Psychosocial stress and severe prematurity.
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Denmark↗
Biomedical subjects
O Pryds
Publications and source records attributed to O Pryds.
Changes in cerebral oxygenation and cerebral blood volume during endotracheal suctioning in ventilated neonates.
The effect of endotracheal suctioning on cerebral haemodynamics was investigated in 29 newborn infants with a mean gestational age of 31 weeks (range 25-40 weeks). Prior to one of two suctioning procedures, the inspiratory fraction of oxygen was increased by 10%. Brain oxygenation and total haemoglobin concentration were estimated continuously by near infrared spectroscopy. Mean arterial blood pressure, arterial blood oxygen saturation and carbon dioxide tension were recorded simultaneously. Brain oxygenation decreased in parallel with arterial oxygen saturation during suctioning. Preoxygenation ameliorated the decrease in brain oxygenation and arterial oxygen saturation whereas there was no benefit with regard to the changes in total haemoglobin concentration, carbon dioxide tension or mean arterial pressure. Changes in total haemoglobin concentration were related closely to concomitant changes in carbon dioxide tension (p less than 0.0001) but unrelated to changes in mean arterial pressure or arterial oxygen saturation. Our findings suggest that cerebral blood volume may react to changes in carbon dioxide tension during endotracheal suctioning in mechanically ventilated neonates. Apparently, preoxygenation prior to suctioning does not ameliorate the stress in normoxic infants.
Blood Pressure↗
Capillary recruitment for preservation of cerebral glucose influx in hypoglycemic, preterm newborns: evidence for a glucose sensor?
Changes in cerebral blood volume (CBV) were investigated by means of near-infrared spectroscopy in 18 preterm newborns during treatment with intravenous bolus glucose. All newborns were breathing spontaneously, and their postnatal age was 2 hours. Blood glucose concentration ranged between 0.3 and 2.2 mmol/L. Cerebral blood volume began to decrease shortly after the glucose infusion was terminated, and steady state was obtained after approximately 3 minutes. The decrease in CBV averaged 0.15 mL/100 g (range 0.02 to 0.40 mL/100 g). Thereafter, CBV remained constant. Individual reductions in CBV were inversely related to the pretreatment concentration of glucose, whereas there was no relation between changes in CBV and alterations in blood gas values or in mean arterial blood pressure. It is suggested that previously unperfused capillaries are recruited to maintain the glucose transport into neurons of hypoglycemic, preterm newborns. The rapidity whereby vessels adjust to alterations in glucose levels indicates the existence of a cerebral glucose sensor.
Blood Glucose↗
Control of cerebral circulation in the high-risk neonate.
A knowledge of neonatal cerebrovascular physiology is essential to the understanding of diseases that frequently affect the subsequent development of the newborn brain. Recent observations indicate that the cerebral vessels of the healthy newborn infant, even the very preterm, respond to physiological stimuli in the same manner as in the mature organism. Thus, cerebral blood flow changes with changes in arterial carbon dioxide tension (PaCO2), oxygen concentration (CaO2), or glucose concentration, whereas cerebral blood flow remains constant at minor fluctuations in arterial blood pressure. In pathological states, pressure autoregulation may become impaired, and in severe cases the vessels do not react to chemical or metabolic stimuli. These infants are at high risk for developing cerebral lesion, and they may be candidates for new "brain-protecting regimens."
Animals↗
Aminophylline reduces cerebral blood flow in stable, preterm infants without affecting the visual evoked potential.
The effect of intravenous aminophylline (10 mg/kg) on cerebral blood flow (CBF) and single flash visual evoked potential (VEP) was investigated in 16 preterm infants (range 25-34 weeks). All infants were weaned from mechanical ventilation and had normal brain ultrasonograms. CBF, PaO2, PaCO2, mean arterial blood pressure and VEP were recorded before, immediately after and 1 h after the administration of aminophylline. When intra-individual changes in PaCO2 were taken into account, mean CBF was 5.5% lower than the baseline value immediately after administration of aminophylline, but this was not statistically significant (P = 0.14). After 1 h, however, CBF had decreased by a mean of 13.8% (P = 0.0003). The cerebral function estimated from VEP was not influenced by aminophylline since the VEP configuration and the VEP parameters remained constant throughout the study. It is concluded that aminophylline reduces cerebral blood flow in stable, preterm infants and apparently without inducing adverse effects on cerebral function.
Aminophylline↗
Estimating cerebral blood flow in newborn infants: comparison of near infrared spectroscopy and 133Xe clearance.
A new method of measuring cerebral blood flow (CBF) in newborn infants by means of near infrared spectroscopy (CBFnirs) was compared with the i.v. 133Xe clearance technique (CBFxe). Forty CBFnirs measurements were obtained during 19 133Xe measurements in 16 infants; 79 other CBFnirs data sets were discarded because the assumptions for their use were not fulfilled. The test-retest variation of repeated near infrared-measurements during each 133Xe clearance was 17.5%. CBFnirs was closely related to CBFxe (r2 = 0.84, p less than 0.0001), with a slope of 0.75 (SEM = 0.064) and a intercept of 1.58 mL/100 g/min (SEM = 0.51). The difference between the measurements obtained by the two methods (CBFnirs-CBFxe) was negative in the high range of CBF, whereas the difference was close to zero in the low range. We conclude that CBF measured with near infrared spectroscopy was in good agreement with the CBF measured with the 133Xe method. The near infrared spectroscopy method has the advantage of being noninvasive, and it does not involve ionizing radiation. Because of methodologic constraints, however, it may underestimate CBF in the high range of flow, and it may have limitations of application in clinical research.
Blood Flow Velocity↗
[Near infrared spectrophotometry--a non-invasive, continuous method for monitoring of cerebral status in newborn infants].
Hypoxic-ischaemic injury to the brain is the commonest cause of permanent neurodevelopmental disability in the very preterm and other children who survive after neonatal intensive care. Non-invasive techniques are therefore needed to examine the mechanisms of damage to the brain. Near infrared spectroscopy provides continuous cot-side information about cerebral oxygenation and metabolism in sick preterm infants by measurements of oxyhaemoglobin, deoxyhaemoglobin and oxidized cytokrom aa3. The cytokrome aa3 signal may, however, be artifactual due to interference from oxyhaemoglobin. Future investigations may clarify this problem.
Brain Damage, Chronic↗
Visual evoked potentials in term light-for-gestational-age infants and infants of diabetic mothers.
The latency and amplitude of the first negative peak of visual evoked potentials (VEP) were evaluated in 52 term infants, investigated within 48 h after birth. Sixteen were light-for-gestational-age (LGA), 16 were appropriate-for-gestational-age (AGA) and 20 were infants of diabetic mothers (IDM). The VEP latency was shorter in LGA infants compared to AGA infants, and it was closely related to the birth weight deviation. The VEP latency was inversely related to gestational age and positively related to head circumference. When corrected for gestational age and head circumference, the VEP latency was not significantly different between the subgroups, nor related to the birth weight deviation, ponderal index or skinfold thickness. Thus, it could be argued that the high conduction velocity in LGA infants is due to stress maturation or alternatively due to the smaller head circumference. The VEP amplitude was higher in LGA infants when compared with AGA infants, and inversely related to the birth weight deviation. No differences were found in VEP latency or VEP amplitude between IDM and AGA infants.
Birth Weight↗
Vasoparalysis associated with brain damage in asphyxiated term infants.
The relationship of cerebral blood flow to acute changes in arterial carbon dioxide and mean arterial blood pressure (MABP) was determined during the first day of life in 19 severely asphyxiated term infants supported by mechanical ventilation. For comparison, 12 infants without perinatal asphyxia were also investigated. Global cerebral blood flow (CBF infinity) was determined by xenon 133 clearance two or three times within approximately 2 hours. During the cerebral blood flow measurement, the amplitude-integrated electroencephalogram and visual-evoked potential were recorded. Changes in arterial carbon dioxide pressure followed adjustments of the ventilator settings, whereas MABP fluctuated spontaneously. Arterial oxygen pressure and blood glucose concentration were in the normal range. Five of the asphyxiated infants had isoelectric electroencephalograms and died subsequently with severe brain damage. They had a high CBF infinity (mean 30.6 ml/100 gm/min) and abolished carbon dioxide and MABP reactivity. Lower CBF infinity (mean 14.7 ml/100 gm/min) and abolished MABP reactivity were found in another five asphyxiated infants with burst-suppression electroencephalograms in whom computed tomographic or clinical signs of brain lesions developed. The carbon dioxide reactivity was preserved in these infants. In the remaining nine asphyxiated infants without signs of central nervous system abnormality, carbon dioxide and MABP reactivity were preserved, as was also the case in the control group. We conclude that abolished autoregulation is associated with cerebral damage in asphyxiated infants and that the combination of isoelectric electroencephalograms and cerebral hyperperfusion is an early indicator of very severe brain damage.
Asphyxia Neonatorum↗
Cerebral blood flow reactivity in spontaneously breathing, preterm infants shortly after birth.
In 18 spontaneously breathing, preterm infants (mean gestational age 30.3 weeks) cerebral blood flow (CBF) was investigated twice, 2 and 3 hours after birth when spontaneous changes in arterial carbon dioxide tension (PaCO2) and mean arterial blood pressure (MABP) were expected. Transcutaneous oxygen tension (TcO2) was kept normal by adjusting the inspiratory oxygen fraction. In 12 infants, plasma adrenaline and noradrenaline were constant throughout the study. Changes in CBF infinity (CBF infinity) were significantly related to changes in PaCO2 (p = 0.0001) whereas neither changes in MABP nor TcO2 reached a significant association to changes in CBF infinity (p = 0.67 and p = 1.0, respectively). The calculated CBF infinity -CO2 reactivity of 28.9% per kPa PaCO2 (95% confidence interval 16.1-43.0) is comparable to findings in older newborns and healthy adults. Only one of 18 infants developed germinal layer haemorrhage (grade I) in spite of the hypercapnic state which was observed during the first hours of life. Periventricular leucomalacia was not detected. It is suggested that the cerebral blood flow is well regulated within physiological variations of PaCO2 and MABP in the healthy, preterm newborn even shortly after birth.
Blood Gas Monitoring, Transcutaneous↗
Carbon dioxide-related changes in cerebral blood volume and cerebral blood flow in mechanically ventilated preterm neonates: comparison of near infrared spectrophotometry and 133Xenon clearance.
Carbon dioxide-induced changes in near infrared spectrophotometry recordings were compared with changes in cerebral blood flow estimated by 133Xenon clearance (global cerebral blood flow (infinity)) at serial measurements in 24 mechanically ventilated preterm infants (mean gestational age 30.2 wk). In all infants, three measurements were taken at different arterial carbon dioxide tension levels (mean 4.4 kPa, range 2.1-7.8) obtained by adjustment of the ventilator settings. Mean arterial blood pressure changed spontaneously, whereas arterial oxygen tension was kept within normal range. At all wavelengths (904, 845, 805, and 775 nm), the OD increased at higher arterial carbon dioxide tension levels, indicating cerebral vasodilation. This conclusion was supported by conversion of the data to changes in oxygenated and deoxygenated Hb concentration. A parallel increase in cerebral blood volume index and global cerebral blood flow (infinity) was found (p less than 0.0001). The oxygenation level of cytochrome aa3 increased with increases in oxygen delivery (p less than 0.0001). This observation, however, may have been artifactual due to cross-talk between the oxidized cytochrome aa3 and the oxygenated Hb signals, as these signals were closely interrelated in the present experimental design. We suggest that near infrared spectrophotometry may be used for estimation of the cerebral blood volume index/cerebral blood flow-CO2 reactivity within a wide range of arterial carbon dioxide tension. Knowledge of the light path length would put this estimation on a quantitative basis.
Birth Weight↗
Increased cerebral blood flow and plasma epinephrine in hypoglycemic, preterm neonates.
Cerebral blood flow, plasma epinephrine, and plasma norepinephrine were measured in 25 spontaneously breathing, preterm neonates (mean gestational age 30.4 weeks) 2 hours after birth, during a routine screening for low blood glucose levels. Increased cerebral blood flow and plasma epinephrine values were observed when blood glucose levels were low, whereas plasma norepinephrine was constant throughout the blood glucose range. Hypoglycemia (defined as blood glucose concentration less than 30 mg/dL) was found in 13 neonates who were treated with intravenous glucose and milk enterally. Blood glucose levels were normal in the remaining 12 control neonates who received milk by a gastric line. Approximately 30 minutes after treatment with intravenous glucose and/or milk, cerebral blood flow had decreased by a mean of 11.3% in the 13 hypoglycemic neonates but was still 37.5% higher than cerebral blood flow in the control neonates despite normalization of plasma epinephrine concentration. Mean arterial blood pressure and blood gas values were identical between groups throughout the investigation. It is suggested that a normal coupling between cerebral metabolic demands and flow is present in very preterm neonates and that epinephrine may play a role in the cerebral hyperperfusion. Although none of the neonates had clinical signs of hypoglycemia, the data suggest that counterregulatory mechanisms are invoked when blood glucose values are less than 30 to 45 mg/dL.
Blood Glucose↗
Determinants of visual evoked potentials in preterm infants.
The latency and amplitude of N1, the first negative peak of single flash visual evoked cortical potentials (VEP) were evaluated in 86 preterm infants (25-34 weeks of gestation), investigated during the first day of life. All infants were regarded stable at the time of investigation and none had experienced severe asphyxia. Both the VEP latency and amplitude were inversely related to gestational age. When latency was corrected for age it was longer in boys than in girls. Age corrected VEP amplitude was inversely related to head circumference, umbilical cord pH and EEG activity. There was no difference between VEP parameters in asymmetrically growth retardated infants compared to those with normal growth. Administration of dexamethasone to the mother before delivery, mode of delivery, presence of hyaline membrane disease, mode of assisted ventilation or imminent development of periintraventricular haemorrhage did not affect the VEP.
Evoked Potentials, Visual↗
Heterogeneity of cerebral vasoreactivity in preterm infants supported by mechanical ventilation.
The reaction of cerebral blood flow to acute changes in arterial carbon dioxide pressure (PaCO2) and mean arterial blood pressure was determined in 57 preterm infants supported by mechanical ventilation (mean gestational age 30.1 weeks) during the first 48 hours of life. All infants had normal brain sonograms at the time of the investigation. In each infant, global cerebral blood flow was determined by xenon-133 clearance two to five times within a few hours at different levels of PaCO2. Changes in PaCO2 followed adjustments of the ventilator settings. Arterial oxygen pressure was intended to be kept constant, and mean arterial blood pressure fluctuated spontaneously between measurements. The data were analyzed by stepwise multiple regression, with changes in global cerebral blood flow, PaCO2, mean arterial blood pressure, and postnatal age or intracranial hemorrhage used as variables. In infants with persistently normal brain sonograms, the global cerebral blood flow-carbon dioxide reactivity was markedly lower during the first day of life (mean 11.2% to 11.8%/kPa PaCO2) compared with the second day of life (mean 32.6/kPa PaCO2), and pressure-flow autoregulation was preserved. Similarly, global cerebral blood flow-carbon dioxide reactivity and pressure-flow autoregulation were present in infants in whom mild intracranial hemorrhage developed after the study. In contrast, global cerebral blood flow reactivity to changes in PaCO2 and mean arterial blood pressure was absent in infants in whom ultrasonographic signs of severe intracranial hemorrhage subsequently developed. These infants also had about 20% lower global cerebral blood flow before hemorrhage, in comparison with infants whose sonograms were normal, a finding that suggests functional disturbances of cerebral blood flow regulation. Several perinatal factors were tested, but only birth after abruptio placentae was related to subsequent periventricular hemorrhage (p = 0.037).
Age Factors↗
Low CBF, discontinuous EEG activity, and periventricular brain injury in ill, preterm neonates.
Cerebral blood flow was measured by intravenous 133Xe clearance one to four times during the first 48 h of life in 20 infants, born after 27 to 33 weeks of gestation, who were under mechanical ventilation and being monitored by amplitude integrated EEG, resulting in 36 sets of simultaneous CBF and EEG measurements. Mean CBF infinity, a measure of global flow to white as well as grey matter, was 10.0 ml/100 g/min +/- 3.5 SD. Definite EEG activity was seen with CBF infinity values as low as 5 ml/100 g/min. CBF infinity was related to the level of EEG activity, discontinuous EEG activity being associated with low CBF infinity (p = 0.014). It was not possible to determine if this relation indicated the presence of marginal ischaemia or primary inhibition of electrical activity resulting in decreased CBF, two infants developing periventricular leucomalacia, however, and one who developed intraparenchymatous hemorrhage were among the seven with CBF infinity values of less than or equal to 8 ml/100 g/min (p = 0.031). This suggests that ischaemia of periventricular white matter may have been present concurrently with cortical electrical activity.
Brain Diseases↗
Effect of PaCO2 and haemoglobin concentration on day to day variation of CBF in preterm neonates.
The CBF was measured on the first three days of life in 22 mechanically ventilated, preterm neonates (mean gestational age 29.5 weeks) with simultaneous recordings of arterial carbon dioxide tension (PaCO2), arterial oxygen tension (PaO2), haemoglobin concentration (Hgb), haemoglobin oxygen saturation and mean arterial blood pressure (MABP). CBF infinity tended to increase slightly with age. The intra-individual variation of CBF infinity was positively related to changes in PaCO2 (p = 0.0004) and inversely related to changes in Hgb (p = 0.029). Neither PaO2 nor MABP achieved a significant relation to changes in CBF infinity. Thus, the mean CBF infinity -CO2 reactivity was calculated to 22.1% per kPa whereas CBF infinity increased by a mean of 11.9% per mM decrease of Hgb thereby providing a constant oxygen delivery to the brain. It is concluded that PaCO2 and Hgb have the expected effect on CBF infinity in preterm neonates even during respiratory distress shortly after birth.
Age Factors↗
Indomethacin and cerebral blood flow in premature infants treated for patent ductus arteriosus.
Central blood flow (CBF) was estimated by an intravenous 133-xenon technique in six preterm infants before and after administration of indomethacin for closure of patent ductus arteriosus. CBF fell in all infants (range 12%-40%), the mean fall was 24% (P less than 0.005). Though none of the infants showed signs of impaired cerebral function during or following the injections, the results do not indicate whether or not the use of indomethacin is a potential hazard.
Cerebrovascular Circulation↗