Lactic acid as a predictor for erythrocyte transfusion in healthy preterm infants with anemia of prematurity

Lactate Production can Function to Increase Human Epithelial Cell Iron Concentration

Introduction

Under conditions of limited iron availability, plants and microbes have evolved mechanisms to acquire iron. For example, metal deficiency stimulates reprogramming of carbon metabolism, increasing activity of enzymes involved in the Krebs cycle and the glycolytic pathway. Resultant carboxylates/hydroxycarboxylates then function as ligands to complex iron and facilitate solubilization and uptake, reversing the metal deficiency. Similarly, human intestinal epithelial cells may produce lactate, a hydroxycarboxylate, during absolute and functional iron deficiency to import metal to reverse limited availability.

Methods

Here we investigate (1) if lactate can increase cell metal import of epithelial cells in vitro, (2) if lactate dehydrogenase (LDH) activity in and lactate production by epithelial cells correspond to metal availability, and (3) if blood concentrations of LDH in a human cohort correlate with indices of iron homeostasis.

Results

Results show that exposures of human epithelial cells, Caco-2, to both sodium lactate and ferric ammonium citrate (FAC) increase metal import relative to FAC alone. Similarly, fumaric, isocitric, malic, and succinic acid coincubation with FAC increase iron import relative to FAC alone. Increased iron import following exposures to sodium lactate and FAC elevated both ferritin and metal associated with mitochondria. LDH did not change after exposure to deferoxamine but decreased with 24 h exposure to FAC. Lactate levels revealed decreased levels with FAC incubation. Review of the National Health and Nutrition Examination Survey demonstrated significant negative relationships between LDH concentrations and serum iron in human cohorts.

Conclusions

Therefore, we conclude that iron import in human epithelial cells can involve lactate, LDH activity can reflect the availability of this metal, and blood LDH concentrations can correlate with indices of iron homeostasis.

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.

How to assess hemodynamic status in very preterm newborns in the first week of life?

BACKGROUND

Assessing hemodynamic status in preterm newborns is an essential task, as many studies have shown increased morbidity when hemodynamic parameters are abnormal. Although oscillometric monitoring of arterial blood pressure (BP) is widely used due to its simplicity and lack of side effects, these values are not always correlated with microcirculation and oxygen delivery.

OBJECTIVES

This review focuses on different tools for the assessment of hemodynamic status in preterm newborns. These include the measurement of clinical (BP, capillary refill time and urinary output (UO)) or biological parameters (lactate analysis), functional echocardiography, and near-infrared spectroscopy (NIRS). We describe the concepts and techniques involved in these tools in detail, and examine the interest and limitations of each type of assessment.

CONCLUSIONS

This review highlights the complementarities between the different parameters used to assess hemodynamic status in preterm newborns during the first week of life. The analysis of arterial BP measured by oscillometric monitoring must take into account other clinical data, in particular capillary refill time and UO, and biological data such as lactate levels. Echocardiography improves noninvasive hemodynamic management in newborns but requires specific training. In contrast, NIRS may be useful in monitoring the clinical course of infants at risk of, or presenting with, hypotension. It holds the potential for early and noninvasive identification of silent hypoperfusion in critically ill preterm infants. However, more data are needed to confirm the usefulness of this promising tool in significantly changing the outcome of these infants.

Hypoxia Biomarkers, Oxidative Stress, and Circulating Microparticles in Pediatric Patients With Thalassemia in Upper Egypt

This study aimed to investigate the oxidative stress, hypoxia biomarkers, and circulating microparticles (MPs) in β thalassemia major. The study included 56 children with thalassemia and 46 healthy controls. Hypoxia biomarkers, oxidative stress biomarkers, and total plasma fragmented DNA (fDNA) were detected by the standard methods. The MPs were assessed by flow cytometry. Hypoxia and oxidative stress biomarkers, fDNA, and MPs were higher and total antioxidant capacity (TAC) was lower in patients with thalassemia than the controls. In splenectomized patients and those who had complications, vascular endothelial growth factor (VEGF), malondialdehyde, fDNA, endothelial, platelet, and activated platelet MP levels were higher while, TAC was lower than the nonsplenectomized patients. In conclusion, the increased tissue hypoxia, oxidative stress in β thalassemia, and its relationship with DNA damage and MPs release could explain many complications of thalassemia and may have therapeutic implications. The VEGF could serve as an important indicator for adequacy of blood transfusion in thalassemia.

Functional echocardiographic assessment of myocardial performance in anemic premature infants: a pilot study

This prospective observational study conducted in a neonatal intensive care unit aimed to evaluate echocardiographic changes provoked by anemia and transfusion of packed red blood cells (pRBCs) in premature infants. In this study, 32 anemic premature infants had serial echocardiographic assessment of left ventricular (LV) systolic performance, LV preload, and afterload immediately before, within 48 h, and up to 120 h after the transfusion of pRBCs. Pretransfusional evaluations also were compared with similar assessments of 71 nonanemic inpatient premature infants analogous for sex, gestational age at birth, and postnatal age. Left ventricular systolic performance was estimated from fractional shortening, LV output, and LV myocardial performance index (LVMPI). The LV preload was estimated from the LV end-diastolic dimension and the ratio of left atrium-to-aortic root dimension (LA/Ao ratio). The LV afterload was estimated from end-systolic wall stress. The LVMPI was found to decrease with increasing corrected gestational age in both the nonanemic (R = 0.173; p = 0.03) and anemic (R = 0.460; p = 0.007) infants. The LVMPI was the only index that changed after transfusion of pRBCs, decreasing in the younger anemic infants (p = 0.011) and increasing in the older anemic infants (p = 0.012). Finally, a significant inverse relationship between pre- and posttransfusional LVMPI values (R = 0.730; p < 0.001) was noted. The LVMPI may allow for identification of preterm infants more likely to be helped by transfusion of pRBCs.

Neonatal red blood cell transfusions: searching for better guidelines

BACKGROUND

Packed red blood cell (RBC) transfusions are often administered to patients in the neonatal intensive care unit. The purpose of this study was to determine whether current blood transfusion guidelines are as useful as care givers' perception in identifying patients in need of a packed RBC transfusion.

DESIGN AND METHODS

Health care providers were asked to complete a pre- and post-transfusion survey on neonates receiving a packed RBC transfusion. These patients were divided into three groups based on reasons for transfusion: (i) guidelines; (ii) care-givers' perceptions of need for packed RBC transfusion; or (iii) both. These three groups were further subdivided into two cohorts according to whether they had a clinical improvement or not. Demographic data and clinical variables were compared between the groups.

RESULTS

Seventy-eight care-givers were surveyed. Eighteen patients (23%) were transfused based on guidelines, 36 (46%) based on care givers' perception and 24 (31%) based on both. Neonates transfused based on guidelines alone were more likely to have received the transfusion in the first week of life, had a higher pre-transfusion haematocrit, were less symptomatic and had a higher trend to require mechanical ventilation. Neonates transfused based on caregivers' perception were more likely to be on non-invasive ventilatory support and were more symptomatic. Neonates who improved after a transfusion had a lower pre-transfusion haematocrit (p=0.02), were more symptomatic (p=0.01) and were more likely to be on non-invasive ventilatory support (p=0.002) when compared to the group without a clinical improvement. The group without improvement had an increase in oxygen requirement (+2.8±6.4) after the transfusion (p=0.0004). Tachycardia was the most sensitive predictor of a benefit from packed RBC transfusion [OR 6.48: p=0.005].

DISCUSSION

Guidelines on when to transfuse stable growing neonates with packed RBC should be re-evaluated to include more care giver judgement and perhaps be more restrictive for critically ill neonates.

Day 1 serum lactate values in preterm infants less than 32 weeks gestation

Base deficit and serum lactate concentrations may be important prognostic indicators in preterm infants. We sought to (1) determine the relationship between day 1 serum lactate values and base deficit and (2) determine the relationship between day 1 biochemical parameters and adverse outcome in preterm infants <32 weeks. This was a retrospective study of all patients less than 32 weeks gestation admitted to neonatal intensive care unit over a 6-month period. All blood gases performed during the first 24 h post delivery were analysed. Adverse outcome was defined as death, severe (grade 3 or 4) intraventricular haemorrhage or periventricular leukomalaica on cranial ultrasonography. Patients were excluded if there was a known lethal malformation or cardiac defect. Seventy-two infants had a total of 473 lactate levels performed in the first 24 h. Mean (SD) gestational age was 29 (2.3) weeks, mean (SD) birth weight 1.28 (0.42) kg. Mean (SD) lactate values in first 6 h was 4.63 (3.69), at 12 h 3.08 (2.6), at 18 h 2.47 (2.68) and 2.08 (2.74) mmol/l at 24 h. There was a strong correlation between lactate values and base deficit values (R value 0.8, p < 0.01). Mean base deficit values at 6 h were 5.9 (4.5), at 12 h 3.8 (3.9), at 18 h 3.6 (3.1) and at 24 h 4.1 (3.8) mmol/l. A single lactate value greater than 5.6 mmol/l had a sensitivity of 100% and specificity of 85% of identifying adverse outcome. Persistently elevated or worsening lactates were associated with adverse outcome. There is a strong correlation between lactate values and base deficit on day 1 of life. Serial lactate measurements greater than 5.6 mmol/l predict adverse outcome and may aid the clinician in bedside decision making.

Bedside detection of low systemic flow in the very low birth weight infant on day 1 of life

We aimed to assess the relationship between the clinical and biochemical parameters of perfusion and superior vena cava (SVC) flow in a prospective observational cohort study of very low birth weight (VLBW) infants. Newborns with congenital heart disease were excluded. Echocardiographic evaluation of SVC flow was performed in the first 24 h of life. Capillary refill time (forehead, sternum and toe), mean blood pressure, urine output and serum lactate concentration were also measured simultaneously. Thirty-eight VLBW infants were examined. Eight patients (21%) had SVC flow less than 40 ml/kg/min. There was a poor correlation between the capillary refill time (in all sites), mean blood pressure, urine output and SVC flow. The correlation coefficient for the serum lactate concentration was r = -0.28, p = 0.15. The median serum lactate concentration was 3.5 (range 2.8-8.5) vs. 2.7 (range 1.2-6.9) mmol/l (p = 0.01) in low flow versus normal flow states. A serum lactate concentration of >2.8 was 100% sensitive and 60% specific for detecting a low flow state. Combining a capillary refill time of >4 s with a serum lactate concentration of >4 mmol/l had a specificity of 97% for detecting a low SVC flow state. Serum lactate concentrations are higher in low SVC flow states. A capillary refill time of >4 s combined with serum lactate concentrations >4 mmol/l increased the specificity and positive and negative predictive values of detecting a low SVC flow state.

Effect of transfusion on the venous blood lactate level in very low-birthweight infants

BACKGROUND

In recent years the blood lactate level can be easily and quickly measured with a small amount of blood, and the availability of an arterial blood lactate level has been reported as an indicator of oxygen deficit in adults. To determine whether venous blood lactate level can serve as such a marker for determining the indications for transfusion, blood lactate and hemoglobin level were monitored before and after transfusion.

METHODS

The study subjects consisted of 12 very low-birthweight infants admitted to the neonatal intensive care unit and who had transfusion between June 2005 and June 2007. The data on the blood lactate and hemoglobin were collected retrospectively by referring to the clinical records.

RESULTS

A total of 18 transfusions was performed. There was no significant relationship between venous blood lactate and hemoglobin concentration before transfusion. The subjects were classified into two groups according to the lactate level before transfusion: > or =3.3 mmol/L and <3.3 mmol/L. In the high-lactate group the lactate decreased significantly after transfusion (P < 0.01) and it continued to decrease thereafter. In the low-lactate group, however, the lactate remained unchanged.

CONCLUSIONS

Venous blood lactate measurements may offer some additional information regarding the optimal time for performing a transfusion. To the authors' knowledge this is the first report to study the changes in lactate levels using venous blood sampling in red blood cell transfusion in very low-birthweight infants.

Evaluation and treatment of hypotension in the preterm infant

A large proportion of very preterm infants receive treatment for hypotension. The definition of hypotension is unclear, and, currently, there is no evidence that treating it improves outcomes or, indeed, which treatment to choose among the available alternatives. Assessment of circulatory adequacy of the preterm infant requires a careful clinical assessment and may also require ancillary investigations. The most commonly used interventions, fluid boluses and dopamine, are problematic: fluid boluses are statistically associated with worse clinical outcomes and may not even increase blood pressure, whereas dopamine increases blood pressure mostly by causing vasoconstriction and may decrease perfusion. For neither intervention is there any reliable data showing clinical benefit. Prospective trials of intervention for hypotension and circulatory compromise are urgently required.

Vascular endothelial growth factor as marker for tissue hypoxia and transfusion need in anemic infants: a prospective clinical study

OBJECTIVE

Oxygen-carrying capacity of blood is reduced in anemic infants because of low hemoglobin levels. Red blood cell transfusions become necessary if low hematocrit causes tissue hypoxia. No reliable parameters exist for detecting chronic tissue hypoxia. Vascular endothelial growth factor is upregulated by hypoxia; hence, elevated vascular endothelial growth factor levels may be a marker for tissue hypoxia and may indicate the need for red blood cell transfusions.

METHODS

In a prospective study, plasma vascular endothelial growth factor levels were measured in 3 groups of infants suspected of requiring red blood cell transfusions to find a vascular endothelial growth factor cutoff value indicative of tissue hypoxia. The 3 groups were acute anemic (an episode of acute bleeding [hematocrit drop > 5%] per day); chronic anemic (hematocrit drop < 5% per day); and nontransfused (hematocrit drop < 5% per day) but not meeting clinical criteria for a transfusion. Blood was sampled before transfusion and again 48 hours after transfusion if required. Plasma vascular endothelial growth factor and erythropoietin concentrations were measured.

RESULTS

Vascular endothelial growth factor concentrations were lower in acutely anemic compared with chronically anemic infants, whereas erythropoietin levels did not differ between these groups. The vascular endothelial growth factor concentration was <140 pg/mL in all acutely anemic infants, and this was deemed the threshold level indicating sufficient tissue oxygenation in subsequent analysis. We found that 30% of chronically anemic and 43% of nontransfused infants had vascular endothelial growth factor levels of >140 pg/mL. In transfused infants, with elevated vascular endothelial growth factor levels, red blood cell transfusion resulted in lowering of vascular endothelial growth factor concentrations.

CONCLUSIONS

Vascular endothelial growth factor concentrations of >140 pg/mL may indicate insufficient oxygen delivery to tissues and may serve as a marker of the need for transfusion or of tissue hypoxia in other diseases.

Current controversies in the management of the anemia of prematurity

Preterm infants, especially those with extremely low birth weight (ELBW) are exposed to frequent blood draws as part of their care in the neonatal intensive care unit. ELBW infants develop the anemia of prematurity (AOP), a hypo-proliferative anemia marked by inadequate production of erythropoietin (Epo). Treatment of AOP includes red blood cell transfusions, which are given to preterm infants based on indications and guidelines (hematocrit/hemoglobin levels, ventilation and oxygen need, apneas and bradycardias, poor weight gain) that are relatively non-specific. In this article we review recent studies evaluating transfusion guidelines, discuss ways to decrease phlebotomy losses and examine the use of red cell growth factors such as Epo in preventing and treating anemia in preterm infants.

Neonatal transfusion practice

Many previously widely accepted neonatal transfusion practices are changing as neonatologists become more aware of the risks to their patients of multiple blood product transfusions. Recent literature and research on neonatal transfusion practice are here reviewed, and practical guidelines and trigger thresholds for blood products commonly used in neonatal medicine are proposed.

Hemodynamic changes in anemic premature infants: are we allowing the hematocrits to fall too low?

OBJECTIVE

Currently, many nurseries allow hematocrits to fall to <21% in apparently "stable" premature infants before considering a blood transfusion. We evaluated clinical changes and hemodynamic changes by echocardiogram in "stable" anemic premature infants before, during, and after transfusion.

METHODS

"Stable" premature infants (< or =32 weeks' gestation) who were to receive transfusions (2 aliquots of 10 mL/kg packed red blood cells, 12 hours apart) were eligible for prospective enrollment. Cardiac function by echocardiography and vital signs were measured 4 times: 1 to 3 hours before and 2 to 4 hours after the initial aliquot and 4 to 7 hours and 27 to 34 hours after the second aliquot. Infants were grouped prospectively according to pretransfusion hematocrit ranges for analysis: < or =21% (low), 22% to 26% (mid), and > or =27% (high).

RESULTS

Thirty-two infants were enrolled. No differences were observed between the groups in sex, birth weight, postconceptional age, or postnatal weight at enrollment. Before transfusion, low- and mid-range groups had higher left ventricular end systolic and diastolic diameters, in comparison with high range. Low range had increased stroke volume in comparison with the high-range group. These changes persisted after transfusion. Mean diastolic blood pressure rose and peak velocity in the aorta fell in the low-range group after transfusion. Pretransfusion hematocrit was correlated with but poorly predictive of echocardiographic measurements. Infants with inappropriate weight gain had increased ventricular end diastolic diameters, consistent with congestive heart failure.

CONCLUSIONS

Apparently "stable" anemic premature infants may be in a clinically unrecognized high cardiac output state, and some echocardiographic measurements do not improve within 48 hours after transfusion. The benefits of transfusion practices guided by measures of cardiac function should be evaluated.

Human recombinant erythropoietin in the prevention and treatment of anemia of prematurity

Human recombinant erythropoietin has been studied extensively as treatment for a variety of anemias. Since in vitro studies showed the primary etiology of the anemia of prematurity to be insufficient serum erythropoietin concentrations, clinical trials have evaluated the administration of human recombinant erythropoietin to preterm infants to treat this indication. These studies were followed by pharmacokinetic determinations in animal models and preterm infants, which revealed that preterm infants required greater doses of human recombinant erythropoietin because of a more rapid clearance and greater volume of distribution. Recent studies have focused on the administration of human recombinant erythropoietin in the first weeks of life to alleviate the anemia caused by excessive phlebotomy losses, and to prevent the anemia of prematurity. In addition, human recombinant erythropoietin has been tried clinically in a variety of neonatal populations in an attempt to decrease or eliminate transfusions. Although much information has been accumulated about the clinical use of human recombinant erythropoietin in preterm infants over the last 15 years, many questions remain unanswered. The evolution of clinical practice in the care of extremely low birthweight infants continues to affect the number of transfusions. It is likely that human recombinant erythropoietin administration in combination with instituting rigorous transfusion guidelines and decreasing phlebotomy losses will have the greatest impact in decreasing transfusion requirements in all preterm and term neonates, regardless of the etiology of their anemia.

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.

The use of erythropoietin in neonates

Although much information has been accumulated about the clinical use of Epo in preterm infants, many questions remain unanswered. The evolution of clinical practice in the care of extremely ill, preterm infants continues to affect the number of transfusions required during hospitalization. Decreasing phlebotomy losses and instituting standardized transfusion guidelines have both been shown significantly to decrease the transfusion requirements of preterm infants. The administration of Epo likely decreases transfusion need even further; however, the direct impact of each of these actions has not been studied prospectively. It is likely that the combination of instituting rigorous and standardized transfusion guidelines, decreasing phlebotomy losses, and the appropriate use of Epo will have the greatest impact in decreasing transfusion requirements in all preterm and term neonates, regardless of the cause of their anemia.

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.

Neonatal laboratory blood sampling: comparison of results from arterial catheters with those from an automated capillary device

PURPOSE

To compare neonatal laboratory results from capillary blood samples drawn using the Tenderfoot automated capillary sampling device with those drawn through arterial catheters.

DESIGN

Prospective, paired comparisons of laboratory results from capillary and arterial blood.

SAMPLE

Twenty-one infants being cared for in an NICU and having indwelling arterial catheters through which a variety of predominantly glucose-containing fluids were being administered.

MAIN OUTCOME VARIABLES

Statistical comparisons of paired capillary and arterial results of pH, PO2, PCO2, lactate, sodium, potassium, ionized calcium, and hematocrit.

RESULTS

No capillary-arterial differences were observed for pH, PCO2, lactate, or sodium. Although capillary results were slightly, but significantly (p < .01), higher for potassium (+0.4 mEq/liter), ionized calcium (+0.47 mg/dl), and hematocrit (+4 percent), these differences fell within acceptable Clinical Laboratories Improvement Act (CLIA) performance criteria. Markedly lower PO2 (-30.2 mmHg) and glucose (-61 mg/dl) values were observed with capillary sampling. With the exception of results for PaO2 and plasma glucose, capillary blood drawn using the Tenderfoot automated device yields laboratory results comparable to those from blood drawn from arterial catheters as assessed by CLIA performance criteria.

Lowering the hemoglobin threshold for transfusion in coronary artery bypass procedures: effect on patient outcome

BACKGROUND

There is controversy regarding the application of transfusion triggers in cardiac surgery. The goal of this study was to determine if lowering the hemoglobin threshold for red cell (RBC) transfusion to 8 g per dL after coronary artery bypass graft surgery would reduce blood use without adversely affecting patient outcome.

STUDY DESIGN AND METHODS

Consecutive patients (n = 428) undergoing elective primary coronary artery bypass graft surgery were randomly assigned to two groups: study patients (n = 212) received RBC transfusions in the postoperative period if the Hb level was < 8 g per dL or if predetermined clinical conditions required RBC support, and control patients (n = 216) were treated according to individual physician's orders (hemoglobin levels < 9 g/dL as the institutional guideline). Multiple demographic, procedure-related, transfusion, laboratory, and outcome data were analyzed. Questionnaires were administered for patient self-assessment of fatigue and anemia.

RESULTS

Preoperative and operative clinical characteristics, as well as the intraoperative transfusion rate, were similar for both groups. There was a significant difference between the postoperative RBC transfusion rates in study (0.9 +/- 1.5 RBC units) and control (1.4 +/- 1.8 RBC units) groups (p = 0.005). There was no difference in clinical outcome, including morbidity and mortality rates, in the two groups; group scores for self-assessment of fatigue and anemia were also similar.

CONCLUSIONS

A lower Hb threshold of 8 g per dL does not adversely affect patient outcome. Moreover, RBC resources can be saved without increased risk to the patient.

Erythropoietin to prevent and treat the anemia of prematurity

Human recombinant erythropoietin was first cloned in 1985, and is currently available for clinical use for a variety of anemias. Following successful clinical trials using erythropoietin to treat adults with the anemia of end-stage renal disease, the first clinical trial evaluating the use of erythropoietin in preterm infants to treat anemia was published in 1990. Since that initial report, numerous clinical trials have reported various levels of success in the treatment of this anemia. Most recently, erythropoietin has been used in the first weeks of life in an attempt to prevent the anemia of prematurity. This review describes mechanisms of erythropoiesis in the fetus and neonate, and focuses on recent clinical trials evaluating the use of erythropoietin to prevent and treat anemia in preterm infants.

Red blood cell transfusions for preterm infants: the role of evidence-based medicine

Increasingly clinicians attempt to base decisions regarding patient management on the results of clinical studies in addition to expert opinion and their own practical experience. In this article, the author reviews the published studies available to assist clinicians to make evidence-based decisions in three topics related to small volume red blood cell (RBC) transfusions for preterm infants; namely, studies examining the effects of RBC transfusions on possible symptoms of anemia such as tachypnea, apnea or other cardiorespiratory irregularities, studies investigating the collection and transfusion of umbilical cord blood and finally studies addressing the duration of storage and use of additive solutions for RBCs for transfusion to neonates. Based on the review of these studies, guidelines for small volume RBC transfusions in preterm infants are suggested.

Association between blood lactate and acid-base status and mortality in ventilated babies

AIM

To investigate the relation between common acid-base parameters and blood lactate concentrations and their prognostic importance in sick, ventilated neonates.

METHODS

Two hundred and seventy eight serial simultaneous measurements of arterial acid-base status and blood lactate concentrations were carried out in 75 mechanically ventilated neonates with indwelling arterial catheters (gestational age and birthweight, median (range) -29 (23-40) weeks, and 1340 (550-4080) g, respectively).

RESULTS

There were no correlations between arterial blood lactate and pH and base excess within subjects (r = 0.07 and r = -0.06, respectively) and only weakly positive but clinically irrelevant positive correlations between subjects (r = 0.28 and r = 0.27) in this group. Even in those infants who had not received any bicarbonate before their initial measurements (n = 48), there were no correlations between initial blood lactate concentrations and pH (r = 0.27), base excess (r = 0.17), or serum bicarbonate concentrations (r = -0.18). There was no relation between peak lactate concentration (PLC) and base excess (r = 0.16), and only a weak correlation between peak lactate concentration (PLC) and pH (r = 0.28). Negative base excess was an insensitive indicator of raised lactate concentrations. Only two out of 33 (6%) instances of hyperlactataemia (lactate > 2.5 mmol/l) would have been identified with a base excess < -10 mmol/l as a cutoff. Lower cutoff values of base excess or pH performed no better. Raised lactate concentrations were associated with increased mortality at all levels. While six of 53 (11%) infants with a PLC < 2.5 mmol/l died, this proportion increased to four of 15 (27%) with a PLC between 2.5-5.0 mmol/l, and four of seven (57%) with a PLC > 5.0 mmol/l. Infants showing little rise or a substantial fall in blood lactate fared better than those with persistently raised values. A clinically important increase in blood lactate preceded the development of clinical markers of deterioration and complications in six infants.

CONCLUSIONS

Contrary to popular belief, pH or base excess cannot be used as proxy measures for blood lactate concentration, and independent measurement of the latter are needed. Blood lactate concentrations may provide an early warning signal and important prognostic information in ill, ventilated neonates. In this regard, serial measurements of blood lactate are more useful than a single value.

Do cardiac output and serum lactate levels indicate blood transfusion requirements in anemia of prematurity?

BACKGROUND

Whether and when to transfuse in anemia of prematurity is highly controversial. Some authors suggest transfusions simply if the hemoglobin (Hb) level is below a defined normal range. Others propose the use of clinical or laboratory parameters in anemic patients to decide whether to transfuse or not.

HYPOTHESIS

A decreasing amount of circulating Hb should cause a compensatory increase in cardiac output (CO) and an increase in arterial serum lactate.

MATERIALS AND METHODS

In 56 anemic preterm infants (not in respiratory or hemodynamic failure) we analyzed CO after the first week of life using a Doppler sonographic method. At the same time serum lactate levels, Hb levels and oxygen saturation were registered. Nineteen of these patients were given transfusion when they demonstrated clinical signs of anemia by tachycardia > 180/min, tachypnea, retractions, apneas and centralization (group 2). The remaining 37 patients were not transfused (group 1). Serum lactate, CO, heart rate (HR), oxygen delivery, respiratory rate, capillary refill and Hb were analyzed in both groups and in group 2 before and 12-24 h after transfusion. Data between groups 1 and 2 and in group 2 before and after transfusion were compared.

RESULTS

In the 56 patients studied no linear correlation between Hb and CO or between Hb and serum lactate was found. Nor could any correlation be demonstrated between the other variables studied. Examining the subgroups separately, a negative linear correlation was demonstrated between serum lactate and oxygen delivery in group 2. No other significant correlations were detected. However, when the pre- and post-transfusion data were compared in group 2 (increase of Hb from 9.45 (SD 3.44) to 12.5 (SD 3.8) g/100 ml), the CO decreased from 281.3 (SD 162.6) to 224 (SD 95.7) ml/kg per min (p < 0.01) and serum lactate decreased significantly from 3.23 mmol/l (SD 2.07) before to 1.71 (SD 0.83) after transfusion. Oxygen delivery was 35.8 (+/- 0.19) ml/kg per min group 1, 27.8 (+/- 0.05) pre- and 43.4 (+/- 0.07) post-transfusion in group 2 (p < 0.01).

CONCLUSIONS

CO measurements and serum lactate levels add little information to the decision-making process for blood transfusions, as neither CO nor serum lactate levels correlate with HB levels in an otherwise asymptomatic population of preterm infants. In infants where the indication for blood transfusion is made based on traditionally accepted clinical criteria, serum lactate is an additional laboratory indicator of impaired oxygenation, as it correlates significantly with oxygen delivery. A significant lower oxygen delivery in patients in whom blood transfusion is indicated and an increase in oxygen induced by transfusion demonstrate the value of these criteria in identifying preterm infants who benefit from transfusion.

Routine measurements of umbilical artery lactate levels in the prediction of perinatal outcome

OBJECTIVE

Our purpose was to compare lactate levels with acid-base balance in the umbilical artery with respect to the prediction of pregnancy outcome.

STUDY DESIGN

A prospective study of 4045 cord samples was performed. Lactate was measured with a new method that requires 5 microliters of blood and provides the result within 1 minute.

RESULTS

The umbilical artery lactate concentrations were significantly elevated in instrumental deliveries (2.65 +/- 1.2 mmol/L) and in emergency cesarean sections (2.44 +/- 1.7 mmol/L) compared with spontaneous vaginal delivery (1.87 +/- 0.94 mmol/L) (p < 0.001, p < 0.001). Lactate correlated significantly to fetal pH, hemoglobin, base deficit, PCO2, and HCO3-. Lactate was comparable to pH and base deficit in sensitivity, specificity, and positive and negative predictive values in relation to morbidity and mortality.

CONCLUSION

Umbilical artery lactate concentration and acid-base balance predicted perinatal outcomes with similar efficacies; however, its simplicity makes lactate analysis an interesting alternative in obstetric care.