The effect of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in newborn infants investigated by near infrared spectrophotometry

Differential responses of cerebral and renal oxygenation to altered perfusion conditions during experimental cardiopulmonary bypass in sheep

We tested whether the brain and kidney respond differently to cardiopulmonary bypass (CPB) and to changes in perfusion conditions during CPB. Therefore, in ovine CPB, we assessed regional cerebral oxygen saturation (rSO2 ) by near-infrared spectroscopy and renal cortical and medullary tissue oxygen tension (PO2 ), and, in some protocols, brain tissue PO2 , by phosphorescence lifetime oximetry. During CPB, rSO2 correlated with mixed venous SO2 (r = 0.78) and brain tissue PO2 (r = 0.49) when arterial PO2 was varied. During the first 30 min of CPB, brain tissue PO2 , rSO2 and renal cortical tissue PO2 did not fall, but renal medullary tissue PO2 did. Nevertheless, compared with stable anaesthesia, during stable CPB, rSO2 (66.8 decreasing to 61.3%) and both renal cortical (90.8 decreasing to 43.5 mm Hg) and medullary (44.3 decreasing to 19.2 mm Hg) tissue PO2 were lower. Both rSO2 and renal PO2 increased when pump flow was increased from 60 to 100 mL kg-1  min-1 at a target arterial pressure of 70 mm Hg. They also both increased when pump flow and arterial pressure were increased simultaneously. Neither was significantly altered by partially pulsatile flow. The vasopressor, metaraminol, dose-dependently decreased rSO2 , but increased renal cortical and medullary PO2 . Increasing blood haemoglobin concentration increased rSO2 , but not renal PO2 . We conclude that both the brain and kidney are susceptible to hypoxia during CPB, which can be alleviated by increasing pump flow, even without increasing arterial pressure. However, increasing blood haemoglobin concentration increases brain, but not kidney oxygenation, whereas vasopressor support with metaraminol increases kidney, but not brain oxygenation.

Differences in Cerebral Tissue Oxygenation in Preterm Neonates Receiving Adult or Cord Blood Red Blood Cell Transfusions

Importance

Repeated transfusions in preterm neonates with anemia of prematurity replace fetal hemoglobin (HbF) with adult Hb (HbA), which has a low oxygen affinity. The reduction of HbF is associated with a higher incidence of retinopathy of prematurity (ROP).

Objective

To assess whether HbF and HbA are differently associated with cerebral tissue oxygenation in preterm neonates.

Design, Setting, and Participants

This cohort study was a single-center, pilot study on cerebral oxygenation kinetics in preterm neonates with a gestational age between 24.0 weeks and 27.9 weeks who were admitted to the neonatal intensive care unit of Policlinico Universitario A. Gemelli IRCCS from December 27, 2021, to May 15, 2023. This study was ancillary to the ongoing, double-blind, multicenter Umbilical or Adult Donor Red Blood Cells in Extremely Low Gestational Age Neonates and Retinopathy of Prematurity (BORN) randomized clinical trial. The BORN trial outcome was ROP severity in neonates randomized to receive standard packed red blood cell (PRBC) transfusions obtained from RBCs of adult donors (A-RBCs) or from cord blood (CB-RBCs). According to standard procedures at the institute's neonatal intensive care unit, patients concurrently received continuous cerebral near-infrared spectroscopy (NIRS) monitoring. This cohort study was not prespecified in the trial protocol.

Exposure

Transfusion with A-RBCs or CB-RBCs.

Main Outcomes and Measures

The main outcome was the kinetics of cerebral regional oxygen saturation (crSO2) and cerebral fraction of tissue oxygen extraction (cFTOE) associated with A-RBC or CB-RBC transfusions. Cerebral NIRS monitoring was performed by neonatologists and nurses, who were blinded to the PRBC type. The NIRS monitoring was conducted starting with the blood product order, during transfusion, and for the subsequent 24 hours after transfusion completion. The mean treatment effects of A-RBCs or CB-RBCs were quantified using a linear mixed model for repeated measures.

Results

Of 23 randomized neonates, 17 (11 male [64.7%]; median gestational age at birth, 25.6 weeks [IQR, 25.3-26.1 weeks]) with a median birth weight of 840 g (IQR, 580-900 g) were included in the study; NIRS was evaluated for 42 transfusion episodes, of which 22 were A-RBCs and 20 were CB-RBCs. Globally considering all posttransfusion time points, the overall crSO2 covariate-adjusted mean after CB-RBC transfusions was 5.27% lower (95% CI, 1.20%-9.34%; P = .01) than that after A-RBC transfusions, while the cFTOE after CB-RBC transfusions was 6.18% higher (95% CI, 1.66%-10.69%; P = .009) than that after A-RBCs.

Conclusions and Relevance

The findings of this cohort study suggest that A-RBC transfusions may be associated with more oxygen delivery to cerebral tissues of preterm neonates than transfusions from CB-RBCs. This finding may explain the previously observed association between low HbF and high ROP risk. It also suggests that use of CB to meet the RBC transfusion needs of neonates with a gestational age of less than 28 weeks may protect cerebral tissues from overexposure to oxygen.

Regional Oxygenation and Perfusion Monitoring to Optimize Neonatal Packed Red Blood Cell Transfusion Practices: A Systematic Review

Contemporary packed red blood cell transfusion practices in anaemic preterm infants are primarily based on measurement of hemoglobin or haematocrit. In neonatal intensive care units, most preterm infants receive at least 1 packed red cell transfusion as standard treatment for anaemia of prematurity. Clinicians are faced with a common question "at what threshold should anaemic preterm infants receive packed red blood cell transfusion?". While evidence from interventional trials offers a range of haemoglobin levels to clinicians on thresholds to initiate red cell transfusion, it does not offer identification of exact haemoglobin level at which regional oxygenation and perfusion gets compromised. Assessment of regional oxygenation using near infrared spectroscopy and perfusion using ultrasound could offer a personalized transfusion medicine approach to optimize transfusion practices. We conducted a systematic review of the literature to identify the role of both regional oxygenation and/or ultrasound-based perfusion monitoring as a potential trigger to initiate packed red blood cell transfusion in anaemic preterm infants. MEDLINE, Embase, Maternity and Infant Care database were searched up to March 2021. Publications identified were screened and relevant data was extracted. Changes to regional oxygenation and/or perfusion monitoring before and after packed red blood cell transfusion were the primary outcomes. 44 out of 755 studies met the inclusion criteria and were included in the final analysis. Most were prospective, observational studies in stable preterm infants. Overall, studies reported an improvement in regional oxygenation and/or ultrasound-based perfusion after packed red blood cell transfusion. These changes were more consistently observed when hemoglobin <9.6g/dL or hematocrit was <0.30. Significant variation was found for patient characteristics, postnatal age at the time of monitoring, criteria for diagnosis of anaemia, and period of monitoring as well as regional oxygenation monitoring methodology. Regional oxygenation and/or perfusion monitoring can identify at-risk anaemic preterm infants and are promising tools to individualize packed red blood cell transfusion practices. However, there is lack of evidence for incorporating this monitoring, in their present form, into standard clinical practice. Additionally, consistency in reporting of study methodology should be improved.

Comparison of basic regional cerebral oxygen saturation values in patients of different ages: a pilot study

Objective

To explore the basic values of regional cerebral oxygen saturation (rSO₂) among different age groups.

Methods

One hundred twenty patients who were scheduled for elective surgery aged 0 to 80 years (American Society of Anesthesiologists [ASA] physical status I or II) or neonates just after birth via cesarean section were enrolled and divided into the following six groups: infant (0 month and ≤12 months), toddler (>1 and ≤3 years old), preschool (>3 and ≤6 years old), school age (>6 and ≤18 years old), adult (>18 and ≤65 years old), and elderly (>65 and ≤80 years old) groups. There were 20 patients in each group.

Results

The basic values of rSO₂ in infant, toddler, preschool, school age, adults, and elderly groups were 70.41% ± 4.66%, 72.43% ± 3.81%, 70.77% ± 3.27%, 70.62% ± 2.20%, 69.76% ± 6.02%, and 62.69% ± 3.14%, respectively. The basic value in the elderly group was lower compared with other five groups. There was no significant difference among infant, toddler, preschool age, school age, and adult groups.

Conclusions

The basic value of rSO₂ in elderly patients is lower. Age is an important factor that affects the underlying value of rSO₂.

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.

Influence of enteral feeding and anemia on tissue oxygen extraction after red blood cell transfusion in preterm infants

BACKGROUND

Understanding factors that impact tissue oxygen extraction may guide red blood cell (RBC) transfusion decision making in preterm infants. Our objective was to assess the influence of enteral feeding and anemia on cerebral and mesenteric oxygen saturation (Csat and Msat) and fractional tissue oxygen extraction (cFTOE and mFTOE) over the entire time course of RBC transfusion.

STUDY DESIGN AND METHODS

Preterm, very low-birth-weight infants receiving RBC transfusions at a single center were enrolled. Near-infrared spectroscopy sensors measured Csat and Msat levels from an hour before transfusion to 24 hours after. During this period, changes in Csat, Msat, cFTOE, and mFTOE were described, and their association with enteral feeding status and pretransfusion degree of anemia were assessed using generalized estimating equations.

RESULTS

RBC transfusion data from 31 preterm infants were included. Infants receiving enteral feeds exhibited lower pretransfusion Msat. Infants with pretransfusion hematocrit greater than 30% exhibited higher pretransfusion Csat and lower pretransfusion cFTOE. Such differences in baseline measurements persisted through 24 hours after transfusion. However, no statistically significant differences in oxygenation measures over time by enteral feeding or anemia status were identified.

CONCLUSION

Compared to NPO, enteral feeding was associated with lower Msat; anemia (hematocrit ≤30%) was associated with lower Csat and higher cFTOE. Over the time course of RBC transfusion, trajectories of Csat, Msat, cFTOE and mFTOE did not differ by enteral feeding or anemia status.

Human recombinant erythropoietin improves motor function in rats with spinal cord compression-induced cervical myelopathy

Objective

Erythropoietin (EPO) is a clinically available hematopoietic cytokine. EPO has shown beneficial effects in the context of spinal cord injury and other neurological conditions. The aim of this study was to evaluate the effect of EPO on a rat model of spinal cord compression-induced cervical myelopathy and to explore the possibility of its use as a pharmacological treatment.

Methods

To develop the compression-induced cervical myelopathy model, an expandable polymer was implanted under the C5-C6 laminae of rats. EPO administration was started 8 weeks after implantation of a polymer. Motor function of rotarod performance and grip strength was measured after surgery, and motor neurons were evaluated with H-E, NeuN and choline acetyltransferase staining. Apoptotic cell death was assessed with TUNEL and Caspase-3 staining. The 5HT, GAP-43 and synaptophysin were evaluated to investigate the protection and plasticity of axons. Amyloid beta precursor protein (APP) was assessed to evaluate axonal injury.

To assess transfer of EPO into spinal cord tissue, the EPO levels in spinal cord tissue were measured with an ELISA for each group after subcutaneous injection of EPO.

Results

High-dose EPO maintained motor function in the compression groups. EPO significantly prevented the loss of motor neurons and significantly decreased neuronal apoptotic cells. Expression of 5HT and synaptophysin was significantly preserved in the EPO group. APP expression was partly reduced in the EPO group. The EPO levels in spinal cord tissue were significantly higher in the high-dose EPO group than other groups.

Conclusion

EPO improved motor function in rats with compression-induced cervical myelopathy. EPO suppressed neuronal cell apoptosis, protected motor neurons, and induced axonal protection and plasticity. The neuroprotective effects were produced following transfer of EPO into the spinal cord tissue. These findings suggest that EPO has high potential as a treatment for degenerative cervical myelopathy.

Recommendations on RBC Transfusion in General Critically Ill Children Based on Hemoglobin and/or Physiologic Thresholds From the Pediatric Critical Care Transfusion and Anemia Expertise Initiative

OBJECTIVES

To present the consensus recommendations and supporting literature for RBC transfusions in general critically ill children from the Pediatric Critical Care Transfusion and Anemia Expertise Initiative.

DESIGN

Consensus conference series of international, multidisciplinary experts in RBC transfusion management of critically ill children.

METHODS

The panel of 38 experts developed evidence-based and, when evidence was lacking, expert-based recommendations and research priorities regarding RBC transfusions in critically ill children. The subgroup on RBC transfusion in general critically ill children included six experts. Electronic searches were conducted using PubMed, EMBASE, and Cochrane Library databases from 1980 to May 30, 2017, using a combination of keywords to define concepts of RBC transfusion and critically ill children. Recommendation consensus was obtained using the Research and Development/UCLA Appropriateness Method. The results were summarized using the Grading of Recommendations Assessment, Development, and Evaluation method.

RESULTS

Three adjudicators reviewed 4,399 abstracts; 71 papers were read, and 17 were retained. Three papers were added manually. The general Transfusion and Anemia Expertise Initiative subgroup developed, and all Transfusion and Anemia Expertise Initiative members voted on two good practice statements, six recommendations, and 11 research questions; in all instances, agreement was reached (> 80%). The good practice statements suggest a framework for RBC transfusion in PICU patients. The good practice statements and recommendations focus on hemoglobin as a threshold and/or target. The research questions focus on hemoglobin and physiologic thresholds for RBC transfusion, alternatives, and risk/benefit ratio of transfusion.

CONCLUSIONS

Transfusion and Anemia Expertise Initiative developed pediatric-specific good practice statements and recommendations regarding RBC transfusion management in the general PICU population, as well as recommendations to guide future research priorities. Clinical recommendations emphasized relevant hemoglobin thresholds, and research recommendations emphasized a need for further understanding of physiologic thresholds, alternatives to RBC transfusion, and hemoglobin thresholds in populations with limited pediatric literature.

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.

Cerebral Oximetry for Cardiac and Vascular Surgery

The technology of transcranial near-infrared spectroscopy (NIRS) for the measurement of cerebral oxygen balance was introduced 25 years ago. Until very recently, there has been only occasional interest in its use during surgical monitoring. Now, however, substantial technologic advances and numerous clinical studies have, at least partly, succeeded in overcoming long-standing and widespread misunderstanding and skepticism regarding its value. Our goals are to clarify common misconceptions about near-infrared spectroscopy and acquaint the reader with the substantial literature that now supports cerebral oximetric monitoring in cardiac and major vascular surgery.

Multi-channel multi-distance broadband near-infrared spectroscopy system to measure the spatial response of cellular oxygen metabolism and tissue oxygenation

We present a multi-channel, multi-distance broadband near-infrared spectroscopy (NIRS) system with the capability of measuring changes in haemoglobin concentrations (Δ[HbO₂], Δ[HHb]), oxidation state of cytochrome-c-oxidase (Δ[oxCCO]) and tissue oxygen saturation (TOI) in the adult human brain. The main components of the instrument are two customized spectrographs and two light sources. Each spectrograph is lens-based to improve light throughput, has a grating enhanced to optimise reflection in the near-infrared (NIR) spectral region and uses a front illuminated cooled CCD camera (-70° C) with a square chip dimension of 12.3 x 12.3 mm (512 x 512 pixels). Each light source uses a 50W halogen bulb with a gold plated mirror to increase the intensity of the NIR light. Each light source was connected to a custom-built bifurcated fibre bundle to create two source fibre bundles (3.2 mm diameter each). Each spectrograph received light input from another custom-built fibre bundle comprised of six individual bundles (one with 0.6 mm diameter and the other five with 1.5 mm diameter). All fibre bundles were fixed on a 3D printed optode holder (two light sources x two fibre bundles each = four probes; and two spectrographs x six fibre bundles each = 12 probes) that allowed 24 multi-distance channels across the forehead (six channels at 20 mm, three channels at 30 mm and 15 channels at 35 mm) and six TOI measurements. We demonstrated the use of the system in a cohort of nine healthy adult volunteers during prefrontal cortex functional activation using the Stroop task. We have observed functional responses identified as significant increase in Δ[HbO₂], decrease in Δ[HHb] and increase in Δ[oxCCO] in five channels (out of 12), that overlay the left and right dorsolateral prefrontal cortices. There was no observable TOI functional response and we have shown small variations in TOI across different sites within the same subject and within the same site across subjects.

Cerebral blood flow and oximetry response to blood transfusion in relation to chronological age in preterm infants

OBJECTIVE

Preterm infants frequently receive blood transfusion (BT) and the aim of this study was to measure the effect of BT on cerebral blood flow and oxygenation in preterm infants in relation to chronological age.

PATIENTS

Preterm infants undergoing intensive care recruited to three chronological age groups: 1 to 7 (Group 1; n=20), 8 to 28 (Group 2; n=21) & ≥29days of life (Group 3; n=18).

METHODS

Pre and post-BT anterior cerebral artery (ACA) time averaged mean velocity (TAMV) and superior vena cava (SVC) flow were measured. Cerebral Tissue Haemoglobin Index (cTHI) and Oxygenation Index (cTOI) were measured from 15-20min before to 15-20min post-BT using NIRS. Vital parameters and blood pressure were measured continuously.

RESULTS

Mean BP increased significantly, and there was no significant change in vital parameters following BT. Pre-BT ACA TAMV was higher in Group 2 and 3 compared to Group 1 (p<0.001). Pre-BT ACA TAMV decreased significantly (p≤0.04) in all 3 groups; pre-BT SVC flow decreased significantly in Group 1 (p=0.03) and Group 3 (p<0.001) following BT. Pre-BT cTOI was significantly lower in Group 3 compared to Group 1 (p=0.02). cTHI (p<0.001) and cTOI (p<0.05) increased significantly post-BT in all three groups. PDA had no effect on these measurements.

CONCLUSION

Baseline cTOI decreases and ACA TAMV increases with increasing chronological age. Blood transfusion increased cTOI and cTHI and decreased ACA TAMV in all groups. PDA had no impact on the baseline cerebral oximetry and blood flow as well as changes following blood transfusion.

Intrauterine inflammation, cerebral oxygen consumption and susceptibility to early brain injury in very preterm newborns

BACKGROUND

In utero exposure to inflammation results in elevated cerebral oxygen consumption. This increased metabolic demand may contribute to the association between chorioamnionitis and intraventricular haemorrhage (P/IVH). We hypothesised that intrauterine inflammation imposes an elevated cerebral metabolic load and increased fractional oxygen extraction (cFTOE) with cFTOE further increased in the presence of early P/IVH.

METHODS

Eighty-three infants ≤30 weeks gestation were recruited. Exposure to intrauterine inflammation was determined by placental histology. Total internal carotid blood flow (Doppler ultrasound) and near infrared spectroscopy were measured and cerebral oxygen delivery (mcerbDO2), consumption (mcerbVO2) and cFTOE were calculated on days 1 and 3 of life. Primary outcome was defined as death or P/IVH >grade II (cranial sonograph) by day 3.

RESULTS

Infants exposed to intrauterine inflammation had higher total internal carotid blood flow (92 vs 63 mL/kg/min) and mcerbDO2 (13.7 vs 10.1 mL/kg/min) than those not exposed to inflammation. Newborns with P/IVH had both higher oxygen consumption and extraction compared with those without sonographic injury regardless of exposure to intrauterine inflammation. Further, in preterms exposed to inflammation, those with P/IVH had higher consumption (6.1 vs 4.8 mL/kg/min) and extraction than those without injury. These differences were observed only on day 1 of life.

CONCLUSIONS

Although P/IVH is multifactorial in preterm newborns, it is likely that cerebral hypoxic-ischaemia plays a central pathophysiological role. These data provide a mechanistic insight into this process and suggests that the increased cerebral metabolic load imposed by the presence of inflammation results in a higher risk of critical hypoxic ischaemia in the preterm with increased susceptibility to significant P/IVH.

Review of the correlation between blood flow velocity and polycythemia in the fetus, neonate and adult: appropriate diagnostic levels need to be determined for twin anemia-polycythemia sequence

Twin anemia-polycythemia sequence (TAPS) is recognized increasingly antenatally by the demonstration of an anemic twin and a polycythemic cotwin using the middle cerebral artery peak systolic velocity (MCA-PSV). While the MCA-PSV has been shown to correlate well with anemia in singleton fetuses, the evidence to support its use to diagnose fetal polycythemia appears to be less clear-cut. We aimed to evaluate fetal, neonatal and adult literature used to support the use of MCA-PSV for the diagnosis of polycythemia. Comprehensive literature searches were performed for ultrasound evidence of polycythemia in the human fetus, neonate and adult using key search terms. Only manuscripts in the English language with an abstract were considered for the review, performed in June 2014. Fifteen manuscripts were found for the human fetus, including 38 cases of TAPS. Nine of these defined fetal polycythemia as MCA-PSV < 0.8 multiples of the median (MoM), five used < 1.0 MoM and one used 0.8-1.0 MoM. Only two studies, involving a total of 15 cases, proposed a diagnostic level, acknowledging false-positive and -negative cases, though neither reported sensitivities or specificities. Six neonatal studies (96 neonates) demonstrated evidence of decreased cerebral velocities in polycythemia and a consequent increase with hemodilution. In the adult, five studies (57 polycythemic adults) demonstrated increased flow or velocity with hemodilution. Neither neonatal nor adult studies conclusively defined levels for screening for polycythemia. Despite widespread adoption of a cut-off of < 0.8 MoM in the published literature for the polycythemic fetus in TAPS, this is based upon minimal evidence, with unknown sensitivity and specificity. We recommend caution in excluding TAPS based purely upon the absence of a reduced MCA-PSV.

Early red cell transfusion favourably alters cerebral oxygen extraction in very preterm newborns

BACKGROUND

Elevated cerebral fractional tissue oxygen extraction (cFTOE; ≥0.4) predicts early brain injury in very preterm infants. While blood transfusion increases oxygen-carrying capacity, its ability to improve cerebral oxygen kinetics in the immediate newborn period remains unknown.

OBJECTIVE

To investigate the effect of red blood cell (RBC) transfusion in the first 24 h of life on cFTOE in infants ≤29 weeks gestation.

METHODS

cFTOE was calculated from cerebral tissue oxygenation index (TOI) and cutaneous oximetry measured over a 30 min epoch before and after transfusion. Infants were dichotomised according to pre-transfusion cFTOE (low <0.4 vs high ≥0.4).

RESULTS

24 babies were included, 12 in each group. Pre- and post-transfusion Hb were similar between the groups. cFTOE significantly reduced after transfusion in the high but not low-extraction group (p<0.01).

CONCLUSIONS

Early RBC transfusion favourably alters cerebral oxygen kinetics in infants with elevated cFTOE, showing potential for modification of the risk of hypoxic (brain) injury.

Volume expansion does not alter cerebral tissue oxygen extraction in preterm infants with clinical signs of poor perfusion

BACKGROUND

Preterm infants with signs of poor perfusion are often treated with volume expansion, although evidence regarding its effect on cerebral perfusion is lacking. Moreover, the effect is questionable in preterm infants with an adequate cerebrovascular autoregulation (CAR). A useful measure to assess perfusion is cerebral fractional tissue oxygen extraction (cFTOE).

OBJECTIVES

To assess the effect of volume expansion on cFTOE in preterm infants with signs of poor perfusion.

METHODS

In this observational study, we assessed cFTOE using near-infrared spectroscopy in preterm infants with signs of poor perfusion before, during and 1 h after volume expansion treatment. Simultaneously, we measured mean arterial blood pressure (MABP). We tested the effect of volume expansion on both cFTOE and MABP, using multi-level analyses. We intended to define a subgroup that responded to volume expansion with an increase in blood pressure and a decrease in cFTOE, suggesting absent CAR.

RESULTS

In 14 preterm infants, with a median gestational age of 26.7 weeks (25.0-28.7 weeks) and a median birth weight of 836 g (615-1,290 g), we found a small increase in MABP during (1.4 ± 1.4 mm Hg, p = 0.003) and after (1.8 ± 1.7 mm Hg, p = 0.001) volume expansion, but no change in cFTOE during (-0.19 ± 0.1% p = 0.44) or after (-0.53 ± 0.1% p = 0.34) volume expansion. We were unable to define a subgroup lacking CAR.

CONCLUSIONS

Cerebral perfusion, as assessed by cFTOE, does not improve in preterm infants with signs of poor perfusion following volume expansion. In these infants, either CAR is present or volume expansion is inadequate to affect cFTOE.

Umbilical cord milking stabilizes cerebral oxygenation and perfusion in infants born before 29 weeks of gestation

OBJECTIVE

To investigate the effects of umbilical cord milking at birth on cerebral perfusion and systemic perfusion in very low birth weight (VLBW) infants.

STUDY DESIGN

Cerebral tissue oxygenation index and cerebral fractional tissue oxygen extraction were monitored in 50 stable VLBW infants (gestational age <29 weeks, birth weight <1250 g), with 26 allocated to the milked group and 24 to the control group. We used near-infrared spectroscopy 3-6, 12, 18, 24, 36, 48, and 72 hours after birth. Left ventricular end-diastolic dimension, left ventricular ejection fraction, left ventricle (LV) Tei index (measurement of left ventricular systolic and diastolic function), left ventricular cardiac output, and superior vena cava flow were measured concurrently using echocardiography.

RESULTS

There were no significant differences in gestational age and birth weight between the 2 groups. Hematocrit, left ventricular end-diastolic dimension, left ventricular cardiac output, and superior vena cava flow were higher in the milked group than in the control group, with improvement in the LV Tei index despite the absence of left ventricular ejection fraction changes within 24 hours after birth. Tissue oxygenation index increased and cerebral fractional tissue oxygen extraction decreased in the milked group within 24 hours after birth.

CONCLUSION

Umbilical cord milking stabilized cerebral oxygenation and perfusion in VLBW infants by improving LV diastolic function by increasing LV preload.

Cerebral oximetry and cognitive dysfunction in elderly patients undergoing surgery for hip fractures: a prospective observational study

Aim:

This study was conducted to examine perioperative cerebral oximetry changes in elderly patients undergoing hip fracture repair and evaluate the correlation between regional oxygen saturation (rSO₂) values, postoperative cognitive dysfunction (POCD) and hospital stay.

Materials and Methods:

This prospective observational study included 69 patients. Data recorded included demographic information, rSO₂ values from baseline until the second postoperative hour and Mini Mental State Examination (MMSE) scores preoperatively and on postoperative day 7. MMSE score ≤23 was considered evidence of cognitive dysfunction. Postoperative confusion or agitation, medications administered for postoperative agitation, and hospital length of stay were also recorded. Data were analyzed with Student’s t-test, Pearson’s correlation or multiple regression analysis as appropriate.

Results:

Patient age was 74±13 years. Baseline left sided rSO₂ values were 60±10 and increased significantly after intubation. Baseline rSO₂ L<50 and <45 was observed in 11.6% and 10.1% of patients respectively. Perioperative cerebral desaturation occurred in 40% of patients. MMSE score was 26.23 ± 2.77 before surgery and 25.94 ± 2.52 on postoperative day 7 (p=0.326). MMSE scores ≤ 23 were observed preoperatively in 6 and postoperatively in 9 patients. Patients with cognitive dysfunction had lower preoperative hematocrit, hemoglobin, SpO₂ and rSO₂ values at all times, compared to patients who did not. There was no correlation between rSO₂ or POCD and hospital stay. Patients with baseline rSO₂ <5 required more medications for postoperative agitation.

Conclusion:

Cognitive dysfunction occurs preoperatively and postoperatively in elderly patients with hip fractures, and is associated with low cerebral rSO₂ values.

Effects of anaemia on haemodynamic and clinical parameters in apparently stable preterm infants

BACKGROUND

The criteria for erythrocyte transfusion in stable premature infants are currently controversial. Haemodynamic measurements are not common in transfusion practice. The purpose of this study was to determine whether haemodynamic measurements could be helpful as objective criterion for transfusion decisions. We, therefore, evaluated clinical and haemodynamic changes in stable, anaemic, premature infants before and after transfusion using our current blood transfusion protocol based on a haematocrit threshold (<24%) and the neonatologist's discretion.

MATERIAL AND METHODS

Stable premature infants with a haematocrit level ≤30% were prospectively enrolled into the study. Cerebral, intestinal and renal blood flow velocities, cardiac function parameters and vital signs were measured up to three times following every routine haematocrit analysis. Moreover, transfused infants were evaluated three more times: directly before transfusion, and 24 hours and 72 hours after transfusion.

RESULTS

Thirty-six infants were enrolled and 23 of them were transfused. Subgroup analysis of transfused infants showed a significant decrease in cerebral blood flow velocities, cardiac output and heart rate. These changes persisted after transfusion. In the entire cohort, the degree of anaemia correlated with the increase of cerebral blood flow velocities, heart rate and cardiac output.

DISCUSSION

Cerebral blood velocities in the anterior cerebral artery might represent an objective Doppler sonographic criterion indicating the need for transfusion. The measurement of these velocities is non-invasive and quick and easy to perform. However, a randomised, controlled trial is necessary before a formal recommendation can be made.

Baseline cerebral oximetry values in elderly patients with hip fractures: a prospective observational study

AIM

This study was conducted to evaluate baseline cerebral tissue regional oxygen saturation (rSO(2)) values and identify risk factors related to severe rSO(2) reductions in elderly patients with hip fractures.

PATIENTS AND METHODS

This was a prospective observational single-centre study on patients undergoing scheduled or urgent operation for isolated hip fracture. The study was approved by the Institution Ethics Committee, and all patients signed informed consent before entering the study. Data were collected on factors potentially related to baseline cerebral rSO(2). Data were analysed with Student's t-test, Pearson's correlation or multiple regression analysis as appropriate.

RESULTS

Sixty-nine patients, aged (mean±standard deviation (SD)) 74±13 years participated. Left baseline rSO(2) was 60.09±10.20 and right baseline rSO(2) was 58.64±9.92. Baseline rSO(2)<45 was observed in 10.1% of patients on the left and 8.7% on the right side. Correlation between left- and right-side baseline cerebral rSO(2) was highly significant (r=0.852, p<0.001). Baseline cerebral rSO(2) had a positive, highly significant correlation with preoperative haematocrit (r=0.50, p<0.001) and arterial haemoglobin oxygen saturation (SpO(2)) (r=0.587, p<0.001), but correlation was negative with the American Society of Anesthesiologists (ASA) physical status (r=-0.42, p<0.001) and age (r=-0.39, p=0.001). Linear regression showed that preoperative haematocrit accounts for 23% (R(2)=0.23) of baseline rSO(2) variability, whereas preoperative haematocrit and SpO(2) combined account for 43.7% of rSO(2) variability (R(2)=0.437). Combined preoperative haematocrit+SpO(2)+age accounted for 51.3% (R(2)=0.513) of observed rSO(2) variability.

CONCLUSION

Low baseline cerebral rSO(2) values are common in elderly hip fracture patients, despite normal haemodynamic and arterial saturation values. Preoperative haematocrit, SpO(2) and age explain a significant portion of cerebral rSO(2) variability. More studies are needed to validate our findings and assess the potential benefit of interventions aimed at improving cerebral rSO(2) in elderly hip fracture patients.

Cerebral Oxygenation Monitoring: A Strategy to Detect IVH and PVL

Premature infants are at risk for intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL) theorized to be a result from fluctuations in cerebral blood flow. Monitoring cerebral oxygenation offers a method to observe changes in cerebral blood flow that may be beneficial for detecting and preventing IVH and PVL. This article explains the potential for cerebral oxygenation monitoring in detecting IVH and PVL using cerebral oximetry, reviews current knowledge known about cerebral oxygenation, and describes current challenges for cerebral oxygenation to be the next neuroprotective vital sign.

Monitoring of cerebral haemodynamics in newborn infants

The most important cerebrovascular injuries in newborn infants, particularly in preterm infants, are cerebral haemorrhage and ischemic injury. The typical cerebral vascular anatomy and the disturbance of cerebral haemodynamics play important roles in the pathophysiology. The term 'cerebral haemodynamics' includes cerebral blood flow (CBF), cerebral blood flow velocity, and cerebral blood volume (CBV). Therapy aimed at changing vascular anatomy is not available. Therefore, prevention of disturbances in CBF and CBV is pivotal. However, continuous monitoring of CBF and CBV is still unavailable for clinical use. Tissue oxygenation may be used as a surrogate for CBF, although precision is still questionable. General knowledge of the regulation of CBF and CBV is important. Although this knowledge is still incomplete, especially regarding autoregulation and the exact role of CBV, it is still useful. Using it even without knowing the exact level of CBF and CBV, it is possible to aim to keep CBF and CBV stable. Future research should focus on development of monitoring tools, gaining more insight in neonatal cerebral autoregulation, and demonstrating clinical benefits of a 'cerebral perfusion-oriented' therapy.

Blood transfusions increase cerebral, splanchnic, and renal oxygenation in anemic preterm infants

BACKGROUND

Multiprobe near infrared spectroscopy (NIRS) has been used to study regional cerebral (rSO(2)C), splanchnic (rSO(2)S), and renal (rSO(2)R) tissue oxygenation in newborns. We used this method to study the effects of red blood cell (RBC) transfusions in anemic preterm infants to assess if thresholds for transfusions were appropriate for recognizing a clinical condition permitting tissue oxygenation improvement.

STUDY DESIGN AND METHODS

Multiprobe NIRS (INVOS 5100, Somanetics) was applied during transfusion to 15 preterm infants with symptomatic anemia of prematurity (hematocrit level of <25%). rSO(2)C, rSO(2)S, and rSO(2)R were recorded at selected times, and then fractional oxygen cerebral extraction ratio [FOEC: (SaO(2)-rSO(2)C)/SaO(2)], fractional oxygen splanchnic extraction ratio [FOES: (SaO(2)-rSO(2)S)/SaO(2)], fractional oxygen renal extraction ratio [FOER: (SaO(2)-rSO(2)R)/SaO(2)], cerebrosplanchnic oxygenation ratio [CSOR: (rSO(2)S/rSO(2)C)], and cerebrorenal oxygenation ratio [CROR: (rSO(2)R/rSO(2)C)] were calculated. In addition, we used Doppler ultrasonography for evaluating cerebral blood flow (CBF), splanchnic blood flow (SBF), and renal blood flow (RBF) velocity.

RESULTS

rSO(2)C, rSO(2)S, and rSO(2)R significantly increased during transfusions, while FOEC, FOES, and FOER decreased. CSOR and CROR increased during transfusions. CBF velocity decreased during the study period, while SBF and RBF velocities did not vary.

CONCLUSION

RBC transfusions performed at used thresholds permitted an increase in cerebral, splanchnic, and renal oxygenation. The associated decreases in oxygen tissue extraction might suggest that transfusions were well timed for preventing tissue hypoxia or too early and theoretically prooxidant. Further studies could help to clarify this issue.

The influence of the timing of cord clamping on postnatal cerebral oxygenation in preterm neonates: a randomized, controlled trial

OBJECTIVE

Our goal was to investigate the effect of placentofetal transfusion on cerebral oxygenation in preterm infants by near-infrared spectroscopy.

SUBJECTS

A total of 39 preterm infants with a median gestational age of 30.4 weeks were randomly assigned to an experiment group (n = 15) and a control group (n = 24).

INTERVENTIONS

The delivery of the infants in the experiment group was immediately followed by maternal administration of syntocinon, the infant was placed 15 cm below the placenta, and cord clamping was delayed by 60 to 90 seconds. The infants in the control group were delivered conventionally. At the ages of 4 and 24 hours, cerebral hemoglobin concentrations, cerebral blood volume, and regional tissue oxygenation were measured by near-infrared spectroscopy.

RESULTS

Cerebral blood volume was not different between the 2 groups at the age of 4 hours (6.1 vs 5.8 mL/100 g of tissue) nor at the age of 24 hours (6.2 vs 6.2 mL/100 g of tissue). Mean regional tissue oxygenation of the experiment group was higher at the ages of 4 hours (69.9% vs 65.5%) and of 24 hours (71.3% vs 68.1%).

CONCLUSION

Delayed clamping of the umbilical cord improves cerebral oxygenation in preterm infants in the first 24 hours.

Noninvasive monitoring of red blood cell transfusion in very low birthweight infants using diffuse optical spectroscopy

Red blood cell (RBC) transfusion guidelines are designed to maintain adequate tissue oxygenation by increasing blood oxygen-carrying capacity. However, since tissue oxygenation is not measured, RBC transfusion guidelines are mostly subjective. Clinical evidence of oxygen transport/consumption mismatches in infants is often unclear and confounded by multiple factors. Invasive hemoglobin measurements can contribute further to anemia if performed too frequently. Diffuse optical spectroscopy (DOS) is a noninvasive quantitative method to measure the tissue oxy, deoxy, and total hemoglobin concentrations (ctO2Hb, ctHb, ctTHb), as well as mixed arterial-venous tissue hemoglobin saturation (stO2). Our objective is to determine if DOS can assess changes in tissue oxygenation in very low birth weight (VLBW) infants undergoing RBC transfusions. DOS measurements of ctO2Hb and ctHb are performed on 10 VLBW infants before and within 24 h after RBC transfusion. Seven nontransfused infants are studied to evaluate hemodynamic variations independent of RBC transfusion. Tissue near-infrared absorption and scattering values are measured using a four-wavelength (690, 750, 810, and 830 nm) frequency-domain tissue oximeter (OxiplexTS, ISS, Champaign, Illinois). In transfused subjects, DOS demonstrates significant increases in ctO2Hb (48+/-13 versus 74+/-20 microM, p<0.002), ctTHb (87+/-17 versus 107+/-24 microM, p=0.004), and stO2 (54+/-8 versus 68+/-6%, p<0.004) post-transfusion. DOS measurements correlate with mean hemoglobin increases for all infants (r=0.83, p<0.0001). No significant DOS changes occurred in the nontransfused group. Calculations of the differential path length for these transfused subjects show high variability (approximately 20%). DOS may serve as a noninvasive bedside tool to assess tissue oxygenation in infants and provide a functionally based transfusion trigger.

Effects of skin on bias and reproducibility of near-infrared spectroscopy measurement of cerebral oxygenation changes in porcine brain

The influence of skin on the bias and reproducibility of regional cerebral oxygenation measurements is investigated using cw near-infrared spectroscopy (NIRS). Receiving optodes are placed over the left and right hemispheres of a piglet (C3, C4 EEG placement code) and one transmitting optode centrally (Cz position). Optical densities (OD) are measured during stable normo, mild, and deep hypoxemia. This is done for skin condition 1: all optodes on the skin; skin condition 2: transmitting optode on the skin and one receiving optode on the skull; and skin condition 3: all optodes on the skull. Absolute changes of oxy- (cO2Hb), deoxyhemoglobin (cHHb), and total hemoglobin (ctHb) concentrations [micromolL] are calculated from the ODs. These absolute changes are calculated for each skin condition with respect to normoxic condition. Additionally, for skin condition 2, the difference of concentration changes between receiver 1 (skull) and receiver 2 (skin) is calculated. The effect of skin removal is an average increase of attenuation changes by a factor of 1.66 (=0.51 OD) and of the concentration changes due to the arterial oxygen saturation steps by 23%. We conclude that skin significantly influences regional oxygenation measurements. Nevertheless, it is hypothesized that the estimated concentration changes are dominated by changes of the oxygenation in the brain.

High Flow Rates During Modified Ultrafiltration Decrease Cerebral Blood Flow Velocity and Venous Oxygen Saturation in Infants

BACKGROUND

The intracranial hemodynamic effects of modified ultrafiltration in children are unknown. We investigated the effects of different blood flow rates during modified ultrafiltration on the cerebral hemodynamics of children with weights above and below 10 kg.

METHODS

Thirty-one children (weights: < or = 10 kg, n = 21; > 10 kg, n = 10) undergoing cardiopulmonary bypass were studied. Middle-cerebral artery blood flow velocities and cerebral mixed venous oxygen saturations were measured before, five minutes from the beginning, and at the end of ultrafiltration. Patients were classified according to their blood flow rates during ultrafiltration in three groups: high (> or = 20 mL/kg/min), moderate (10-19 mL/kg/min), and low flow rates (< 10 mL/kg/min).

RESULTS

During modified ultrafiltration, blood pressures and hematocrit increased (p < 0.001), but cerebral blood flow velocities and mixed venous oxygen saturations decreased (p < 0.001). A significant correlation was found between blood flow rates of ultrafiltration and the decline in mean cerebral blood flow velocity (r = - 0.48; p = 0.005) and cerebral oxygen saturation (r = - 0.49; p = 0.005) or hematocrit increase (r = 0.59; p = 0.001). Infants exposed to high flow rates had greater reduction of cerebral blood flow velocity and regional mixed venous saturation and higher hematocrit at the end of ultrafiltration compared with those subjected to moderate and low flow rates (p < 0.04). No significant difference was found between moderate and low flow groups. The flow rate of ultrafiltration was the only independent predictor of the changes in cerebral mixed venous oxygen saturation (p = 0.033).

CONCLUSIONS

High blood flow rates through the ultrafilter during modified ultrafiltration transiently decrease the cerebral circulation in young infants compared with lower blood flow rates. These effects may be related to an increased diastolic runoff from the aorta into the ultrafiltration circuit that leads to a "stealing" effect from the intracranial circulation, which may be important in infants with dysfunctional cerebral autoregulation.

Cerebral fractional oxygen extraction is inversely correlated with oxygen delivery in the sick, newborn, preterm infant

Cerebral blood flow (CBF) is known to be low in newborn infants, but this has not been shown to be damaging. The purpose of this study was to investigate the relationships between cerebral haemoglobin flow, blood flow, oxygen delivery, oxygen consumption, venous saturation, and fractional oxygen extraction (OEF) in newborn, preterm infants. Measurements were made by near-infrared spectroscopy in 13 very preterm, extremely low birth weight infants (median gestation 25 weeks) during the first 3 days after birth. There was a negative correlation between cerebral oxygen delivery and OEF (n=13, r=-0.5, P=0.03), which implies that when there is a reduction in cerebral oxygen delivery in sick preterm infants, increased cerebral oxygen extraction may be responsible for maintaining oxygen availability to the brain. During the first 3 days after birth CBF (n=13, r=0.7, P=0.01), oxygen delivery (n=13, r=0.5, P=0.03), and oxygen consumption (n=13, r=0.7, P=0.004) all increased. This increase in oxygen consumption indicates increased cerebral metabolic activity after birth, which is likely to be a normal adaptation to extrauterine life. The increases in blood flow and oxygen delivery may also be normal adaptations that facilitate this increase in metabolic activity. There was a decrease (P=0.04) in mean (+/-s.d.) cerebral OEF between day 1 (0.37+/-0.10) and day 2 (0.29+/-0.09), with no change between day 2 and day 3. Taking into account the negative correlation between OEF and oxygen delivery, this decrease in OEF may be because of increased oxygen delivery during this time.

Monitoring cerebral perfusion using near-infrared spectroscopy and laser Doppler flowmetry

This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infrared spectroscopy (NIRS) and a continuous wave NIR laser Doppler flow system (LDF) to measure changes in the blood oxygenation, blood concentration and blood flow velocity in the brain. A piglet was used as animal model. A controlled change in the arterial CO2 pressure (PaCO2) was applied for achieving changes in the listed cerebrovascular parameters. The time courses of blood concentration parameters (NIRS) and RMS blood flow velocity (LDF) were found to correspond closely with those of carotid blood flow and arterial carbon dioxide pressure (PaCO2). This result shows the additional value of LDF when combined with NIRS, preferably in one instrument. Development of pulsed LDF for regional blood flow measurement is indicated.

[Neonatal Doppler velocimetry in full term small-for-gestational age newborns]

This study aimed to evaluate the cerebral blood flow of full term small-for-gestational age newborns, using cranial ultrasound Doppler at birth. This study was performed at CAISM/UNICAMP (Tertiary Health Center for Women). Sixty term newborns were selected and divided in two groups: appropriate-for-gestational age (AGA) (36 neonates) and small-for-gestational age (SGA) (24 neonates). Cranial ultrasound Doppler evaluation was performed on both groups, between 24 and 48 hours after birth. Cerebral blood flow velocity (CBFV) was lower in the small-for-gestational age group, in the anterior cerebral artery (ACA). Doppler measurements were different statistically between the groups only for values related to peak systolic flow velocity (PSFV) and mean flow velocity (MFV) in the ACA. There was no significant difference for any evaluated parameters of flow velocity in the middle cerebral artery (MCA). It was concluded that SGA newborns showed PSFV and MFV significantly reduced only in the ACA. Weight/gestational age, neonatal polycythemia and mean arterial blood pressure values were statistically related to MFV in the ACA. In presence of fetal suffering, mean arterial blood pressure values and smoking in the pregnancy were statistically related to MFV in the MCA.

Influence of Patient Variables and Sensor Location on Regional Cerebral Oxygen Saturation Measured by INVOS 4100 Near-Infrared Spectrophotometers

Cerebral oximeter based on near-infrared spectroscopy has been used as a continuous, noninvasive monitoring of regional cerebral oxygen saturation (rSO2). Although the absolute rSO2 values have a wide range of variability, the factors affecting a variability of rSO2 values have not been extensively investigated. The authors investigated the influence of patient variables and sensor location on rSO2 measured by the cerebral oximeter INVOS 4100 in 111 patients anesthetized with sevoflurane, fentanyl, and nitrous oxide in oxygen. The sensors for rSO2 measurements were applied on the right forehead (R), 1 cm lateral to R (R1), on the left forehead (L), 1 cm lateral to L (L1), and on the center of the forehead (C). The relationship between the rSO2 values and patient variables were also analyzed. Values of rSO2 at R1 and L1 were significantly lower than those at R and L, respectively. Values of rSO2 at C were significantly higher compared with those at other sites. There were no significant correlations between the rSO2 values and values of weight, height, and head size. Values of rSO2 were similar between males and females. A significant negative correlation between the rSO2 values and age and a positive correlation between the rSO2 values and hemoglobin concentration were observed. These data indicate that patient age, hemoglobin concentration at the measurement, and sensor location can affect rSO2 values.

Assessment of local changes of cerebral perfusion and blood concentration by ultrasound harmonic B-mode contrast measurement in piglet

This study tested the hypothesis that changes in the blood concentration, and possibly in the perfusion, of different areas in the brain can be assessed by the use of ultrasound contrast agent (CA) and (linear) echo densitometry. The experiments were performed with piglets (n=3) under general anesthesia and artificial ventilation. Ultrasound CA was administered through a femoral vein as a short bolus. First passage wash-in curve was measured from image gray level during continuous low level (mechanical index<0.2) ultrasound imaging. This curve was obtained from 1-cm2 areas of the cortex (surface), the brain stem (inner) and the left carotid artery (vessel). Cerebral hemoglobin concentration changes were measured with near-infrared spectroscopy (NIRS). This approach enabled a cross-validation of these techniques. The measurements were repeated under conditions of normocapnia, mild hypercapnia and deep hypercapnia. Several physiologic signals, as well as the carotid blood flow, were measured simultaneously and related to gray level by linear regression analysis. The most significant results found were a high R2-statistic of the regression of the percentage change of the peak of the surface and inner wash-in curves with the arterial carbon dioxide pressure (R2=0.63 and R2=0.70, respectively), the blood pH (R2=0.79 and R2=0.81), the carotid flow (R2=0.75 and R2=0.72) and the partial arterial oxygen pressure (R2=0.47 and R2=0.55). Finally, a high correlation of peak gray level with total hemoglobin concentration change, independently measured by NIRS, was found (R2=0.69). In conclusion, these experiments show a reasonable intersubject variability of various relative measures derived from gray level ultrasound wash-in curves. High sensitivity to physiologic changes related to hypercapnia was observed for the peak contrast of wash-in curves. For up-slope and area-under-the-curve (first passage) this was lower but still highly significant. The gray-level ultrasound measures are highly correlated to changes in regional hemoglobin concentration in brain tissue assessed by NIRS.

Cerebral and peripheral oxygen saturation during red cell transfusion

BACKGROUND

Changes in regional hemoglobin oxygen saturation occur in response to blood transfusion and can be measured by near infrared spectroscopy.

PATIENTS AND METHODS

Cerebral (CsO2) and peripheral (PsO2) oxygen saturation were monitored with an INVOS 4100 near infrared spectroscopy oximeter in 29 patients undergoing 84 intraoperative blood transfusions during aortic or spinal surgery. Hemoglobin concentration was measured before and after transfusion. Mean arterial pressure, end tidal carbon dioxide tension, and arterial oxygen saturation were also monitored.

RESULTS

Mean arterial pressure, arterial oxygen saturation and end tidal carbon dioxide tension remained stable during transfusion, while CsO2 rose by a mean (95% CI) of 4.2 (3.2-5.2%; P = 0.001) and PsO2 rose by a mean (95% CI) of 1.6 (0.3-2.8%; P = 0.016). The rise in CsO2 correlated well with the rise in hemoglobin (r = 0.59, P < 0.001) and with the volume transfused (r = 0.58, P < 0.001). PsO2 correlated with the volume transfused (r = 0.35, P = 0.019) but not with hemoglobin concentration (r = 0.08, P = 0.47).

CONCLUSIONS

Near infrared spectroscopy detected significant rises in tissue oxygenation in response to blood transfusion, particularly in the cerebral cortex. CsO2 may be developed into a blood loss monitor if further research confirms our findings.

Regional tissue oxygenation during hemorrhage: can near infrared spectroscopy be used to monitor blood loss?

We investigated whether near infrared spectroscopy could be used to monitor regional tissue oxygenation during uncompensated hemorrhage in man. A Somanetics INVOS 4100 oximeter was used to measure regional hemoglobin oxygen saturation in the cerebral cortex (CsO2, left frontal area) and from the left calf muscle (PsO2) in 40 volunteers donating 470 mL of the whole blood. A Critikon 2001 Cerebral Redox Instrument was used to monitor total (tHb), oxygenated (O2Hb), and deoxygenated (HHb) hemoglobin in the right calf muscle. The oxygenation index, [HbD] = [O2Hb] - [HHb] was derived. CsO2 decreased by a mean (95% CI) of 2 (1-3.3%) (P < 0.001), PsO2 decreased by a mean (95% CI) of 3.2 (1.7-4.6%) (P < 0.001), and HbD decreased by a median (95% CI) of 6.4 (2.65-10.16) delta microM/cm (P < 0.001) during blood collection. There was an inverse correlation between blood loss and CsO2 (R = -0.59, P < 0.001), PsO2 (R = -0.61, P < 0.001), and HbD (R = -0.5, P < 0.001). Regional tissue oxygenation decreases in proportion to uncompensated blood loss. Near infrared spectroscopy may potentially be developed into a transfusion trigger.

Blood transfusion: influence of transfusion therapy on outcome

Few studies have addressed the influence of different transfusion therapies on outcome in a convincing way. Proven adverse impact of allogeneic blood on outcome is minimal. Acute mortality has declined to about 1 : 500,000 and the rate of transfusion-transmitted infections is decreasing, too. Data on postoperative infections and non-Hodgkin's lymphoma as possible adverse effects are controversial. Evidence for an increased risk of tumour recurrences is lacking. Alternatives to allogeneic blood may have appreciable risks: perioperative blood recovery had a fatality rate of more than 1 : 40,000. Reduction of allogeneic blood exposure may not be equated with improved outcome.