Oxygen affinity of haemoglobin modulates cerebral blood flow in premature infants: a study with the non-invasive Xe-133 method. Acta Paediatr Scand Suppl 360: 26, 1989. Low cerebral blood flow (CBF) is thought to cause ischaemic brain lesions in premature infants, but a normal outcome has also been observed. Low oxygen affinity of haemoglobin and high arterial oxygen content, independently, reduce CBF under normal, physiological conditions. Transfusions lower the amount of fetal haemoglobin [HbF] and therefore the oxygen affinity of premature babies. In 47 premature babies (range of gestational age 25-34 weeks, birthweight 740-1370 g), CBF was measured with the i.v. Xenon 133 method on days 1, 3 and 7. The relative amount of fetal

Hypoxic-ischaemic brain lesions may be detected as low density (LD) areas by means of computerized tomography (CT), but the clinical significance of such LD areas has been controversial. Since timing might be a critical factor, we studied the temporal evolution of LD areas in 9 asphyxiated term babies who had had two or more CT, and compared the changes to the neurodevelopmental outcome. Scans were classified according to the elapsed time after asphyxia as early (day 1-7, n = 6), intermediate (week 2-4, n = 7; week 4-7, n = 3) and late CT (3 months or more, n = 7). In early scans, no, or only ill defined, LD areas were seen in the periventricular region. In intermediate CT's, LD-zones were further diminished in those babies who later were normal. Sharply accentuated LD areas, however, appeared in those who later suffered from neurodevelopmental disorders. These LD areas, probably representing hypoxic-ischaemic lesions, were located periventricularly, extending into the subcortical white matter and the cortex, and usually involved both hemispheres symmetrically. They began to disappear at 4 to 7 weeks in some regions, possibly because of glial proliferation. LD persisting more than 4-7 weeks tended to transform into cyst-like lesions, or marked atrophy. We conclude (1) that hypoxic-ischaemic lesions appear as zones of low density on CT scans performed after the first week and (2) that the extent of such lesions can best be assessed between 9 to 23 days after asphyxia.

We constructed a Xenon-133 inhalation and trapping system in order to measure cerebral blood flow of ventilated premature babies by means of the noninvasive 133Xe clearance method. The completely lead-shielded inhalation device is a closed system driven by the baby's own respirator and can thus be safely used at the patients bedside in the intensive care unit. Reproducible proximal airway concentrations of 133Xe (with or without leaks around the endotracheal tube) were obtained by in vitro simulation.