Cerebral Oximetry in Ugandan Children With Severe Anemia: Clinical Categories and Response to Transfusion

Neurocognitive impairment in Ugandan children with sickle cell anemia compared to sibling controls: a cross-sectional study

Introduction

The neurocognitive functions in Ugandan children aged 1-12 years with sickle cell anemia (SCA) were compared to their non-SCA siblings to identify risk factors for disease-associated impairment.

Methods

This cross-sectional study of the neurocognitive functions in children with SCA (N = 242) and non-SCA siblings (N = 127) used age- and linguistically appropriate standardized tests of cognition, executive function, and attention for children ages 1-4 and 5-12. Test scores were converted to locally derived age-normalized z-scores. The SCA group underwent a standardized stroke examination for prior stroke and transcranial Doppler ultrasound to determine stroke risk by arterial flow velocity.

Results

The SCA group was younger than their siblings (mean ages 5.46 ± 3.0 vs. 7.11 ± 3.51 years, respectively; p < 0.001), with a lower hemoglobin concentration (7.32 ± 1.02 vs. 12.06 ± 1.42, p < 0.001). The overall cognitive SCA z-scores were lower, -0.73 ± 0.98, vs. siblings, -0.25 ± 1.12 (p < 0.001), with comparable findings for executive function of -1.09 ± 0.94 vs. -0.84 ± 1.26 (p = 0.045), respectively. The attention z-scores for ages 5-12 for the SCA group and control group were similar: -0.37 ± 1.4 vs. -0.11 ± 0.17 (p = 0.09). The overall differences in SCA status were largely driven by the older age group, as the z-scores in the younger subsample did not differ from controls. Analyses revealed the strongest predictors of poor neurocognitive outcomes among the SCA sample to be the disease, age, and prior stroke (each p < 0.001). The impacts of anemia and SCA were indistinguishable.

Discussion

Neurocognitive testing in children with SCA compared to non-SCA siblings revealed poorer SCA-associated functioning in children older than age 4. The results indicate the need for trials assessing the impact of disease modification on children with SCA.

Neurocognitive Impairment in Ugandan Children with Sickle Cell Anemia Compared to Sibling Controls: A cross-sectional study

Introduction

Neurocognitive function in Ugandan children aged 1-12 years with sickle cell anemia (SCA) were compared to their non-SCA siblings to identify risk factors for disease-associated impairment.

Methods

This cross-sectional neurocognitive function study of children with SCA (N=242) and non-SCA siblings (N=127) used age- and linguistically-appropriate standardized tests of cognition, executive function and attention for children ages 1-4 and 5-12 years. Test scores were converted to locally derived age-normalized z-scores. The SCA group underwent standardized stroke examination for prior stroke and transcranial doppler ultrasound (TCD) to determine stroke risk by arterial flow velocity.

Results

The SCA group was younger than siblings (mean ages 5.46±3.0 versus 7.11±3.51 years, respectively; p <.001), with lower hemoglobin concentration (7.32±1.02 vs. 12.06±1.42, p <.001). Overall cognitive SCA z-scores were lower: -0.73 ±0.98 vs. siblings -0.25 ±1.12 (p<.001), with comparable findings for executive function of -1.09±0.94 versus -0.84±1.26 (p=0.045), respectively. Attention z-scores for ages 5-12 for the SCA group and controls were similar: -0.37±1.4 vs. -0.11±0.17 (p=.09). Overall differences by SCA status were largely driven by the older age group, as z-scores in the younger sub-sample did not differ from controls. Analyses revealed the strongest predictors of poor neurocognitive outcomes among the SCA sample to be the disease, age and prior stroke (each p<.001). Impact from anemia and SCA were indistinguishable.

Discussion

Neurocognitive testing in children with SCA compared to non-SCA siblings revealed poorer SCA-associated functioning in children older than age 4. Results indicate need for trials assessing impact from disease modification for children with SCA.

Increased brain microvascular hemoglobin concentrations in children with cerebral malaria

Brain swelling is associated with death from cerebral malaria, but it is unclear whether brain swelling is caused by cerebral edema or vascular congestion-two pathological conditions with distinct effects on tissue hemoglobin concentrations. We used near-infrared spectroscopy (NIRS) to noninvasively study cerebral microvascular hemoglobin concentrations in 46 Malawian children with cerebral malaria. Cerebral malaria was defined by the presence of the malaria parasite Plasmodium falciparum on a blood smear, a Blantyre coma score of 2 or less, and retinopathy. Children with uncomplicated malaria (n = 33) and healthy children (n = 29) were enrolled as comparators. Cerebral microvascular hemoglobin concentrations were higher among children with cerebral malaria compared with those with uncomplicated malaria [median (25th, 75th): 145.2 (95.2, 190.0) μM versus 82.9 (65.7, 105.4) μM, P = 0.008]. Cerebral microvascular hemoglobin concentrations correlated with brain swelling score determined by MRI (r = 0.37, P = 0.03). Fluctuations in cerebral microvascular hemoglobin concentrations over a 30-min time period were characterized using detrended fluctuation analysis (DFA). DFA determined self-similarity of the cerebral microvascular hemoglobin concentration signal to be lower among children with cerebral malaria compared with those with uncomplicated malaria [0.63 (0.54, 0.70) versus 0.91 (0.82, 0.94), P < 0.0001]. The lower self-similarity of the hemoglobin concentration signal in children with cerebral malaria suggested impaired regulation of cerebral blood flow. The elevated cerebral tissue hemoglobin concentration and its correlation with brain swelling suggested that excess blood volume, potentially due to vascular congestion, may contribute to brain swelling in cerebral malaria.

Quantifying the Cerebral Hemometabolic Response to Blood Transfusion in Pediatric Sickle Cell Disease With Diffuse Optical Spectroscopies

Red blood cell transfusions are common in patients with sickle cell disease who are at increased risk of stroke. Unfortunately, transfusion thresholds needed to sufficiently dilute sickle red blood cells and adequately restore oxygen delivery to the brain are not well defined. Previous work has shown that transfusion is associated with a reduction in oxygen extraction fraction and cerebral blood flow, both of which are abnormally increased in sickle patients. These reductions are thought to alleviate hemometabolic stress by improving the brain's ability to respond to increased metabolic demand, thereby reducing susceptibility to ischemic injury. Monitoring the cerebral hemometabolic response to transfusion may enable individualized management of transfusion thresholds. Diffuse optical spectroscopies may present a low-cost, non-invasive means to monitor this response. In this study, children with SCD undergoing chronic transfusion therapy were recruited. Diffuse optical spectroscopies (namely, diffuse correlation spectroscopy combined with frequency domain near-infrared spectroscopy) were used to quantify oxygen extraction fraction (OEF), cerebral blood volume (CBV), an index of cerebral blood flow (CBF_i), and an index of cerebral oxygen metabolism (CMRO_2i) in the frontal cortex immediately before and after transfusion. A subset of patients receiving regular monthly transfusions were measured during a subsequent transfusion. Data was captured from 35 transfusions in 23 patients. Transfusion increased median blood hemoglobin levels (Hb) from 9.1 to 11.7 g/dL (p < 0.001) and decreased median sickle hemoglobin (HbS) from 30.9 to 21.7% (p < 0.001). Transfusion decreased OEF by median 5.9% (p < 0.001), CBFi by median 21.2% (p = 0.020), and CBV by median 18.2% (p < 0.001). CMRO_2i did not statistically change from pre-transfusion levels (p > 0.05). Multivariable analysis revealed varying degrees of associations between outcomes (i.e., OEF, CBF_i, CBV, and CMRO_2i), Hb, and demographics. OEF, CBF_i, and CBV were all negatively associated with Hb, while CMRO_2i was only associated with age. These results demonstrate that diffuse optical spectroscopies are sensitive to the expected decreases of oxygen extraction, blood flow, and blood volume after transfusion. Diffuse optical spectroscopies may be a promising bedside tool for real-time monitoring and goal-directed therapy to reduce stroke risk for sickle cell disease.

Prevalence and significance of anaemia in childhood bacterial meningitis: a secondary analysis of prospectively collected data from clinical trials in Finland, Latin America and Angola

OBJECTIVES

To describe the prevalence and severity of anaemia and to examine its associations with outcome in children with bacterial meningitis (BM).

DESIGN

Secondary analysis of descriptive data from five randomised BM treatment trials.

SETTING

Hospitals in Finland, Latin America and Angola.

PARTICIPANTS

Consecutive children from 2 months to 15 years of age admitted with BM and who had haemoglobin (Hb) measured on admission.

OUTCOME MEASURES

Prevalence and degree of anaemia using the WHO criteria, and their associations with recovery with sequelae or death.

RESULTS

The median Hb was 11.8 g/dL in Finland (N=341), 9.2 g/dL in Latin America (N=597) and 7.6 g/dL in Angola (N=1085). Of the children, 79% had anaemia, which was severe in 29%, moderate in 58% and mild in 13% of cases. Besides study area, having anaemia was independently associated with age <1 year, treatment delay >3 days, weight-for-age z-score <-3 and other than meningococcal aetiology. Irrespective of the study area, anaemia correlated with the markers of disease severity. In children with severe to moderate anaemia (vs mild or no anaemia), the risk ratio for death was 3.38 and for death or severe sequelae was 3.07.

CONCLUSION

Anaemia, mostly moderate, was common in children with BM, especially in Angola, in underweight children, among those with treatment delay, and in pneumococcal meningitis. Poor outcome was associated with anaemia in all three continents.

TRIAL REGISTRATION NUMBER

The registration numbers of Angolan trials were ISRCTN62824827 and NCT01540838.

Measurement of Tissue Oxygen as a Novel Approach to Optimizing Red Blood Cell Quality Assessment

The effectiveness of blood transfusions can be impacted by storage and extensive processing techniques that involve treatment of red blood cells (RBCs) with pathogen reduction technologies (e.g., UV-light and chemical treatment), ex vivo stem cell derivation/maturation methods, and bioengineering of RBCs using nanotechnology. Therefore, there is a need to have methods that assess the evaluation of the effectiveness of transfusions to achieve their intended purpose: to increase oxygenation of critical tissues. Consequently, there has been intense interest in the development of techniques targeted at optimizing the assessment of RBC quality in preclinical and clinical settings. We provide a critical assessment of the ability of currently used methods to provide unambiguous information on oxygen levels in tissues and conclude that they cannot do this. This is because they are based on surrogates for the true goal of transfusion, which is to increase oxygenation of critical organs. This does not mean that they are valueless, but it does indicate that other methods are needed to provide direct measurements of oxygen in tissues. We report here on the initial results of a method that can provide direct assessment of the impact of the transfusion on tissue oxygen: EPR oximetry. It has the potential to provide such information in both preclinical and clinical settings for the assessment of blood quality posttransfusion.

Near Infrared Spectroscopy in Anemia Detection and Management: A Systematic Review

Red cell transfusions are intended to improve oxygen delivery to tissues. Although studies comparing hemoglobin concentration triggers for transfusion have been done, the hemoglobin threshold for clinical benefit remains uncertain. Direct measurement of tissue oxygenation with non-invasive near infrared spectroscopy has been proposed as a more physiological transfusion trigger, but its clinical role remains unclear. This systematic review examined the role of near infrared spectroscopy for detection of anemia and guiding transfusion decisions. Abstracts were identified up until May 2019 through searches of PubMed, EMBASE and The Web of Science. There were 69 studies meeting the inclusion criteria, most (n = 65) of which were observational studies. Tissue oxygen saturation had been measured in a wide range of clinical settings, with neonatal intensive care (n = 26) and trauma (n = 7) being most common. Correlations with hemoglobin concentration and tissue oxygenation were noted and there were correlations between changes in red cell mass and changes in tissue oxygenation through blood loss or transfusion. The value of tissue oxygenation for predicting transfusion was determined in only four studies, all using muscle oxygen saturation in the adult trauma setting. The overall sensitivity was low at 34% (27%-42%) and while it had better specificity at 78% (74%-82%), differing and retrospective approaches create a high level of uncertainty with respect to these conclusions. There were four prospective randomized studies involving 540 patients, in cardiac and neurological surgery and in neonates that compared near infrared spectroscopy to guide transfusion decisions with standard practice. These showed a reduction in the number of red cells transfused per patient (OR: 0.44 [0.09-0.79]), but not the number of patients who received transfusion (OR: 0.71 [0.46-1.10]), and no change in clinical outcomes. Measuring tissue oxygen saturation has potential to help guide transfusion; however, there is a lack of data upon which to recommend widespread implementation into clinical practice. Standardization of measurements is required and greater research into levels at which tissue oxygenation may lead to adverse clinical outcomes would help in the design of future clinical trials.

Severe low cerebral oximetry in difficult cardiopulmonary bypass weaning of low body-weight infant: a case report and literature review

Background

For infants undergoing complex cardiac surgery, hemodynamic management after cardiopulmonary bypass (CPB) is challenging because of severe myocardial edema, vasomotor dysfunction and weak tolerance to a change in blood volume. More importantly, the lack of availability of equipment for advanced monitoring, such as transesophageal echocardiography or transthoracic echocardiography, restricts the accurate assessment of hemodynamics.

Case presentation

This is a case of severe hypotension and non-detectable pulse oxygen saturation (SpO₂) after CPB in a low-weight infant who had normal blood pressure and oxygen saturation before surgery. Epinephrine and milrinone were administered with cerebral oximetry monitoring rather than blood pressure measurements because cerebral oximetry was more responsive to treatment than blood pressure. Under the guidance of cerebral oximetry, the infant was successfully weaned from CPB and recovered after surgery without adverse neurological events.

Conclusions

For infants who develop refractory hypotension and failure in SpO₂ monitoring during the CPB weaning period, cerebral oximetry provides an index for assessing brain perfusion and valuable guidance for appropriate inotropic treatment.

Effect of anemia on muscle oxygen saturation during submaximal exercise

BACKGROUND

Objective measures to assess the need for transfusion in chronic anemia are lacking. Near-infrared spectroscopy may be used, but there is wide variability. Assessment of muscle oxygen saturation (SmO₂ ) during exercise could be used to measure the impact of anemia on performance of everyday activities.

STUDY DESIGN AND METHODS

Hematology patients and controls were recruited to undertake a 6-minute walk test (6MWT) and a 20-second isometric handgrip exercise. Muscle oxygen saturation in the exercising muscles was measured before and during exercise. Changes in saturation during exercise were described. Correlations between identified variables, hemoglobin concentration, and 6MWT distance were undertaken. The effect of transfusion was assessed on a transfused subset.

RESULTS

There were 95 sets of exercises conducted in 74 participants. Baseline SmO₂ correlated with hemoglobin concentration and negatively with 6MWT distance. Paradoxically, a higher hemoglobin was associated with a greater SmO₂ fall during the 6MWT, likely due to greater consumption from improved walk distances. The fall in SmO₂ was independent of hemoglobin during isometric contraction, although levels were lower during contraction due to the lower starting SmO₂ . There was a longer time to peak SmO₂ during recovery following isometric exercise in anemia. There were 17 paired tests following a change in hemoglobin, with SmO₂ not predicting improvement in those who had improved exercise capacity.

CONCLUSION

While baseline SmO₂ correlated with hemoglobin concentration, the correlation was not strong enough to predict transfusion requirements. Recovery after isometric forearm contraction correlated with hemoglobin and warrants further investigation.

Effects of dietary intake and nutritional status on cerebral oxygenation in patients with chronic kidney disease not undergoing dialysis: A cross-sectional study

BACKGROUND

Dietary management is highly important for the maintenance of renal function in patients with chronic kidney disease (CKD). Cerebral oxygen saturation (rSO2) was reportedly associated with the estimated glomerular filtration rate (eGFR) and cognitive function. However, data concerning the association between cerebral rSO2 and dietary intake of CKD patients is limited.

METHODS

This was a single-center observational study. We recruited 67 CKD patients not undergoing dialysis. Cerebral rSO2 was monitored using the INVOS 5100c oxygen saturation monitor. Energy intake was evaluated by dietitians based on 3-day meal records. Daily protein and salt intakes were calculated from 24-h urine collection.

RESULTS

Multivariable regression analysis showed that cerebral rSO2 was independently associated with energy intake (standardized coefficient: 0.370) and serum albumin concentration (standardized coefficient: 0.236) in Model 1 using parameters with p < 0.10 in simple linear regression analysis (body mass index, Hb level, serum albumin concentration, salt and energy intake) and confounding factors (eGFR, serum sodium concentration, protein intake), and the energy/salt index (standardized coefficient: 0.343) and Hb level (standardized coefficient: 0.284) in Model 2 using energy/protein index as indicated by energy intake/protein intake and energy/salt index by energy intake/salt intake in place of salt, protein and energy intake.

CONCLUSIONS

Cerebral rSO2 is affected by energy intake, energy/salt index, serum albumin concentration and Hb level. Sufficient energy intake and adequate salt restriction is important to prevent deterioration of cerebral oxygenation, which might contribute to the maintenance of cognitive function in addition to the prevention of renal dysfunction in CKD patients.

Can molecular markers of oxygen homeostasis and the measurement of tissue oxygen be leveraged to optimize red blood cell transfusions?

PURPOSE OF REVIEW

The clinical indication for transfusing red blood cells (RBCs) is to restore or maintain adequate oxygenation of respiring tissue. Oxygen (O2) transport, delivery, and utilization following transfusion are impacted by perfusion, hemoglobin (Hb) allosteric saturation/desaturation, and the concentration of tissue O2. Bioavailable O2 maintains tissue utilization and homeostasis; therefore, measuring imbalances in supply and demand could be valuable to assessing blood quality and transfusion effectiveness. O2 homeostasis is critically intertwined with erythropoietic response in blood loss and anemia and the hormones that modulate iron mobilization and RBC production (e.g., erythropoietin, erythroferrone, and hepcidin) are intriguing markers for the monitoring of transfusion effectiveness in acute and chronic settings. The evaluation of RBC donor unit quality and the determination of RBC transfusion needs are emerging areas for biomarker development and minimally invasive O2 measurements.

RECENT FINDINGS

Novel methods for assessing circulatory and tissue compartment biomarkers of transfusion effectiveness are suggested. In addition, monitoring of tissue oxygenation by indirect and direct measurements of O2 is available and applied in experimental settings.

SUMMARY

Herein, we discuss tissue O2 homeostasis, related aspects of erythropoiesis, molecular markers and measurements of tissue oxygenation, all aimed at optimizing transfusion and assessing blood quality.

Electron paramagnetic resonance oximetry as a novel approach to monitor the effectiveness and quality of red blood cell transfusions

BACKGROUND

The goal of red blood cell transfusion is to improve tissue oxygenation. Assessment of red blood cell quality and individualised therapeutic needs can be optimised using direct oxygen (O₂) measurements to guide treatment. Electron paramagnetic resonance oximetry is capable of accurate, repeatable and minimally invasive measurements of tissue pO₂. Here we present preclinical proof-of-concept of the utility of electron paramagnetic resonance oximetry in an experimental setting of acute blood loss, transfusion, and post-transfusion monitoring.

MATERIALS AND METHODS

Donor rat blood was collected, leucocyte-reduced, and stored at 4 °C in AS-3 for 1, 7 and 14 days. Red blood cell morphology, O₂ equilibrium, p50 and Hill numbers from O₂ binding and dissociation curves were evaluated in vitro. Recipient rats were bled and maintained at a mean arterial pressure of 30-40 mmHg and hind limb muscle (biceps femoris) pO₂ at 25-50% of baseline. Muscle pO₂ was monitored continuously over the course of experiments to assess the effectiveness of red blood cell preparations at different stages of blood loss and restoration.

RESULTS

Red blood cell morphology, O₂ equilibrium and p50 values of intra-erythrocyte haemoglobin were significantly altered by refrigerated storage for both 7 and 14 days. Transfusion of red blood cells stored for 7 or 14 days demonstrated an equivalently impaired ability to restore hind limb muscle pO₂, consistent with in vitro observations and transfusion with albumin. Red blood cells refrigerated for 1 day demonstrated normal morphology, in vitro oxygenation and in vivo restoration of tissue pO₂.

DISCUSSION

Electron paramagnetic resonance oximetry represents a useful approach to assessing the quality of red blood cells and subsequent transfusion effectiveness.

Pathophysiology of Sickle Cell Disease

Since the discovery of sickle cell disease (SCD) in 1910, enormous strides have been made in the elucidation of the pathogenesis of its protean complications, which has inspired recent advances in targeted molecular therapies. In SCD, a single amino acid substitution in the β-globin chain leads to polymerization of mutant hemoglobin S, impairing erythrocyte rheology and survival. Clinically, erythrocyte abnormalities in SCD manifest in hemolytic anemia and cycles of microvascular vaso-occlusion leading to end-organ ischemia-reperfusion injury and infarction. Vaso-occlusive events and intravascular hemolysis promote inflammation and redox instability that lead to progressive small- and large-vessel vasculopathy. Based on current evidence, the pathobiology of SCD is considered to be a vicious cycle of four major processes, all the subject of active study and novel therapeutic targeting: ( a) hemoglobin S polymerization, ( b) impaired biorheology and increased adhesion-mediated vaso-occlusion, ( c) hemolysis-mediated endothelial dysfunction, and ( d) concerted activation of sterile inflammation (Toll-like receptor 4- and inflammasome-dependent innate immune pathways). These molecular, cellular, and biophysical processes synergize to promote acute and chronic pain and end-organ injury and failure in SCD. This review provides an exhaustive overview of the current understanding of the molecular pathophysiology of SCD, how this pathophysiology contributes to complications of the central nervous and cardiopulmonary systems, and how this knowledge is being harnessed to develop current and potential therapies.

Individual, maternal and household risk factors for anaemia among young children in sub-Saharan Africa: a cross-sectional study

OBJECTIVE

Anaemia affects the majority of children in sub-Saharan Africa (SSA). Previous studies of risk factors for anaemia have been limited by sample size, geography and the association of many risk factors with poverty. In order to measure the relative impact of individual, maternal and household risk factors for anaemia in young children, we analysed data from all SSA countries that performed haemoglobin (Hb) testing in the Demographic and Health Surveys.

DESIGN AND SETTING

This cross-sectional study pooled household-level data from the most recent Demographic and Health Surveys conducted in 27 SSA between 2008 and 2014.

PARTICIPANTS

96 804 children age 6-59 months.

RESULTS

The prevalence of childhood anaemia (defined as Hb <11 g/dL) across the region was 59.9%, ranging from 23.7% in Rwanda to 87.9% in Burkina Faso. In multivariable regression models, older age, female sex, greater wealth, fewer household members, greater height-for-age, older maternal age, higher maternal body mass index, current maternal pregnancy and higher maternal Hb, and absence of recent fever were associated with higher Hb in tested children. Demographic, socioeconomic factors, family structure, water/sanitation, growth, maternal health and recent illnesses were significantly associated with the presence of childhood anaemia. These risk factor groups explain a significant fraction of anaemia (ranging from 1.0% to 16.7%) at the population level.

CONCLUSIONS

The findings from our analysis of risk factors for anaemia in SSA underscore the importance of family and socioeconomic context in childhood anaemia. These data highlight the need for integrated programmes that address the multifactorial nature of childhood anaemia.

Cerebral Oximetry for Detecting High-mortality Risk Patients with Cryptococcal Meningitis

Background

Cryptococcus is the commonest cause of adult meningitis in Africa, with 50%–70% experiencing increased intracranial pressure. Cerebral oximetry is a noninvasive near-infrared spectroscopy technology to monitor percent regional cerebral tissue oxygenation (rSO₂). We assessed if cerebral oximetry predicts meningitis mortality.

Methods

We performed cerebral oximetry within 14 days of cryptococcal meningitis diagnosis on 121 Ugandans from April 2016 to September 2017. We evaluated baseline rSO₂ association with mortality by multivariable logistic regression and correlation with other clinical factors. We compared groups formed by initial rSO₂ <30% vs ≥30% for longitudinal change with mixed effects models. We measured change in %rSO₂ before and after lumbar puncture (LP).

Results

The median initial rSO₂ (interquartile range) was 36% (29%–42%), and it was <30% in 29% (35/121). For 30-day mortality, the unadjusted odds ratio (per 5% increase in rSO₂) was 0.73 (95% confidence interval [CI], 0.58 to 0.91; P = .005). Those with initial rSO₂ <30% had 3.4 (95% CI, 1.5 to 8.0) higher odds of 30-day mortality than those with initial rSO₂ ≥30%. Hemoglobin correlated with initial rSO₂ (rho = .54; P < .001), but rSO₂ did not correlate with pulse oximetry, intracranial pressure, cerebral perfusion pressure, or quantitative cerebrospinal fluid culture, and rSO₂ was unchanged pre/post–lumbar punctures. The longitudinal rSO₂ measurements change was 15% (95% CI, 12% to 18%) lower in the group with initial rSO₂ <30%.

Conclusions

Individuals with cryptococcal meningitis and low cerebral oximetry (rSO₂ < 30%) have high mortality. Cerebral oximetry may be useful as a prognostic marker of mortality. Targeted interventions to improve rSO₂ should be tested in trials to try to decrease mortality in meningitis.

Anatomical and Physiological Differences between Children and Adults Relevant to Traumatic Brain Injury and the Implications for Clinical Assessment and Care

General and central nervous system anatomy and physiology in children is different to that of adults and this is relevant to traumatic brain injury (TBI) and spinal cord injury. The controversies and uncertainties in adult neurotrauma are magnified by these differences, the lack of normative data for children, the scarcity of pediatric studies, and inappropriate generalization from adult studies. Cerebral metabolism develops rapidly in the early years, driven by cortical development, synaptogenesis, and rapid myelination, followed by equally dramatic changes in baseline and stimulated cerebral blood flow. Therefore, adult values for cerebral hemodynamics do not apply to children, and children cannot be easily approached as a homogenous group, especially given the marked changes between birth and age 8. Their cranial and spinal anatomy undergoes many changes, from the presence and disappearance of the fontanels, the presence and closure of cranial sutures, the thickness and pliability of the cranium, anatomy of the vertebra, and the maturity of the cervical ligaments and muscles. Moreover, their systemic anatomy changes over time. The head is relatively large in young children, the airway is easily compromised, the chest is poorly protected, the abdominal organs are large. Physiology changes—blood volume is small by comparison, hypothermia develops easily, intracranial pressure (ICP) is lower, and blood pressure normograms are considerably different at different ages, with potentially important implications for cerebral perfusion pressure (CPP) thresholds. Mechanisms and pathologies also differ—diffuse injuries are common in accidental injury, and growing fractures, non-accidental injury and spinal cord injury without radiographic abnormality are unique to the pediatric population. Despite these clear differences and the vulnerability of children, the amount of pediatric-specific data in TBI is surprisingly weak. There are no robust guidelines for even basics aspects of care in children, such as ICP and CPP management. This is particularly alarming given that TBI is a leading cause of death in children. To address this, there is an urgent need for pediatric-specific clinical research. If this goal is to be achieved, any clinician or researcher interested in pediatric neurotrauma must be familiar with its unique pathophysiological characteristics.

An observational study of the optimal placement of a cerebral oximeter probe to avoid the frontal sinus in children

The frontal sinus is an airspace behind the brow ridge in the skull and can affect the accuracy of the regional cerebral oxygen saturation measurements. We evaluated the optimal location for placement of a cerebral oximeter probe while avoiding the frontal sinus in pediatric patients. This retrospective observational study included 203 pediatric patients aged 3-17 years who had undergone brain computed tomography from November 2010 to December 2015. The patients were divided into five subgroups based on their age. The frontal sinus height was measured from the superior orbital rim. Pneumatization of the frontal sinus was not visible in 78% (3-5 years) and 22% (6-8 years) of the patients. The mean (SD) of the frontal sinus height was 5.9 (3.4), 9.5 (4.1), 14.0 (6.2) 18.6 (8.4), and 21.1 (7.9) mm in the 3-5, 6-8, 9-11, 12-14, and 15-17 year age-groups, respectively. Age was positively correlated with the frontal sinus height (r = 0.61, P < 0.001, 95% confidence interval [CI] 0.513-0.688). A frontal sinus height shorter than 1, 2, and 3 cm were seen in 10 of 11 (91%), 69 of 74 (94%), and 108 of 118 (90%) patients aged 3-5, 6-10, and 11-17 years, respectively. When oximeter probes are applied in pediatric patients, placement based on age can help avoid the frontal sinus.

Transfusion Decision Making in Pediatric Critical Illness

Transfusion decision making (TDM) in the critically ill requires consideration of: (1) anemia tolerance, which is linked to active pathology and to physiologic reserve, (2) differences in donor RBC physiology from that of native RBCs, and (3) relative risk from anemia-attributable oxygen delivery failure vs hazards of transfusion, itself. Current approaches to TDM (e.g. hemoglobin thresholds) do not: (1) differentiate between patients with similar anemia, but dissimilar pathology/physiology, and (2) guide transfusion timing and amount to efficacy-based goals (other than resolution of hemoglobin thresholds). Here, we explore approaches to TDM that address the above gaps.

Targeted treatment in severe traumatic brain injury in the age of precision medicine

In recent years, much progress has been made in our understanding of traumatic brain injury (TBI). Clinical outcomes have progressively improved, but evidence-based guidelines for how we manage patients remain surprisingly weak. The problem is that the many interventions and strategies that have been investigated in randomized controlled trials have all disappointed. These include many concepts that had become standard care in TBI. And that is just for adult TBI; in children, the situation is even worse. Not only is pediatric care more difficult than adult care because physiological norms change with age, but also there is less evidence for clinical practice. In this article, we discuss the heterogeneity inherent in TBI and why so many clinical trials have failed. We submit that a key goal for the future is to appreciate important clinical differences between patients in their pathophysiology and their responses to treatment. The challenge that faces us is how to rationally apply therapies based on the specific needs of an individual patient. In doing so, we may be able to apply the principles of precision medicine approaches to the patients we treat.

The impact of red blood cell storage duration on tissue oxygenation in cardiac surgery

OBJECTIVE

Although storage alters red blood cells, several recent, randomized trials found no differences in clinical outcomes between patients transfused with red blood cells stored for shorter versus longer periods of time. The objective of this study was to see whether storage impairs the in vivo ability of erythrocytes to traverse the microcirculation and deliver oxygen at the tissue level.

METHODS

A subset of subjects from a clinical trial of cardiac surgery patients randomized to receive transfusions of red blood cells stored ≤10 days or ≥21 days were assessed for thenar eminence and cerebral tissue hemoglobin oxygen saturation (S_tO₂) via the use of near-infrared spectroscopy and sublingual microvascular blood flow via side-stream darkfield videomicroscopy.

RESULTS

Among 55 subjects, there was little change in the primary endpoint (thenar eminence S_tO₂ from before to after transfusion of one unit) and the change was similar in the 2 groups: +1.7% (95% confidence interval, -0.3, 3.8) for shorter-storage and +0.8% (95% confidence interval, -1.1, 2.9) for longer-storage; P = .61). Similarly, no significant differences were observed for cerebral S_tO₂ or sublingual microvascular blood flow. These parameters also were not different from preoperatively to 1 day postoperatively, reflecting the absence of a cumulative effect of all red blood cell units transfused during this period.

CONCLUSIONS

There were no differences in thenar eminence or cerebral S_tO₂, or sublingual microcirculatory blood flow, in cardiac surgery patients transfused with red blood cells stored ≤10 days or ≥21 days. These results are consistent with the clinical outcomes in the parent study, which also did not differ, indicating that storage may not impair oxygen delivery by red blood cells in this setting.