular fibrillation. Coronary perfusion pressure was significantly less (P < 0.001) in the anemic animals. We conclude that in this experimental model, maximal shivering as measured by VO(2) was limited in hemodiluted animals, and left ventricular oxygen balance was marginal, as evidenced by a decreased lactate uptake and extraction.

IMPLICATIONS

The effect of acute increases in oxygen consumption (shivering) on severely anemic individuals has not been evaluated. In this experimental model, left ventricular oxygen balance was marginal, as evidenced by decreased lactate extraction.

Red cell transfusion "trigger": a review

Despite the publication of several consensus guidelines that set forth recommendations for the transfusion of red cells, actual clinical practice continues to vary widely. Animal data and studies in human volunteers and patients support a red cell transfusion threshold of 7 to 8 g/dl in most patients. However, conflicting data, particularly in cardiac patients and in the elderly, suggest that it may be impossible to define a single red cell "trigger" for all patients. A well-designed, randomized, controlled trial is still needed to establish a safe threshold for red cell transfusion in adults with coronary artery disease.

Blood Transfusion Issues in the Critically Ill

Anemia is a common clinical problem seen in the critically ill and results in a large RBC transfusion requirement for these patients. The view that RBC transfusion is risk-free is no longer tenable today. There is the accumulating evidence that allogeneic blood transfusion is immunosuppressive. More reently, attention has focused on the age of RBCs transfused. Transfused RBCs, especially during the time period immeditely following transfusion, are not normal. The duration of RBC storage may be an important determinant of the efficacy of RBCs as oxygen carriers as well as a determinant of transusion related morbidity. Adding to the controversy about risk/benefit ratio for RBC transfusion are recent data showing that an aggressive RBC transfusion strategy may decrease the likelihood of survival in selected subpopulations of critically ill adults. The optimal hematocrit for the ICU patient remains to be determined. It seems clear that hemoglobin levels falling significantly below the “10/30” threshold can be tolerated. However, it is not clear that this is applicable to the critically ill ICU patient population. Therefore, while hemoglobin levels in the 7-10 mg/dL range are well tolerated in the “stable” “nontressed” patient, this range might not be optimal for the critcally ill patient. Conservative transfusion thresholds as well as strategies to minimize loss of blood and increase the producion of RBCs are important in the management of critically ill patients.

Cold continuous antegrade blood cardioplegia: high versus low hematocrit

OBJECTIVE

Cold continuous antegrade blood cardioplegia (CCABCP) is used with different hematocrit values. We investigated the consequences of CCABCP with low hematocrit (LH: 20-25%) versus high hematocrit (HH: 40-45%).

METHODS

Anesthetized open chest pigs (25 kg) were placed on cardiopulmonary bypass (CPB). The hearts were arrested for 30 min by 6 degrees C CCABCP with either LH or HH (n=8, each): After an initial 3 min application of high potassium (20 mEq) BCP the hearts were arrested for subsequent 27 min by normokalemic 6 degrees C cold blood delivered continuously antegradely. Thereafter the hearts underwent perfusion with warm systemic blood for an additional 30 min on CPB. Biochemical cardiac data (MVO(2) (ml min(-1)100 g(-1)), release of creatine kinase (CK; units min(-1)100 g(-1))) and lactate (mg min(-1)100 g(-1))) and the coronary vascular resistance index (CVRI (mmHg ml(-1)ming)) were measured during CPB. Total tissue water content (%) and left and right ventricular stroke work indices (LV-and RV-SWI (g m kg(-1))) were assessed 30 min after discontinuation of CPB and compared to pre-CPB controls.

RESULTS

The hearts of the LH group had no biochemical or functional disturbance. The HH group showed marked CK leakage (0.6+/-0.2* vs. 0.1+/-0.1, *P<0.05 for comparison of LH vs. HH with Student's t-test for unpaired data), impaired initial oxygen consumption (4+/-1* vs. 7+/-1) after cardiac arrest, an increased CVRI (82+/-12* vs. 50+/-8), the formation of myocardial edema (81.0+/-1.3* vs. 77.5+/-1.2), and poor functional recovery (LVSWI 0.2+/-0.1* vs. 1.0+/-0.1; RVSWI 0.1+/-0.1* vs. 0.5+/-0.1). The absence of lactate production in both groups was in accord with the non-ischemic protocol.

CONCLUSIONS

CCABCP with a low hematocrit of 20-25% is cardioprotective. In contrast, CCABCP with a high hematocrit of 40-45% jeopardizes the heart despite avoiding ischemic periods, and should be avoided.

Hematocrit value on intensive care unit entry influences the frequency of Q-wave myocardial infarction after coronary artery bypass grafting. The Institutions of the Multicenter Study of Perioperative Ischemia (McSPI) Research Group

OBJECTIVES

No data exist regarding "the best" hematocrit value after coronary artery bypass graft surgery. Transfusion practice varies, because neither an optimal hematocrit value nor a uniform transfusion trigger criterion has been determined.

METHODS

To investigate the optimal hematocrit value, we studied 2202 patients undergoing coronary bypass. The hematocrit value on entry into the intensive care unit (IHCT) was categorized into three groups: high (> or = 34%), medium (25% to 33%), and low (< or = 24%). Characteristics and adverse events (outcomes) were compared, and the effect of IHCT on the risk of myocardial infarction was determined by logistic regression.

RESULTS

High IHCT (> or = 34%) was associated with an increased rate of myocardial infarction (8.3% vs 5.5% vs 3.6%; p < or = 0.03, high, medium vs low) and with more severe left ventricular dysfunction (11.7% vs 7.4% and 5.7%; p=0.006, high, medium vs low). Mortality rate increased with higher IHCT when all the high-risk subgroups were combined (8.6% vs 4.5% vs 3.2%; p < 0.001, high, medium vs low). By multivariate analysis, IHCT remained the most significant predictor of adverse outcomes (relative risk high vs low 2.22, 95% confidence interval: 1.04 to 4.76). No characteristic, event, medication, or transfusion therapy confounded the relationship between IHCT and outcome.

CONCLUSION

High IHCT is associated with a higher rate of myocardial infarction and is an independent predictor of infarction. On the basis of the risk of myocardial infarction, there is no rationale for transfusion to an arbitrary level after coronary artery bypass grafting.

Impact of ultrafiltration on blood use for atrial septal defect closure in infants and children

BACKGROUND

Infants and children undergoing open cardiac operations have a high incidence of blood product transfusion. Ultrafiltration has been shown to reverse hemodilution and improve myocardial function and hemodynamics after cardiopulmonary bypass (CPB).

METHODS

The effect of ultrafiltration on the amount of blood transfusion and hospital charge in 39 consecutive patients who underwent elective atrial septal defect repair was examined. Patients in group I (n=26) had a conventional cardiopulmonary circuit prime with blood, whereas 13 patients had bloodless prime (group II). Ultrafiltration was used immediately after weaning from CPB in group II. The patients in group I received blood products after discontinuation of CPB to achieve a hematocrit of 30%. The amount of blood product used, hematocrit immediately after CPB and on arrival in intensive care unit, postoperative hemodynamics and saturations, total operating room charge, blood charge, hospital stay, and hospital charge were compared.

RESULTS

Mean body weight (15.8 kg in group I versus 17.5 kg in group II) and preoperative hematocrit values (35.6% in group I versus 34.2% in group II) were similar. Mean hematocrit immediately after CPB was 22% and 14% in group I and II, respectively (p < 0.0001). The mean hematocrit upon arrival to the intensive care unit was 34% in group I and 22% in group II (p < 0.0001). The amount of blood product transfusion was 32 mL/kg in group I and 3 mL/kg in group II patients (p < 0.0001). The patients in group II had significantly less blood bank charges; however, operating room charges and total hospital charges were similar between the two groups.

CONCLUSIONS

Elective atrial septal defect repair was performed with no blood product transfusion without increased morbidity or hospital stay. Ultrafiltration can be used to reverse hemodilution resulting from a bloodless CPB prime without an increase in hospital charge.

A prospective, randomized trial limiting perioperative red blood cell transfusions in vascular patients

BACKGROUND

Patients undergoing major arterial reconstruction have traditionally been transfused with red blood cells to keep hemoglobin concentrations above 10 g/dL in order to prevent anemia-induced myocardial ischemia. There are no data to support this practice. The hypothesis that vascular patients will tolerate a hemoglobin concentration of 9 g/dL was examined.

METHODS

Ninety-nine patients undergoing elective aortic and infrainguinal arterial reconstructions were prospectively randomized preoperatively to receive transfusions to maintain a hemoglobin level of either 10 g/dL or 9 g/dL.

RESULTS

Despite significantly different postoperative hemoglobin levels of 11.0 +/- 1.2 versus 9.8 +/- 1.3 g/dL (P <0.0001), there were no differences in mortality or cardiac morbidity rates or length of hospital stay. There were no differences in hemodynamic parameters. Oxygen delivery was lower in the group with lower hemoglobin levels, but there was no difference in O2 consumption between the groups.

CONCLUSIONS

A lower hemoglobin concentration was tolerated without adverse clinical outcome. Patients did not compensate for anemia by increased myocardial work, but by increasing O2 extraction in the peripheral tissues.

Hemodynamic effects of isovolemic hemodilution during descending thoracic aortic cross clamping and lower torso reperfusion

BACKGROUND

Isovolemic hemodilution has been suggested for blood conservation and to improve hemodynamic tolerance to abdominal aortic cross clamping. However, the hemodynamic effects of hemodilution during descending thoracic aortic cross clamping (DAC) have not been established. We evaluated them in anesthetized swine.

METHODS

Hemodilution (n = 7) was produced by the isovolemic exchange of blood for 6% hetastarch to a target hematocrit of 20%. Hematocrit in control pigs (n = 7) remained at 30%. DAC was performed at the T9 level for 45 minutes. During a 60-minute reperfusion period, control pigs were infused with lactated Ringer's solution; shed blood was returned to hemodilution pigs, followed by lactated Ringer's. If hypotension occurred despite left atrial pressure of 10 mm Hg or greater, boluses of phenylephrine were given to keep mean arterial pressure above 60 mm Hg.

RESULTS

Hemodilution caused a marked reduction in hematocrit and in global oxygen delivery (DO2). DAC produced a significant increase in proximal arterial pressure, cardiac index, and DO2 and oxygen consumption (VO2) was markedly reduced in both groups. A significant increase in systemic vascular resistance during DAC occurred only in control pigs. After reperfusion, vascular resistance was significantly lower than baseline in hemodilution pigs, requiring a sixfold greater dose of phenylephrine to avoid hypotension. A lower global DO2 and supply-limited VO2 were also observed in hemodilution pigs.

CONCLUSIONS

Isovolemic hemodilution maintains hemodynamic stability during DAC. During lower torso reperfusion, however, hemodilution caused hemodynamic instability, decreased global DO2, and limited VO2, which may offset its potential benefits.

Reduction in requirements for allogeneic blood products: nonpharmacologic methods

BACKGROUND

Various strategies have been proposed to decrease bleeding and allogeneic transfusion requirements during and after cardiac operations. This article attempts to document the usefulness, or lack thereof, of the nonpharmacologic methods available in clinical practice.

METHODS

Blood conservation methods were reviewed in chronologic order, as they become available to patients during the perisurgical period. The literature in support of or against each strategy was reexamined critically.

RESULTS

Avoidance of preoperative anemia and adherence to published guidelines for the practice of transfusion are of paramount importance. Intraoperatively, tolerance of low hemoglobin concentrations and use of autologous blood (predonated or harvested before bypass) will reduce allogeneic transfusions. The usefulness of plateletpheresis and retransfusion of shed mediastinal fluid remains controversial. Intraoperatively and postoperatively, maintenance of normothermia contributes to improved hemostasis.

CONCLUSIONS

Several approaches have been shown to be effective. An efficient combination of methods can reduce, and sometimes abolish, the need for allogeneic blood products after cardiac operations, inasmuch as all those involved in the care of cardiac surgical patients adhere thoughtfully to existing transfusion guidelines.

Effect of hemoglobin on the oxygen uptake of patients with coronary artery disease

BACKGROUND

Oxygen uptake (VO2) is frequently measured or predicted in patients referred to cardiac rehabilitation programs to quantify functional capacity and prescribe exercise. When entering Phase II programs, some patients are in an anemic state that normalizes over the course of the program. The purpose of this study was to evaluate the relationship between the change in hemoglobin levels and the change in VO2 in a group of Phase II cardiac rehabilitation patients.

METHODS

Sixty-six cardiac patients (45 men and 21 women) underwent a graded exercise test with the collection of expired air before and following participation in a Phase II cardiac rehabilitation program. Blood was sampled before each test for hemoglobin-hematocrit analysis. The change in absolute VO2 over the course of the rehabilitation program was chosen as the response variable in a simple regression model designed to measure the effect of normalization of hemoglobin levels during that period.

RESULTS

A simple regression of the change in absolute VO2 on patient age and the changes in hemoglobin concentration and maximal work rate produced coefficient estimates that are statistically significant and have the signs one would expect. A bootstrap re-estimation of the regression model gives essentially the same coefficients and supports the results of the simple model.

CONCLUSIONS

These results indicate that low levels of hemoglobin concentration adversely affect the VO2 of patients with cardiac disease and should be accounted for when assessing functional capacity. This may be even more critical when estimating rather than measuring VO2. Finally, absolute VO2 may not be the best measure of functional capacity. A submaximal marker, such as the VO2 at the ventilatory threshold, may be a more useful response variable.

Perfluorocarbon emulsions and cardiopulmonary bypass: a technique for the future

Artificial blood has been sought for a considerable period of time and two major lines of research have led to FDA testing of some possible compounds. The two major types of compounds are polymerized hemoglobin moieties and perfluorocarbon emulsions (PFC). Polymerized hemoglobin preparations have the ability to carry oxygen and release it in a manner similar to the oxyhemoglobin dissociation curve of whole blood. PFCs carry oxygen, nitrogen and carbon dioxide, as well as all other non-polar gases, by enhanced chemical solubility. Therefore, all dissolved gases are available for metabolic utilization and no sinusoidal release curve of oxygen is encountered. Early PFC emulsions had problems with toxicity of the emulsifier and were difficult to get into their emulsion for infusion. Furthermore they were very dilute in the active ingredient for gas transport. Today there are second generation PFCs becoming available that have a 40% concentration of the PFC and therefore the potential for gas transport is greatly increased. The PFC emulsions have a very small size, 0.1 microns, so the surface for gas exchange is massively increased as well as the potential increased for perfusion into areas of potentially sludged erythrocytes. Work with the PFCs has shown them now to be able to carry adequate oxygen to work as blood substitutes. They have shown protection from air embolism in a number of animal and end-organ models. What makes the PFCs unique is their ability to carry/absorb nitrogen and therefore protect from gas embolization. There are data in animal models showing significant cerebral protection in cardiopulmonary bypass models. The new PFCs should sometime in the not-too-distant future be tested in human bypass with assessments of neuropsychiatric dysfunction and stroke.

Does hemoglobin concentration affect perioperative myocardial lactate flux in patients undergoing coronary artery bypass surgery?

Increasing concern over complications related to blood transfusions has prompted a reevaluation of what constitutes an "adequate" perioperative hemoglobin concentration, particularly in patients undergoing coronary artery bypass graft (CABG) surgery. Data from 224 patients with preserved ventricular function (ejection fraction > 50%), undergoing CABG surgery, previously studied under a variety of anesthetic protocols, were reexamined to determine the effect of hemoglobin (HGB) concentration on myocardial lactate flux (MLF) (as an index of ischemia). The interaction of MLF and HGB concentration, anesthetic technique (ANES), and hemodynamic variables (including systemic and pulmonary arterial pressures (SAP and PAP), cardiac output (CO), and myocardial oxygen consumption (MVO2) was determined from a pool of 1598 data sets obtained from 224 patients. Data were collected from just prior to induction of anesthesia until 24 h postoperatively. Univariate analysis revealed a statistically significant relationship between MLF and HGB concentration (P < 0.001) but the correlation coefficient was only 0.09. Multiple regression analysis did not determine HGB concentration to be a significant independent term affecting MLF in either the overall group or in a subgroup of 22 patients having an adverse outcome (myocardial infarction, stroke, or death). For patients undergoing CABG surgery, HGB concentrations within the range of 58-172 g/L were not a significant variable in production of global myocardial ischemia as evidenced by MLF. This suggests that HGB concentrations as low as 60-70 g/L in the perioperative period are well tolerated and are not associated with an increased incidence of myocardial ischemia.