The study looked at children with severe asthma who were taking theophylline to prevent asthma attacks. They found that even when the theophylline levels were stable, some children still had asthma attacks. The researchers analyzed the severity of the attacks, the theophylline levels in the blood during attacks, and possible factors contributing to the attacks. They discovered that in most cases, the theophylline levels were lower during attacks than when there were no attacks. The attacks mostly occurred in the evening and night, and children with fever during attacks had lower theophylline levels. This suggests that maintaining a consistent theophylline level in children with asthma can be challenging due to various factors like infections and irregular daily routines.