THE PULMONARY EQUILIBRATION OF CYCLOPROPANE IN INFANTS AND CHILDREN: Lack of Functional Brown Adipose Tissue in the Anaesthetized Surgical Infant

Abstract

Pulmonary equilibration of a mixture containing 0.5% cyclopropane and 3% nitrous oxide was studied in four infants and four older children who were anaesthetized for surgery using 0.75% halothane, tubocurarine and a constant volume ventilator. Cyclopropane end-tidal concentration approached inspiratory concentration faster in the infants than in the older children. The difference in FE/FI ratios between the cyclopropane and nitrous oxide equilibration curves was smaller in the infants than in the older children. This was interpreted to mean relatively less absorption of cyclopropane into adipose tissue in the infant group. It suggested that brown adipose tissue was not functional in these infants, in spite of a cold stress of 1° to 2.2 °C. These results were compared with those of a previous study of pulmonary equilibration of the same gas mixture in awake, spontaneously breathing adults. Both the infants and the older children approached equilibrium with cyclopropane faster and had smaller differences in the FE/FI ratios between the cyclopropane and nitrous oxide curves. This suggested relatively less absorption of cyclopropane into all adipose tissue in the younger age groups.