Fluctuating Pressure-Passivity Is Common in the Cerebral Circulation of Sick Premature Infants

Abstract

Cerebral blood flow pressure-passivity results when pressure autoregulation is impaired, or overwhelmed, and is thought to underlie cerebrovascular injury in the premature infant. Earlier bedside observations suggested that transient periods of cerebral pressure-passivity occurred in premature infants. However, these transient events cannot be detected reliably by intermittent static measurements of pressure autoregulation. We therefore used continuous bedside recordings of mean arterial pressure (MAP; from an indwelling arterial catheter) and cerebral perfusion [using the nearinfrared spectroscopy (NIRS) Hb difference (HbD) signal) to detect cerebral pressure-passivity in the first 5 d after birth in infants with birth weight Ͻ1500 g. Because the Hb difference (HbD) signal [HbD ϭ oxyhemoglobin (HbO2) Ϫ Hb] correlates with cerebral blood flow (CBF), we used coherence between MAP and HbD to define pressure-passivity. We measured the prevalence of pressurepassivity using a pressure-passive index (PPI), defined as the percentage of 10-min epochs with significant low-frequency coherence between the MAP and HbD signals. Pressure-passivity occurred in 87 of 90 premature infants, with a mean PPI of 20.3%. Cerebral pressure-passivity was significantly associated with low gestational age and birth weight, systemic hypotension, and maternal hemodynamic factors, but not with markers of maternal infection. Future studies using consistent serial brain imaging are needed to define the relationship between PPI and cerebrovascular injury in the sick premature infant. C erebral pressure autoregulation maintains CBF relatively constant despite changes over a range of systemic blood pressures known as the autoregulatory plateau (1). Conversely, when changes in blood pressure result in concordant changes in CBF, the cerebral circulation is deemed "pressure passive." Current understanding is that cerebral pressurepassivity develops when changes in blood pressure exceed the capacity of the intact cerebral autoregulatory system or when the system is impaired by illness, injury, or vasoactive medications. Cerebral pressure-passivity is considered a risk factor for cerebrovascular injury in the sick premature infant (2-4). The current study extends our earlier work (3) using bedside NIRS to measure continuously cerebrovascular responses to spontaneous fluctuations in blood pressure. In our previous studies, we observed that cerebral pressure-passivity may wax and wane over relatively short periods in premature infants. To study the fluctuating nature of cerebral pressure-passivity and quantify its prevalence over time, we developed a continuous recording and analysis system because previously described techniques using intermittent static measurements (5-7) would be unable to measure the prevalence of fluctuating cerebral pressure-passivity over the highest risk for brain injury in premature infants. The principal aim of this technique is to make quantitative measurements of the prevalence of cerebral pressure-passivity rather...

Respiratory support for premature neonates in the delivery room: effects on cardiovascular function and the development of brain injury

“…However, preterm infants commonly have episodes of impaired autoregulation, primarily due to immaturity of or injury to the cerebral vascular bed (40). Episodes of impaired autoregulation occur in 87 of 90 premature infants <30 wk gestation and may be present 50% of the time during the first 5 d after birth (41). The combination of developmental immaturity and an inability to autoregulate CBF can render the preterm neonatal brain susceptible to injury in response to systemic circulatory disturbances occurring as a result of suboptimal ventilation.…”

The Instrumented Fetal Sheep as a Model of Cerebral White Matter Injury in the Premature Infant

“…The sheep fetus displays cerebral hemodynamics similar to humans and permits repeated physiological measurements in utero in the unanesthetized state. Importantly, similar to the human fetus [77][78][79][80], the fetal sheep displays a very limited range of cerebral autoregulation under normal conditions and a pressure-passive cerebral circulation when subjected to systemic hypoxia and associated hypotension [66,[81][82][83][84]. Moreover, measurements of BP, electroencephalography, blood oxygenation, and other vital variables can be correlated with acute changes in cerebral blood flow and metabolism.…”

Measuring cerebrovascular autoregulation in preterm infants using near-infrared spectroscopy: an overview of the literature

“…seizures or IVH) and control preterm infants [28]. Soul et al found impaired cerebrovascular autoregulation in about 20% of the recording time using NIRS in 87 out of 90 very preterm infants during the first 5 days after birth [29]. Other studies also reported on fluctuating autoregulation impairment during the first days after birth [6,[30][31][32][33].…”

“…Clinical factors related to impaired cerebrovascular autoregulation are lower gestational age (GA) [29,34,35], lower birth weight (BW), lower glucose levels [29,34,36], higher clinical risk index for babies (CRIB) score [34], increased infant mortality [34,37], and higher PaCO 2 levels [15,38,39]. Perinatal risk factors such as pregnancy induced hypertension; antepartum hemorrhage and placental infarction are also associated with impaired cerebrovascular autoregulation [29].…”

“…Perinatal risk factors such as pregnancy induced hypertension; antepartum hemorrhage and placental infarction are also associated with impaired cerebrovascular autoregulation [29]. Other pathologies associated with impaired autoregulation include RDS [33] and necrotizing enterocolitis [40].…”