Cerebral blood flow velocity recordings and the prediction of intracranial haemorrhage and ischaemia

Preterm Infants off Positive Pressure Respiratory Support Have a Higher Incidence of Occult Cerebral Hypoxia

OBJECTIVE

To use cerebral near-infrared spectroscopy (NIRS) to quantify occult cerebral hypoxia across respiratory support modes in preterm infants.

STUDY DESIGN

In this prospective, longitudinal, observational study, infants ≤32 weeks gestation underwent serial pulse oximetry (oxygen saturation [SpO2]) and cerebral NIRS monitoring (4-6 hours per session) following a standardized recording schedule (daily for 2 weeks, every other day for 2 weeks, then weekly until 35 weeks corrected gestational age). Four calculations were made: median cerebral saturation, median cerebral hypoxia burden (proportion of NIRS samples below the hypoxia threshold [<67%]), median systemic saturation, and median systemic hypoxia burden (proportion of SpO2 samples below the desaturation threshold [<85%]). During each recording session, respiratory support mode was noted (room air, low-flow nasal cannula, high-flow nasal cannula, noninvasive positive pressure ventilation, continuous positive airway pressure, and invasive ventilation).

RESULTS

There were 1013 recording sessions made from 174 infants with a median length of 6.9 hours. Although the systemic (SpO2) hypoxia burden was significantly greater for infants on the highest respiratory support (invasive and noninvasive positive pressure ventilation), the cerebral hypoxia burden was significantly greater during recording sessions made on the lowest respiratory support (8% for room air; 29% for low-flow nasal cannula).

CONCLUSIONS

Premature infants on the highest levels of respiratory support have less cerebral hypoxia than those on lower respiratory support. These results raise concern about unrecognized cerebral hypoxia during lower acuity periods of neonatal intensive care unit hospitalization and adverse outcomes.

The effect of umbilical cord milking on cerebral blood flow in very preterm infants: a randomized controlled study

OBJECTIVE

To compare the effect of umbilical cord milking (UCM) vs. early cord clamping (ECC) on cerebral blood flow (CBF).

METHOD

Preterm infants <31 weeks' gestation were randomized to receive UCM or ECC at birth. Blood flow velocities and resistive & pulsatility indices of middle and anterior cerebral arteries were measured at 4-6 and 10-12 h after birth as an estimate of CBF.

RESULTS

Randomization allocated 37 infants to UCM and 36 to ECC. Maternal and antenatal variables were similar. There were no significant differences between groups in middle or anterior CBF velocities and resistive indices at either study time point. CBF variables were not correlated with mean blood pressure, systemic blood flow, or intraventricular hemorrhage.

CONCLUSIONS

In very preterm infants, UCM compared with ECC was not shown to change CBF indices during the first 12 h of age or correlate with other hemodynamic measures or with intraventricular hemorrhage.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01487187.

Diagnostic and predictive value of Doppler ultrasound for evaluation of the brain circulation in preterm infants: a systematic review

INTRODUCTION

Very and extremely preterm infants frequently have brain injury-related long-term neurodevelopmental problems. Altered perfusion, for example, seen in the context of a hemodynamically significant patent ductus arteriosus (PDA), has been linked to injury of the immature brain. However, a direct relation with outcome has not been reviewed systematically.

METHODS

A systematic review was conducted to provide an overview of the value of different cerebral arterial blood flow parameters assessed by Doppler ultrasound, in relation to brain injury, to predict long-term neurodevelopmental outcome in preterm infants.

RESULTS

In total, 23 studies were included. Because of heterogeneity of studies, a meta-analysis of results was not possible. All included studies on resistance index (RI) showed significantly higher values in subjects with a hemodynamically significant PDA. However, absolute differences in RI values were small. Studies using Doppler parameters to predict brain injury and long-term neurodevelopmental outcome were inconsistent.

DISCUSSION

There is no clear evidence to support the routine determination of RI or other Doppler parameters in the cerebral arteries to predict brain injury and long-term neurodevelopmental outcome in the preterm infant. However, there is evidence that elevated RI can point to the presence of a hemodynamically significant PDA.

Cerebral Oxygenation in Preterm Infants With Germinal Matrix–Intraventricular Hemorrhages

Background and Purpose— Preterm infants are at risk of developing germinal matrix hemorrhages–intraventricular hemorrhages (GMH-IVH). Disturbances in cerebral perfusion are associated with GMH-IVH. Regional cerebral tissue oxygen saturation (r c SO 2 ), measured with near-infrared spectroscopy, and fractional tissue oxygen extraction (FTOE) were calculated to obtain an indication of cerebral perfusion. Our objective was to determine whether r c SO 2 and FTOE were associated with GMH-IVH in preterm infants.

Methods— This case–control study included 17 preterm infants with Grade I to III GMH-IVH or periventricular hemorrhagic infarction (median gestational age, 29.4 weeks; range, 25.4 to 31.9 weeks; birth weight, 1260 g; range, 850 to 1840 g). Seventeen preterm infants without GMH-IVH, matched for gestational age and birth weight, served as control subjects (gestational age, 29.9 weeks; range, 26.0 to 31.6 weeks; birth weight, 1310 g; range, 730 to 1975 g). R c SO 2 and transcutaneous arterial oxygen saturation were measured during 2 hours on Days 1 to 5, 8, and 15 after birth. FTOE was calculated as FTOE=(transcutaneous arterial oxygen saturation−r c SO 2 )/transcutaneous arterial oxygen saturation.

Results— Multilevel analyses showed that r c SO 2 was lower and FTOE higher in infants with GMH-IVH on Days 1, 2, 3, 4, 5, 8, and 15. The largest difference occurred on Day 5 with r c SO 2 median 64% in infants with GMH-IVH versus 77% in control subjects and FTOE median 0.30 versus 0.17. R c SO 2 and FTOE were not affected by the grade of GMH-IVH.

Conclusions— Preterm infants with GMH-IVH had lower r c SO 2 and higher FTOE during the first 2 weeks after birth irrespective of the grade of GMH-IVH. This suggests that cerebral perfusion is decreased persistently for 2 weeks in infants with GMH-IVH, even in the presence of mild hemorrhages.

Which to measure, systemic or organ blood flow? Middle cerebral artery and superior vena cava flow in very preterm infants

AIM

To describe, in very preterm babies, postnatal changes in measures of middle cerebral artery (MCA) Doppler variables. To relate these peripheral measures to echocardiographic measures of systemic blood flow and ductal shunting, and to study their relation to subsequent intraventricular haemorrhage (IVH).

METHODS

126 babies born before 30 weeks were studied with serial echocardiography and cerebral and Doppler ultrasound of the MCA at 5, 12, 24, and 48 hours of age. Echocardiographic measures included superior vena cava (SVC) flow and colour Doppler diameter of the ductal shunt. MCA Doppler measures included mean velocity, pulsatility index (PI), and estimated colour Doppler diameter.

RESULTS

MCA mean velocity increased whereas the PI decreased significantly over the first 48 hours. Babies with low SVC flow had significantly lower MCA mean velocity and estimated diameter than babies with normal SVC flow. There was no difference in PI. On multivariant analysis, the significant associations with MCA mean velocity were mean blood pressure (MBP), heart rate, SVC flow, and lower calculated vascular resistance. The significant associations with PI were larger ductal diameter and lower mean MBP. The significant associations with MCA diameter were higher SVC flow and lower calculated vascular resistance. After controlling for gestation, there was a highly significant association between lowest SVC flow and subsequent IVH but no association between IVH and lowest MCA mean velocity, estimated diameter, PI, or MBP.

CONCLUSIONS

These data are consistent with the speculation that SVC flow is a reflection of cerebral blood flow. Low SVC flow is more strongly associated with subsequent IVH than cerebral artery Doppler measures or MBP.

Cross-spectral analysis of cerebral autoregulation dynamics in high risk preterm infants during the perinatal period

In preterm infants intraventricular hemorrhage occurs predominantly within the perinatal period, which may be due to a "lost autoregulation" of cerebral blood flow (CBF). In this study, perinatal autoregulation dynamics were investigated in high risk preterm infants by cross-spectral analysis (CSA), which is a statistical tool in the analysis of time series. In 15 ventilated preterm infants of 25-32 gestational weeks, a total number of 30 records were made between 24 and 96 h of life. Doppler-derived CBF velocity (CBFv), used as a quantitative measure for CBF, and direct mean arterial blood pressure (MABP) were measured continuously for 10 min. The spectral power of low frequency (LF, 0.02-0.2 Hz) oscillations in CBFv and MABP was quantified by spectral analysis. From the results of CSA, a LF phase-shift between the CBFv and MABP LF oscillations was calculated in each record. Within the study group, the LF spectral power of CBFv and MABP was initially low and increased significantly until 96 h of life. The LF phase-shift was about 0 degrees at 24 h and increased significantly to 55 degrees at 96 h of life. The initially low LF spectral power of CBFv and MABP may indicate a perinatal depression of autonomic nervous centers, which are thought to control LF oscillations of vital parameters. In the light of a high pass filter model for autoregulation, the initially low LF phase-shift may indicate an initially impaired autoregulation, which supports the "lost autoregulation" hypothesis.

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.

Asymmetry of the cerebral blood flow: an ultrasound Doppler study in preterm newborns

The purpose of this study was to investigate whether the preference of periventricular hemorrhage (PVH) for the left hemisphere is due to asymmetry of cerebral blood flow (CBF) and, if so, whether this asymmetry is due to patent ductus arteriosus (PDA). Thirty-three preterm newborns at risk for PVH were followed during their first 5 days after birth. Internal carotid CBF velocity (CBFV) and the flow direction in the common pulmonary artery, both determined by ultrasound Doppler, served as measures of CBF and PDA, respectively. The difference between right and left CBFV was analyzed statistically, with outcome, PDA, capillary PCO2, behavior, heart rate, and the average of right and left CBFV as covariates. Infants who developed PVH (n = 7) exhibited CBFV asymmetry to the disadvantage of the left side. This finding was partially attributable to PDA. Without PVH there was no significant CBFV asymmetry. Because all hemorrhages were bilateral, a relationship with the side of the hemorrhage could not be explored. In conclusion, asymmetry of CBFV is not normal, but is associated with PVH and PDA.

Effect of rapid thoracic compression on the cerebral blood flow-velocity patterns of small infants

We measured the middle cerebral artery (MCA) flow-velocities of 12 small infants (mean weight, 2,882 +/- 602 g) before, during, and after the rapid thoracic compression (RTC) maneuvers of partial forced expiratory flow-volume studies. Cerebral flow-velocities were measured using transcranial Doppler ultrasonography. RTC increased MCA end diastolic flow-velocities and Pourcelot indices of all infants (P less than 0.001). These values returned to baseline immediately after the release of chest compression. We also measured the MCA flow-velocities of several preterm infants during their normal daily activities. The changes in flow-velocity patterns observed during normal daily life were similar to those observed during RTC. These findings demonstrate that RTC produces real, but likely not pathologic, changes in cerebral blood flow-velocities.