Analysis of cranial 133-Xenon clearance in the newborn infant by the two-compartment model

Abstract

Cranial and chest clearance curves after intravenous administration of 133-Xenon was obtained on 112 occasions in 62 newborn infants admitted to our neonatal intensive care unit. The mean postnatal age was 5.1 days. The cranial clearance curves were submitted to two-compartment analysis. The compartmental clearance rate constants were 1.49±0.61/min and 0.099±0.033/min respectively while the fractional flow to the fast compartment was 0.51±0.14. Possible artefacts, particularly relevant to newborns, were analysed by computer simulation. It is concluded that the cranial 133-Xenon clearance curves varied considerably within the group of ill newborns and that the mean two-compartment parameter values differed considerably from those of healthy premature infants or adults, with or without cerebral illness. But the computer simulations demonstrated that the two-compartment parameters had high coefficients of variation and were significantly biased by right-to-left shunting of blood through the foramen ovale, by heterogeneity of the flow to the fastest compartment and by contamination of the cranial clearance curves by 133-Xenon in the airways. The radiation dose was 1.3 mGy to the lungs and 0.2 mGy to other tissues.

Key Words:

• airway artefact
• cerebral blood flow
• computer simulation
• heterogeneity
• 133-Xenon kinetics
• right-to-left shunt