Anemia in Critically Ill Patients

E. Potolidis, E. Vakouti, and D. Georgopoulos

z Introduction

Anemia is a common problem in critically ill patients. Indeed it has been shown that at intensive care unit (ICU) admission the mean hemoglobin concentration (Hb) of critically ill patients is *11 g/dl, while in 60% and 30% of such patients, the mean Hb is less than 12 and 10 g/dl, respectively [1, 2]. It is of interest to note that in these patients the rate of hemoglobin decline is approximately 0.5 g/dl/day during the first days after ICU admission and continues to decline, particularly in patients with severe illness [1]. Thus the majority of critically ill patients exhibit anemia on ICU admission, which persists throughout the duration of their ICU stay. z Causes of Anemia in Critically Ill Patients

Several factors contribute to anemia in critically ill patients. The withdrawal of large amounts of blood for diagnostic reasons is an important but largely ignored factor for development of anemia in patients in ICUs [3]. Smoller and Kruskall showed that one half of patients who received blood transfusions had blood losses from phlebotomy that exceeded the equivalent of one unit of blood [4]. A recent European multicenter study (the ABC study) demonstrated that in critically ill patients the blood loss through blood sampling for diagnostic purposes is consider- able, averaging 41 ml/day [1]. Nguyen and colleagues [5] also documented that the mean volume of blood drawn daily for laboratory studies was approximately 40 ml. Considering only septic patients this amount increased to 49 ml. In patients under- going renal replacement therapies the blood loss due to blood sampling may be in the range of 60 ml per day [6]. Obviously this type of blood loss has an impact on blood transfusion. Indeed, Corwin et al. showed a positive relationship between the number of phlebotomies performed for diagnostic purposes and the amount of red blood cell (RBC) transfusions [7]. Furthermore, in the ABC study [1] a positive correlation was observed between organ dysfunction and the number of blood draws and total volume drawn. We should note that in the process of blood sampling the ICU health care work- er has to discard a significant blood volume in order to obtain accurate results. This volume depends on medical practice and may vary from 2 to 10 ml [5]. It is recommended that the discard volume should not be greater than twice the catheter dead-space [8, 9]. Occult bleeding is another important factor that may contribute to anemia in critically ill patients [3]. Stress gastritis (stress ulcer) is a potential source for blood 492 E. Potolidis et al.

loss. Surgical patients often have anemia in the postoperative period and should be monitored carefully. Blood loss into the retro-peritoneal space should be suspected and carefully investigated in patients with abdominal trauma who exhibit acute decline in hemoglobin. An important cause of anemia in critically ill patients is functional iron deficiency [10, 11]. Typically, critically ill patients have elevated serum ferritin concentrations, low transferrin saturation, and low serum iron concentration [11, 12]. There- fore, the low serum iron levels are not able to support the heme biosynthesis and the erythropoiesis. Systemic inflammatory response syndrome (SIRS) may be the pathogenic mechanism for this pattern. Cytokines that are released during the in- flammation process, like tumor necrosis factor (TNF)-a and interleukin (IL)-6, may induce the transcription and translation of ferritin and are able to down-regulate transferrin receptor messenger mRNA (iron uptake) [13]. In addition, it has been reported that nitric oxide (NO), which is increased in vasodilator shock, has the ability to reduce the ferrochelatase activity [14], thus contributing to the functional iron deficiency. Ineffective erythropoiesis in patients with critical illness could be the result of vitamin B12 or folic acid deficiency. Data in the literature indicate that these deficiencies do not play an important role in the pathogenesis of the anemia in these patients. Indeed, a recent study showed that 2% of critically ill patients were deficient in vitamin B12 and another 2% were deficient in folic acid [15]. Nevertheless, these deficiencies are rapidly correctable causes of ineffective erythropoiesis. It has been shown that IL-6 and TNF-a are both able to decrease the life span of RBCs [16, 17]. In addition to the reduced RBC life span due to proinflammatory cytokines, the erythrocytes of critically ill patients show decreased deformability [18]. Reactive oxygen species, increased concentrations of 2,3-DPG into the RBCs, and alterations in intracellular calcium content could be factors responsible for the decreased RBCs deformability [18]. The decrease in RBC deformability may play a role in disturbances in microcirculation, observed in critically ill patients. Inflammatory mediators released during SIRS may also influence the differentiation of erythroid progenitor cells. It is well known that cytokines are able to inhibit the differentiation of erythroid progenitor cells [19]. In addition, interferon (IFN)-c is able to induce apoptosis of the human erythroid colony forming cells via Fas expression and caspase activation [19]. Papadaki et al. reported that patients with rheumatoid arthritis (anemia of chronic disease which shares similar characteristics to that of critical illness) exhibit reduced apoptosis of erythroid cells in the bone marrow after treatment with anti-TNF-a antibodies [20]. Histiocytic hyperplasia with hemophagocytosis (HHH), a syndrome observed during sepsis or malignancies, may contribute to anemia in critically ill patients. The syndrome is characterized by single cytopenia (anemia, neutropenia or throm- bocytopenia) or pancytopenia. Strauss et al. [21], in a postmortem clinicopathologic study investigated 107 patients who were hospitalized and died in the ICU, showed that histiocytic hyperplasia with hemophagocytosis was present in 69 patients (64.5%). Predictors of histiocytic hyperplasia syndrome were treatment in- tensity and non-cardiovascular cause of death. This study demonstrated that sepsis and blood transfusion were triggering factors with a possible synergistic effect [21]. Peritubular interstitial cells in the renal cortex and parenchymal liver cells pro- duce a glycoprotein hormone named erythropoietin (EPO). This hormone binds to the EPO receptor on erythroid progenitor cells and promotes their maturity, while Anemia in Critically Ill Patients 493 on the other hand it decreases their apoptosis. Several studies have shown that EPO also has a neuroprotective effect [22, 23]. In patients with iron deficiency anemia, EPO concentration and Hb levels have a negative semilogarithmic correlation [24]. This is not the case in critically ill patients. It has been shown that in these patients for a given hematocrit (Hct) or hemoglobin, EPO plasma levels are significantly lower than those observed in patients with iron-deficiency anemia [25] (Fig. 1). von Ahsen et al. [12] calculated the erythropoietin response (Dlog/DHb) in ICU patients and noted that it was on average half of the response of patients with uncomplicated non-renal anemia. This phenomenon is referred to as blunted erythropoietic response. Studies have shown that the inappropriate low levels of erythropoietin significantly contribute to anemia in critically ill patients [26]. The blunted erythropoietic response is thought to result from decrease of erythropoietin gene expression by inflammatory mediators, such as TNF-a, IL-1 and IL-6 [3]. z RBC Transfusion

Anemia in critically ill patients results in significant RBCs transfusions. Approxi- mately 40% of critically ill patients receive at least one unit of RBCs, relatively early after ICU admission [1, 2]. The mean number of RBC units transfused approaches five, while the pre-transfusion Hb is *8.5 g/dl, indicating that the large number of transfusions is not due to a very high Hb transfusion threshold [1, 2]. Corwin et al., investigated the transfusion practice of their tertiary care center and found that 85% of critically ill patients with an ICU length of stay greater than one week, received blood transfusions, with a mean of approximately 9.5 units per patient [7]. It follows that the rate of blood transfusions in these patients is very high [7, 25]. The amount of oxygen delivered to the whole blood (DO2) is given by the following equation:

DO2 CO Â CaO2 where CO is cardiac output (CO=SV´HR, SV is stroke volume and HR is heart rate) and CaO2 is the oxygen concentration of arterial blood (CaO2 = 1.36 Hb´SaO2+0.003´PaO2). It is apparent that Hb reduction decreases the amount of oxygen delivered to tissues and under certain circumstances may result in tissue hypoxia. It follows that the main goal of RBC transfusion in anemic patients is to prevent or reverse tissue hypoxia by increasing the oxygen-carrying capacity of the blood. We should note however, that in critically ill patients regional blood flow is an important determinant of oxygen supply to cells; severe tissue hypoxia may en- sue despite a normal value of Hb and global DO2 [28, 29]. RBC transfusion is associated with numerous adverse events (Table 1), including infection transmission [30], transfusion associated immunosuppression [27, 31±33], transfusion related acute lung injury (TRALI) [34], disturbances in microcirculation due to blood storage [35, 36], and allergic reactions [33]. The first reported cases of transfusion-associated human immunodeficiency virus (HIV) transmission occurred in 1982. Since then cases of HIV transmission have decreased due to development of antibody detection and p24 antigen detection [27, 37]. Hepatitis B virus (HBV) infection due to transfusion decreased after the introduction of screening tests for HbsAg in 1975 and the risk of transfusion trans- 494 E. Potolidis et al.

Fig. 1. Log plasma concentration of erythropoietin (EPO) concentration as a function of hematocrit (Hct) in patients with uncomplicated iron deficiency anemia (control) and in various groups of critically ill patients. Observe that the in patients with critical illness the relationship has been shifted to the left of that in control group (solid line). This phenomenon is referred to as a blunted erythropoietic response. (From [25] with permission) Anemia in Critically Ill Patients 495

Table 1. Potential hazards of red blood cell transfusion

z Infection transmission z Transfusion-associated immunosuppression z Transfusion related acute lung injury (TRALI) z Disturbances in microcirculation z Allergic reactions

mitted hepatitis C virus (HCV) is currently 1 in 103000 transfusions [38]. Trans- mission of B19 parvovirus can occur, but is not significant except in patients with hemolytic diseases, immunosuppression, and in pregnancy. Human T-cell lympho- tropic virus types I and II (HTLV-I,II) have been associated with myelopathy and adult T cell leukemia. Infection will occur in 20 to 60% of recipients of blood infected with HTLV-I,II [39]. Bacterial contamination of the RBCs is another transfusion-associated risk. Yer- sinia enterocolitica is often implicated, but other Gram-negative organisms have been reported also [40]. Theakston et al. reported that the rate of contamination by Yersinia enterocolitica was 1 per 65000 red cell units transfused [41]. Transfusion mediated transmission of Trypanosoma cruzi is possible in Central and South America where this type of infection is endemic [42]. Potential infectious threats are also malaria and babesiosis [42]. The latter may occur particularly in immuno- compromised and asplenic individuals. West Nile virus, a flavirus which cause encephalitis and meningitis, could be transmissed by RBCs transfusions. This virus was first recognized in 1999, in an outbreak of encephalitis in New York [43]. Mos- quito bites permit the transmission from birds to humans. Hemolytic reactions to RBC transfusion are often due to ABO incompability. De- layed reaction to transfusion may also occur, and its incidence is estimated to be 1 for 1000 patients [44]. TRALI is a noncardiogenic pulmonary edema with a significant morbidity and mortality. The frequency of this adverse event has been estimated to be 1 in 5000 transfusions [34, 45]. However, the actual incidence of this syndrome may be higher since the association of acute lung injury (ALI) and RBC transfusion may not al- ways be recognized. The syndrome may occur within a few hours after transfusion. The pathogenesis of TRALI may be explained by a `two-hit' hypothesis, with the first `hit' being a predisposing inflammatory condition commonly present in the operating room or ICU [34]. The second hit may involve the passive transfer of neutrophil or HLA antibodies from the donor or the transfusion of biologically active lipids from older, cellular blood products. Treatment is supportive, with a prognosis substantially better than most causes of ALI. However, TRALI remains the third most common cause of transfusion-associated death [34]. In recent years, accumulating evidence has indicated that RBC transfusion alters the immune system of the host (transfusion related immunomodulation, TRIM) [32, 46]. Although the exact pathogenetic mechanism underlying this immunomodulation is not known, recent evidence suggests that transfusion of white blood cells may be responsible. It has been reported that white blood cells from the donor may persist in the recipient blood for up to 18 months [47, 48]. It is suggested that TRIM is able to cause cancer recurrences, although this issue is currently highly controversial [47]. More importantly, it is thought that TRIM may increase the risk 496 E. Potolidis et al.

Fig. 2. Age of red blood cells (RBCs) transfused in critically ill patients. Notice that in the majority of transfusions the transfused blood is older than 10 days. (From [35] with permission)

of nosocomial infections [47]. Taylor et al. investigated whether critically ill patients who received RBC transfusion were at increased risk of acquiring infections and showed that the transfusion groupwas six times more likely to developnoso- comial infections compared to the non-transfusion group [49]. They further demonstrated that for each unit of RBCs transfused, the odds of developing nosocomial infection were increased by a factor of 1.5 [49]. Shorr et al. in a multicenter, prospective observational study showed that RBC transfusion was independently associated with an increase risk for ventilator associated pneumonia (VAP) [50]. Finally, it should be kept in mind that stored blood is often `old' blood. Indeed, it has been shown that in the majority of transfusions, the age of blood is >10 days (Fig. 2). This may have an adverse effect on the microcirculation. Marik and Sibbald showed that critically ill patients receiving old transfused RBCs (>10 days) developed evidence of tissue hypoxia, as indicated by a significant decrease in gastric intramucosal pH (pHi) [35] (Fig. 3). It follows that RBC transfusion is not without risk and may considerably increase morbidity and mortality. This is particularly true for critically ill patients. Large observational studies in these patients have shown that RBC transfusion is an independent risk factor for increased mortality [1, 2] (Fig. 4). Vincent et al. [1] demonstrated that receipt of a blood transfusion increased the risk of dying by a factor of 1.4 (all other variables being equal). Although the mechanism through which RBC transfusion may increase mortality is currently unknown, it is believed that the likely factors contributing to mortality are related to immunosuppression and disturbances in microcirculation as opposed to allergic reaction or infectious transmission [35, 49±50]. For several years a Hb concentration of 10 g/dl and Hct of 30% were the transfusion thresholds. Considering the risks associated with RBC transfusion it would be appropriate to explore whether lower transfusion triggers may be used in critically ill patients. In a multicenter, randomized controlled clinical trial involving 838 critically ill patients, Hebert et al. [51] showed that a restrictive transfusion strategy was at least as effective and possibly superior to the strategy of liberal transfu- Anemia in Critically Ill Patients 497

Fig. 3. Relationship between the age of transfused RBCs and the change in gastric intramucosal pH. (From [35] with permission)

Fig. 4. Survival analysis by transfusion status among propensity-matched critically ill patients. a Data from [1] with permission. b Data from [2] with permission 498 E. Potolidis et al.

sion. The Hb concentration of patients assigned to the restrictive strategy was maintained between 7±9 g/dl (transfusion threshold 7 g/dl), whereas in the liberal transfusion groupHb was maintained in the range of 10±12 g/dl (transfusion threshold 10 g/dl). This study showed that 30-day all-cause mortality did not differ between the two groups. In a post-hoc analysis, the investigators demonstrated that in patients with an APACHE II score less than 20 and in patients younger than 55 years, the mortality rate was significantly lower in restrictive group. These findings indicate that in critically ill patients a transfusion triggering threshold of 7 g/dl may be preferable to one of 10 g/dl. This, however, may not apply in patients with acute myocardial infarction and unstable angina, in whom higher transfusion triggering thresholds may be appropriate. Although the trial of Hebert et al. [51] defined an appropriate transfusion practice for critically ill patients, physicians dealing with these patients are reluctant to follow these rules. Indeed, a recent large observational study [1] found that mean pretransfusion Hb levels remain substantially higher (8.4 g/dL for all patients transfused, and 8.5 g/dL for those without active bleeding) than the threshold suggested by the findings of the study of Hebert et al.

z Prevention of Anemia in Critically Ill Patients

Considering on one hand the risks associated with RBC transfusion and on the other hand the relationshipbetween the level of anemia and morbidity and mortality, measures that prevent anemia in critically ill patients are of great importance and should achieve high priority. The use of a blood conservation device in critically ill patients to minimize diagnostic phlebotomy blood loss has been documented to be efficacious. A prospective, randomized, controlled trial in 100 medical ICU patients confirmed that there was significant blood conservation with a device incorporated into the arterial pressure monitoring system [52]. In a recent postal survey of arterial blood sampling practices in 280 ICUs of England and Wales it was found that few measures were taken to minimize blood losses from arterial sampling in adult intensive care patients [53]. The average volume of blood withdrawn to clear the arterial line be- fore sampling was 3.2 ml. Specific measures to reduce the blood sample size by the routine use of pediatric sample tubes in adult patients occurred in only 9.3% of ICUs. In pediatric ICUs, the average volume withdrawn was 1.9 ml, which was rou- tinely returned in 67% of units. Obviously strategies should be implemented to reduce blood loss related to diagnostic phlebotomy, including use of pediatric tubes, low-volume adult tubes, and blood conservation devices [54]. In addition, the need for arterial blood gas samples may be minimized in selected patients by using con- tinuous pulse oximetry to monitor SaO2 and capnometry to monitor end-tidal CO2 [55±57]. Decreasing the use of medications that result in perioperative bleeding (nonste- roidal anti-inflammatory drugs and acetylsalicylic acid) might also be helpful. Stress ulcer prophylaxis may be warranted in patients at high risk, such as those receiving mechanical ventilation [58]. Nevertheless, the use of stress ulcer prophylaxis in all critically ill patients should be avoided since it may increase the risk of nosocomial pneumonia [59]. Iron therapy can help to optimize EPO treatment (see below) since iron deficiency may be a contributing factor to the resistance to EPO treatment in critically ill patients [60, 61]. Moreover, adjuvant therapy, such as Anemia in Critically Ill Patients 499 ascorbic acid, to increase oral iron absorption and physiologic utilization, has been widely used and should be studied in critically ill patients [62]. The use of antifi- brinolytics has been found to reduce perioperative RBC transfusions and the need for re-operation because of bleeding [63]. Clotting factors such as activated factor VII are under investigation. Selective use of salvage and autotransfusion in critically ill patients with very large postoperative recoverable blood loss may be effective at limiting the acute development of anemia and transfusion requirements [64, 65]. Acute normovolemic hemodilution describes the removal of whole blood from a patient immediately be- fore surgery and concurrent replacement of that volume with crystalloids or col- loids [27]. The blood is later re-transfused. It is not known if this may be applica- ble in critically ill patients. Exogenous administration of recombinant human erythropoietin (rHuEPO) in patients with critical illness is a preventive strategy that has attracted much atten- tion in recent years. The rational for rHuEPO therapy in critically ill patients is that increased erythropoiesis will result in higher Hb levels and subsequently will reduce the need for RBC transfusion. It is considered that critically ill patients have a limited ability to compensate for the fall in Hb concentration [66, 67]. Indeed in these patients, anemia is associated with increased morbidity and mortality, particularly in patients with pre-existing cardiac disease [66, 67]. Preventing anemia by administration of rHuEPO on one hand minimizes the risks of anemia without on the other hand, exposing the critically ill to the deleterious effects of RBC transfusion. Van Iperen et al. [68] in a randomized open trial studied three groups of critically ill patients. One group received intravenous folic acid daily from days 1 to 14 (control group), a second group received i.v. folic acid and iron (iron group), and a third groupreceived folic acid, iron and rHuEPO, administered subcutaneously on study days 1, 3, 5, 7 and 9 in a dose of 300 IU/Kgr. The study clearly showed that rHuEPO increased the concentration of reticulocytes and serum transferrin receptors (Fig. 5). Similarly Gabriel et al. [69] showed in patients with multiple organ failure, that rHuEPO therapy (600 units/kg) stimulated erythropoiesis. These findings indicate that the bone marrow of critically ill patients is able to respond to exogenous EPO and this therapy might be useful in increasing Hb level and reducing the need for RBC transfusion. Two randomized, double blind, placebo controlled studies have documented that this is the case. Corwin et al. [70] randomized 160 critically ill patients to receive either rHuEPO (300 units/kg of rHuEPO for 5 conse- cutive days and then every other day to achieve a hematocrit concentration >38%) or placebo. This study showed that rHuEPO therapy resulted in an almost 50% reduction in RBC transfusions as compared with placebo. It is of interest to note that despite receiving fewer RBC transfusions, patients in the rHuEPO group had a significantly greater increase in hematocrit. The same groupof investigators, in a second larger study [71], randomized 1302 patients to receive either rHuEPO or placebo. rHuEPO was given weekly at a fixed dose of 40000 units. All patients received three weekly doses, and patients who remained in the ICU on study day 21 received a fourth dose. Treatment with rHuEPO resulted in a 10% reduction in the number of patients receiving any RBC transfusion (60.4% with placebo versus 50.5% with rHuEPO) and a 20% reduction in the total number of RBC units transfused (1963 units with placebo versus 1590 units with rHuEPO) (Fig. 6). The optimal dose of rHuEPO therapy is not known. In a just completed randomized multicenter trial in critically ill patients, we found that the transfusion require- 500 E. Potolidis et al.

Fig. 5. a Reticulocytes and b serum transferrin receptors in three groups of critically ill patients receiving folic acid (control group, closed circles), folic acid and iron (iron group, open circles) and folic acid, iron and recombinant human erythropoietin (rHuEPO group, closed triangles). (From [68] with permission)

Fig. 6. Cumulative units of red blood cells transfused in patients randomized to receive recombinant human erythropoietin (rHuEPO) or placebo. The difference between the two groups was significant. (From [71] with permission) Anemia in Critically Ill Patients 501 ments were not influenced by two dosing regimes of rHuEPO (40000 units once or three times per week), whereas there was a clear dose response of Hb and Hct to rHuEPO (unpublished data). These results indicate that dose of rHuEPO in critically ill patients should be titrated depending on the desired goal (decrease transfusion requirements or increase in Hb). Although rHuEPO therapy considerably decreases the exposure of critically ill patients to allogenic RBCs, it seems that the outcome of critically ill patients is not influenced by this therapy. In the large study of Corwin et al. [72] neither morbidity nor mortality differed significantly between groups. The interpretation of these results is however complicated by the fact that the majority of patients receiving rHuEPO were anemic by the end of the study and the Hb level differed slightly between groups (approximately 0.3 g/dl). Considering the relationship between the level of anemia and morbidity and mortality [66, 67] the inability of this rHuEPO regimen to increase Hb to normal levels may have an impact on morbidity and mortality data. Further studies are needed to resolve this issue. z Conclusion

The majority of critically ill patients exhibit anemia at some time during the course of their illness, resulting in multiple RBC transfusions. The pathogenesis of anemia in these patients is multifactorial, with blood loss and blunted erythropoietic response being the most important contributors. Although RBC transfusion remains a common practice in critically ill patients, it is associated with significant risks, such as disturbances in microcirculation and immunosuppresion. Because of these risks, transfusion practice is currently under systematic scrutiny and transfusion benefits are being critically re-evaluated. Measures to prevent rather than to treat anemia in critically ill patients should achieve high priority. Strategies to decrease blood loss, such as the development of simple techniques to decrease the blood volume withdrawn for diagnostic purposes, should be implemented in every ICU. Ad- ministration of rHuEPO in selected ICU patients may significantly decrease RBC transfusion requirements, although the impact of this therapy on patient outcome needs further study.

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