Blood Pressure and Tissue Oxygenation in the Newborn Baby at Risk of Brain Damage

Abstract

A cardinal aim of neonatal intensive care is the maintenance of an adequate oxygen supply to the tissues, particularly the brain. This process depends on several factors. These include an adequate blood oxygen content, blood flow to the tissues and the ability of cells to extract and utilise oxygen. Oxygen carriage depends on ventilation and haemoglobin concentration and type. Blood flow depends on cardiac output (in turn dependent on cardiac contractility, heart rate, blood pressure and vascular resistance). Different tissues also have different oxygen demands depending on their oxygen consumption, which are likely to vary within the tissue itself and with the activity of the infant. This paper discusses evidence that suggests that even in preterm neonates, cerebral blood flow may be independent of blood pressure, and that even very low cerebral blood flow seems to be consistent with healthy survival. Evidence is considered that cardiac output rather than blood pressure may be more important in determining brain tissue oxygenation. We have found a negative correlation between cardiac output and cerebral oxygen extraction in preterm infants, but no relationship between mean arterial blood pressure and cerebral oxygen extraction.