The effects of intermittent positive airway and continuous negative extrathoracic pressure ventilation on cerebral blood volume in preterm infants were studied using near infrared spectroscopy. In 12 infants continuous negative extrathoracic pressure caused a median decrease in cerebral blood volume of 0.14 ml/100 ml brain (95% confidence intervals (CI) 0.035-0.280) compared with no respiratory support. Oxygenated and deoxygenated haemoglobin also decreased, implying increased venous drainage as the main effect. In 17 infants intermittent positive pressure ventilation also caused a median reduction in cerebral blood volume of 0.06 ml/100 ml brain (95% CI 0.010-0.115) compared with endotracheal positive airway pressure. Deoxygenated haemoglobin increased by 0.07 ml/100 ml brain (95% CI 0.010-0.100) while oxygenated haemoglobin decreased by 0.10 ml/100 ml brain (95% CI 0.005-0.175). The increase in deoxygenated haemoglobin implies decreased venous drainage and the decrease in oxygenated haemoglobin implies that other factors may also be significant. Heart rate, blood pressure and oxygen saturation were monitored continuously and remained stable.

Near infrared spectroscopy (NIRS) is a relatively new method which is suitable for monitoring oxygenation in blood and tissue in the brain of the fetus and the neonate. The technique involves in vivo determination of the absorption of light in the wavelength range 775 to 900nm through such tissue and converting such changes in absorbance to provide information about the changes in the concentration of oxygenated and de-oxygenated haemoglobin (Hb02 and Hb). Recent developments of the methodology now enable the calculation of changes in cerebral blood volume (CBV) as well as absolute CBV and cerebral blood flow (CBF). The attraction of this method is it's applicability to monitor cerebral function in wide variety of patient groups. Although primarily developed for neontal use it is today applied on the fetus to investigate fetal hypoxia and on adults undergoing surgery.