Associations between "early" red blood cell transfusion and severe intraventricular hemorrhage, and between "late" red blood cell transfusion and necrotizing enterocolitis

Association between neurodevelopmental outcomes and concomitant presence of NEC and IVH in extremely low birth weight infants

OBJECTIVE

To quantify the association between necrotizing enterocolitis (NEC) and neurodevelopmental disability (NDI) in extremely low birth weight (ELBW) infants with intraventricular hemorrhage (IVH).

STUDY DESIGN

ELBW survivors born 2011-2017 and evaluated at 16-26 months corrected age in the Vermont Oxford Network (VON) ELBW Follow-Up Project were included. Logistic regression determined the adjusted relative risk (aRR) of severe NDI in medical or surgical NEC compared to no NEC, stratified by severity of IVH.

RESULTS

Follow-up evaluation occurred in 5870 ELBW survivors. Compared to no NEC, medical NEC had no impact on NDI, regardless of IVH status. Surgical NEC increased risk of NDI in patients with no IVH (aRR 1.69; 95% CI 1.36-2.09), mild IVH (aRR 1.36;0.97-1.92), and severe IVH (aRR 1.35;1.13-1.60).

CONCLUSIONS

ELBW infants with surgical NEC carry increased risk of neurodevelopmental disability within each IVH severity stratum. These data describe the additive insult of surgical NEC and IVH on neurodevelopment, informing prognostic discussions and highlighting the need for preventative interventions.

Cardiorespiratory monitoring of red blood cell transfusions in preterm infants

Clinical improvement after red blood cell (RBC) transfusions in preterm infants remains debated. This study aims to investigate the effect of RBC transfusion on the occurrence of desaturations and hypoxia, and other cardiorespiratory outcomes in preterm infants. In this longitudinal observational study, prospectively stored cardiorespiratory parameters of preterm infants who received at least one RBC transfusion between July 2016 and June 2017 were retrospectively analyzed. Sixty infants with 112 RBC transfusions, median GA of 26.7 weeks, were included. The number of desaturations and area < 80% SpO₂ limit, as a measure of the hypoxic burden, were calculated in 24 h before and after RBC transfusion. A mixed effects model was used to account for repeated measurements. Overall, the mean (SE) number of desaturations per hour decreased from 3.28 (0.55) to 2.25 (0.38; p < 0.001), and area < 80% SpO₂ limit decreased from 0.14 (0.04) to 0.08 (0.02) %/s (p = 0.02). These outcomes were stratified for the number of desaturations in 24 h prior to RBC transfusion. The largest effect was observed in the group with the highest mean number of desaturations (≥ 6) prior to RBC transfusion, with a decrease from 7.50 (0.66) to 4.26 (0.38) (p < 0.001) in the number of desaturations and 0.46 (0.13) to 0.20 (0.06) in the area < 80% SpO₂. Perfusion index increased significantly after RBC transfusion (p < 0.001). No other significant effects of RBC transfusion on cardiorespiratory data were observed.Conclusions: RBC transfusions in preterm newborns could help decrease the incidence of desaturations and the area < 80% SpO₂ as a measure of the hypoxic burden. The higher the number of desaturations prior to the RBC transfusion, the larger the effect observed. What is Known: •Red blood cell transfusions potentially prevent hypoxia in anemic preterm infants by increasing the circulatory hemoglobin concentration and improving tissue oxygenation. •There is not a predefined hemoglobin concentration cut-off for the occurrence of symptomatic anemia in preterm infants. What is New: •Oxygen desaturations and hypoxia in anemic preterm infants can be improved by RBC transfusions, especially if more desaturations have occurred before transfusion. •Cardiorespiratory monitor data may help identify infants who will benefit most from red blood cell transfusions.

Impact of a “Brain Protection Bundle” in Reducing Severe Intraventricular Hemorrhage in Preterm Infants <30 Weeks GA: A Retrospective Single Centre Study

Background: despite advances in perinatal care, periventricular/intraventricular hemorrhage (IVH) continues to remain high in neonatal intensive care units (NICUs) worldwide. Studies have demonstrated the benefits of implementing interventions during the antenatal period, stabilization after birth (golden hour management) and postnatally in the first 72 h to reduce the incidence of IVH. Objective: to compare the incidence of severe intraventricular hemorrhage (IVH ≥ Grade III) before and after implementation of a “brain protection bundle” in preterm infants <30 weeks GA. Study design: a pre- and post-implementation retrospective cohort study to compare the incidence of severe IVH following execution of a “brain protection bundle for the first 72 h from 2015 to 2018. Demographics, management practices at birth and in the NICU, cranial ultrasound results and short-term morbidities were compared. Results: a total of 189 and 215 infants were included in the pre- and post-implementation phase, respectively. No difference in the incidence of severe IVH (6.9% vs. 9.8%, p = 0.37) was observed on the first cranial scan performed after 72 h of age. Conclusion: the implementation of a “brain protection bundle” was not effective in reducing the incidence of severe IVH within the first 72 h of life in our centre.

Effect of blood transfusions on cognitive development in very low birth weight infants

OBJECTIVE

Preterm infants frequently receive red cell transfusions; however, the effect of transfusions on cognition is unclear. We evaluated the relationship between transfusions and cognitive outcomes in preterm infants enrolled in a randomized trial of erythropoiesis stimulating agents (ESAs).

STUDY DESIGN

Preterm infants were randomized to ESAs or placebo during initial hospitalization, and transfusions recorded. Children were evaluated using standard developmental tests of cognition at 18-22 months (56 ESA, 24 placebo) and 3.5-4 years (39 ESA, 14 placebo).

RESULTS

Cognitive scores at 18-22 months were inversely correlated with transfusion volume (p = 0.02). Among those receiving ≥1 transfusion, cognitive scores were significantly higher in the ESA-treated group (p = 0.003). At 3.5-4 years, transfusions were not correlated with cognitive scores.

CONCLUSIONS

In the placebo group, transfused children had lower cognitive scores than did non-transfused children at 18-22 months. In the ESA group, cognitive scores did not differ by transfusion status, suggesting ESAs might provide neuroprotection.

Effects of blood transfusion on regional tissue oxygenation in preterm newborns are dependent on the degree of anaemia

AIM

Most of the preterm infants are transfused at least once during their stay in the neonatal intensive care unit (NICU). The aims of this study were to demonstrate if packed red blood cell (pRBC) transfusion modulates regional (cerebral, abdominal, renal) tissue oxygen saturation measured by near-infrared spectroscopy (NIRS) and to demonstrate if we can use NIRS to guide transfusion decisions in neonates.

METHODS

A multi-probe NIRS device was applied to anaemic preterm infants of gestational age <33 weeks for 30-60 min before and 24 h after pRBC transfusion. We evaluated the results separately in the subgroup with a pre-transfusion haemoglobin (Hb) < 8 g/dL. Cerebral, abdominal and renal tissue oxygen saturation (rSO₂ ) and abdominal/cerebral, abdominal/renal and renal/cerebral rSO₂ ratios before and 24 h after transfusion were compared.

RESULTS

There was no significant difference in cerebral rSO₂ and abdominal/renal rSO₂ ratios before and 24 h after transfusion, but abdominal and renal rSO₂ and abdominal/cerebral and renal/cerebral rSO₂ ratios at the 24th h following transfusion increased significantly. This increase was observed in the subgroup with pre-transfusion Hb < 8 g/dL. Although statistically significant, the increase in renal oxygenation was within the limits of variability.

CONCLUSIONS

The increase in tissue oxygenation in abdominal region after pRBC transfusion suggests decreased tissue oxygenation of intestines during severe anaemia despite cerebral oxygenation being maintained at that particular Hb level. The impact of the increase on renal oxygenation with pRBC transfusion is unclear and might need further investigation. Increase in abdominal rSO₂ may cause reperfusion injury, oxidative damage and trigger necrotising enterocolitis.

The contribution of red blood cell transfusion to neonatal morbidity and mortality

Anaemia of prematurity will affect 90% of all very preterm infants, resulting in at least one red blood cell (RBC) transfusion. A significant proportion of preterm infants require multiple transfusions over the course of hospital admission. Growing evidence supports an association between transfusion exposure and adverse neonatal outcomes. In adults, transfusion-associated sepsis, transfusion-related acute lung injury and haemolytic reactions are the leading causes of transfusion-related morbidity and mortality; however, these are seldom recognised in newborns. The association between transfusion and adverse outcomes remains inconclusive. However, the evidence from preclinical studies demonstrates that RBC products can directly modulate immune cell function, a pathway termed transfusion-related immunomodulation (TRIM), which may provide a mechanism linking transfusion exposure with neonatal morbidities. Finally, we discuss the impact of TRIM on transfusion medicine, how we may address these issues and the emerging areas of research aimed at improving the safety of transfusions in this vulnerable population.

Risk of Necrotizing Enterocolitis Following Packed Red Blood Cell Transfusion in Very Low Birth Weight Infants

OBJECTIVE

To evaluate the association between red blood cell (RBC) transfusion leading to necrotizing enterocolitis (NEC) within 48 h, known as transfusion-associated necrotizing enterocolitis (TANEC).

METHODS

A nested case-control study using historical data was conducted in the neonatal intensive care unit of Songklanagarind Hospital, Thailand. All very low birth weight (VLBW) infants delivered between November 2009 and July 2016 were enrolled. The infants were identified as RBC transfusion received and NEC developed. Logistic regression was used to evaluate risk factors for transfusion and the association between RBC transfusion and NEC.

RESULTS

Four hundred and forty-four VLBW infants were enrolled in the study. The median (interquartile range) gestational age was 29 (27, 31) wk. The overall incidence of NEC was 13%. Three (5.2%) of the NEC infants had TANEC. The infants who received RBC transfusion had a lower gestational age [odds ratio, OR 0.64; 95% confidence interval (95%CI) 0.57, 0.73, p < 0.001] and were more likely to have pneumonia (OR 9.86; 95%CI 5.02, 19.35, p < 0.001) or to have received H₂ blocker (OR 2.92; 95%CI 1.73, 4.93, p < 0.001). The ORs (95% CI) after adjusting for confounders, the association between RBC transfusion and NEC for transfusions ≤2 d, >2 to 4 d, and > 4 to 6 d prior to NEC were 1.83 (0.41, 8.16; p = 0.43), 1.7 (0.26, 11.16; p = 0.58) and 1.19 (0.31, 4.62; p = 0.80) respectively.

CONCLUSIONS

After controlling of confounders, no evidence of association was found between RBC transfusion and TANEC.

Transfusion practice in neonates

Neonates, especially extremely low birth weight infants, are among the groups of patients undergoing transfusion frequently. Since they are exposed to higher specific transfusion risks compared to the patients of other age groups, there are many special aspects that must be considered for transfusion therapy in neonates. The transfusion risks in neonates include adverse outcomes specific for preterm infants as well as increased metabolic, immunologic, and infectious complications. To reduce the risks of transfusion-transmitted cytomegalovirus infection and transfusion-associated graft-versus-host disease, leukoreduced and irradiated cellular blood products should be used for all neonates. This review summarizes the risks of neonatal transfusion therapy, specific methods to reduce risk, and current trends and practices of red blood cell and platelet transfusions in neonates, to facilitate decision-making for neonatal transfusion.

Evaluation and Treatment of Anemia in Premature Infants

Introduction:

Anemia in preterm infants is the pathophysiological process with greater and more rapid decline in hemoglobin compared to the physiological anemia in infants. There is a need for transfusions and administration of human recombinant erythropoietin.

Aim:

To determine the frequency of anemia in premature infants at the Pediatric Clinic, University Clinical Center Sarajevo, as well as parameter values in the blood count of premature infants and to explore a relationship between blood transfusions with the advent of intraventricular hemorrhage (determine treatment outcome in preterm infants).

Patients and methods:

Research is retrospective study and it included the period of six months in year 2014. Research included 100 patients, gestational age < 37 weeks (premature infants). Data were collected by examining the medical records of patients at the Pediatric Clinic, UCCS.

Results:

The first group of patients were premature infants of gestational age ≤ 32 weeks (62/100) and the second group were premature infants of gestational age 33-37 weeks (38/100). Among the patients, 5% were boys and 46% girls. There was significant difference in birth weight and APGAR score among the groups. In the first group, there were 27.42% of deaths, while in the second group, there were only 10.53% of deaths. There was a significant difference in the length of treatment. There was a statistically significant difference in the need for transfusion among the groups. 18 patients in the first group required a transfusion, while in the second group only 3 patients.

Conclusions:

Preterm infants of gestational age ≤ 32 weeks are likely candidates for blood transfusion during treatment. Preterm infants of gestational age ≤ 32 weeks have the risk of intracranial bleeding associated with the application of blood transfusion in the first week of life.

Adverse effects of red blood cell transfusions in neonates: a systematic review and meta-analysis

BACKGROUND

Controversy exists regarding the contribution of blood transfusions to a range of adverse clinical outcomes in neonates. The aim of our systematic review was to identify the broader literature on harmful effects and associations potentially attributable to red blood cell (RBC) transfusions.

STUDY DESIGN AND METHODS

A comprehensive search of MEDLINE (PubMed) and EMBASE was undertaken. Eligible studies included both randomized controlled trials (RCTs) and nonrandomized studies examining the effects of small volume (10-20 mL/kg) RBC transfusions on neonates. Primary outcomes of interest were mortality, chronic lung disease, retinopathy of prematurity, necrotizing enterocolitis, and intraventricular hemorrhage. Two independent authors conducted a review of abstracts and then of full-text article reviews as well as data extraction and quality assessments.

RESULTS

Sixty-one studies were eligible for inclusion, including 16 (26%) randomized studies. The majority of studies were nonrandomized (n = 45; 74%), which included 32 observational studies with and 13 studies without a comparator group. There was no evidence that rates of mortality differed between restrictive and liberal strategies for transfusion (eight RCTs: risk ratio, 1.24; 95% confidence interval, 0.89-1.672, heterogeneity = 0%) or for necrotizing enterocolitis (five RCTs: risk ratio, 1.45; 95% confidence interval, 0.91-2.33; heterogeneity = 0%). A liberal strategy also was not superior to restrictive transfusion practice in the pooled randomized studies for rates of retinopathy of prematurity, chronic lung disease, or intraventricular hemorrhage.

CONCLUSIONS

Statistically significant differences in a range of harmful outcomes between neonates exposed to restrictive and liberal RBC transfusion practice were not found. However, the risks of bias identified in many studies and the lack of consistent reporting and definitions of events limits our conclusions.

Anemia and transfusion in the neonate

Neonatal anemia is a frequent occurrence in neonatal intensive care units. Red blood cell transfusion criteria in case of blood loss are clearly defined but optimal hemoglobin or hematocrit thresholds of transfusion for anemia due to decreased production or increased destruction are less evident. This review focuses on the causes of anemia in the newborn period and the most recent evidence-based treatment options, including transfusion and erythropoiesis-stimulating agents.

Prevention of the anaemia of prematurity

Despite recent advances in neonatal and perinatal medicine, extremely low birth weight infants (ELBW) are at high risk of developing anaemia of prematurity (AOP) requiring packed red blood cell (RBC) transfusions. The benefit of transfusing allogenic RBCs for AOP is a controversial issue, except for disturbances in tissue oxygenation. Although the role of erythropoietin (EPO) in the pathophysiology of AOP is well known, neither early nor late recombinant human EPO therapy alters the number or volume of RBC transfusions. It is also known that one-half of the feto-placental blood volume remains outside the newborn infant's circulation at 30 weeks of gestation if the umbilical cord is clamped immediately. Delayed cord clamping (DCC) and umbilical cord milking (UCM) are the main methods for enhancing placental transfusion. The basic principle of these approaches depends on providing high haemoglobin (Hb) levels to premature infants in the delivery room. The enhancement of placental transfusion clearly results in higher Hb levels at birth, reducing the need for RBC transfusions as well as creating a better haemodynamic status during the initial hours of life. To date, enhancement of placental transfusion in the delivery room by either DCC or UCM seems to be the best preventive measure for AOP. Yet, studies on the associated neurodevelopmental outcomes are insufficient to reach a conclusion. This review summarizes the pathophysiology, treatment and preventative strategies of anaemia of prematurity in light of the current literature.

The effect of red blood cell transfusion on intermittent hypoxemia in ELBW infants

OBJECTIVE

To test the hypothesis that the effect of red blood cell (RBC) transfusion on intermittent hypoxemia (IH) in extremely low birth weight (ELBW) infants is dependent on postnatal age.

STUDY DESIGN

Oxygen saturation of 130 ELBW infants, who required transfusion, was monitored continuously for the first 8 weeks of life. We compared the characteristics of IH (SpO2⩽80% for ⩾4 s and ⩽3 min), 24 h before and both 24 h and 24 to 48 h after each RBC transfusion at three distinct time periods: Epoch 1, 1 to 7 days; Epoch 2, 8 to 28 days; and Epoch 3, >28 days.

RESULT

In Epoch 1, the frequency and severity of IH events were not significantly different before and after transfusion. In both Epochs 2 and 3 there was a decrease in IH frequency and severity 24 h after RBC transfusion that persisted for 48 h. In addition, there was a decrease in the overall time spent with SpO2 ⩽80% which persisted for 24 h after transfusion in Epochs 1 and 3, and for 48 h in Epoch 3.

CONCLUSION

The benefit of RBC transfusion on IH is age dependent as improvement in the frequency and severity of IH after transfusion only occurs beyond the first week of life. These observations will aid clinician's decision making by clarifying the benefit of RBC transfusions on patterns of oxygenation in preterm infants.

Placental transfusion strategies in very preterm neonates: a systematic review and meta-analysis

OBJECTIVE

To investigate the effects of interventions promoting placental transfusion at delivery (delayed cord clamping or umbilical cord milking) compared with early cord clamping on outcomes among premature neonates of less than 32 weeks of gestation.

DATA SOURCES

A systematic search was conducted of PubMed, Embase, and ClinicalTrials.gov databases (January 1965 to December 2013) for articles relating to placental transfusion strategies in very preterm neonates.

METHODS OF STUDY SELECTION

Literature searches returned 369 articles with 82 considered in full. We only included data from studies with an average gestational age of less than 32 weeks of gestation enrolled in randomized trials of enhanced placental-fetal transfusion interventions (delayed cord clamping or umbilical cord milking) compared with early cord clamping.

TABULATION, INTEGRATION, AND RESULTS

We identified 12 eligible studies describing a total of 531 neonates with an average gestation of 28 weeks. Benefits of greater placental transfusion were decreased mortality (eight studies, risk ratio 0.42, 95% confidence interval [CI] 0.19-0.95, 3.4% compared with 9.3%, P=.04), lower incidence of blood transfusions (six studies, risk ratio 0.75, 95% CI 0.63-0.92, 49.3% compared with 66%, P<.01), and lower incidence of intraventricular hemorrhage (nine studies, risk ratio 0.62, 95% CI 0.43-0.91, 16.7% compared with 27.3%, P=.01). There was a weighted mean difference of -1.14 blood transfusions (six studies, 95% CI -2.01-0.27, P<.01) and a 3.24-mmHg increase in blood pressure at 4 hours of life (four studies, 95% CI 1.76-4.72, P<.01). No differences were observed between the groups across all available safety measures (5-minute Apgar scores, admission temperature, incidence of delivery room intubation, peak serum bilirubin levels).

CONCLUSIONS

Results of this meta-analysis suggest that enhanced placental transfusion (delayed umbilical cord clamping or umbilical cord milking) at birth provides better neonatal outcomes than does early cord clamping, most notably reductions in overall mortality, lower risk of intraventricular hemorrhage, and decreased blood transfusion incidence. The optimal umbilical cord clamping practice among neonates requiring immediate resuscitation remains uncertain.

Adverse effects of small-volume red blood cell transfusions in the neonatal population

BACKGROUND

Adverse transfusion reactions in the neonatal population are poorly understood and defined. The incidence and pattern of adverse effects due to red blood cell (RBC) transfusion are not well known, and there has been no systematic review of published adverse events. RBC transfusions continue to be linked to the development of morbidities unique to neonates, including chronic lung disease, retinopathy of prematurity, intraventricular haemorrhage and necrotising enterocolitis. Uncertainties about the exact nature of risks alongside benefits of RBC transfusion may contribute to evidence of widespread variation in neonatal RBC transfusion practice.Our review aims to describe clinical adverse effects attributed to small-volume (10-20 mL/kg) RBC transfusions and, where possible, their incidence rates in the neonatal population through the systematic identification of all relevant studies.

METHODS

A comprehensive search of the following bibliographic databases will be performed: MEDLINE (PubMed/OVID which includes the Cochrane Library) and EMBASE (OVID). The intervention of interest is small-volume (10-20 mL/kg) RBC transfusions in the neonatal population.We will undertake a narrative synthesis of the evidence. If clinical similarity and data quantity and quality permit, we will also carry out meta-analyses on the listed outcomes.

DISCUSSION

This systematic review will identify and synthesise the reported adverse effects and associations of RBC transfusions in the neonatal population. We believe that this systematic review is timely and will make a valuable contribution to highlight an existing research gap.

TRIAL REGISTRATION

PROSPERO, CRD42013005107http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42013005107.

Instituting a program to reduce the erythrocyte transfusion rate was accompanied by reductions in the incidence of bronchopulmonary dysplasia, retinopathy of prematurity and necrotizing enterocolitis

Bronchopulmonary dysplasia (BPD), retinopathy of prematurity (ROP), and necrotizing enterocolitis (NEC) all likely involve oxidative damage to immature tissues. It has been postulated that transfusions of adult erythrocytes contribute to the risk of developing these morbidities, as a consequence of adult hemoglobin releasing non-physiological quantities of O₂ to developing tissues. In 2009, we instituted a concerted effort to diminish erythrocyte transfusions in our NICU, and in 2013 we performed a before vs. after practice change analysis of the incidence of BPD, ROP and NEC during the 8-year period spanning this change. The transfusion rate fell from a high of 14.8% of admissions in 2007 to a low of 6.3% in 2011 (p < 0.001). Concordant with this reduction patients had a lower incidence of; BPD (from 3.2% to 0.9%; OR, 3.722; CI 1.897-7.302), ROP (from 4.6% to 2.4%; OR 1.958, CI 1.247-3.073), and a trend toward less NEC (from 0.7% to 0.2%; OR 3.090, CI 0.835-11.443).

Whole-blood viscosity in the neonate: effects of gestational age, hematocrit, mean corpuscular volume and umbilical cord milking

OBJECTIVE

The American College of Obstetrics and Gynecology Committee on Obstetric Practice recently endorsed delayed cord clamping at preterm delivery. However, the committee report expressed the concern by some practitioners that delayed clamping or cord milking might induce hyperviscosity in preterm neonates. To address this issue we: (1) established reference ranges for whole-blood viscosity among preterm neonates (viscosity reference ranges had previously been reported only in term neonates) and (2) determined the effect of umbilical cord milking at deliveries <32 weeks gestation on subsequent blood viscosity measurements.

STUDY DESIGN

This was a prospective study in two Neonatal Intensive Care Units. Blood viscosity was measured using a cone and plate viscometer. Associations were sought with gestation, hematocrit/hemoglobin and mean corpuscular volume. Reference ranges were determined for preterm infants <32 weeks gestation. Then, after umbilical cord milking at deliveries <32 weeks, viscosity was measured at birth and again during the 12 h after birth. In neonates with viscosities >95th % range, we sought signs of hyperviscosity (plethora, hypotonia, hypoglycemia, hyperbilirubinemia, thrombocytopenia).

RESULT

Viscosity at higher and lower sheer rates were linearly related (n=32, r=0.971). Within the range of hematocrits measured (29-63%) viscosity correlated with hematocrit (r=0.877) and hemoglobin (r=0.853) but not with erythrocyte size (r=0.179). Viscosity was related to gestational age (n=58), primarily due to the lower hematocrits at lower gestational ages. In the 12 h after cord milking viscosity ranged from 3.1 to 9.5 centipoise. Three of twenty preterm, neonates had viscosities >95th % reference range. However, all values were well below those where hyperviscosity is defined in term neonates and all lacked features of hyperviscosity.

CONCLUSION

Cord blood viscosity is directly proportional to hematocrit/hemoglobin, lower at early gestation and not associated with erythrocyte size. Cord milking at preterm delivery is associated with a low risk of clinical hyperviscosity. Practioners should not refrain from cord milking at preterm delivery because of a concern that it will commonly cause neonatal hyperviscosity.

Recent advances toward defining the benefits and risks of erythrocyte transfusions in neonates

Like many treatments available to small or ill neonates, erythrocyte transfusions carry both benefits and risks. This review examines recent publications aimed at better defining those benefits and those risks, as means of advancing evidence-based neonatal intensive care unit transfusion practices. Since decisions regarding whether to not to order an erythrocyte transfusion are based, in part, on the neonate's blood haemoglobin concentration, the authors also review recent studies aimed at preventing the haemoglobin from falling to a point where a transfusion is considered.