Electrocardiographic ST-segment changes during acute, severe isovolemic hemodilution in humans

[Tolerance to perioperative anemia. Mechanisms, influencing factors and limits]

The expected cost explosion in transfusion medicine increases the socio-economic significance of specific institutional transfusion programs. In this context the estimated use of the patient's physiologic tolerance represents an integral part of any blood conservation concept. The present article summarizes the mechanisms, influencing factors and limits of this natural tolerance to anemia and deduces the indication for perioperative red blood cell transfusion. The current recommendations coincide to the effect that perioperative transfusion is unnecessary up to a Hb concentration of 10 g/dl (6.21 mmol/l) even in older patients with cardiopulmonary comorbidity and is only recommended in cases of Hb <6 g/dl (<3.72 mmol/l) in otherwise healthy subjects including pregnant women and children. Critically ill patients with multiple trauma and sepsis do not seem to benefit from transfusions up to Hb concentrations >9 g/dl (>5.59 mmol/l). In cases of massive hemorrhaging and diffuse bleeding disorders the maintenance of a Hb concentration of 10 g/dl (6.21 mmol/l) seems to contribute to stabilization of coagulation.

Predictive Risk Factors for Upper Gastrointestinal Bleeding with Simultaneous Myocardial Injury

The aims of this study were to: (1) evaluate the epidemiology of simultaneous upper gastrointestinal bleeding (UGIB) and myocardial injury using parameters including troponin I (TnI); and (2) investigate the predictive risk factors of this syndrome. One hundred and fifty-five patients (101 men, 54 women; mean age, 64.7+/-10.4 years; range, 38-94 years) at the emergency department (ED) with the major diagnosis of UGIB were included. They underwent serial electrocardiography (ECG) and cardiac enzyme follow-up. Emergent gastroendoscopy was performed within 24 hours in most patients except for those who refused or were contraindicated. Mild myocardial injury was defined as the presence of any of the following: typical ST-T change on ECG, elevated creatine kinase-MB (CK-MB)>12 U/L, or TnI>0.2 ng/dL. Moderate myocardial injury was defined as the presence of any two of the previously mentioned conditions. In total, 51 (32.9%) and 12 (7.74%) patients developed mild and moderate myocardial injuries, respectively. Myocardial injury was more common among patients with variceal bleeding (20/25=80.0%) than those with ulcer bleeding (23/112=20.5%). It could partially be attributed to a higher baseline TnI level in cirrhotic patients. After adjusting for significant risk factors revealed by the univariate analysis, UGIB patients with a history of liver cirrhosis and more than three cardiac risk factors comprised a high-risk group for simultaneously developing myocardial injury. Other factors including age, gender, the color of nasogastric tube irrigation fluid, history of nonsteroidal anti-inflammatory drug use, vasopressin or terlipressin administration, vital signs, and creatinine recorded at the ED were not significant predictors. Those who developed myocardial injury had a longer hospital stay (mean duration, 8.73+/-6.94 vs. 6.34+/-2.66 days; p=0.03) and required transfusion of more units of packed erythrocytes.

Hydroxyethyl starch is superior to lactated Ringer as a replacement fluid in a pig model of acute normovolaemic haemodilution

BACKGROUND

Tissue tolerance to oxygen privation during acute normovolaemic haemodilution with different fluids remains unclear. We tested the hypothesis that hydroxyethyl starch (HES) is superior to lactated Ringer's solution in pigs for preserving tissue perfusion during acute normovolaemic haemodilution.

METHODS

Twenty-four animals were randomized into control, lactated Ringer's solution and HES groups. All groups, except the control, underwent acute normovolaemic haemodilution. Haemodynamics, oxygen parameter indices, global anaerobic metabolic markers, echocardiographic parameters, gastric tonometry and serum osmolarity were monitored at baseline, immediately after (0 min) and 60 and 120 min after the end of haemodilution. Myocardial, liver, stomach and intestine samples were collected for further evaluation.

RESULTS

Cardiac and oxygen parameter index responses to acute normovolaemic haemodilution were comparable. However, the increment in cardiac index, stroke volume index, and left ventricular stroke work index were more sustained in the starch group. In the lactated Ringer's group, gastric pH decreased significantly and was accompanied by a significant increase in lactate. Myocardial ultrastructure was better preserved in the starch group. The other tissue samples presented no change.

CONCLUSIONS

In this model of ANH, the starch group had a superior haemodynamic response. Minor loss of myocardial cellular integrity and preserved gastric pHi reinforce these findings.

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.

[Tolerance to perioperative anemia. Mechanisms, influencing factors and limits]

The expected cost explosion in transfusion medicine (increasing imbalance between donors and potential recipients, treatment of transfusion-associated complications) increases the socio-economic significance of specific institutional transfusion programs. In this context the estimated use of the patient's physiologic tolerance to anemia enables 1) the tolerance of larger blood losses (loss of "diluted blood"), 2) the onset of transfusion to the time after surgical control of bleeding to be delayed and 3) the perioperative collection of autologous red blood cells. The present review article summarizes the mechanisms, influencing factors and limits of this natural tolerance to anemia and deduces the indication for perioperative red blood cell transfusion. Under strictly controlled conditions (anesthesia, normovolemia, complete muscular relaxation, hyperoxemia, mild hypothermia) extremely low hemoglobin concentrations [Hb <3 g/dl (<1.86 mmol/l)] are tolerated without transfusion by individuals with no cardiopulmonary disease. In the clinical routine these situations are limited to borderline situations e.g. unexpected massive blood losses in Jehovah's Witnesses or unexpected shortcomings in blood supply. The current recommendations coincide to the effect that perioperative red blood cell transfusion 1) is unnecessary up to a Hb concentration of 10 g/dl (6.21 mmol/l) even in older patients with cardiopulmonary comorbidity and 2) is only recommended in cases of Hb <6 g/dl (<3.72 mmol/l) in otherwise healthy subjects including pregnant women and children. Critically ill patients with multiple trauma and sepsis do not seem to benefit from transfusions up to Hb concentrations >9 g/dl (>5.59 mmol/l). In cases of massive hemorrhaging and diffuse bleeding disorders the maintenance of a Hb concentration of 10 g/dl (6.21 mmol/l) seems to contribute to stabilization of coagulation.

Ventilator associated pneumonia and transfusion, is there really an association? (the NAVTRA study)

Background

Anemic syndrome is a frequent problem in intensive care units. The most probable etiology is the suppression of the erythropoietin response due to the direct effects of cytokines, as well as frequent blood sampling.

Transfusions are not free of complications, therefore transfusion reactions are estimated to occur in 2% of the total packed red blood cells (pRBCs) transfused.

In the past several years, several trials had tried to compare the restrictive with the more liberal use of transfusions, and they were found to be equally effective.

Nosocomial pneumonia is the most common nosocomial infection in intensive care units; the prevalence is 47% with an attributive mortality of 33%.

There are multiple risk factors for the development of nosocomial pneumonia. Colonization of the upper airways is the most important pathophysiological factor but there are other factors implicated like, sedation techniques, inappropriate use of antibiotics and recumbent positioning.

A secondary analysis of the CRIT study describes transfusion therapy and its practices in the United States. They found that transfusion practice is an independent risk factor for the development of nosocomial pneumonia.

Methods

This is a multicenter, prospective cohort study in different intensive care units in Colombia. A total of 474 patients were selected who had more than 48 hours of mechanical ventilation.

The primary objective is to try to demonstrate the hypothetical relationship between the use of transfusions and nosocomial pneumonia.

Secondly, we will try to determine which other factors are implicated in the development of pneumonia in intensive care units and describe the incidence of pneumonia and transfusion practices.

Discussion

Ventilator associated pneumonia is a primary problem in the intensive care unit, multiple factors have been associated with its presence in this study we try to explore the possible association between pneumonia and transfusion, describe all other factors associated with this, and the possible association with other nosocomial infections.

Transfusion in the intensive care unit

OBJECTIVE

To summarize the incidences of anemia and blood transfusions in critically ill patients, assess their comparative risks and benefits, and briefly speculate on the possible effects of leukoreduction and blood storage on the need to reevaluate transfusion triggers.

DESIGN

A review of the current literature was performed.

RESULTS

Anemia is common in intensive care unit patients and is associated with increased mortality. Some 20-53% of intensive care unit patients will receive a blood transfusion during their stay, and these have also been associated with worse outcomes. Leukoreduction may limit some of the infectious and immunomodulatory risks associated with blood transfusion.

CONCLUSIONS

Data on the risks and benefits of blood transfusion are conflicting, and with recent changes in blood transfusion practice, including the widespread introduction of leukoreduction, it is time to reevaluate our transfusion triggers.

Therapeutic efficacy and safety of red blood cells treated with a chemical process (S-303) for pathogen inactivation: a Phase III clinical trial in cardiac surgery patients

BACKGROUND

A randomized, double-blind trial is reported of the clinical efficacy of red blood cells (RBCs) treated for pathogen inactivation with S-303, a synthetic labile alkylating agent.

STUDY DESIGN AND METHODS

Patients undergoing complex cardiac surgeries were randomly assigned to receive either S-303-treated (test) or conventional (control) RBC transfusion during surgery and for 6 days thereafter. Efficacy was evaluated by comparing the occurrence of a composite primary endpoint of treatment-related morbidity (myocardial infarction and renal failure) and mortality.

RESULTS

Two-hundred twenty-three patients were randomly assigned and 148 patients who received transfusions (74 with S-303-treated RBCs and 74 with control RBCs) were evaluable. The incidence of the primary endpoint was equivalent between the two groups (22 and 21% in the S-303-treated and control RBC groups, respectively). Secondary endpoints, including hemoglobin increment (mean, 1.4 vs. 1.5 g/dL), number of RBC transfusions (mean, 4.4 vs. 3.8 units), and other blood product support, were also comparable. The adverse event profile was similar between groups; however, patients who received S-303 RBCs were significantly more likely to develop constipation and less likely to suffer supraventricular extrasystoles. Four patients (2 test and 2 control) demonstrated positive indirect antiglobulin tests with reactivity for S-303 RBCs at one or more time points before or after transfusion, without evidence of hemolysis.

CONCLUSION

S-303-treated and conventional RBCs were equivalent with respect to clinical efficacy and safety in supporting the transfusion needs of cardiac surgery patients. Investigations are under way to ascertain the significance of S-303 RBC antibodies and to prevent their occurrence.

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

STUDY OBJECTIVES

We hypothesized that lowering blood viscosity with acute normovolemic hemodilution (ANH) would confer additional cardioprotection in patients undergoing coronary artery bypass surgery (CABG) with aortic cross-clamping.

DESIGN

In a prospective, randomized controlled trial, we studied the efficacy of ANH in anesthetized patients prior to cardiopulmonary bypass for the prevention of myocardial injuries.

SETTING

Cardiac surgical center in a university hospital.

PATIENTS AND METHODS

Patients scheduled to undergo elective CABG entered the study protocol and were randomly allocated to one of two groups: ANH (n = 43 patients) or standard care management (n = 41 patients). In the ANH group, the whole-blood/colloid exchange was aimed to achieve a hematocrit value of 28%. All patients were managed with standard myocardial preservation techniques including cold-blood cardioplegia and anesthetic preconditioning. The outcome measures included the release of myocardial enzymes (plasma troponin I and creatinine phosphokinase), perioperative hemodynamic changes, need for pharmacologic cardiovascular support, and cardiac complications.

RESULTS

In the hemodilution group, the postoperative release of troponin I (mean peak plasma concentration, 1.4 ng/mL; 95% confidence interval, 1.0 to 1.8) and myocardial fraction of creatine kinase (mean, 29 U/L; 95% confidence interval, 23 to 35) were significantly lower than in the control group (mean, 3.8 ng/mL; 95% confidence interval, 3.2 to 4.5; and 71 U/L; 95% confidence interval, 53 to 89). Requirement for inotropic support was significantly lower in the protocol patients (7 of 41 patients vs 15 of 39 patients), and fewer patients presented with either atrial fibrillation, atrioventricular conduction blockade, or combined disorders (12 of 41 patients vs 26 of 39 patients, p < 0.05).

CONCLUSIONS

In addition to conventional myocardial preservation techniques, preoperative ANH achieved further cardiac protection in patients undergoing on-pump myocardial revascularization.

Anemia and Clinical Outcomes

This article discusses the impact of anemia in the context of the perioperative setting. Relevant data from animal and human studies, the adaptive mechanisms in anemia, and current views on transfusion triggers are evaluated. Recommendations are provided for the anesthesiologist for transfusion of red blood cells.

Strategies for transfusion therapy

Transfusion of allogeneic red blood cells (RBCs), fresh frozen plasma (FFP) and platelets is associated with risks, and outcome studies comparing liberal and restrictive transfusion regimens are lacking in surgical patients. Therefore, guidelines have been established. They recommend first maintaining normovolaemia by the use of crystalloids and colloids. RBC transfusions are recommended for haemoglobin levels < 6 g/dl and for physiological signs of inadequate oxygenation such as haemodynamic instability, oxygen extraction > 50% and myocardial ischaemia (new ST-segment depressions > 0.1 mV, new ST-segment elevations > 0.2 mV or new wall motion abnormalities in transoesophageal echocardiography). FFP transfusions are recommended for urgent reversal of anticoagulation, known coagulation factor deficiencies, microvascular bleeding in the presence of elevated (> 1.5 times normal) prothrombin time (PT) or partial thromboplastin time (PTT) and microvascular bleeding after the replacement of more than one blood volume when PT or PTT cannot be obtained. Platelet transfusions are recommended prior to major operations in patients with platelet counts < 50,000/microl, intraoperatively with microvascular bleeding at platelet counts < 50,000/microl and in the range of 50,000-100,0000/microl following cardiopulmonary bypass and in patients undergoing surgery where already minimal bleeding may cause major damage such as in neurosurgery.

Allogeneic red blood cell transfusions: efficacy, risks, alternatives and indications

Careful assessment of risks and benefits has to precede each decision on allogeneic red blood cell (RBC) transfusion. Currently, a number of key issues in transfusion medicine are highly controversial, most importantly the influence of different transfusion thresholds on clinical outcome. The aim of this article is to review current evidence on blood transfusions, to highlight 'hot topics' with respect to efficacy, outcome and risks, and to provide the reader with transfusion guidelines. In addition, a brief synopsis of transfusion alternatives will be given. Based on up-to-date information of current evidence, together with clinical knowledge and experience, the physician will be able to make transfusion decisions that bear the lowest risk for the patient.

Transfusion in the cardiac patient

Transfusion guidelines in patients with coexisting cardiac diseases are similar to the ones in patients without such comorbidity, in that allogeneic blood transfusions most often are indicated at hemoglobin levels of less than 6.0 g/dL and hardly ever at hemoglobin levels greater than 10 g/dL. In the hemoglobin range of 6 to 10 g/dL, signs of impaired oxygenation should serve as transfusion indications, and such signs may be reached at higher hemoglobin values than in healthy patients. An inadequate oxygenation may become manifest globally in the form of a general hemodynamic instability with a tendency to hypotension and tachycardia despite normovolemia or an oxygen extraction of greater than 50%. An inadequate oxygenation in the form of myocardial ischemia may be manifested by new ST-segment depressions of greater than 0.1 mV, new ST-segment elevations greater than 0.2 mV, or new wall motion abnormalities in transesophageal echocardiography. Institutional guidelines also should consider local logistic characteristics such as the level of knowledge of physician and nurse staff caring for patients and the level of surveillance possible justifying eventually higher hemoglobin transfusion triggers, particularly in the postoperative period.

Evaluation of heart fatty acid–binding protein as a rapid indicator for assessment of myocardial damage in pediatric cardiac surgery

OBJECTIVES

Perioperative myocardial damage is a major determinant of postoperative cardiac dysfunction for congenital heart disease. Heart fatty acid-binding protein is reported to be a rapid marker of perioperative myocardial damage that peaks earlier than creatine kinase isoenzyme MB or cardiac troponin T in adults. The objective of this study was to assess the suitability of using serum concentrations of heart fatty acid-binding protein for evaluation of perioperative myocardial damage in pediatric cardiac surgery.

METHODS

After institutional review board approval and informed consent, 100 children undergoing open procedures for congenital heart disease were prospectively enrolled in the study. Mean age at operation was 4.9 +/- 0.4 years. Serum concentrations of heart fatty acid-binding protein, creatine kinase isoenzyme MB, and cardiac troponin T were measured serially before operation and at 0, 1, 2, 3, and 6 hours after aortic declamping. Relationships between serum peak level of heart fatty acid-binding protein and intraoperative and postoperative clinical variables were evaluated.

RESULTS

Serum heart fatty acid-binding protein reached its peak level at 1 hour after declamping in 95 patients (95%), which was significantly earlier (P <.01) than serum creatine kinase isoenzyme MB or cardiac troponin T. In addition, serum heart fatty acid-binding protein level immediately after declamping correlated strongly with serum peak heart fatty acid-binding protein level (r = 0.91, P <.01). The serum peak level of heart fatty acid-binding protein correlated with those of creatine kinase isoenzyme MB (r = 0.77, P <.01) and cardiac troponin T (r = 0.80, P <.01). In the forward stepwise multiple regression analysis, age (P <.0001), aortic crossclamp time (P <.0001), the presence of a ventriculotomy (P <.001), and the lowest hematocrit level during cardiopulmonary bypass (P <.05) were significant intraoperative variables that influenced the release of heart fatty acid-binding protein. There were significant relationships between serum peak heart fatty acid-binding protein level and postoperative inotropic support, duration of intubation, and intensive care unit stay (P <.01 for each).

CONCLUSIONS

Heart fatty acid-binding protein is a rapid marker for assessment of myocardial damage and clinical outcome in pediatric cardiac surgery. In particular, serum heart fatty acid-binding protein level immediately after aortic declamping may be a potentially useful prognostic indicator of myocardial damage as well as clinical outcome in pediatric cardiac surgery.

The Effect of Erythropoietin on Allogeneic Blood Requirement in Patients Undergoing Elective Liver Resection: A Model Simulation

We investigated whether recombinant human erythropoietin (rHuEPO) administration would reduce red blood cell (RBC) transfusion requirements in patients undergoing elective liver resection. We retrospectively investigated 200 patients undergoing elective liver resection. Factors likely to predict perioperative RBC transfusion were studied using a logistic regression analysis. A mathematical model was used to simulate RBC transfusion requirements if (a). transfusion thresholds had been predefined at a hemoglobin concentration of 7-8 g/dL, (b). preoperative hemoglobin concentrations had been increased to 15 g/dL by rHuEPO administration in patients with preoperative hemoglobin concentration in the range 10-13 g/dL, and (c). both interventions had been used. A cost/benefit evaluation of rHuEPO administration formed part of this simulation. RBC transfusion was correlated with major and median liver resection, total liver vascular exclusion, and a combined nonhepatic abdominal surgery but was not correlated with a preoperative hemoglobin concentration in the range 10-13 g/dL. Adherence to a small transfusion threshold or rHuEPO administration alone would have resulted in a slight reduction in transfusion requirements and transfusion rates for the whole population. However, the two interventions in combination would have significantly reduced both variables. One-hundred-eighteen patients undergoing median and major liver resection received 92% of RBC transfused. Sixty-six of these 118 patients had preoperative hemoglobin concentrations in the range 10-13 g/dL and could have received rHuEPO before surgery. rHuEPO alone would have avoided the transfusion of 63 RBC packs of 203 in this subgroup and 12 transfused patients of 31 (P = 0.02). rHuEPO administration to these 66 patients would have cost 186000 Euro. The 63 RBC saved would have cost 10,710 Euro.

IMPLICATIONS

A mathematical model simulation suggests that the routine preoperative administration of erythropoietin to patients scheduled for major and median liver resection presenting with a preoperative hemoglobin concentration in the range 10-13 g/dL could reduce blood transfusion requirements. However, the cost/benefit ratio warrants consideration.

Clinical consequences of anemia and red cell transfusion in the critically ill

Despite the frequent use of red cell transfusions, only one large randomized trial has examined red cell administration perioperative and in the critical care setting. However, the TRICC Trial does not provide sufficient evidence to determine optimal transfusion practice in postoperative care, in critically ill children, or in patients with a myocardial infarction or acute coronary syndromes. In addition, most transfusion practice guidelines published before the completion of the TRICC Trial are now dated and need to have expert opinion informed by solid evidence in diverse clinical settings. In the next several years,several randomized trials will provide additional evidence in support of bedside decision-making. For example, two transfusion studies will be evaluating transfusion triggers, including one in premature infants and the other in critically ill children. At this juncture, high-quality clinical evidence is not yet available for many decisions related to red cell transfusions. We anticipate that risks and benefits of red cells and alternatives will be elucidated in the coming years.

Anaemia and red blood cell transfusion in the critically ill patient

Anaemia is a common finding in critically ill patients. There are often multiple causes. Obvious causes include surgical bleeding and gastrointestinal haemorrhage but many patients have no overt bleeding episodes. Phlebotomy can be a significant source of blood loss. In addition, critically ill patients have impaired erythropoiesis as a consequence of blunted erythropoietin production and direct inhibitory effects of inflammatory cytokines. The ability of a patient to tolerate anaemia depends on their clinical condition and the presence of any significant co-morbidity; maintenance of circulating volume is of paramount importance. There is no universal transfusion trigger. Current guidelines for critically ill and perioperative patients advise that at Hb values <70 g/L red blood cell transfusion is strongly indicated and at Hb values >100 g/L transfusion is unjustified. For patients with Hb values in the range 70 to 100 g/L the transfusion trigger should be based on clinical indicators. Most stable critically ill patients can probably be managed with a Hb concentration between 70 and 90 g/L. Uncertainties exist concerning the most appropriate Hb concentration for patients with significant cardio-respiratory disease.

Hemodilution does not alter arterial baroreflex control of heart rate in anesthetized dogs

The cardiovascular effects of acute normovolemic hemodilution (ANH) are characterized by increased cardiac output and decreased systemic vascular resistance. However, whether arterial baroreflex function is altered by ANH remains undetermined. We assigned 23 anesthetized, mechanically ventilated dogs to mild ANH (hemoglobin, 7-8 g/dL; n = 11) or profound ANH (hemoglobin, 4-5 g/dL; n = 12) achieved by phlebotomy and simultaneous exchange with lactated Ringer's solution at 1:3 ratio to maintain constant central venous pressure and pulmonary artery occluded pressure. Baroreflex sensitivity was assessed by measurements of RR intervals of the electrocardiogram and mean arterial blood pressure (MAP) through a femoral artery catheter. Baroreflex responses were triggered by bolus IV injections of phenylephrine (25-75 micro g) and nitroprusside (50-100 micro g). The linear portion of the baroreflex curves relating RR intervals and MAP were used to determine baroreflex sensitivities. Compared with the predilution period, both ANH groups had significant increases in cardiac output and decreases in systemic vascular resistance (P < 0.01), whereas MAP and heart rate (HR) remained unchanged. However, no significant difference was detected between pre-ANH and post-ANH baroreflex sensitivities in either group. Our results indicate that arterial baroreflex control of HR is preserved during ANH to a hemoglobin concentration of 4-5 g/dL in anesthetized dogs.

IMPLICATIONS

Acute normovolemic hemodilution may be preoperatively used to minimize the requirement of allogeneic blood products during major surgery. We found that baroreflex function is preserved during mild (hemoglobin concentration, 7-8 g/dL) and profound hemodilution (hemoglobin concentration, 4-5 g/dL) in pentobarbital-anesthetized dogs.

Beta-adrenergic stimulation restores oxygen extraction reserve during acute normovolemic hemodilution

Compensatory increases in oxygen extraction (EO(2)) during acute normovolemic hemodilution (ANH) have the effect of decreasing tissue oxygen tension values, thus increasing the threat of tissue hypoxia. We hypothesized that if the beta-adrenergic agonist isoproterenol (ISOP) could augment cardiac output (CO) during ANH, it could reverse the increases in EO(2) and restore the margin of safety for tissue oxygenation. Studies were performed in seven anesthetized (isoflurane) dogs. CO was measured by using thermodilution, and regional blood flow (RBF) was measured by using radioactive microspheres. Systemic oxygen delivery (DO(2)), oxygen consumption (OV0312;O(2)), and EO(2), as well as regional DO(2), were calculated. Measurements were obtained under the following conditions in each dog: 1) baseline-1, 2) ISOP (0.1 micro g. kg(-1). min(-1) IV), 3) baseline-2, 4) ANH, and 5) ISOP during ANH. Hematocrit was 45% +/- 3% under baseline conditions and 18% +/- 3% during ANH. Before ANH, ISOP caused parallel increases in CO and systemic DO(2), which, in the presence of an unchanged OV0312;O(2), reduced EO(2). RBF increased in myocardium and spleen, decreased in pancreas, and did not change in brain, spinal cord, or other tissues. ANH caused increases in CO, which were insufficient to offset the decrease in arterial oxygen content, and thus systemic DO(2) declined; systemic OV0312;O(2) was maintained by an increase in EO(2). ANH-related increases in RBF maintained DO(2) in myocardium, brain, duodenum, and pancreas, whereas DO(2) declined in kidney and spleen. ISOP during ANH increased CO and systemic DO(2), which returned systemic EO(2) to baseline, and it increased RBF in myocardium, kidney, duodenum, and spleen. We conclude that 1) beta-adrenergic stimulation with ISOP restored the systemic EO(2) reserve during ANH, without apparent adverse effects in the individual body tissues, and that 2) the use of inotropic drugs, such as ISOP, may extend the limit to which hematocrit can be reduced safely during ANH.

IMPLICATIONS

By restoring the oxygen extraction reserve, isoproterenol and other inotropic drugs can enhance the margin of safety and extend the limit to which hematocrit can be reduced safely during acute normovolemic hemodilution. The use of this approach will depend on the degree of hemodilution, the extent of mixed venous oxygen desaturation, and whether increases in cardiac output are possible or desirable.

Hemodilution with albumin, but not Hextend, results in hypercoagulability as assessed by Thrombelastography in rabbits: role of heparin-dependent serpins and factor VIII complex

Isovolemic hemodilution (IVHD) has been advocated as an effective method of reducing the need for transfusion but has been associated with hypercoagulability. We tested the hypothesis that IVHD enhances hemostatic function by decreasing circulating antithrombin activity in rabbits. Furthermore, it was determined whether different replacement solutions would affect hemostasis. Sedated rabbits were randomly assigned to groups that underwent IVHD (40% blood volume removed) with 5% human albumin (n = 10) or a 6% hetastarch solution (Hextend). Antithrombin and Factor VIII complex (VIII:C) activities were determined, and thrombelastography(R) was performed with or without platelet inhibition. IVHD resulted in a significant (P < 0.05) decrease in antithrombin (32%-39%) without fluid-specific differences observed. VIII:C did not change in the albumin group, whereas the hetastarch group had a significant (P < 0.05) decrease (43%) in VIII:C that was also significantly (P < 0.05) less than the albumin group. The time to clot initiation was decreased, and the rate of clot formation increased significantly via thrombelastography(R) in albumin animals. No significant change in clot kinetics was observed in hetastarch animals. In rabbits, the primary determinant of hemostasis after IVHD was the interaction of changes in antithrombin activity and VIII:C. These data serve as a rational basis to determine whether IVHD-mediated hypercoagulability encountered clinically may be attenuated or exacerbated by the choice of colloid administered.

IMPLICATIONS

Isovolemic hemodilution (IVHD) is associated with hypercoagulability. Rabbits hemodiluted with albumin, but not Hextend, became hypercoagulable secondary to a loss of antithrombin activity with simultaneous maintenance of Factor VIII complex activity (VIII:C). Hextend-treated animals had proportionate decreases in both antithrombin activity and VIII:C. IVHD-mediated hypercoagulability encountered clinically may be attenuated or exacerbated by the choice of colloid administered.

Re-evaluating the transfusion trigger: how low is safe?

Concerns about transfusion-associated complications, in particular viral transmission, have motivated a more restrained pattern of clinical transfusion practice. This change in practice has allowed for an evaluation of the risks of withholding transfusion and the benefits of providing transfusion. The recognized risks of transfusion have declined, and this reduction in risks has been brought about by improved screening, better testing strategies and tests, and leuko-reduction at the time of donation. There are benefits to transfusion, in limiting hypoxic morbidity and mortality. These benefits are clearly evident only at very low levels of serum hemoglobin concentrations in healthy patients who tolerate moderate levels of anemia without morbidity. However, the benefits of transfusion are apparent at higher initial serum level concentrations in patients with cardiovascular disease who are less tolerant of anemia.

Mortality and morbidity in patients with very low postoperative Hb levels who decline blood transfusion

BACKGROUND

Guidelines for allogeneic transfusion emphasize minimizing use to avoid transmission of serious illness. However, there is little information on the risks associated from withholding transfusion.

STUDY DESIGN AND METHODS

A retrospective cohort study of patients who declined RBC transfusions for religious reasons was performed. This analysis was restricted to consecutive patients > or = 18 years old, who underwent surgery in the operating room from 1981 to 1994 and had a postoperative Hb count of 8 g per dL or less. The primary outcome was defined as any inhospital death occurring within 30 days of the surgery. Secondary outcome was 30-day mortality or in-hospital 30-day morbidity. Morbidity was defined as myocardial infarction, arrhythmia, congestive heart failure, or infection.

RESULTS

Of 2083 eligible patients, 300 had postoperative Hb counts of 8 g per dL or less. The study population was predominantly female (70.3%) with a mean age of 57 years (SD, +/- 17.7). In patients with a postoperative Hb level of 7.1 to 8.0, 0 died (upper 95% CI, 3.7%), and 9.4 percent (95% CI, 4.4-17.0%) had a morbid event. In patients with a postoperative Hb level of 4.1 to 5.0, 34.4 percent (95% CI, 18.6-53.2%) died and 57.7 percent (95% CI, 36.9-76.6%) had a morbid event or died. After adjusting for age, cardiovascular disease, and Acute Physiology and Chronic Health Evaluation II score, the odds of death in patients with a postoperative Hb level of < or = 8 g per dL increased 2.5 times (95% CI, 1.9-3.2) for each gram decrease in Hb level.

CONCLUSIONS

The risk of death was low in patients with postoperative Hb levels of 7.1 to 8.0 g per dL, although morbidity occurred in 9.4 percent. As postoperative blood counts fall the risk of mortality and/or morbidity rises and becomes extremely high below 5 to 6 g per dL.