Total circulating red cells versus haematocrit as the primary descriptor of oxygen transport by the blood

Physiological-based cord clamping stabilised cardiorespiratory parameters in very low birth weight infants

AIM

We investigated the influence of physiological-based cord clamping (PBCC) on cardiorespiratory stability in very low birth weight (VLBW) infants during the first 72 h of life.

METHODS

This retrospective study comprised VLBW infants born at <32 + 0 weeks of gestation and admitted to the neonatal intensive care unit of the Medical University of Graz, Austria, from December 2014 to April 2021. VLBW infants delivered with PBCC were matched by gestational age and birth weight to delayed cord clamping controls. The PBCC group was stabilised after birth with an intact cord. Routine monitoring parameters were compared between the groups.

RESULTS

We included 54 VLBW infants. The mean gestational ages of the PBCC group and controls were 27.4 ± 1.9 versus 27.4 ± 1.8 weeks (p = 0.87), and the mean birth weights were 912 ± 288 versus 915 ± 285 g (p = 0.96), respectively. The mean cord clamping time was 191 ± 78 s in the PBCC group. Heart rate was lower in the PBCC group during the first 3 days after birth, reaching significance by 10 h. Other monitoring parameters did not reveal any differences between the two groups.

CONCLUSION

PBCC stabilised cardiorespiratory parameters in VLBW infants. The lower heart rate in the PBCC group suggested higher blood volume following intact cord resuscitation.

Back to the "Gold Standard": How Precise is Hematocrit Detection Today?

Introduction

The commonly used method for hematocrit detection, by visual examination of microcapillary tube, known as “micro-HCT”, is subjective but remains one of the key sources for fast hematocrit evaluation. Analytical automation techniques have increased the standardization of RBC index detection; however, indirect hematocrit measurements by blood analyzer, the automated HCT, do not correlate well with “micro-HCT” results in patients with hematological pathologies. We aimed to overcome those disadvantages in “micro-HCT” analysis using “ImageJ” processing software.

Methods

223 blood samples from the “general population” and 19 from sickle cell disease patients were examined in parallel for hematocrit values using the automated HCT, standard “micro-HCT,” and “ImageJ” micro-HCT methods.

Results

For the “general population” samples, the “ImageJ” values were significantly higher than the corresponding values evaluated by standard “micro-HCT” and automated HCT, except for the 0 to 2 month old newborns, in which the automated HCT results were similar to the “ImageJ” evaluated HCT. Similar to the “general population” cohort, we found significantly higher values measured by “ImageJ” compared to either “micro-HCT” or the automated HCT in SCD patients. Correspondent differences for the MCV and MCHC were also found.

Discussion

This study introduces the “micro-HCT” assessment technique using the image-analysis module of “ImageJ” software. This procedure allows overcoming most of the data errors associated with the standard “micro-HCT” evaluation and can replace the use of complicated and expensive automated equipment. The presented results may also be used to develop new standards for calculating hematocrit and associated parameters for routine clinical practice.

Perioperative blood loss: estimation of blood volume loss or haemoglobin mass loss?

BACKGROUND

Perioperative blood loss is an essential parameter in research into Patient Blood Management. However, currently there is no "gold standard" method to quantify it. Direct measurements of blood loss are considered unreliable methods, and the formulae to estimate it have proven to be significantly inaccurate. Given the need for better research tools, this study evaluated an estimation of haemoglobin mass loss as an alternative approach to estimate perioperative blood loss, and compared it to estimations based on blood volume loss.

MATERIAL AND METHODS

We studied one hundred consecutive patients undergoing urological laparoscopic surgery. Both haemoglobin mass loss and blood volume loss were directly measured during surgery, under highly controlled conditions for a reliable direct measurement of blood loss. Three formulae were studied: 1) a haemoglobin mass loss formula, which estimated blood loss in terms of haemoglobin mass loss, 2) the López-Picado's formula and 3) an empirical volume formula that estimated blood loss in terms of blood volume loss. The empirical volume formula was developed within the study with the aim of providing the best possible estimation of blood volume loss in the studied population. The formulae were evaluated and compared by assessing their agreements with their respective direct measurements of blood loss.

RESULTS

The haemoglobin mass loss formula met the predefined agreement criterion of ±71 g, with 95% limits of agreement ranging from 0.6 to 44.1 g and a moderate overestimation of 22.4. In comparison to both blood volume loss formulae, the haemoglobin mass loss formula was superior in every agreement parameter evaluated.

DISCUSSION

In this study, the estimation of haemoglobin mass loss was found to be a more accurate method to estimate perioperative blood loss. This estimation method could be a robust research tool, although more studies are needed to establish its reliability.

Detection of blood volumes and haemoglobin mass by means of CO re-breathing and indocyanine green and sodium fluorescein injections

The main aim of the present study was to quantify the magnitude of differences introduced when estimating a given blood volume compartment (e.g. plasma volume) through the direct determination of another compartment (e.g. red cell volume) by multiplication of venous haematocrit and/or haemoglobin concentration. However, since whole body haematocrit is higher than venous haematocrit such an approach might comprise certain errors. To test this experimentally, four different methods for detecting blood volumes and haemoglobin mass (Hb_mass) were compared, namely the carbon monoxide (CO) re-breathing (for Hb_mass), the indocyanine green (ICG; for plasma volume [PV]) and the sodium fluorescein (SoF; for red blood cell volume [RBCV]) methods. No difference between ICG and CO re-breathing derived PV could be established when a whole body/venous haematocrit correction factor of 0.91 was applied (p = 0.11, r = 0.43, mean difference -340 ± 612 mL). In contrast, when comparing RBCV derived by the CO re-breathing and the SoF method, the SoF method revealed lower RBCV values as compared to the CO re-breathing method (p < 0.05, r = 0.95, mean difference -728 ± 184 mL). However, compared to the ICG and the SoF methods, the typical error (%TE) and hence reliability of the CO re-breathing method was lower for all measured parameters. Therefore, estimating blood volume compartments by the direct assessment of another compartment can be considered a suitable approach. The CO re-breathing method proved accurate in determining the induced phlebotomy and is at the same time judged easier to perform than any of the other methods.

Milking compared with delayed cord clamping to increase placental transfusion in preterm neonates: a randomized controlled trial

OBJECTIVE

To compare two strategies to enhance placento-fetal blood transfusion in preterm neonates before 33 weeks of gestation.

METHODS

We recruited women at risk for singleton preterm deliveries. All delivered before 33 completed weeks of gestation. In this single-center trial, women were randomized to either standard treatment (clamping the cord for 30 seconds after delivery) or repeated (four times) milking of the cord toward the neonate. Exclusion criteria included inadequate time to obtain consent before delivery, known congenital abnormalities of the fetus, Rhesus sensitization, or fetal hydrops.

RESULTS

Of 58 neonates included the trial, 31 were randomized to cord clamping and 27 were randomized to repeated milking of the cord. Mean birth weight was 1,263±428 g in the clamping group and 1,235±468 g in the milking group, with mean gestational age of 29.2±2.3 weeks and 29.5±2.7 weeks, respectively. Mean hemoglobin values for each group at 1 hour after birth were 17.3 g/L for clamping and 17.5 g/L for milking (P=.71). There was no significant difference in number of neonates undergoing transfusion (clamping group, 15; milking group, 17; P=.40) or the median number of transfusions within the first 42 days of life (median [range]: clamping group 0 [0-7]; milking group 0 [0-20]; P=.76).

CONCLUSION

Milking the cord four times achieved a similar amount of placento-fetal blood transfusion compared with delaying clamping the cord for 30 seconds.

CLINICAL TRIAL REGISTRATION

National Research Register UK, www.nihr.ac.uk/Pages/default.aspx, N0051177741.

LEVEL OF EVIDENCE

I.

Comparison of multiple red cell volume methods performed concurrently in premature infants following allogeneic transfusion

BACKGROUND

Study of the pathophysiology and treatment of anemia of prematurity is facilitated by direct measurement of red cell volume (RCV) utilizing microliter quantities of blood samples. Our objective was to compare concurrent measurements of multiple direct RCV methods in infants.

METHODS

Eighteen preterm infants receiving clinically indicated transfusions had concurrent flow cytometric determinations of RCV and 24-h red blood cell (RBC) recovery based on donor-recipient differences of biotin-labeled RBCs (BioRBCs), Kidd antigen mismatched RBCs, and fetal hemoglobin-positive (HbF(+)) RBCs. High-performance liquid chromatography (HPLC) was also used for measuring HbF and adult hemoglobin protein concentrations for the determination of RCV.

RESULTS

Concurrent RCV measurements using BioRBCs (18 and 54 µg/ml), Kidd antigen, and HbF flow cytometry were not statistically different compared with RCVs measured using the reference BioRBC density (6 µg/ml). By contrast, the HbF-HPLC method overestimated RCV by 45% compared with the reference method. All the methods demonstrated 100% 24-h posttransfusion RBC recovery (PTR24).

CONCLUSION

Because BioRBC, Kidd antigen, and fetal hemoglobin (HbF) flow cytometry are safe and accurate methods requiring <10 µl of patient blood for determining RCV and PTR24 in preterm infants, they can be useful in clinical and research studies of anemia and other conditions.

The maintenance and monitoring of perioperative blood volume

The assessment and maintenance of perioperative blood volume is important because fluid therapy is a routine part of intraoperative care. In the past, patients undergoing major surgery were given large amounts of fluids because health-care providers were concerned about preoperative dehydration and intraoperative losses to a third space. In the last decade it has become clear that fluid therapy has to be more individualized. Because the exact determination of blood volume is not clinically possible at every timepoint, there have been different approaches to assess fluid requirements, such as goal-directed protocols guided by invasive and less invasive devices.

This article focuses on laboratory volume determination, capillary dynamics, aspects of different fluids and how to clinically assess and monitor perioperative blood volume.

Effect of placental transfusion on the blood volume and clinical outcome of infants born by cesarean section

Delay in cord clamping up to 30 to 40 seconds is feasible and should be practiced in preterm and term infants born by cesarean section. In term infants, this maneuver may decrease iron deficiency anemia at 6 months of age. Premature infants may have a higher blood volume and hematocrit initially requiring fewer transfusions. They also have a decreased incidence of intraventricular hemorrhage. The effect of compounding factors, such as maternal blood pressure, uterine contraction, medications, bleeding, and their effects on the infant's immediate and long-term outcome are unclear.

The effect of early and late umbilical cord clamping on neonatal hematocrit

OBJECTIVE

To compare the effect of early and late cord clamping (LCC) on neonatal hematocrit at 2 and 18 h of life.

STUDY DESIGN

In this double-blind randomized trial, 64 healthy full-term vaginally born neonates were randomly allocated to either early (30 s) or late (3 min) umbilical cord clamping. During the interval between delivery and cord clamping, the attendant held the neonate supine at the level of the introitus. Neonatal venous hematocrit was measured at 2 and 18 h of life.

RESULT

Neonatal hematocrit at 2 h of life (61+/-4.9 vs 61.6+/-4.5%) and 18 h of life (56.9+/-4.1 vs 56.2+/-3.9%) was not significantly different between the two groups. This was also true for neonatal polycythemia (20 vs 23.5%). In the LCC group, placental residual blood volume (PRBV) was 39.5% lower and estimated neonatal blood volume (ENBV) was 7.1% higher than that in the early cord clamping (ECC) group (P<0.001).

CONCLUSION

Late cord clamping does not lead to a significant difference in the hematocrit level of the neonate or neonatal polycythemia, but is associated with a significant increase in ENBV and a significant decrease in PRBV. Further trials should examine the effect of delaying cord clamping for a longer period of time or changing the position that the neonate is held in to determine whether these variations result in more clinically significant results.

A randomized clinical trial comparing immediate versus delayed clamping of the umbilical cord in preterm infants: short-term clinical and laboratory endpoints

BACKGROUND

Most neonates less than 1.0 kg birth weight need red blood cell (RBC) transfusions. Delayed clamping of the umbilical cord 1 minute after delivery transfuses the neonate with autologous placental blood to expand blood volume and provide 60 percent more RBCs than after immediate clamping. This study compared hematologic and clinical effects of delayed versus immediate cord clamping.

STUDY DESIGN AND METHODS

After parental consent, neonates not more than 36 weeks' gestation were randomly assigned to cord clamping immediately or at 1 minute after delivery. The primary endpoint was an increase in RBC volume/mass, per biotin labeling, after delayed clamping. Secondary endpoints were multiple clinical and laboratory comparisons over the first 28 days including Score for Neonatal Acute Physiology (SNAP).

RESULTS

Problems with delayed clamping techniques prevented study of neonates of less than 30 weeks' gestation, and 105 neonates 30 to 36 weeks are reported. Circulating RBC volume/mass increased (p = 0.04) and weekly hematocrit (Hct) values were higher (p < 0.005) after delayed clamping. Higher Hct values did not lead to fewer RBC transfusions (p > or = 0.70). Apgar scores after birth and daily SNAP scores were not significantly different (p > or = 0.22). Requirements for mechanical ventilation with oxygen were similar. More (p = 0.03) neonates needed phototherapy after delayed clamping, but initial bilirubin levels and extent of phototherapy did not differ.

CONCLUSIONS

Although a 1-minute delay in cord clamping significantly increased RBC volume/mass and Hct, clinical benefits were modest. Clinically significant adverse effects were not detected. Consider a 1-minute delay in cord clamping to increase RBC volume/mass and RBC iron, for neonates 30 to 36 weeks' gestation, who do not need immediate resuscitation.

Development and validation of a mathematical algorithm for quantifying preoperative blood volume by means of the decrease in hematocrit resulting from acute normovolemic hemodilution

BACKGROUND

The interindividual variability of blood volume (BV) is high. The aim of this work was to use the decrease in large-vessel hematocrit (HK(LV)) during acute normovolemic hemodilution (ANH) as an instrument for estimating preoperative BV.

STUDY DESIGN AND METHODS

In 39 patients, (Group 1) preoperative ANH was performed. Plasma volume, red cell volume, and HK(LV) were measured before and 30 minutes after ANH, respectively. In a retrospective analysis, a mathematical algorithm was developed for estimating BV before ANH by means of the measured changes in HK(LV) and the amount of blood removed during ANH. To validate the method prospectively, ANH was performed in an additional 10 patients (Group 2). Preoperative BV was estimated and measured in the same way as in Group 1.

RESULTS

In Group 1, the mean difference between estimated and measured BV before ANH was 200 +/- 403 mL (5.14 +/- 10.12%; p > 0.05; r = 0.8). In Group 2, the estimated BV before ANH was 41 +/- 348 mL (-0.53 +/- 7.84%) lower than the measured BV (p > 0.05; r = 0.94). In this group, however, two patients with an extraordinarily small (2691 mL) and large (6172 mL) preoperative BV, respectively, were identified correctly by means of the algorithm.

CONCLUSIONS

The changes in HK(LV) determined during ANH provide a good "bedside" estimation of preoperative BV.

Blood transfusion practice today

In trying to develop a cohesive and logical transfusion strategy, one must try to keep all of the previously mentioned information in mind. While recognizing that RBC transfusions are an integral part of care for critically ill patients, one also must recognize that there are large amounts of data that associate multiple transfusions of allogeneic blood with increased risk of morbidity and mortality. Some data exist showing causation and association, such as studies demonstrating the immunomodulatory effects of allogeneic transfusions. In addition, the blood supply is a limited resource that should not be used indiscriminately. It therefore behooves clinicians to subject each unit of blood transfused to scrutiny. In all likelihood, patients who are not actively bleeding and who are not hypovolemic probably get little to no benefit from allogeneic blood transfusions while their hemoglobin is greater than 7 g/dL. They do, however, get needless exposure to a potentially toxic substance. Although it is the authors' hope that more research will be performed to clarify the risks and benefits of blood transfusion, the authors also hope that knowledge of already published studies will continue to spread and replace the unfounded practices of the past.

Is it possible to predict the blood volume of a sick preterm infant?

OBJECTIVE

To investigate the relation between the measured intravascular blood volume (BV) and current methods of indirectly assessing BV status in sick preterm infants on the first day of life.

METHODS

Thirty eight preterm infants of gestation 24-32 weeks (median 30) and weight 480-2060 g (median 1220) were studied. Red cell volume was measured by the fetal haemoglobin dilution method in six infants and by the biotin labelled autologous red cell dilution method in the remaining 32. Total BV was calculated by dividing red cell volume by packed cell volume. Indirect assessments of BV status using heart rate (HR), core-peripheral temperature difference, mean arterial pressure, base excess, and packed cell volume were recorded.

RESULTS

The mean (SD) initial measured BV was 71 (12) ml/kg (range 53-105). The mean HR was 148 beats/min (range 130-180), which correlated positively (r = 0.39, p = 0.02) with BV (higher HR was associated with higher BV). The mean base excess was -3.19 mmol/l (range -18 to +6.2). The negative base excess correlated significantly positively (r = 0.41, p < 0.01) with BV (more acidotic babies tended to have higher BV). There was no significant correlation between core-peripheral temperature difference, mean arterial pressure, or packed cell volume and BV. Regression analysis showed that base excess and HR were significantly related to BV; base excess alone can predict variability in BV only to 17%, and base excess with HR can predict variability in BV to 29%.

CONCLUSION

The conventional clinical and laboratory indices are poor predictors of measured blood volume.

RBCs labeled at two biotin densities permit simultaneous and repeated measurements of circulating RBC volume

BACKGROUND

The extend potential applications of a nonradioactive method for measuring circulating RBC volume, we tested the hypothesis that RBC volume could be determined independently using two populations of RBCs labeled with low-density biotin (LDB1) and high-density biotin (HDB).

STUDY DESIGN AND METHODS

In 10 healthy adults, autologous RBCs were labeled with HDB, LDB, or 51Cr. The labeled RBCs were mixed and transfused. RBC volume was measured in postinfusion peripheral venous blood by quantitating dilution of each population of labeled RBCs.

RESULTS

RBC volume measured using either LDB or HDB cells agreed well with RBC volume measured using 51Cr. For the regression of RBC volume by LDB versus RBC volume by 51Cr, correlation = 0.994 and slope = 0.933. For HDB versus 51Cr, correlation = 0.982 and slope = 0.953. RBC volume measured a second time in four subjects with HDB agreed well; mean CV for the differences between HDB and 51Cr were less than 5 percent.

CONCLUSIONS

Using RBCs labeled with two different densities of biotin, RBC volume can be accurately measured simultaneously and repeatedly in the same subject without radiation exposure.

Clinically practical blood volume assessment with fluorescein-labeled HES

BACKGROUND

Standard techniques for measuring blood volume (BV) entail administering radioactivity and human albumin. This is laborious, expensive, and impractical in acute settings. An alternative method suitable for widespread routine application was assessed.

STUDY DESIGN AND METHODS

Seventy-nine ambulant outpatients and 18 intensive care unit (ICU) patients were prospectively recruited. Measurements of RBC volume (RCV) and plasma volume (PV) were performed with radiochromium-labeled RBCs (51Cr), radioiodinated albumin (125I), and fluorescein-labeled HES (FITC-HES). Small molecules overestimate PV because of vascular endothelial dysfunction (ED) and increased capillary permeability; a reference value for PV was therefore derived with the RCV and Hct.

RESULTS

Mean PV with 125I dilution was 230 mL (SD, 185 mL) greater than that with FITC-HES in outpatients. This difference was more exaggerated, 345 mL (SD, 371 mL), in ICU patients likely to have ED. Both the PV measured with FITC-HES and the 125I dilution correlated closely with the PV derived with RCV and Hct (r = 0.950 and 0.925, respectively) in the ICU patients.

CONCLUSION

FITC-HES estimates PV more accurately than 125I. FITC-HES should replace radioactive tracers for assessing BV. Comparing the estimates of PV with molecules of differing molecular weights may have clinical utility as an indicator of ED.

Immediate and delayed cord clamping in infants born between 24 and 32 weeks: a pilot randomized controlled trial

OBJECTIVE

This pilot study's aim was to establish feasibility of a protocol for delayed cord clamping (DCC) versus immediate cord clamping (ICC) at preterm birth and to examine its effects on initial blood pressure and other outcomes.

STUDY DESIGN

A randomized controlled trial recruited 32 infants between 24 and 32 weeks. Immediately before delivery, mothers were randomized to ICC (cord clamped at 5 to 10 seconds) or DCC (30- to 45-second delay in cord clamping) groups.

RESULTS

Intention-to-treat analyses revealed that the DCC group were more likely to have higher initial mean blood pressures (adjusted OR 3.4) and less likely to be discharged on oxygen (adjusted OR 8.6). DCC group infants had higher initial glucose levels (ICC=36 mg/dl, DCC=73.1 mg/dl; p=0.02).

CONCLUSION

The research design is feasible. The immediate benefit of improved blood pressure was confirmed and other findings deserve consideration for further study.

Circulating RBC volume, measured with biotinylated RBCs, is superior to the Hct to document the hematologic effects of delayed versus immediate umbilical cord clamping in preterm neonates

BACKGROUND

One problem assessing the hematologic physiology of preterm infants after delivery and/or the efficacy and toxicity of therapeutic interventions affecting RBC measurements is the inability of blood Hct values to accurately reflect circulating RBC volume-owing to changes in plasma volume that influence Hct (i.e., a fall in plasma volume concentrates RBCs to increase Hct; a rise in plasma volume dilutes RBCs to decrease Hct).

STUDY DESIGN AND METHODS

As part of a randomized, clinical trial testing the hypothesis that delayed clamping of the umbilical cord at delivery expands neonatal circulating RBC volume, blood Hct was compared to circulating RBC volume results measured directly with autologous, biotinylated RBCs or estimated mathematically with neonatal body weight and Hct values in neonates after immediate or delayed (60 sec) cord clamping.

RESULTS

Circulating RBC volume measured directly with biotinylated RBCs significantly increased (p=0.04) in neonates after delayed (42.1 +/- 7.8 mL/kg) versus immediate (36.8 +/- 6.3 mL/kg) cord clamping-a difference not detected indirectly by measuring Hct or estimating circulating RBC volume mathematically.

CONCLUSIONS

Because true hematologic effects of delayed versus immediate cord clamping may not be apparent or may be misinterpreted, when based on indirect measurements of Hct or calculations of circulating RBC volume, it is important to measure circulating RBC volume directly-as done with autologous, biotinylated RBCs-to document whether delayed cord clamping truly results in a transfer of significant quantities of RBCs from placenta to neonate. The clinical benefits and potential toxicities of increased RBC transfer to neonates require further studies.

A new method to determine the feto-placental volume based on dilution of fetal haemoglobin and an estimation of plasma fluid loss after intrauterine intravascular transfusion

OBJECTIVES

(1) To calculate the feto-placental volume (FPV), using the haematocrit (Ht) values and the percentages of fetal haemoglobin (HbF), before and after red blood cell transfusion. (2) To estimate the transfusion-induced loss of plasma fluid.

DESIGN

Retrospective analysis of data of 42 anaemic fetuses at the first transfusion [gestational age (GA) 19-36 weeks].

SETTING

Department of Obstetrics, Leiden University Medical Centre, The Netherlands.

SAMPLE

Fifteen hydropic and 27 non-hydropic fetuses.

METHODS

Donor blood volume (V(donor)) and Ht (Ht(donor)), fetal pre- and post-transfusion Ht values (Ht(initial), Htfinal) and percentages of HbF (HbF(initial) and HbF(final)) were used to calculate the FPV. The total red cell volume after transfusion (RCV(final)) and Ht(final) were used to estimate the plasma fluid loss.

MAIN OUTCOME MEASURES

Feto-placental blood volume and loss of plasma fluid.

RESULTS

The equations that use Htfinal over-estimate the FPV when the formula does not account for the difference between donor and post-transfusion Ht (FPV(Ht) = 21.36 * GA, - 390; r = 0.89). FPV is underestimated (FPV(Ht) = 9.90 * GA - 172; r = 0.84) when the blood volume increases with a volume less than the added donor blood volume. The calculation of FPV, using HbF percentages and the initial fetal RCV, is independent of volume changes (FPVHbF = 15.10 * GA - 279; r = 0.85). Comparing RCV(final) and Ht(final) values showed that 31.1 +/- 14.5% of the transfused volume was lost. Results of the hydropic fetuses did not differ from those of the non-hydropic fetuses.

CONCLUSIONS

FPV values based on Ht values are less reliable than those based on RCV and HbF findings. When, for practical reasons, Ht values have to be used, we propose an adapted equation for the calculation of the necessary volume of donor blood: V(donor) = FPV(HbF) * (Ht(final) - Ht(initial) / (Ht(donor) - 0.70 * Ht(final)).

Neonatal transitional physiology: a new paradigm

Early clamping of the umbilical cord at birth, a practice developed without adequate evidence, causes neonatal blood volume to vary 25% to 40%. Such a massive change occurs at no other time in one's life without serious consequences, even death. Early cord clamping may impede a successful transition and contribute to hypovolemic and hypoxic damage in vulnerable newborns. The authors present a model for neonatal transition based on and driven by adequate blood volume rather than by respiratory effort to demonstrate how neonatal transition most likely occurs at a normal physiologic birth.

A pilot randomised controlled trial of peripheral fractional oxygen extraction to guide blood transfusions in preterm infants

BACKGROUND

Peripheral fractional oxygen extraction (FOE) may be a better indicator of the need for transfusion than the haemoglobin concentration (Hb) because it is a measure of the adequacy of oxygen delivery to meet demand. A randomised controlled trial of the use of peripheral FOE to guide the need for blood transfusions in preterm infants was carried out to test this hypothesis.

METHOD

Infants less than 1500 g birth weight who were stable and less than 2 weeks old were randomised to receive transfusions guided by either a conventional protocol based on Hb (conventional group) or a protocol based on measurements of peripheral FOE made by near infrared spectroscopy (NIRS group). Measurements of Hb and FOE were made on all infants from randomisation until discharge. The primary outcome measures were number of transfusions received, rate of weight gain, and postmenstrual age at discharge.

RESULTS

Thirty seven infants were randomised to each group. Birth weight (median, range) (1200, 1004-1373 v 1136, 1009-1285 g) and Hb (median, range) at randomisation (160, 149-179 v 155, 145-181 g/l) did not differ between the two groups. The total number of transfusions given to the NIRS group was 56 and to the conventional group 84. The median number of transfusions per infant, the median volume of blood transfused to each group, and the total number of donors to which infants were exposed were similar in the two groups. Infants transfused according to the conventional protocol were more likely to be transfused earlier and at a higher Hb than those transfused in the NIRS group. Infants in the conventional group spent a significantly shorter period than those in the NIRS group with Hb < 100 g/l. Of the 56 transfusions given to the NIRS group, 33 (59%) were given because of clinical concerns rather than because of high FOE. There was no difference in the rate of weight gain, rate of linear growth, postmenstrual age at discharge, or the incidence of chronic lung disease or retinopathy of prematurity.

CONCLUSIONS

FOE measurements failed to identify many infants felt by clinicians to require blood transfusion. This may have been because clinicians relied on conventional indicators of transfusion that are vague and non-specific, or a peripheral FOE of 0.47 alone may not be a sensitive enough predictor of the need for transfusion. This requires further study.

Current best evidence: a review of the literature on umbilical cord clamping

Immediate clamping of the umbilical cord can reduce the red blood cells an infant receives at birth by more than 50%, resulting in potential short-term and long-term neonatal problems. Cord clamping studies from 1980 to 2001 were reviewed. Five hundred thirty-one term infants in the nine identified randomized and nonrandomized studies experienced late clamping, ranging from 3 minutes to cessation of pulsations, without symptoms of polycythemia or significant hyperbilirubinemia. Higher red blood cell flow to vital organs in the first week was noted, and term infants had less anemia at 2 months and increased duration of early breastfeeding. In seven randomized trials of preterm infants, benefits associated with delayed clamping in these infants included higher hematocrit and hemoglobin levels, blood pressure, and blood volume, with better cardiopulmonary adaptation and fewer days of oxygen and ventilation and fewer transfusions needed. For both term and preterm infants, few, if any, risks were associated with delayed cord clamping. Longitudinal studies of infants with immediate and delayed cord clamping are needed.

Hematocrit correlates well with circulating red blood cell volume in very low birth weight infants

Although circulating red blood cell (RBC) volume is a better measure of total body oxygen delivering capacity than hematocrit (HCT), circulating RBC volume is more difficult to measure. Thus, the HCT is often used in RBC transfusion decisions. However, several previous studies of low birth weight infants have reported that the correlation between HCT and circulating RBC volume is poor. Using a robust nonradioactive method based on in vivo dilution of biotinylated RBC enumerated by flow cytometry, the present study reexamined the correlation between HCT and circulating RBC volume in very low birth weight infants. Venous and capillary HCT levels were compared with circulating RBC volume measured using the biotin method. Twenty-six stable very low birth weight infants with birth weights less than 1300 g were studied on 43 occasions between 7 and 79 d of life. Venous HCT values correlated highly with circulating RBC volume (r = 0.907; p < 0.0001). However, the mean 95% confidence limits for prediction of circulating RBC volume from venous HCT (the average error of prediction) was +/-13.4 mL/kg. The correlation between HCT and circulating RBC volume is strong in older stable very low birth weight infants. However, clinically important uncertainty exists in estimating circulating RBC volume and the associated RBC transfusion needs of an individual infant based on venous HCT. Because direct measurement of circulating RBC volume is not yet practical, the HCT (or the blood Hb concentration) remains the best available indirect indicator.

Peripheral fractional oxygen extraction and other measures of tissue oxygenation to guide blood transfusions in preterm infants

The physiological effects of anemia in the preterm infant are complex and the indications for transfusions in preterm infants are controversial. A measure of the adequacy of tissue oxygenation may be a better guide to the need for transfusions than currently used criteria. This article considers 2 measures of tissue oxygenation of preterm infants: 1) The whole blood lactate concentration, and 2) Peripheral fractional oxygen extraction (FOE) by using near infrared spectroscopy. Several studies have shown falls in blood lactate concentration after blood transfusion, but it has been difficult to establish a convincing link between raised lactate concentrations and significant anemia because even anemic infants have lactate concentrations that are within or close to the normal range. Lactate concentrations may be affected by the haematocrit of the blood sample. Peripheral FOE can be measured by using near infrared spectroscopy with partial venous occlusion and has been studied in preterm infants with symptomatic and asymptomatic anaemia. Mean (SD) FOE was significantly higher in symptomatic [0.425 (0.06)] (P< .01) but not asymptomatic [0.334 (0.05)] compared to controls [0.352 (0.06)], (P = .22). After transfusion there was a significant fall in FOE in symptomatic infants to 0.367 (0.06) (P = .001) but there was no change in infants who were asymptomatic. FOE correlated with other measures known to reflect the adequacy of oxygen availability during anemia. These results suggest that peripheral FOE may be suitable as a guide to the need for blood transfusions. A pilot randomized controlled trial is currently being undertaken to test this hypothesis.

Red blood cell transfusions in very and extremely low birthweight infants under restrictive transfusion guidelines: is exogenous erythropoietin necessary?

OBJECTIVE

To examine the number and volume of red blood cell transfusions (RBCTs) in very and extremely low birthweight infants under restrictive red blood cell transfusion guidelines without erythropoietin administration, and to compare the results with those reported in similar infants receiving erythropoietin.

METHODS

From April 1996 to June 1999, all RBCTs given to infants with a birth weight of less than 1500 g were prospectively recorded. Data on RBCT combined with erythropoietin treatment and RBCT guidelines were extracted from four prospective randomised trials of erythropoietin for anaemia of prematurity.

RESULTS

When the restrictive RBCT guidelines were followed, the number of RBCTs and volume transfused were similar to those reported during erythropoietin administration.

CONCLUSIONS

RBCT guidelines may have a similar impact on RBCT in very low birthweight infants to the administration of erythropoietin. The effect of RBCT guidelines on RBCT frequency should be considered when evaluating the efficacy of erythropoietin administration to preterm infants.

Adaptive responses during anemia and its correction in lambs

There is limited information available on which to base decisions regarding red blood cell (RBC) transfusion treatment in anemic newborn infants. Using a conscious newborn lamb model of progressive anemia, we sought to identify accessible metabolic and cardiovascular measures of hypoxia that might provide guidance in the management of anemic infants. We hypothesized that severe phlebotomy-induced isovolemic anemia and its reversal after RBC transfusion result in a defined pattern of adaptive responses. Anemia was produced over 2 days by serial phlebotomy (with plasma replacement) to Hb levels of 30-40 g/l. During the ensuing 2 days, Hb was restored to pretransfusion baseline levels by repeated RBC transfusion. Area-under-the-curve methodology was utilized for defining the Hb level at which individual study variables demonstrated significant change. Significant reciprocal changes (P < 0.05) of equivalent magnitude were observed during the phlebotomy and transfusion phases for cardiac output, plasma erythropoietin (Epo) concentration, oxygen extraction ratio, oxygen delivery, venous oxygen saturation, and blood lactate concentration. No significant change was observed in resting oxygen consumption. Cardiac output and plasma Epo concentration increased at Hb levels <75 g/l, oxygen delivery and oxygen extraction ratio decreased at Hb levels <60 g/l, and venous oxygen saturation decreased and blood lactate concentration increased at Hb levels <55 g/l. We speculate that plasma Epo and blood lactate concentrations may be useful measures of clinically significant anemia in infants and may indicate when an infant might benefit from a RBC transfusion.

Changing practices of red blood cell transfusions in infants with birth weights less than 1000 g

OBJECTIVE

Extremely low birth weight (ELBW) infants frequently undergo transfusion because they are critically ill, often need artificial ventilation, and have the highest blood sampling loss in relation to their weight. During the last decade our transfusion guidelines were changed 3 times to become more restrictive. We hypothesized that these modifications substantially decreased the number of transfusions in our ELBW infants.

METHODS

We performed a single-center analysis of 256 infants with birth weights from 500 to 999 g who were admitted from 1989 to 1997 and included 3 study periods, each starting with newly modified transfusion guidelines in April 1989, September 1991, and January 1995. We evaluated prospectively recorded clinical data and retrospective chart analysis for transfusion-related information.

RESULTS

The median number of transfusions per infant decreased from 7 in the first period to 2 in the third period, whereas donor exposure decreased from 5 to 1 and blood volume transfused decreased from 131 to 37 mL/kg birth weight (P <.01). The median venous hematocrit measured before transfusion decreased from 43% to 35% in infants who underwent ventilation and from 41% to 31% in spontaneously breathing infants. The median birth weight decreased from 870 to 740 g and the median gestational age from 27 to 25 completed weeks (P <.01). The overall survival rate was 75% and did not change. The incidences of retinopathy, intraventricular hemorrhage, and patent ductus arteriosus remained unchanged.

CONCLUSION

Over this 9-year period with increasingly restrictive transfusion guidelines, the transfusion number decreased by 71% and the donor exposure by 80% in ELBW infants without adverse clinical effects.

Measurement of circulating red cell volume using biotin-labeled red cells: validation against 51Cr-labeled red cells

BACKGROUND

Anemia is a serious problem in the fetus and preterm infant. To investigate the physiology and pathophysiology of anemia and to assess responses to blood transfusions or erythropoietin therapy, measurement of circulating red cell volume would be useful. Because the standard 51Cr method exposes the subject to radiation, a method of measuring circulating red cell volume without radiation exposure, sufficiently sensitive for use in fetuses and infants, was developed.

STUDY DESIGN AND METHODS

In 10 healthy adults whose body mass ranged from 56.8 to 115.9 kg, aliquots of autologous red cells were labeled with biotin or with 51Cr, mixed, and transfused intravenously. Circulating red cell volume was measured in posttransfusion blood by quantitating the in vivo dilution of biotinylated red cells. Biotinylated red cells were detected by two methods: 1) 125I-streptavidin and 2) fluorescein-labeled avidin with flow cytometry.

RESULTS

Circulating red cell volume measured by 125I-streptavidin detection agreed well with that measured by 51Cr (slope = 1.07, y-intercept = -97, correlation = 0.987). Similarly, circulating red cell volume measured by flow cytometry agreed well with that measured by 51Cr (slope = 1.05, y-intercept = -20, correlation = 0.987).

CONCLUSIONS

Circulating red cell volume measured by the use of biotin with either 125I-streptavidin or flow cytometry agrees with that measured by 51Cr. Each system provides a method of performing these studies without exposing the subject to radiation.

Low degree of regionalization and high transfusion rates in very low birthweight infants: a survey in Germany

Although anemia is common in very low birthweight (VLBW) infants, widely accepted guidelines for red blood cell transfusions are lacking. Questionnaires regarding transfusion policy in VLBW infants in 1994 were sent to 391 German pediatric departments. 208 questionnaires were returned. 51 departments reported not to admit VLBW infants. Thus, results are based on 157 completed questionnaires. 54% of the respondents admitted less than 30 VLBW infants per year and 52% of the VLBW infants were admitted to departments with less than 50 VLBW infants per year. Overall transfusion rate ranged from 0 to 100% (median 65%). This range narrowed with the departments' size indicating stricter guidelines with less variation. Indication for transfusion varied considerably depending on the infants' postnatal age and need for ventilatory support. 34% of the respondents applied directed transfusions, most frequently from the infant's father. 70% used satellite packs. 51% stored the packs up to 7 days, 10% longer than 14 days. Red cells were irradiated in 35%, and washed in 23% of the departments. Median single transfusion volume was 12 ml/kg. We conclude that regionalization of VLBW infants in Germany is far from completeness and that hospital policies for transfusion show large variety especially in small departments.

Changing patterns of red blood cell transfusion in very low birth weight infants

OBJECTIVE

Anemia develops in increasing numbers of critically ill very low birth weight (VLBW) infants who survive the neonatal period, and they receive multiple red blood cell (RBC) transfusions. Despite their need for prolonged medical treatment, we hypothesized that VLBW infants presently receive fewer RBC transfusions as a result of the growing awareness of transfusion risks and improvement of neonatal care.

METHODS

RBC transfusion practices and clinical outcomes in infants with birth weights of 1.5 kg or less were analyzed retrospectively in three selected years: 1982, before awareness of the human immunodeficiency virus; 1989, before surfactant availability; and 1993, before erythropoietin approval.

RESULTS

Progressive declines in RBC transfusions, donor exposures, and transfusion volumes occurred concurrently with decreases in morbidity and mortality rates. Transfusions per infant (mean +/- SD) declined from 7.0 +/- 7.4 in 1982 to 5.0 +/- 5.8 in 1989 to 2.3 +/- 2.7 in 1993 (p < 0.001). This decline was associated with a decrease in pretransfusion hematocrit (33.6% +/- 2.8% in 1982, 34.2% +/- 3.7% in 1989, and 29.8% +/- 5.1% in 1993; p < 0.001). The distribution of RBC transfusions given by week of life among study years did not change; 70% of RBC transfusions were given within the first 4 weeks, when infants are sickest. Although the percentage of VLBW infants weighing more than 1 kg at birth and never receiving any RBC transfusions increased with time (17% in 1982, 33% in 1989, and 64% in 1993), more than 95% of infants weighing 1 kg or less in all years received transfusions.

CONCLUSIONS

Overall administration of neonatal transfusions has decreased markedly, most likely because of multiple factors. Because most RBC transfusions are given to infants weighing 1 kg or less in the first weeks of life, therapeutic strategies should focus on this group of VLBW infants during this critical period. The temporal changes observed in transfusion patterns emphasize the importance of including concurrent controls in future studies evaluating transfusion interventions.

Flow cytometric determination of pre-transfusion red cell volume in fetuses and neonates requiring transfusion based on RhD+ dilution by transfused D- red cells

We report a case of feto-maternal haemorrhage and describe a new flow-cytometric method of determining a fetus's or infant's pre-transfusion red cell volume (RCV). We validate this method against an established technique, employing fetal haemoglobin (HbF) dilution, for determining the RCV in fetuses and neonates requiring intravascular transfusion. We discuss advantages and other potential applications of this new method.

The roles and vital importance of placental blood to the newborn infant

At 30 weeks' gestation, half of the approximately 110 ml/kg total blood volume (BV) of the feto-placental circulation is in the fetus, rising, by term, to about 90 ml/kg. In preterm infants at birth, subnormal blood volume is the rule, because of immediate cord clamping. Blood volume, typically 50-60 ml/kg during critical care, limits systemic oxygen (O2) transport and, because of shunting, causes hepato-splanchnic ischaemia and impaired lung function. Haemoconcentration results from plasma extravasation because of vascular endothelial damage. This elevates the haematocrit, masking the red cell lack. By allowing placental transfusion at birth, delaying cord clamping by 30-60 seconds, initial oligovolaemia is obviated, and post-natal lung adaptation greatly facilitated. The complications and costs of care can thereby be much reduced. Losses of haemopoietic stem cells are reduced, vital for haematologic and immunologic constitution and for response to haemopoietic growth factors. Further work is urgently needed to determine how to optimize this vital opportunity in preventive medicine in perinatology, with the objective of preventing complications, and reducing costs of all kinds, in management of the infant born preterm.

Erythropoiesis of very low-birth-weight infants dependent on prenatal growth rate and protein status

This study investigated erythropoiesis in very low-birth-weight infants with special reference to the role of protein status in the regulation of erythropoiesis in 22 appropriate- and 11 small-for-gestational-age infants. Blood samples were drawn at three and six weeks of age. The serum concentrations of erythropoietin, estimated by a solid-phase enzyme immunoassay, were similar in the two groups at both study ages. The total circulating erythrocyte volume and the serum concentration of prealbumin were higher in the appropriate- than in the small-for-gestational-age infants at three and six weeks of age. The former group had a better protein status, although their protein intake was similar or lower. We conclude that erythropoiesis in very low-birth-weight infants is influenced more by protein status and prenatal growth than by serum concentration of erythropoietin.

Umbilical cord clamping and preterm infants: a randomised trial

OBJECTIVE

To investigate the clinical effects of regulating umbilical cord clamping in preterm infants.

DESIGN

A prospective randomised study.

SETTING

The Queen Mother's Hospital, Glasgow.

SUBJECTS

36 vaginally delivered infants over 27 and under 33 weeks' gestation.

INTERVENTION

Holding the infant 20 cm below the introitus for 30 seconds before clamping the umbilical cord ("regulated" group, 17 patients), or conventional management ("random" group, 19 patients).

MAIN OUTCOME MEASURES

Initial packed cell volume, peak serum bilirubin concentrations, red cell transfusion requirements, and respiratory impairment (assessed by ventilatory requirements, arterial-alveolar oxygen tension ratio over the first day in ventilated infants, and duration of dependence on supplemental oxygen).

RESULTS

There were statistically significant differences between the two groups in mean initial packed cell volume (regulated group 0.564, random group 0.509) and median red cell transfusion requirements (regulated group zero, random group 23 ml/kg). 13 infants from each group underwent mechanical ventilation and showed significant differences in mean minimum arterial-alveolar oxygen tension ratio on the first day (regulated group 0.42, random group 0.22) and in median duration of dependence on supplemental oxygen (regulated group three days, random group 10 days). Differences in final outcome measures such as duration of supplemental oxygen dependence and red cell transfusion requirements were mediated primarily through arterial-alveolar oxygen tension ratio and also packed cell volume.

CONCLUSIONS

This intervention at preterm deliveries produces clinical and economic benefits.

Measurement of plasma volume in neonates

There is no reliable and safe method for measuring plasma volume in ill newborn infants. We describe an adaptation of the dye dilution technique using indocyanine green as the plasma label, which can be used in the sickest and smallest of infants with the minimum of disturbance. To avoid the need to take large volumes of blood from the infant, samples were diluted 1:1 with distilled water and pooled adult sera was used to construct the dye dilution standard curves. Eighteen preterm and fullterm infants were studied on 30 occasions. The measured plasma volume ranged between 21.4 and 106 ml/kg. Paired measurements were performed within 30-90 minutes of each other in seven infants. In five infants estimations of plasma volume were made shortly before and 30 minutes after the infusion of a known quantity of plasma. In eight out of 12 infants who had two measurements made there was close agreement between the second measured volume and the first measured volume, taking into account how much plasma had been given to or taken from the infant between the two measurements. The error ranged from 0.2 to 5.2 ml and the plasma recovery error ranged from -2.9% to +4.7%. In the remaining four infants the errors ranged from 2.1 to 9.5 ml and -14.2% to +8.8%. Errors in the measurement of plasma volume may arise as the result of sampling too early before full mixing of the dye has occurred, and there is a potential error in the measurement due to the distribution of albumin in the extracellular space in sick infants resulting in an overestimation of the plasma volume. Proposals for reducing sources of errors are discussed.

Recombinant erythropoietin compared with erythrocyte transfusion in the treatment of anemia of prematurity

To assess the risks and benefits of erythropoietin versus erythrocyte transfusion in the treatment of the anemia of prematurity, we randomly assigned 19 anemic preterm infants (birth weight 988 +/- 227 gm; gestational age 27.6 +/- 1.2 weeks; age 41 +/- 15 days; all values mean +/- SD) to receive either transfusion or subcutaneously administered erythropoietin (200 units/kg every other day for 10 doses). In the 10 erythropoietin recipients, corrected reticulocyte counts increased from 2% +/- 1% to 7% +/- 2% (p less than 0.001) and hematocrits increased from 27% +/- 2% to 30% +/- 4% (p less than 0.05). In the nine infants who underwent transfusion, reticulocyte counts did not increase, but hematocrits increased from 28% +/- 4% to 41% +/- 2% after initial transfusion (p less than 0.001) and had decreased to 34% +/- 5% by day 20. Signs attributed to anemia (tachycardia, apnea with bradycardia, and poor weight gain) declined in both the erythropoietin recipients and those who underwent transfusion. However, five of nine infants who underwent transfusion had symptoms within 10 to 14 days and were given further transfusions. Marrow aspiration performed after 7 to 10 days of treatment showed that infants receiving erythropoietin had greater percentages of erythropoietic precursors (p less than 0.01), greater concentrations of mature erythroid progenitors (p less than 0.001), and higher cycling rates of erythroid progenitors (p less than 0.001). The percentage of mature stored neutrophils in marrow was lower in the erythropoietin group than in the transfusion group, resulting in an inverse myeloid/erythroid ratio (0.5:1 vs 6.2:1; p less than 0.001). After 20 days, absolute blood neutrophil counts were lower in the erythropoietin recipients (1.8 +/- 0.9 x 10(3) cells/microliters) than in the infants who underwent transfusion (3.9 +/- 1.9 x 10(3) cells/microliters; p less than 0.05). Administration of erythropoietin thus stimulated erythropoiesis and relieved signs attributed to anemia; the significance of the relative neutropenia remains to be determined. We conclude that erythropoietin administration offers promise as an alternative to erythrocyte transfusion in neonates with symptomatic anemia of prematurity.