Cerebral oxygenation in the preterm neonate

Abstract

Although survival rates of preterm infants are improving, preterm birth is still associated with significant morbidity.The brain is one of the most vulnerable organs in preterm infants. Neonatal brain injury can have a large impact on the quality of life. Monitoring the immature brain is therefore important. Cerebral oxygenation can be monitored with near-infrared spectroscopy (NIRS), a method which sends near-infrared light (700 – 1000nm) through brain tissue and calculates regional cerebral oxygen saturation, which reflects oxygen supply, and cerebral fractional tissue oxygen extraction, reflecting oxygen utilization. The balance between oxygen supply and utilization provides insight in cerebral (patho-)physiology. In our neonatal intensive care unit, cerebral oxygenation monitoring is standard clinical care, together with the amplitude-integrated electro-encephalogram, cranial ultrasound, magnetic resonance imaging (MRI), and the monitoring of vital parameters. With cerebral NIRS, the neonatologist has a tool to monitor the oxygenation of the brain non-invasively. In this thesis we have analysed several factors that affect cerebral oxygenation, in order to gain a better understanding of the (patho-)physiology of the brain. First of all, it is important to take the type of NIRS device and sensor into account, as differences may exist between neonatal sensors and the adult sensors. Reference values for the first 3 days of life in preterm neonates have now been published for both the adult and the neonatal sensors. These values are based on a large cohort of 999 infants. Additionally, the effects of gender, a patent ductus arteriosus (hsPDA) and birth weight have been analysed. Cerebral oxygenation can be affected by several clinical factors. It can be lower in female neonates than in males, or in case of a hsPDA. A hsPDA can negatively affect cerebral perfusion and oxygenation by the ductal steal effect. Additionally, hypocapnia can induce cerebral vasoconstriction and decrease cerebral oxygenation. Cerebral oxygenation is higher with advancing postnatal age and gestational age, in male neonates, and in infants born small-for-gestation-age (SGA). Even though SGA infants have a higher cerebral oxygenation, presumably due to the brain sparing effect by intrauterine growth retardation, they are more severely affected by the negative effect of a hsPDA. Furthermore, hypercapnia can induce cerebral vasodilation with an increase in cerebral oxygenation. The safe range of regional cerebral oxygen saturation is presumed to be between 55-85%. Prolonged exposure to values outside this range has been associated with cerebral injury: especially low cerebral oxygenation has been associated with poor cognitive outcome at early school age in infants with a hsPDA. Early detection of these deteriorations of cerebral oxygenation with appropriate interventions might avoid situations with unfavourable cerebral homeostasis and prevent injury, thereby improving neurodevelopmental outcome. Awareness of which factors affect cerebral oxygenation, and in what way, is therefore of the utmost importance.