The Relationship between Cardiac Output, Cerebral Electrical Activity, Cerebral Fractional Oxygen Extraction and Peripheral Blood Flow in Premature Newborn Infants

Abstract

Cardiac output is a determinant of systemic blood flow and its measurement may therefore be a useful indicator of abnormal hemodynamics and tissue oxygen delivery. The purpose of this study was to investigate in very premature newborn infants the relationships between cardiac output (left and right ventricular outputs), systemic blood pressure, peripheral blood flow (PBF) and two indicators of cerebral oxygen delivery (cerebral electrical activity and cerebral fractional oxygen extraction (CFOE)). This was a prospective observational study performed on 40 infants of less than 30 wk gestation. Digital electroencephalograms (EEGs) were recorded for one hour every day during the first four days after birth and subjected to qualitative and quantitative analysis. Left and right ventricular outputs, mean blood pressure (MBP), CFOE, PBF and arterial blood gases were measured at the same time. Within the ranges studied, there was no apparent relationship between left or right ventricular output (RVO), PBF and indicators of cerebral perfusion (cerebral electrical activity and CFOE). The EEG was normal in infants with low left and right ventricular outputs (Ͻ150 mL/kg/min) and MBP Ͼ 30 mm Hg. Infants with low cardiac output and normal MBP seem able to maintain cerebral perfusion, possibly through vasodilatation of the cerebral microvasculature. Clinicians rely on its absolute value to guide therapy and the prescription of volume expanders and inotropes. However, systemic blood pressure is the product of systemic vascular resistance and cardiac output and is not a direct indicator of the systemic blood flow. Nevertheless, the clinician's approach is based on the assumption that hypotension causes decreased organ perfusion, including that of the brain, resulting in tissue damage. Furthermore, the relationship between MBP and cerebral blood flow remains unclear (1,2); it is presumed that cerebral blood flow is preserved by autoregulation even in very preterm babies but the limits of autoregulation are uncertain.Although cardiac output might reasonably be expected to be a major determinant of systemic blood flow (and therefore of tissue oxygen delivery), the relationship is not a simple one.Thus, a study of preterm infants with closed or insignificant patent ductus arteriosus, showed a weak but significant correlation between mean blood pressure (MBP) and left ventricular output (LVO) overall, but LVO was normal for some babies with low MBP, while for others MBP was normal when ventricular output was low (3).There have been relatively few studies of the relationship between cardiac output and cerebral perfusion in the human preterm infant. A recent study of infants between 24 and 30 wk gestation measured cerebral fractional oxygen extraction (CFOE) as a proxy measure of cerebral oxygen delivery: CFOE is increased when cerebral oxygen delivery is low. There was a weak but significant negative correlation between LVO and cerebral fractional oxygen extraction (4). Infants were particularly vulnerable to poor cerebral o...

Relationship between systemic blood flow, blood pressure, inotropes, and aEEG in the first 48 h of life in extremely preterm infants

“…A study by Victor et al (11), which assessed 40 preterm infants born at <30 wk gestation in the first 4 d of life, did not identify any statistically significant relationship between leftventricular output, RVO, or BP with cerebral electrical activity (measured using digital EEG) or cerebral fraction oxygen extraction. Qualitative assessment of the EEG was normal in all infants with BP >30 mmHg, even when cardiac output (leftventricular output and RVO) was low.…”

“…Several studies have assessed the relationship between BP or systemic blood flow and CBF (5-10), with a range of conclusions. Few previous studies have assessed the relationships between hemodynamic parameters in neonates and EEG (11,12) in preterm neonates in the first 48 h of life. A study by West et al (12), which assessed the relationships between RVO, SVC flow, BP, aEEG amplitude, and EEG continuity in the first 48 h of life in 40 infants born at <31 wk gestation, found similar associations between BP, RVO, and aEEG amplitude at 12 h, with only limited associations beyond 12 h. In the study by West et al, SVC flow was not associated with aEEG parameters.…”

“…Hellström-Westas et al (4) investigated the effect of surfactant treatment on continuous aEEG recordings and found a short (<10 min) but significant decrease in cerebral activity in almost all the neonates immediately after the surfactant instillation, despite improved pulmonary function. Although a number of studies have assessed the relationship between hemodynamic parameters and CBF in neonates (5)(6)(7)(8)(9)(10), few studies have assessed the relationship between hemodynamic parameters and aEEG in the first 48 h after birth (11,12).…”

“…There is a paucity of evidence looking at the effect of systemic blood flow on the electrocortical activity of extremely preterm infants as measured by aEEG (3,10,12) and EEG (11) in the first 48 h of life. The little information that is available is conflicting: some studies have found an association between abnormal aEEG activity and low cardiac output, specifically low RVO (12,18); other studies do not show an association (3,10,11). The aim of this study was to assess the associations between SVC flow, RVO, BP, and quantitative aEEG parameters in the first 48 h of life in infants born at 24-28 wk gestation.…”

Effect of permissive hypercapnia on background cerebral electrical activity in premature babies

“…Prolonged EEG IBIs of more than 30 s in preterm infants born at less than 28 wk gestation and more than 25 s in preterm infants born at more 28 wk gestation have been associated with increased incidence of death or developmental motor abnormalities (6,7). EEG has been studied in relation to age, hypotension, hypo and hypercapnia, and cardiac output in preterm babies born before 30 wk gestation during the first 72 h after birth (8)(9)(10)(11). Lower levels of blood carbon dioxide have been associated with slowing of cerebral electrical activity and increased cerebral fractional oxygen extraction, while hypercapnia was associated with suppression of cerebral electrical activity during the first 48 h after birth (9).…”