Abstract
Survival of extremely preterm infants has greatly improved over the last decades. Despite this, perinatal brain damage with adverse neurodevelopmental outcome is still affecting a considerable number of these infants. Although the etiology of brain damage is multifactorial and even partly unknown, hypoxia, hyperoxia and hemodynamic instability during the first
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days of life seem to play an important role. The present thesis describes and discusses the clinical use of a promising non-invasive brain monitoring technique, the near infrared spectroscopy (NIRS)-monitored regional cerebral oxygen saturation (rScO2) and cerebral fractional tissue oxygen extraction (cFTOE). The study investigates the patterns of rScO2 and cFTOE in preterm infants with a gestational age of less than 32 weeks during the first days of life, together with other monitoring parameters during different clinical conditions. The technique is based on the transparency of biological tissue to near infrared light and its subsequent absorption by chromophores (hemoglobin). Absorption changes in near infrared light can be converted into concentration changes of oxygenated and deoxygenated hemoglobin and from here to regional oxygen saturation (rScO2). Together with the arterial oxygen saturation (SaO2), cFTOE can be calculated ((SaO2-rScO2)/SaO2). Reference values of rScO2 range from 61 to 75% in the human neonate. An important finding was that during stable and physiological SaO2-values no differences between left- and right sided NIRS-monitored values were noted. This suggests that unilateral NIRS-monitoring can serve as trend monitoring in these infants to detect important changes in cerebral oxygenation. Although there was a larger variance in preterm infants suffering from severe respiratory distress syndrome (RDS), mean values of rScO2 and cFTOE did not differ from a control group without RDS. However, RDS infants had more periods of a significant correlation between rScO2 (and cFTOE) and mean arterial blood pressure, suggesting more periods of lack of cerebral-vascular autoregulation. No changes of rScO2 and cFTOE were measured during treatment of RDS with the InSurE-procedure: i.e. short term Intubation for exogenous Surfactant treatment followed by Extubation, a method to prevent mechanical ventilation induced lung damage. Therefore, this method seems not to affect the cerebral oxygen supply. The study demonstrated also that infants with a persistent ductus arteriosus (PDA), a common problem in preterm infants, had lower rScO2‘s and higher cFTOE’s compared with a control group up to 24 hours after initiating pharmacological treatment with indomethacin. Twelve out of twenty infants with PDA treated with surgery after pharmalogical treatment failed showed a further decrease of rScO2 during surgery. Therefore, the study shows also that surgical closure of a duct carries the risk for a further decrease of an already compromised cerebral oxygenation in infants with a PDA. Finally, the relation between rScO2 and neurodevelopmental outcome was investigated in 36 infants. Despite the small sample size, it was surprising that rScO2s on day 1 were higher (rScO2 >70%) in infants with a suboptimal neurodevelopmental outcome. At this stage NIRS-monitored oxygenation of the immature brain by rScO2 lacks precision to be used as robust quantitative variable to monitor cerebral oxygenation, but when used merely as a trend monitor in the individual patient, substantial changes of rScO2 and consequently of cFTOE, can yield important clinical information that may lead to intervention. One of the main problems is that the precision of the commercially available devices is not optimal and that the sensors are not optimized for the smallest infants. Devices that are more precise and sensors that are smaller will have to be developed for the use in the very small preterm infant. Furthermore, lower and upper limits of rScO2 will have to be defined in more detail.
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