Response of erythropoiesis and iron metabolism to recombinant human erythropoietin in intensive care unit patients

Anemia and blood transfusions in critically ill patients

Anemia is common in critically ill patients. As a consequence packed red blood cell (PRBC) transfusions are frequent in the critically ill. Over the past two decades a growing body of literature has emerged, linking PRBC transfusion to infections, immunosuppression, organ dysfunction, and a higher mortality rate. However, despite growing evidence that risk of PRBC transfusion outweighs its benefit, significant numbers of critically ill patients still receive PRBC transfusion during their intensive care unit (ICU) stay. In this paper, we summarize the current literature concerning the impact of anemia on outcomes in critically ill patients and the potential complications of PRBC transfusions.

The use of erythropoiesis-stimulating agents in the intensive care unit

Anemia is common in critically ill patients, but treatment with red blood cell transfusions can have unwanted effects. Limiting the occurrence and severity of anemia by using erythropoietic agents (iron and/or recombinant erythropoietin), therefore, remains an attractive option during the intensive care unit stay but also after hospital discharge. Moreover, these agents may have additional beneficial properties. In this article the authors review the rationale for the administration of iron and/or erythropoietin in critically ill patients.

Anemia in the ICU: anemia of chronic disease versus anemia of acute illness

Anemia is common in the ICU, increasing morbidity and mortality. Its etiology is multifactorial but anemia of inflammation is the most common cause, followed closely by iron deficiency. The two conditions often coexist and it can be difficult to diagnose iron deficiency in the context of anemia of inflammation. Blood transfusions and use of erythropoietin agonists are two modalities used to correct anemia in critically ill patients. Randomized controlled trials have not supported the use of either therapy except in well defined clinical situations. Better understanding of the pathophysiology of anemia of inflammation may lead to development of novel therapies.

Efficacy and toxicity of intravenous iron in a mouse model of critical care anemia*

OBJECTIVE

Anemia is common in critically ill patients, due to inflammation and blood loss. Anemia can be associated with iron deficiency and low serum hepcidin levels. However, iron administration in this setting remains controversial because of its potential toxicity, including oxidative stress induction and sepsis facilitation. The objective of this work was to determine the efficacy and toxicity of iron administration using a mouse model mimicking critical care anemia as well as a model of acute septicemia.

DESIGN

Prospective, randomized, open label controlled animal study.

SETTING

University-based research laboratory.

SUBJECTS

C57BL/6 and OF1 mice.

INTERVENTIONS

Intraperitoneal injection of zymosan inducing generalized inflammation in C57BL/6 mice, followed in our full model by repeated phlebotomies. A dose equivalent to 15 mg/kg of ferric carboxymaltose was injected intravenously on day 5. To assess the toxicity of iron in a septicemia model, OF1 mice were simultaneously injected with iron and different Escherichia coli strains.

MEASUREMENTS AND MAIN RESULTS

To investigate the effect of iron on oxidative stress, we measured reactive oxygen species production in the blood using luminol-amplified chemiluminescence and superoxide dismutase 2 messenger RNA levels in the liver. These markers of oxidative stress were increased after iron administration in control mice but not in zymosan-treated mice. Liver catalase messenger RNA levels decreased in iron-treated control mice. Iron administration was not associated with increased mortality in the septicemia model or in the generalized inflammation model. Iron increased hemoglobin levels in mice fed with a low iron diet and subjected to phlebotomies and zymosan 2 wks after treatment administration.

CONCLUSIONS

Adverse effects of intravenous iron supplementation by ferric carboxymaltose seem to be minimal in our animal models. Furthermore, iron appears to be effective in correcting anemia, despite inflammation. Studies of efficacy and safety of iron in critically ill patients are warranted.

Red blood cell clearance in inflammation

SUMMARY

Anemia is a frequently encountered problem in the critically ill patient. The inability to compensate for anemia includes several mechanisms, collectively referred to as anemia of inflammation: reduced production of erythropoietin, impaired bone marrow response to erythropoietin, reduced iron availability, and increased red blood cell (RBC) clearance. This review focuses on mechanisms of RBC clearance during inflammation. We state that phosphatidylserine (PS) expression in inflammation is mainly enhanced due to an increase in ceramide, caused by an increase in sphingomyelinase activity due to either platelet activating factor, tumor necrosis factor-α, or direct production by bacteria. Phagocytosis of RBCs during inflammation is mediated via RBC membrane protein band 3. Reduced deformability of RBCs seems an important feature in inflammation, also mediated by band 3 as well as by nitric oxide, reactive oxygen species, and sialic acid residues. Also, adherence of RBCs to the endothelium is increased during inflammation, most likely due to increased expression of endothelial adhesion molecules as well as PS on the RBC membrane, in combination with decreased capillary blood flow. Thereby, clearance of RBCs during inflammation shows similarities to clearance of senescent RBCs, but also has distinct entities, including increased adhesion to the endothelium.

Erythropoietin in the intensive care unit: beyond treatment of anemia

Erythropoietin (EPO) is the major hormone stimulating the production and differentiation of red blood cells. EPO is used widely for treating anemia of critical illness or anemia induced by chemotherapy. EPO at pharmacological doses is used in this setting to raise hemoglobin levels (by preventing the apoptosis of erythroid progenitor cells) and is designed to reduce patient exposure to allogenic blood through transfusions. Stroke, heart failure, and acute kidney injury are a frequently encountered clinical problem. Unfortunately, in the intensive care unit advances in supportive interventions have done little to reduce the high mortality associated with these conditions. Tissue protection with EPO at high, nonpharmacological doses after injury has been found in the brain, heart, and kidney of several animal models. It is now well known that EPO has anti-apoptotic effects in cells other than erythroid progenitor cells, which is considered to be independent of EPOs erythropoietic activities. This review article summarizes what is known in preclinical models of critical illness and discusses why this does not correlate with randomized, controlled clinical trials.

[The "Seville" Consensus Document on Alternatives to Allogenic Blood Transfusion. Sociedades españolas de Anestesiología (SEDAR), Medicina Intensiva (SEMICYUC), Hematología y Hemoterapia (AEHH), Transfusión sanguínea (SETS) Trombosis y Hemostasia (SETH)]

The Consensus Document on Alternatives to Allogenic Blood Transfusion (AABT) has been drawn up by a panel of experts from 5 scientific societies. The Spanish Societies of Anesthesiology (SEDAR), Critical Care Medicine and Coronary Units (SEMICYUC), Hematology and Hemotherapy (AEHH), Blood Transfusion (SETS) and Thrombosis and Hemostasis (SETH) have sponsored and participated in this Consensus Document. Alternatives to blood transfusion have been divided into pharmacological and non-pharmacological, with 4 modules and 12 topics. The main objective variable was the reduction of allogenic blood transfusions and/or the number of transfused patients. The extent to which this objective was achieved by each AABT was evaluated using the Delphi method, which classifies the grade of recommendation from A (supported by controlled studies) to E (non-controlled studies and expert opinion). The experts concluded that most of the indications for AABT were based on middle or low grades of recommendation, "C", "D", or "E", thus indicating the need for further controlled studies.

Anemia and transfusion therapy: an update

Anemia is one of the most prevalent diseases in the general population and is a very frequently found condition in medical and surgical patients in all medical specialties. A good evaluation of its clinical impact and its therapeutic possibilities is essential. Allogenic blood transfusion is a useful procedure in anemia management, although it has important adverse effects. It is the responsibility of the clinician to know and to take into account all the available alternatives for the treatment of anemia. Blood transfusions, erythropoiesis-stimulating agents, iron therapy (oral and endovenous) and other therapeutic alternatives must be rationally used, in accordance with the currently available clinical evidence. This review article summarizes some epidemiological characteristics of anemia, its clinical evaluation and the main therapeutic possibilities based on the present knowledge, placing special emphasis on the critically ill patient.

Disorders of iron metabolism. Part 1: molecular basis of iron homoeostasis

IRON FUNCTIONS: Iron is an essential micronutrient, as it is required for satisfactory erythropoietic function, oxidative metabolism and cellular immune response. IRON PHYSIOLOGY: Absorption of dietary iron (1-2 mg/day) is tightly regulated and just balanced against iron loss because there are no active iron excretory mechanisms. Dietary iron is found in haem (10%) and non-haem (ionic, 90%) forms, and their absorption occurs at the apical surface of duodenal enterocytes via different mechanisms. Iron is exported by ferroportin 1 (the only putative iron exporter) across the basolateral membrane of the enterocyte into the circulation (absorbed iron), where it binds to transferrin and is transported to sites of use and storage. Transferrin-bound iron enters target cells-mainly erythroid cells, but also immune and hepatic cells-via receptor-mediated endocytosis. Senescent erythrocytes are phagocytosed by reticuloendothelial system macrophages, haem is metabolised by haem oxygenase, and the released iron is stored as ferritin. Iron will be later exported from macrophages to transferrin. This internal turnover of iron is essential to meet the requirements of erythropoiesis (20-30 mg/day). As transferrin becomes saturated in iron-overload states, excess iron is transported to the liver, the other main storage organ for iron, carrying the risk of free radical formation and tissue damage. REGULATION OF IRON HOMOEOSTASIS: Hepcidin, synthesised by hepatocytes in response to iron concentrations, inflammation, hypoxia and erythropoiesis, is the main iron-regulatory hormone. It binds ferroportin on enterocytes, macrophages and hepatocytes triggering its internalisation and lysosomal degradation. Inappropriate hepcidin secretion may lead to either iron deficiency or iron overload.

Roles of Intravenous Iron Therapy in Various Patient Settings

Objective:

To provide clinical information on intravenous iron products and their role in chronic kidney disease (CKD), dialysis, oncology, critical illness, and heart failure.

Data Sources:

Intravenous iron products information, national clinical practice guidelines, and the latest primary literature available were reviewed. PubMed and MEDLINE databases were searched from January 2000-December 2009.

Study Selection and Data Extraction:

All FDA-approved intravenous iron products information, available national clinical practice guidelines, and primary literature were included.

Data Synthesis:

Iron deficiency is common in patients with CKD, dialysis, oncology, critical illness, and heart failure. Routine supplementation with intravenous iron therapy is indicated in patients with CKD, including those receiving dialysis; however, its role in oncology, critical illness, and heart failure is not clearly defined. Assessing patients for iron deficiency, evaluating their status, and knowing the risks of adverse events are important in determining the roles of intravenous iron therapy in each setting. If patients are initiated on intravenous iron, they must be closely monitored for signs and symptoms of adverse drug reactions, as well as clinical worsening. Additionally, intravenous iron must be discontinued upon resolution of iron deficiency.

Conclusions:

The importance of intravenous iron therapy is well established in patients with CKD, including those receiving dialysis, who have iron deficiency. Its roles in oncology, critical illness, and heart failure should be assessed on a case-by-case basis.

Bench to bedside: A role for erythropoietin in sepsis

Sepsis is the systemic inflammatory response to infection and can result in multiple organ dysfunction syndrome with associated high mortality, morbidity and health costs. Erythropoietin is a well-established treatment for the anaemia of renal failure due to its anti-apoptotic effects on red blood cells and their precursors. The extra-haemopoietic actions of erythropoietin include vasopressor, anti-apoptotic, cytoprotective and immunomodulating actions, all of which could prove beneficial in sepsis. Attenuation of organ dysfunction has been shown in several animal models and its vasopressor effects have been well characterised in laboratory and clinical settings. Clinical trials of erythropoietin in single organ disorders have suggested promising cytoprotective effects, and while no randomised trials have been performed in patients with sepsis, good quality data exist from studies on anaemia in critically ill patients, giving useful information of its pharmacokinetics and potential for harm. An observational cohort study examining the microvascular effects of erythropoietin is underway and the evidence would support further phase II and III clinical trials examining this molecule as an adjunctive treatment in sepsis.

[Anemia and transfusion therapy: an update]

Anemia is one of the most prevalent diseases in the general population and is a very frequently found condition in medical and surgical patients in all medical specialties. A good evaluation of its clinical impact and its therapeutic possibilities is essential. Allogenic blood transfusion is a useful procedure in anemia management, although it has important adverse effects. It is the responsibility of the clinician to know and to take into account all the available alternatives for the treatment of anemia. Blood transfusions, erythropoiesis-stimulating agents, iron therapy (oral and endovenous) and other therapeutic alternatives must be rationally used, in accordance with the currently available clinical evidence. This review article summarizes some epidemiological characteristics of anemia, its clinical evaluation and the main therapeutic possibilities based on the present knowledge, placing special emphasis on the critically ill patient.

Hemoglobin concentration variations over time in general medical inpatients

BACKGROUND

A decrease in hemoglobin concentration [Hb] with no apparent cause is frequently observed in critically ill patients. Scarce information is available about this situation in general ward-admitted patients (GWAP).

OBJECTIVES

To describe [Hb] variation with no obvious cause in GWAP, and to estimate the prevalence and predictors of patients with [Hb] decreases > or =1.5 g/dL.

DESIGN, SETTING AND PATIENTS

Prospective, observational study in internal medicine GWAP, carried out at two teaching hospitals in Buenos Aires, Argentina. Patients with a history of, or admitted for diseases associated with decreases in [Hb], as well as those with length of stay less than three days, were excluded.

MEASUREMENTS

Upon hospitalization, complete personal and clinical data were recorded. Furthermore, Katz index, APACHE II acute physiology score (APS) and Charlson score were calculated. [Hb] and hematocrit (HCT) were also assessed during hospitalization.

RESULTS

A total of 338 patients were evaluated, 131 were included. A mean [Hb] decrease of 0.71 g/dL was observed between admission and discharge (P < 0.001; 95% CI, 0.47-0.97). Forty-five percent of the included patients had decreases in [Hb] > or = 1.5 g/dL. This was associated with a higher APS, a higher [Hb] at admission, and a discharge diagnosis of infectious or gastrointestinal disease. No bleeding episodes were observed.

CONCLUSIONS

An [Hb] decrease was frequently observed during GWAP hospitalization with no evident blood loss. Even though this decrease has multiple causes, the severity of the acute illness seems to play a major role.

Management of adult Jehovah's Witness patients with acute bleeding

Because of the firm refusal of transfusion of blood and blood components by Jehovah's Witnesses, the management of Jehovah's Witness patients with severe bleeding is often complicated by medical, ethical, and legal concerns. Because of a rapidly growing and worldwide membership, physicians working in hospitals should be prepared to manage these patients. Appropriate management of a Jehovah's Witness patient with severe bleeding entails understanding of the legal and ethical issues involved, and meticulous medical management, including treatment of hypovolemic shock, local hemostatic interventions, and administration of prohemostatic agents, when appropriate. In addition, high-dose recombinant erythropoietin in combination with supplemental iron may enhance the speed of hemoglobin synthesis.

Removal of erythropoietin from anaemia trauma practice guideline does not increase red blood cell transfusions and decreases hospital utilization costs

INTRODUCTION

We previously demonstrated that utilization of erythropoietin (r-EPO) did not significantly reduce blood utilization in trauma patients. We undertook this study to analyze blood utilization 1 year after r-EPO removal from our trauma service anaemia practice management guideline.

METHODS

Electronic records of patients admitted to the trauma service were retrospectively reviewed for units of packed red blood cells (pRBCs) transfused and for units of r-EPO administered 12 months before the initiation of an anaemia practice guideline (PRE), 12 months during the use of an anaemia guideline (GUIDE), and 12 months following removal of r-EPO from the guideline (POST). Hospital acquisition cost was also reviewed for the respective time periods. Nominal data were analyzed using chi-squared or Fisher's exact tests, and interval data were compared using ANOVA followed by Tukey's test where appropriate. Results were considered significant for P<0.05.

RESULTS

Over the 3-year study period, 4881 patients were admitted to the trauma service and included in this study. The hospital length of stay, intensive care unit length of stay, and units of pRBC transfused were similar among all three groups. Group I (PRE) received a total of 228 doses of r-EPO at a cost of $102,600. Group II (GUIDE) received a total of 410 doses at a cost of $184,500. Group III (POST) received 28 doses of r-EPO at a cost of $12,600.

CONCLUSION

Removal of erythropoietin from our trauma service anaemia practice management guideline did not result in increased blood utilization. However, it yielded a hospital acquisition cost savings of $171,900.

An update on iron physiology

Iron is an essential micronutrient, as it is required for adequate erythropoietic function, oxidative metabolism and cellular immune responses. Although the absorption of dietary iron (1-2 mg/d) is regulated tightly, it is just balanced with losses. Therefore, internal turnover of iron is essential to meet the requirements for erythropoiesis (20-30 mg/d). Increased iron requirements, limited external supply, and increased blood loss may lead to iron deficiency (ID) and iron-deficiency anemia. Hepcidin, which is made primarily in hepatocytes in response to liver iron levels, inflammation, hypoxia and anemia, is the main iron regulatory hormone. Once secreted into the circulation, hepcidin binds ferroportin on enterocytes and macrophages, which triggers its internalization and lysosomal degradation. Thus, in chronic inflammation, the excess of hepcidin decreases iron absorption and prevents iron recycling, which results in hypoferremia and iron-restricted erythropoiesis, despite normal iron stores (functional ID), and anemia of chronic disease (ACD), which can evolve to ACD plus true ID (ACD + ID). In contrast, low hepcidin expression may lead to iron overload, and vice versa. Laboratory tests provide evidence of iron depletion in the body, or reflect iron-deficient red cell production. The appropriate combination of these laboratory tests help to establish a correct diagnosis of ID status and anemia.

Lipopolysaccharide evokes resistance to erythropoiesis induced by the long-acting erythropoietin analogue darbepoetin alfa in rats

BACKGROUND

Anemia is common in patients with sepsis but its mechanism is unknown. We tested the hypothesis that effects on erythropoiesis evoked by darbepoetin alfa (DA), a long-acting erythropoietin analog, are diminished by lipopolysaccharide (LPS).

METHODS

We performed a prospective, controlled, randomized animal study (male Lewis rats n = 44). The interventions we used were intraperitoneal injection of Escherichia coli LPS (10 mg/kg) or vehicle followed by either DA (25 microg/kg) or vehicle (four experimental groups). Blood and reticulocyte counts and variables of iron metabolism were measured at baseline and 3 and 14 days after interventions.

RESULTS

Animals treated with DA alone showed an eightfold increase in reticulocyte count from baseline on Day 3, whereas no increase was seen in animals administered LPS or LPS/DA. On Day 14, the red blood cell count and hemoglobin concentration had increased by approximately 10% from baseline (P < 0.001) in the DA group but had decreased after LPS on Days 3 and 14 (P < 0.05) and in animals administered LPS/DA. Consumption of iron was seen on Day 3 in the DA group but not after LPS or LPS/DA combined. Values of ferritin and transferrin did not change between groups.

CONCLUSION

LPS abolishes erythropoiesis and iron use evoked by DA and this is accompanied by a decrease in hemoglobin concentration and red blood cell concentration. Accordingly, endotoxin suppresses DAs ability to increase erythropoiesis.

Randomized, double-blind, placebo-controlled trial of effects of enteral iron supplementation on anemia and risk of infection during surgical critical illness

BACKGROUND

Critical illness is characterized by hypoferremia, iron-deficient erythropoiesis (IDE), and anemia. The relative risks and benefits of iron supplementation in this setting are unknown.

METHODS

Anemic, critically ill surgical patients with an expected intensive care unit length of stay (ULOS) >or= 5 days were randomized to either enteral iron supplementation (ferrous sulfate 325 mg three times daily) or placebo until hospital discharge. Outcomes included hematocrit, iron markers (i.e., serum concentrations of iron, ferritin, and erythrocyte zinc protoporphyrin [eZPP]), red blood cell (RBC) transfusion, transfusion rate (mL RBC/study day), nosocomial infection, antibiotic days, study length of stay (LOS), ULOS, and death. Iron-deficient erythropoiesis was defined as an elevated eZPP concentration.

RESULTS

Two hundred patients were randomized; 97 received iron, and 103 received placebo. Socio-demographics, baseline acuity, hematocrit, and iron markers were similar in the two groups. No differences were observed between the iron and placebo groups with respect to either hematocrit or iron markers following up to 28 days. However, patients treated with iron were significantly less likely to receive an RBC transfusion (29.9% vs. 44.7%, respectively; p = 0.03) and had a significantly lower transfusion rate (22.0 mL/day vs. 29.9 mL/day; p = 0.03). Subgroup analysis revealed that these differences were observed in patients with baseline IDE only. Iron and placebo groups did not differ with respect to incidence of infection (46.8% vs. 48.9%; p = 0.98), antibiotic days (14 vs. 16; p = 0.45), LOS (14 vs. 16 days; p = 0.24), ULOS (12 vs. 14 days; p = 0.69), or mortality rate (9.4% vs. 9.9%; p = 0.62).

CONCLUSIONS

Enteral iron supplementation of anemic, critically ill surgical patients does not increase the risk of infection and may benefit those with baseline IDE by decreasing the risk of RBC transfusion. A trial comparing enteral and parenteral iron supplementation in this setting is warranted (ClinicalTrials.gov number, NCT00450177).

Anemia and red blood cell transfusion in neurocritical care

INTRODUCTION

Anemia is one of the most common medical complications to be encountered in critically ill patients. Based on the results of clinical trials, transfusion practices across the world have generally become more restrictive. However, because reduced oxygen delivery contributes to 'secondary' cerebral injury, anemia may not be as well tolerated among neurocritical care patients.

METHODS

The first portion of this paper is a narrative review of the physiologic implications of anemia, hemodilution, and transfusion in the setting of brain-injury and stroke. The second portion is a systematic review to identify studies assessing the association between anemia or the use of red blood cell transfusions and relevant clinical outcomes in various neurocritical care populations.

RESULTS

There have been no randomized controlled trials that have adequately assessed optimal transfusion thresholds specifically among brain-injured patients. The importance of ischemia and the implications of anemia are not necessarily the same for all neurocritical care conditions. Nevertheless, there exists an extensive body of experimental work, as well as human observational and physiologic studies, which have advanced knowledge in this area and provide some guidance to clinicians. Lower hemoglobin concentrations are consistently associated with worse physiologic parameters and clinical outcomes; however, this relationship may not be altered by more aggressive use of red blood cell transfusions.

CONCLUSIONS

Although hemoglobin concentrations as low as 7 g/dl are well tolerated in most critical care patients, such a severe degree of anemia could be harmful in brain-injured patients. Randomized controlled trials of different transfusion thresholds, specifically in neurocritical care settings, are required. The impact of the duration of blood storage on the neurologic implications of transfusion also requires further investigation.

A US multicenter, retrospective, observational study of erythropoiesis-stimulating agent utilization in anemic, critically ill patients admitted to the intensive care unit

BACKGROUND

Anemia is a common comorbid condition among patients admitted to the intensive care unit (ICU). Darbepoietin alfa and epoetin alfa are erythropoiesis-stimulating agents (ESAs) used to manage anemia in the ICU, although neither drug has an indication in critically ill patients.

OBJECTIVE

This study describes ESA practice patterns in anemic, critically ill patients admitted to the ICU.

METHODS

A total of 19 hospitals participated in this US multicenter, retrospective, observational study of adult patients not receiving chronic hemodialysis who were admitted to the ICU for >or=24 hours between February 2005 and September 2005 and who received >or=1 dose of darbepoietin alfa or epoetin alfa. Data on ESA doses, dosing frequencies, hemoglobin levels, and red blood cell (RBC) transfusions were abstracted from electronic medical records.

RESULTS

A total of 438 patients were included in the analysis, of whom 201 (46%) were treated with darbepoietin alfa and 237 (54%) were treated with epoetin alfa. In the respective groups, similar proportions were male (121/201 [60%] and 126/237 [53%]) and white (146/195 [75%] and 140/184 [76%]); age was also similar (mean [SD], 62 [19] and 60 [18] years). The mean (SD) dose during the first week of ICU stay was 96.5 (40.5) microg with darbepoietin alfa and 33,439 (23,508) U with epoetin alfa. The most commonly prescribed dosing frequency with darbepoietin alfa was once weekly (88.1% of all prescribed doses), with a mean (SD) number of injections of 1.8 (1.75). With epoetin alfa, the most common dosing frequencies were 3 times weekly (35.9%), 1-time dosing (28.5%), and once weekly (24.0%), with a mean (SD) number of injections of 2.9 (4.2). In both groups, the duration of therapy was <or=1 week in ~50% of patients, and the mean change in hemoglobin concentration was 0.8 g/dL. Overall, 47% (darbepoietin alfa) and 44% (epoetin alfa) of patients were RBC transfusion independent (ie, did not require a transfusion during their ICU or hospital stay) after receiving the first ESA dose.

CONCLUSION

Based on these results, it is apparent that the practice patterns associated with ESA treatment of critically ill patients admitted to the ICU between February 2005 and September 2005 were highly variable.

[Is there still a role for recombinant erythropoietin in the management of anaemia of critical illness?]

There is a high prevalence of anaemia among patients admitted to the intensive care unit (ICU), and it may have a negative effect on patient's outcome. The most common treatment for anaemia in the ICU patient is allogeneic blood transfusion (ABT), yet it has been found to be a risk factor associated with an increased risk of morbidity and mortality in critical care patients. As a reduction of erythropoietin secretion and action is observed in most ICU patients, the administration of (rHuEPO) has emerged as a therapeutic option. Unfortunately, the results from different studies show that rHuEPO treatment results in a small reduction of ABT requirements when "restrictive" transfusion criteria are applied, which has only been supported by three of the studies. Yet this did not result in a decreased mortality rate, except for patients with a diagnosis on admission of trauma in two studies, even though one study reported a dose-dependent increase of thrombotic vascular events among patients without thromboprophylaxis. Altogether, clinical data suggest a role for rHuEPO in the treatment of anaemia in trauma patients, especially in those sustaining neurotrauma, whereas for non-trauma patients without an approved indication, rHuEPO administration is an expensive approach, does not seem to improve outcome, and might result in serious adverse effects. Consequently, more basic and clinical studies are required to ascertain which patients are more likely to benefit from these treatments, as well as to identify the optimal doses and administration schedules, and iron administration.

Anemia of critical illness

Anemia of critical illness, a commonly encountered clinical situation, is hematologically similar to that of chronic anemia, except that the onset is generally sudden. The etiology is usually multifactorial, occurring as a consequence of direct inhibitory effects of inflammatory cytokines, erythropoietin deficiency, blunted erythropoietic response, blood loss, nutritional deficiencies, and renal insufficiency. Although anemia is not well tolerated by critically ill patients, aggressive treatment of anemia can be just as detrimental as no treatment. Different types of anemia may coexist in a patient in the intensive care unit, making diagnosis and differentiation among these anemias complex, therefore requiring good diagnostic skills. Although several therapeutic options are available to treat anemia, critically ill patients often receive a transfusion, and yet, most recent studies indicate that blood transfusions in critically ill patients are associated with worse outcomes, including higher morbidity and mortality. These studies have generated interest in the administration of exogenous erythropoietin and iron therapy. Unfortunately, the accurate determination of iron status can be a rather difficult task, an undertaking that is made even more difficult by the presence of comorbid conditions that can affect the commonly used parameters for guiding iron therapy. The use of erythropoiesis-stimulating agents is rapidly gaining acceptance, although they also present potential problems of their own.

Anemia in the Critically Ill Patient

Anemia in critically ill patients has been described as an acute form of anemia of inflammatory disease and is characterized by a blunted erythropoietic response due in part to proinflammatory mediators. Management of anemia in critically ill patients is a complex issue and is best approached via a multiprofessional team regarding the use of allogenic blood, iron, nutritional therapy, and erythropoietic agents. Indiscriminant, ``routine'' red blood cell transfusions may not only be unnecessary, but may pose unnecessary risk to the intensive care unit patient. Most intensive care unit patients can tolerate lower hemoglobin/hematocrit concentrations than the typically accepted ``10/30 rule.'' Lower transfusion triggers with an overall transfusion strategy is warranted in the intensive care unit patient. The use of recombinant human erythropoietic agents may not be necessary with appropriate transfusion practices.

Phlebotomies or erythropoietin injections allow mobilization of iron stores in a mouse model mimicking intensive care anemia

OBJECTIVE

Anemia in critically ill patients is frequent and consists of chronic disease associated with blood losses. These two mechanisms have opposite effects on iron homeostasis, especially on the expression of the iron regulatory hormone hepcidin. We developed a mouse model mimicking the intensive care anemia to explore iron homeostasis.

DESIGN

Experimental study.

SETTING

University-based research laboratory.

SUBJECTS

C57BL/6 mice.

INTERVENTIONS

Mice received either a single intraperitoneal injection of lipopolysaccharide followed 1 week later by zymosan, or were subjected to repeated phlebotomies by retro-orbital punctures, or both. Several subsets of mice were analyzed over a 14-day period to describe the mouse model of intensive care anemia. Additional mice received erythropoietin injections with or without the zymosan treatment and were killed at day 5, to perform a more detailed analysis.

MEASUREMENTS AND MAIN RESULTS

We observed anemia as soon as 5 days after zymosan injection, together with increased messenger RNA (mRNA) levels for interleukin-6 and hepcidin. Phlebotomies alone fully suppressed hepcidin mRNA expression. Interestingly, in mice treated with zymosan and phlebotomies, hepcidin expression was suppressed, despite the persistent increase in interleukin-6. Stimulation of erythropoiesis by erythropoietin injections also led to a decrease in hepcidin mRNA in zymosan-treated mice. In these situations combining inflammation and erythropoiesis stimulation, there was no change in ferroportin, the membrane iron exporter, at the mRNA level, whereas ferroportin protein increased. Macrophage iron stores (assessed by histology using diaminobenzidine staining, or by quantification of nonheme iron and ferritin concentrations) were depleted in the spleen.

CONCLUSIONS

These results suggest that the erythroid factor dominates over inflammation for hepcidin regulation, and that iron could be mobilized in these situations combining inflammation and erythropoiesis stimulation.

Efficacy and safety of intravenous iron therapy as an alternative/adjunct to allogeneic blood transfusion

Anaemia is a common condition among patients admitted to hospital medicosurgical departments, as well as in critically ill patients. Anaemia is more frequently due to absolute iron deficiency (e.g. chronic blood loss) or functional iron deficiency (e.g. chronic inflammatory states), with other causes being less frequent. In addition, preoperative anaemia is one of the major predictive factors for perioperative blood transfusion. In surgical patients, postoperative anaemia is mainly caused by perioperative blood loss, and it might be aggravated by inflammation-induced inhibition of erythropoietin and functional iron deficiency (a condition that cannot be corrected by the administration of oral iron). All these mechanisms may be involved in the anaemia of the critically ill. Intravenous iron administration seems to be safe, as very few severe side-effects were observed, and may result in hastened recovery from anaemia and lower transfusion requirements. However, it is noteworthy that many of the recommendations given for intravenous iron treatment are not supported by a high level of evidence and this must be borne in mind when making decisions regarding its application to a particular patient. Nonetheless, this also indicates the need for further large, randomized controlled trials on the safety and efficacy of intravenous iron for the treatment of anaemia in different clinical settings.

Erythropoietin improves skeletal muscle microcirculation and tissue bioenergetics in a mouse sepsis model

Introduction

The relationship between oxygen delivery and consumption in sepsis is impaired, suggesting a microcirculatory perfusion defect. Recombinant human erythropoietin (rHuEPO) regulates erythropoiesis and also exerts complex actions promoting the maintenance of homeostasis of the organism under stress. The objective of this study was to test the hypothesis that rHuEPO could improve skeletal muscle capillary perfusion and tissue oxygenation in sepsis.

Methods

Septic mice in three experiments received rHu-EPO 400 U/kg subcutaneously 18 hours after cecal ligation and perforation (CLP). The first experiment measured the acute effects of rHuEPO on hemodynamics, blood counts, and arterial lactate level. The next two sets of experiments used intravital microscopy to observe capillary perfusion and nicotinamide adenine dinucleotide (NADH) fluorescence post-CLP after treatment with rHuEPO every 10 minutes for 40 minutes and at 6 hours. Perfused capillary density during a three-minute observation period and NADH fluorescence were measured.

Results

rHuEPO did not have any effects on blood pressure, lactate level, or blood cell numbers. CLP mice demonstrated a 22% decrease in perfused capillary density compared to the sham group (28.5 versus 36.6 capillaries per millimeter; p < 0.001). Treatment of CLP mice with rHuEPO resulted in an immediate and significant increase in perfused capillaries in the CLP group at all time points compared to baseline from 28.5 to 33.6 capillaries per millimeter at 40 minutes; p < 0.001. A significant increase in baseline NADH, suggesting tissue hypoxia, was noted in the CLP mice compared to the sham group (48.3 versus 43.9 fluorescence units [FU]; p = 0.03) and improved with rHuEPO from 48.3 to 44.4 FU at 40 minutes (p = 0.02). Six hours after treatment with rHuEPO, CLP mice demonstrated a higher mean perfused capillary density (39.4 versus 31.7 capillaries per millimeter; p < 0.001) and a lower mean NADH fluorescence as compared to CLP+normal saline mice (49.4 versus 52.7 FU; p = 0.03).

Conclusion

rHuEPO produced an immediate increase in capillary perfusion and decrease in NADH fluorescence in skeletal muscle. Thus, it appears that rHuEPO improves tissue bioenergetics, which is sustained for at least six hours in this murine sepsis model.

Erythropoietin pharmacology

Anaemia is a frequent complication in cancer patients and may be multifactorial in origin. Treatment with recombinant human erythropoietin (rHuEPO) is an alternative to red blood cell transfusion. The evidence from clinical trials has established that patients with chemotherapy-induced anaemia with a haemoglobin concentration below 10 g/dl benefit from epoetin therapy. The native glycoprotein hormone consists of 165 amino acids with three N-glycosylation and one O-glycosylation sites. Epoetin and darbepoetin bind to the EPO receptor to induce intracellular signalling by the same intracellular molecules as native EPO. There are some differences in the glycosylation pattern which lead to variations in the pharmacokinetics and pharmacodynamics profiles. Pharmacokinetic and therapeutic studies have examined the use of rHuEPO administered intravenously and subcutaneously and there is accumulating evidence that the latter route has several advantages in cancer patients. After subcutaneous administration, the bioavailability of epoetin is about 20-30% and has a plasma half-life of >24 h. Darbepoetin has a longer half-life after subcutaneous administration of 48 h. The general recommendations are based on evidence from trials in which epoetin was administered 150 U/kg thrice weekly. The recommended initial dose for darbepoetin alpha is 2.25 mug/kg per week. The most serious adverse effects are hypertension, bleeding and increased risk of thrombotic complications. Caution is advised when used in patients who are at high risk for thromboembolic events. In the management of anaemic cancer patients, physicians should closely follow the National Comprehensive Cancer Network (NCCN) and American Society of Clinical Oncology (ASCO)/American Society of Hematology (ASH) guidelines.

[Prevalence and treatment of anemia in critically ill patients]

Anemia is a common condition among medical and surgical patients admitted to the intensive care unit (ICU) and generally has a multifactorial origin. In order to avoid the deleterious effects of anemia, 40% of ICU patients receive allogenic blood transfusion (ABT). This figure increases up to 70% if the ICU stay is longer than 7 days. However, ABT is associated with a dose-dependent increase in morbidity and mortality. In contrast, the administration of exogenous erythropoietin plus iron supplements, especially iv iron, improves anemia and reduces ABT requirements, although it does not reduce mortality. To ascertain whether treatment of anemia in the critically ill with exogenous erythropoietin and iron might improve outcomes and to optimize drug administration schedules and dosage, further studies with sufficient statistical power and adequate follow-up are warranted.

A meta-analysis of randomized controlled trials in critically ill patients to evaluate the dose-response effect of erythropoietin

The use of erythropoietin in critically ill patients has been investigated in multiple randomized clinical trials and its role in decreasing the number of units of blood transfused has been demonstrated in some trials. A meta-analysis was conducted to determine the pooled estimate of the decrease in number of units of blood transfused with the use of erythropoietin and investigated its dose-response effect. A systematic search was performed of the MEDLINE, EMBASE, and the Current Controlled Trials Register to identify randomized clinical trials investigating the role of erythropoietin in critically ill patients. Of 664 studies identified in the search, 5 randomized clinical trials met the inclusion criteria. The pooled estimate of the decrease of number of units of blood transfused was -1.64 (95% CI -2.6 to -0.67). Sensitivity analysis to establish the influence of temporal bias, quality of the study and comorbidities such as age and Acute Physiology and Chronic Health Evaluation (APACHE) II score were undertaken and did not reveal a significant difference. The inclusion of studies with higher doses of erythropoietin revealed a greater decrease in the number of units of blood transfused (-2.15; 95% CI -3.06 to -1.24). Despite the limitations of a meta-analysis we believe that the use of erythropoietin significantly decreases the number of units of blood transfused per patient. Our study also reveals the possibility of a dose-response effect of erythropoietin in decreasing the number of units of blood transfused.

Blood management: a primer for clinicians

Blood transfusions are common in the hospital setting. Despite the large commitment of resources to the delivery of blood components, many clinicians have only a vague understanding of the complexities associated with blood management and transfusion therapy. The purpose of this primer is to broaden the awareness of health care practitioners in terms of the risks versus benefits of blood transfusions, their economics, and alternative treatments. By developing and implementing comprehensive blood management programs, hospitals can promote safe and clinically effective blood utilization practices. The cornerstones of blood management programs are the implementation of evidence-based transfusion guidelines to reduce variability in transfusion practice, and the employment of multidisciplinary teams to study, implement, and monitor local blood management strategies. Pharmacists can play a key role in blood management programs by providing technical expertise as well as oversight and monitoring of pharmaceutical agents used to reduce the need for allogeneic blood.

Short-term benefits and risks of intravenous iron: a systematic review and meta-analysis

BACKGROUND

Intravenous (IV) iron may correct anemia more efficiently than oral iron, but it has been associated with allergic and hemodynamic reactions, and it may increase the risks of infectious complications. The objective of this systematic review and meta-analysis was to clarify these controversial issues.

STUDY DESIGN AND METHODS

Studies evaluating the use of IV iron compared to enteral or no iron with outcomes within 2 months of treatment initiation were identified. Only randomized controlled trials were included. When a meta-analysis was possible, studies were combined with the Review Manager of the Cochrane Collaboration Group 2003. Statistics were calculated as standardized mean differences (SMDs), with a random-effect model.

RESULTS

Thirteen studies met inclusion criteria. Meta-analysis revealed a significant increase in the reticulocyte count (SMD, 0.70; 95% confidence interval [CI], 0.10-1.29; p = 0.02) and in ferritin levels (SMD, 1.18; 95% CI, 0.69-1.68; p = 0.00001), but it also showed that in such a short period of time, IV iron does not correct hemoglobin (Hb)-hematocrit (Hct) better than enteral or no iron. In a sensitivity analysis, however, the increase in Hb-Hct became significant in the nondextran group (SMD, 0.27; 95% CI, 0.04-0.51; p = 0.02). No increase in transferrin saturation was observed. Meta-analysis of the allergic and hemodynamic reactions was not possible as most studies did not clearly describe these outcomes.

CONCLUSION

Our results suggest that treatment with nondextran IV iron may benefit a wide variety of patients. Randomized controlled studies are definitively needed to further evaluate the usefulness and safety of IV iron.

Erythropoietin-receptor agonists in critically ill patients: a meta-analysis of randomized controlled trials

INTRODUCTION

Anemia and the need for red blood cell transfusions are common among patients admitted to intensive care units. Erythropoietin has been used to decrease the need for transfusions; however, its ability to improve clinical outcomes is unknown. We evaluated the effect of erythropoietin-receptor agonists on clinically important outcomes, including mortality, length of stay in hospital or intensive care unit, ventilator use, transfusion requirements and major adverse events.

METHODS

To identify relevant studies, we searched electronic databases covering 1950 to 2007 (MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and the Scopus database). We also searched conference proceedings and grey literature sources. We selected all randomized controlled trials involving critically ill patients that compared an erythropoietin-receptor agonist with a placebo or no intervention. No language restrictions were considered. Data were extracted using a standardized extraction template. We used a fixed effects model to calculate all summary measures of treatment effects.

RESULTS

Of 673 identified records, 9 studies that investigated erythropoietin alpha met the eligibility criteria and were included in our analysis. Erythropoietin, compared with placebo or no intervention, had no statistically significant effect on overall mortality (odds ratio [OR] 0.86, 95% confidence interval [CI] 0.71-1.05, I2 = 0%). The treatment and control groups did not differ in the length of stay in hospital or intensive care unit, or in the duration of mechanical ventilation, in the 3 studies that reported these outcomes. Erythropoietin, compared with placebo, significantly reduced the odds of a patient receiving at least 1 transfusion (OR 0.73, 95% CI 0.64-0.84, I2 = 54.7%). The mean number of units of blood transfused per patient was decreased by 0.41 units in the erythropoietin group (95% CI 0.10-0.74, I2 = 79.2%). Most of the included studies were performed before the widespread adoption of a restrictive transfusion strategy. Only 1 study provided detailed reports of adverse events, and none of the studies systematically evaluated all patients for venous thromboembolism.

INTERPRETATION

At this time, we do not recommend the routine use of erythropoietin-receptor agonists in critically ill patients. The reduction in red blood cell transfusions per patient was very small, and there is insufficient evidence to determine whether this intervention results in clinically important benefits with acceptable risks.

Erythropoietic response to two epoetin alfa regimens in critically ill patients: a pilot study

STUDY OBJECTIVE

To compare the erythropoietic responses and tolerability of two recombinant human erythropoietin (EPO) regimens.

DESIGN

Prospective, open-label, multicenter study.

SETTING

Three multidisciplinary intensive care units in Québec, Canada.

PATIENTS

Sixty critically ill patients.

INTERVENTION

The first 30 patients received EPO 40,000 U/week (group A); the next 30 received 40,000 U twice/week (group B).

MEASUREMENTS AND MAIN RESULTS

Percent change from baseline in reticulocyte count and hemoglobin concentration were evaluated in both groups on study days 7 and 14. The numbers of adverse events were also compared between the two groups. No statistically significant differences were found in the results between the two groups.

CONCLUSION

Although the study had limitations, it suggested that EPO 40,000 U twice/week did not increase or sustain stimulation of the erythropoietic response compared with EPO 40,000 U/week in critically ill patients.

Diagnosis and management of iron-related anemias in critical illness

OBJECTIVE

To review of the prevalence, pathogenesis, diagnosis, and management of iron (Fe)-related anemias in critical illness.

DATA SOURCE

A MEDLINE/PubMed search from 1966 to October 2005 was conducted. References from relevant articles were manually cross-referenced with additional original articles, review articles, correspondence, and chapters from selected textbooks.

DATA EXTRACTION AND SYNTHESIS

Both Fe metabolism and erythropoiesis are affected by the inflammatory response that accompanies critical illness. As a result, many critically ill patients develop the anemia of inflammation, which may be compounded by an underlying Fe deficiency. Most commonly available markers of total body Fe detect Fe deficiency unreliably in the setting of inflammation. Among these tests, the serum transferrin receptor assay is relatively accurate in reflecting total body Fe, regardless of inflammation. Treatment options for Fe-related anemias in critical illness include Fe replacement and recombinant human erythropoietin therapy. The decision to implement these therapies is complex and centers on a critical evaluation of ability to affect anemia, morbidity, and mortality in critical illness and on the potential risks of therapy.

CONCLUSIONS

Fe deficiency anemia and the anemia of inflammation may co-exist in critical illness. Diagnosis of and differentiation between these two anemias involves careful interpretation of multiple markers of total body Fe stores. The utility of treatment with both Fe and recombinant human erythropoietin for these disorders during critical illness requires further investigation.

Pharmacokinetics and pharmacodynamics of once-weekly subcutaneous epoetin alfa in critically ill patients: results of a randomized, double-blind, placebo-controlled trial

OBJECTIVE

To describe the erythropoietin pharmacokinetic profile after once-weekly epoetin alfa treatment in critically ill patients. Secondary objectives were to compare pharmacodynamic and safety profiles between active treatment and placebo in these patients.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Medical, surgical, or mixed medical/surgical intensive care units.

PATIENTS

A total of 73 anemic critically ill adults with an expected stay of >3 days and a hematocrit value of <38%.

INTERVENTIONS

Patients were randomized 2:1 to epoetin alfa, 40,000 IU, administered subcutaneously once weekly (n=48) or matching placebo (n=25) for up to 4 wks.

MEASUREMENTS AND MAIN RESULTS

Serum erythropoietin concentration and hematologic variables (percentage reticulocytes [RETI], hemoglobin [Hb], and total red blood cell [RBC] counts) were measured, and area under the serum concentration-time curve from time 0 to the last blood sampling time at time t (t: 120, 144, or 168 hrs) postdose (AUC0-Tlast) for these three variables was determined. Mean serum erythropoietin concentrations in placebo patients were slightly higher than typical physiologic levels of erythropoietin in healthy subjects, although not appropriate for the degree of anemia in these patients. Overall, exposure of endogenous erythropoietin in the placebo group (in terms of AUC0-Tlast) was only about 20% of exposure to exogenous erythropoietin in the epoetin alfa group. Baseline hemoglobin levels were the same in both groups (9.9 g/dL). Mean change in hemoglobin level from baseline through day 29 was 1.9 g/dL and 1.6 g/dL in the epoetin alfa and placebo groups, respectively. Mean AUC(RETI)0-Tlast was higher with epoetin alfa than with placebo and was related to the AUC of erythropoietin. There were no apparent differences in AUC(Hb)0-Tlast and AUC(RBC)0-Tlast between epoetin alfa and placebo groups, which was most likely due to bleeding and transfusion events. Epoetin alfa was safe and well tolerated, with a rate of treatment-emergent complications similar to that seen with placebo.

CONCLUSION

Epoetin alfa, once weekly, augmented the erythropoietic response in critically ill patients as indicated by the increased erythropoietin levels and larger AUC(RETI)0-Tlast in treated patients.

Alternatives to blood product transfusion in the critically ill: erythropoietin

OBJECTIVE

To present information regarding the use of recombinant human erythropoietin (rHuEPO) to treat anemia in intensive care unit (ICU) patients

MAIN RESULTS

Anemia is common in critically ill patients. Approximately 95% of patients have subnormal hemoglobin (Hb) values by day 3 of their ICU stay. ICU-associated anemia often requires replacement of red blood cells (RBCs) via transfusion. Recent surveys of ICU practice document that approximately 50% of ICU patients receive RBC transfusions. ICU-associated anemia is largely the result of the cumulative effects of blood loss and decreased RBC production. Blood loss in critically ill patients may be overt, occult, or due to phlebotomy. Decreased RBC production is the other major factor influencing the development of anemia. Decreased RBC production is due to the combined effects of abnormal iron metabolism, inappropriately low erythropoietin production, diminished response to erythropoietin, and direct suppression of RBC production. Inflammatory mediators play a pivotal role in the pathogenesis of decreased RBC production. Clinical trials have shown that, compared with nontreated subjects, rHuEPO-treated ICU patients will have increased serum erythropoietin concentrations, increased reticulocyte counts, and increased hemoglobin and hematocrit values and require fewer RBC transfusions. These clinical trials have not detected significant differences in outcomes in association with rHuEPO, however.

CONCLUSIONS

rHuEPO can be used to increase hemoglobin and hematocrit values and decrease the number of RBC transfusions in ICU patients. Further investigation is necessary to identify the appropriate target population of ICU patients for treatment, to clarify the appropriate dosing schedule, and to ascertain whether such therapy has a positive impact on outcomes.

Erythropoiesis abnormalities contribute to early-onset anemia in patients with septic shock

RATIONALE

The intimate mechanisms of early onset anemia observed in critically ill patients with septic shock remain unclear.

OBJECTIVES

We investigated erythropoiesis abnormalities in this setting by studying morphologic, functional, and biochemical patterns of erythroid lineage.

METHODS

Erythroid lineage in the bone marrow from patients with septic shock who developed early-onset anemia was compared with that of healthy control subjects. Survival and proliferation capacities were quantified in both groups. Biochemical and flow cytometry patterns of apoptosis were dissected by exploring antiapoptotic (erythropoietin [Epo] receptor-dependent) and proapoptotic (death receptor-dependent) pathways.

MEASUREMENTS AND MAIN RESULTS

Erythroid lineage was morphologically similar in both groups. Apoptosis of glycophorin-A-positive erythroid precursors was increased in patients versus control subjects as assessed by labeling with annexin V (26.1 +/- 8.8 vs. 3.1 +/- 2.9%, p < 0.05) or 3-3'-dihexyloxacarbocyanine iodide (55.9 +/- 10.5 vs. 19.1 +/- 5.4%, p < 0.05), respectively. This was associated with significant overexpression of Fas on erythroid precursors and higher tumor necrosis factor-alpha plasma levels in patients with septic shock vs. control subjects. Moreover, growth capacities of late erythroid progenitors of burst-forming unit erythroids (BFU-Es) at Day 10 were impaired in the presence of serum from patients with septic shock as compared with the effect of serum from control subjects (27 +/- 12 vs. 109 +/- 27 per 10(5) seeded cells, respectively; p < 0.001). Saturating concentrations of recombinant human Epo (rHuEpo) restored growth capacity of patients' BFU-Es (72 +/- 14 per 10(5) seeded cells) in autologous conditions of serum.

CONCLUSIONS

Early-onset anemia that may be observed in patients with septic shock is associated with defective erythropoiesis related to an excess of apoptosis that can be counterbalanced in vitro by rHuEpo.

Population pharmacokinetics of erythropoietin in critically ill subjects

The effects of various covariate factors on the pharmacokinetics of erythropoietin (EPO) in subjects who are critically ill and admitted to an intensive care unit were evaluated. Nonlinear mixed-effects modeling was used to analyze the data from 48 patients receiving subcutaneous doses of 40,000 IU/wk epoetin alfa enrolled in a randomized, double-blind, placebo-controlled, multicenter study. The pharmacokinetics of EPO follows a 1-compartment disposition model with first-order absorption and an endogenous input rate. For a patient weighing 70 kg, the typical apparent clearance (CL/F) and apparent volume of distribution (V/F) were estimated to be 1.86 L/h and 27.8 L. The interindividual variability in CL/F and V/F was estimated to be 57.2% and 83.8%. CL/F and V/F of EPO increased with body weight, as described by the following relation: CL/F = (CL/F)std*(W/W(std))0.75, and V/F = (V/F)std*(W/W(std))1.37, where W is individual weight, and W(std) is the median weight of the study population. There was a 46% drop in exposure of EPO from the first to the subsequent dosing events. The endogenous EPO production rate was found to decrease progressively with the course of the study. In addition, the modeled endogenous EPO production rate increased with body weight. The net effect of this increase on the endogenous plasma EPO levels may not be significant because EPO clearance was found to increase with body weight. All other factors investigated (eg, Sequential Organ Failure Assessment [SOFA] scores and APACHE II scores) had no significant effect on EPO pharmacokinetics. The typical population estimate of CL/F of EPO was close to previously reported values in healthy volunteers.

The Role of Erythropoietin Therapy in the Critically Ill

Critically ill patients receive an extraordinarily large number of blood transfusions. Between 40% and 50% of all patients admitted to intensive care units (ICUs) receive at least one allogeneic red blood cell (RBC) unit and average close to 5 U of RBCs during their ICU admission. RBC transfusion is not risk-free, and there is little evidence that "routine" transfusion of stored allogeneic RBCs is beneficial to critically ill patients. It is clear that most critically ill patients can tolerate hemoglobin levels as low as 7 g/dL, and therefore, a more conservative approach to RBC transfusion is warranted. Anemia of critical illness is a distinct clinical entity characterized by blunted erythropoietin (EPO) production and abnormalities in iron metabolism identical to what is commonly referred to as anemia of chronic disease. As such, the bone marrow in many of these patients responds to the administration of exogenous EPO, in spite of their underlying critical illness. The efficacy of perioperative recombinant human erythropoietin (rHuEPO) has been demonstrated in a variety of elective surgical settings. Similarly, in critically ill patients, rHuEPO therapy will also stimulate erythropoiesis. In randomized placebo-controlled trials, therapy with rHuEPO resulted in a significant reduction in allogeneic RBC transfusions. Strategies to increase the production of RBCs are complementary to other approaches to reduce blood loss in the ICU and decrease the transfusion threshold in the management of all critically ill patients.