Cerebral blood flow fluctuation in low-risk preterm newborns

A Scoping Review of Cerebral Doppler Arterial Waveforms in Infants

Cerebral Doppler ultrasound has been an important tool in pediatric diagnostics and prognostics for decades. Although the Doppler spectrum can provide detailed information on cerebral perfusion, the measured spectrum is often reduced to simple numerical parameters. To help pediatric clinicians recognize the visual characteristics of disease-associated Doppler spectra and identify possible areas for future research, a scoping review of primary studies on cerebral Doppler arterial waveforms in infants was performed. A systematic search in three online bibliographic databases yielded 4898 unique records. Among these, 179 studies included cerebral Doppler spectra for at least five infants below 1 y of age. The studies describe variations in the cerebral waveforms related to physiological changes (43%), pathology (62%) and medical interventions (40%). Characteristics were typically reported as resistance index (64%), peak systolic velocity (43%) or end-diastolic velocity (39%). Most studies focused on the anterior (59%) and middle (42%) cerebral arteries. Our review highlights the need for a more standardized terminology to describe cerebral velocity waveforms and for precise definitions of Doppler parameters. We provide a list of reporting variables that may facilitate unambiguous reports. Future studies may gain from combining multiple Doppler parameters to use more of the information encoded in the Doppler spectrum, investigating the full spectrum itself and using the possibilities for long-term monitoring with Doppler ultrasound.

Pathogenesis and prevention of intraventricular hemorrhage

Intraventricular hemorrhage (IVH) is a major neurologic complication of prematurity. Pathogenesis of IVH is attributed to intrinsic fragility of germinal matrix vasculature and to the fluctuation in the cerebral blood flow. Germinal matrix exhibits rapid angiogenesis orchestrating formation of immature vessels. Prenatal glucocorticoid exposure remains the most effective means of preventing IVH. Therapies targeted to enhance the stability of the germinal matrix vasculature and minimize fluctuation in the cerebral blood flow might lead to more effective strategies in preventing IVH.

The role of systemic hemodynamic disturbances in prematurity-related brain injury

Premature infants who experience cerebrovascular injury frequently have acute and long-term neurologic complications. In this article, we explore the relationship between systemic hemodynamic insults and brain injury in this patient population and the mechanisms that might be at play.

Risk factors for neonatal seizures in very low birthweight infants: population-based survey

The developing brain has an increased susceptibility to seizure activity, and neonatal seizures can adversely affect neurodevelopmental outcome. This study aimed to determine the incidence of neonatal seizures in very low birthweight infants and to identify perinatal and postnatal factors associated with the occurrence of clinical seizures. A population-based cohort of 6525 very low birthweight infants born from 1995 through 1999 comprised the study group. Maternal, perinatal, or postnatal variables that showed a significant association with neonatal seizures in a univariate analysis were tested by a multiple logistic regression to assess the independent effect of each variable on the risk of seizures. The overall incidence of seizures was 5.6%. Significant independent predictors of neonatal seizures were decreasing gestational age, male gender, respiratory distress syndrome, pulmonary air leak (pneumothorax and pulmonary interstitial emphysema), intraventricular hemorrhage, periventricular leukomalacia, patent ductus arteriosus, surgical ligation of patent ductus arteriosus, necrotizing enterocolitis, and surgical treatment of necrotizing enterocolitis. Neonatal seizures appear to be associated with major morbidities and surgical interventions in very low birthweight infants. Continuous electroencephalographic monitoring could be warranted in infants following surgical treatment.

Brain Imaging Studies of the Anatomical and Functional Consequences of Preterm Birth for Human Brain Development

Premature birth can have devastating effects on brain development and long-term functional outcome. Rates of psychiatric illness and learning difficulties are high, and intelligence on average is lower than population means. Brain imaging studies of infants born prematurely have demonstrated reduced volumes of parietal and sensorimotor cortical gray matter regions. Studies of school-aged children have demonstrated reduced volumes of these same regions, as well as in temporal and premotor regions, in both gray and white matter. The degrees of these anatomical abnormalities have been shown to correlate with cognitive outcome and with the degree of fetal immaturity at birth. Functional imaging studies have shown that these anatomical abnormalities are associated with severe disturbances in the organization and use of neural systems subserving language, particularly for school-aged children who have low verbal IQs. Animal models suggest that hypoxia-ischemia may be responsible at least in part for some of the anatomical and functional abnormalities. Increasing evidence suggests that a host of mediators for hypoxic-ischemic insults likely contribute to the disturbances in brain development in preterm infants, including increased apoptosis, free-radical formation, glutamatergic excitotoxicity, and alterations in the expression of a large number of genes that regulate brain maturation, particularly those involved in the development of postsynaptic neurons and the stabilization of synapses. The collaboration of both basic neuroscientists and clinical researchers is needed to understand how normal brain development is derailed by preterm birth and to develop effective prevention and early interventions for these often devastating conditions.

Remifentanil and the tunnelling phase of paediatric ventriculoperitoneal shunt insertion. A double-blind, randomised, prospective study

Sixty-two children were randomly allocated to receive, during inhalational anaesthesia with isoflurane and nitrous oxide, either 1.0 microg x kg(-1) remifentanil (n = 33) or saline (n = 29) just before the tunnelling phase of ventriculoperitoneal shunt insertion, in a double-blind study. The remifentanil group showed little stress response to tunnelling as indicated by median (interquartile range [range]) change in heart rate -5.2 (-11.4 to 9.8 [-19.4 to 30.4])%, mean arterial pressure -5.0 (-20.8 to 15.5 [-40.9 to 42.9])% or plasma norepinephrine -13.5 (-38.1 to -2.5 [-77.7 to 81.5])% compared with the saline group, in which the changes were 20.1 (11.5-36.1 [2.1-83.1])%, 42.7 (27.1-56.8 [3.2-73.5])% and 13.3 (0.8-70.0 [-45.2 to 337.5])%, respectively (p < 0.001 for all comparisons). These changes were consistent across most different age categories. The cardiovascular response in the saline group lasted for 8 (4-15 [0-39]) min. Tracheal extubation occurred after 3 (2-4 [1-8]) min in the remifentanil group and 3 (2-6 [0-15]) min in the saline group (p = 0.29), with transfer to the recovery area and discharge to the ward, respectively, 4 (4-5 [1-10]) min and 9 (7-13 [2-32]) min in the remifentanil group and 7 (4-8 [2-18]) min and 14 (10-19 [7-44]) min in the saline group (p = 0.06 and 0.01, respectively). Postoperatively there was some evidence of respiratory depression and increased oxygen requirements in all age categories, but this was similar in both groups. Overall, the maximum increase from baseline in transcutaneous carbon dioxide tension was 41.2 (11.3-66.7 [-2.0 to 141.7])% in the remifentanil group compared with 30.7 (20.5-55.1 [1.7-159])% in the saline group (p = 0.8), and the time taken for transcutaneous carbon dioxide tension to decrease to < 6.0 kPa was 4 (0-13 [0-60]) min compared with 7 (0-13 [0-60]) min, respectively (p = 0.75). There was no difference between the two groups in postoperative analgesic requirements or in blood loss and there were no significant side-effects. We conclude that remifentanil is an appropriate and safe analgesic to provide balanced anaesthesia to cover the tunnelling phase of paediatric ventriculoperitoneal shunt insertion.

Closure of persistently patent arterial duct and its impact on cerebral circulatory haemodynamics in children

PURPOSE

Closure of a patent arterial duct (PDA) is suggested as a risk factor associated with intraventricular haemorrhage and/or cerebral ischemia in neonates. This study evaluate the effects of transcatheter closure of a patent arterial duct in children on cerebral blood flow velocity.

METHODS

Twelve children, aged from one to eight years were enrolled. Anaesthesia induction consisted of thiopentone, fentanyl and diazepam. Tracheal intubation was facilitated with vecuronium. Anaesthesia was maintained with N2O 70% in O2 and a PaCO2 between 35 to 40 mmHg. No cerebral vasoactive agents were used. Mean arterial pressure (MAP), central venous pressure (CVP), heart rate were continuously recorded. Systolic (Vs) and diastolic (Vd) cerebral blood flow velocity (CBFV) were recorded. Cerebral perfusion pressure (CPP) was calculated. The mean CBFV, the systolic-mean ratio and the cerebral blood volume were estimated from the area under the velocity-time curve (AUC) before PDA closure, immediately after and for 10 min following occlusion.

RESULTS

The mean (+/- SD) age and weight were 30 +/- 22 mo and 13 +/- 5 kg, respectively. Continuous recording during duct closure showed an abrupt increase in Vd (P < 0.05) whereas Vs remained constant. The AUC increased after closure and persisted for 10 min (P < 0.05).

CONCLUSION

This study confirms that closure of a PDA leads to acute changes in intracerebral diastolic flow and volume. This observation gives weight to mechanisms involved in IVH in smaller infants after arterial surgical duct closure. The anaesthetic technique used for arterial duct closure in these procedure could influence these observations.

Magnetic resonance imaging of periventricular leukomalacia and its clinical correlation in children

The prevalence of periventricular leukomalacia and its association with clinical neurological signs in school-age preterm children are unknown. We matched 42 eight-year-old children who were born before term with birth weights lower than 1,750 gm (mean, 1,410 gm; gestational age, 31 weeks) with 42 children who were born at term and of normal birth weight, to compare clinical neurological status and magnetic resonance imaging findings. Of the children born prematurely, 9.5% had cerebral palsy and 31% had minor neurological dysfunction whereas 9% of the children born at term had minor neurological dysfunction and none had cerebral palsy. Deviations in tongue movements, heel walking. Fogs test results, and finger opposition, as well as behavioral disturbances, differentiated the preterm from the full-teem group. The prevalence of periventricular leukomalacia among all children born prematurely was 32%. It was observed in all children with cerebral palsy, in 25% with minor neurological dysfunction, and in 25% of the clinically healthy preterm children. None of the children born at term had evidence of periventricular leukomalacia. Children with periventricular leukomalacia especially demonstrated poor performance on heel walking and Fogs test. Though commonly found in preterm children, periventricular leukomalacia is not uniformly associated with abnormal neurological findings. A thorough neurological examination is a better predictor of later developmental problems than is magnetic resonance imaging.

Prolonged low-dose indomethacin therapy for patent ductus arteriosus in very low birthweight infants

OBJECTIVE

To determine the efficacy and side-effects of prolonged low-dose indomethacin therapy in very low birthweight (VLBW; < 1500 g) infants with a haemodynamically significant patent ductus arteriosus (hsPDA).

METHODOLOGY

Very low birthweight infants admitted over a 16 month period were studied (8 months, retrospectively and 10 months, prospectively). Cross-sectional and M-Mode echocardiograms with pulsed-wave and colour Doppler were performed to assess the significance of ductal patency.

RESULTS

Forty-one (28%) of 148 VLBW infants were diagnosed to have hsPDA. Indomethacin therapy was successful in 90% after the first course, increasing to 95% after the second course. The recurrence rate after the first course was 3%. Minor and transient complications included oliguria, urea retention, hyponatraemia and thrombocytopenia. Although three infants had focal bowel perforation and the fourth had bowel perforation associated with necrotizing enterocolitis, the incidence of gastrointenstinal pathology was not significantly different from infants without hsPDA and not given indomethacin.

CONCLUSIONS

Very low birthweight infants with hsPDA have a high response rate and low recurrence rate to prolonged low-dose indomethacin therapy. Side-effects were mild and transient. However, it is prudent to be cautious when administering indomethacin in critically ill infants < 1000 g with hsPDA who manifest clinical features of bowel ischaemia.

Cerebral blood flow velocity and pulsation in neonatal respiratory distress syndrome and periventricular hemorrhage

The present study addressed the hypotheses that cerebral ischemia and/or excessive cerebral blood pulsation contribute to periventricular hemorrhage in preterm newborns with respiratory distress and that the pulse width is a valuable tool to estimate the contribution of cerebral blood pulsation. These hypotheses were tested by following preterm newborns at risk for respiratory distress and periventricular hemorrhage. We monitored for cerebral blood flow velocity (CBFV), cerebral pulse width, and cerebral pulsatility index; for patent ductus arteriosus, capillary Pco2, heart rate (HR) and behavior; and for the occurrence of respiratory distress and periventricular hemorrhage (PVH). The data obtained were analyzed with linear regression with the mode of respiration (spontaneous or supported) and postnatal age as additional covariates. We observed that (a) respiratory distress, either uncomplicated or complicated by PVH, correlates with a low CBFV and a high cerebral pulsatility index; (b) PVH also correlates with a high cerebral pulse width; (c) the increased pulse width precedes the onset of the hemorrhage; and (d) these CBF alterations can be partly attributed to ductal shunting and are ameliorated by mechanical ventilation.

Variability in cerebral blood flow velocity: observations over one minute in preterm babies

Cerebral blood flow velocity (CBFV) was measured using Doppler ultrasound on the first day of life in a consecutively admitted cohort of 52 very low birthweight infants. Recordings were made for a period of 1 min. The coefficient of variation for the area under the curve of 20 successive cardiac cycles was calculated, and a 20 cycle moving window then applied to the whole recording. This showed that the coefficient of variation varied widely during 1 min in any individual, the range being from 2% to 28% (median 8%). There was a strong correlation between the variability in CBFV and that in systemic blood pressure (BP). Variability in CBFV was significantly higher in babies with hypotensive episodes (P = 0.026). Babies who died had a higher maximum coefficient of variation than those who survived (P = 0.05), but we were unable to confirm any association with brain injury or patent ductus arteriosus.

Influence of end expiratory pressure on cerebral blood flow in preterm infants

The effect of interruption of positive and expiratory pressure (PEEP) on cerebral blood flow velocity (CBFV) and CBF fluctuation (CBFF) in the internal carotid arteries and on heart rate, restlessness and wakefulness has been studied in 17 mechanically ventilated neonates with RDS. A decrease in CBFV was found, but no significant change in CBFF. Multiple regression analysis showed that the decrease in CBFV is less pronounced if the PEEP interruption is accompanied by restlessness. It further appeared that the decrease in CBFV is more pronounced if CBFV is high, the ductus arteriosus is patent, or RDS follows a complicated course. These findings indicate that PEEP supports CBF, probably by a decrease in ductal stealing from the brain. Therewith PEEP protects against cerebral hypoperfusion which is one of the major risks in RDS and immaturity. Furthermore, our findings suggest that the decrease in CBF during PEEP interruption is moderated by restlessness and accentuated by brain damage.

Cerebral blood flow fluctuation in neonatal respiratory distress and periventricular haemorrhage

The relationship of cerebral blood flow fluctuation (CBFF) with periventricular haemorrhage (PVH) and respiratory distress syndrome (RDS) was studied in 35 preterm newborns. CBFF was defined as the interquartile range in the ensemble of pulses of a 20-s Doppler recording of CBF velocity (CBFV) in the internal carotid artery. We found a statistically significant increase in end diastolic CBFF in PVH and RDS. This increase was related to the mode of respiration (spontaneous or mechanically supported), the state of the ductus arteriosus, and the level of end diastolic CBFV. Differences before and after the onset of PVH were not found. In view of this, we conclude that RDS increases CBFF, that this increase is related to pleural pressure fluctuations, that these can be damped by mechanical ventilation, and that their propagation to the CBF is promoted by patency of the ductus arteriosus and foramen ovale. Whether the CBFF increase causes PVH, or is merely an expression of coincident RDS, remains a question that needs further investigation.