Effects of age and cardiac shunts on the measured uptake of nitrous oxide in children

The uptake of nitrous oxide (N₂O) was calculated by using a new application of pharmacokinetics involving cumulative fractional expired N₂O concentration at 90 percent steady state. The effect of age on N₂O uptake was investigated in 33 normal children undergoing non-cardiac surgery. Uptake was also investigated in 17 children with right-to-left cardiac stunts and 18 children with left-to-right shunts undergoing corrective or palliative cardiac surgery. There was a significant correlation of N₂O elimination half-life (T( 1/2 )) with age for normal children (p < 0.001), and for children with right-to-left (p <0.001) or left-to-right (p = 0.05) shunts. Elimination T( 1/2 ) in children with left-to-right shunts correlated significantly with the calculated shunt fraction (p <0.05). By providing a useful means for comparison, this method of measuring N₂O uptake permits determination of the effects of age, weight and cardiac shunts on the uptake kinetics of N₂O.