The relationship between arterial blood gases and serum theophylline clearance in critically ill patients.

Theophylline clearances were monitored at 8-h intervals in a group of critically ill patients and changes in the clearances were correlated with changes in the arterial blood gases. A total of 183 samples from 20 patients were analyzed. The initial theophylline clearance ranged from 20 to 89 ml/kg/h. The initial clearances could not be predicted from the patient's age, arterial blood gases, or the presence of congestive heart failure, liver dysfunction, or other medical problems. For individual patients, the theophylline clearance varied markedly during the study, with the mean maximal clearance averaging 54% higher than the mean minimal clearance. Changes in clearances were not correlated with changes in the arterial blood gases. On the basis of this study, we recommend an initial aminophylline infusion rate of 0.5 mg/kg/h in all critically ill patients. Serum theophylline concentrations should then be determined at 24-h intervals until stabilization and at 48-h intervals thereafter with appropriate adjustments in aminophylline doses.