Transcutaneous Oxygen Monitoring in Aminophylline-Treated Apneic Infants

Abstract

Transcutaneous PO₂ (tcPO₂) monitoring offers a new approach to the evaluation of drug effects. We investigated the effect of theophylline on ten premature infants with apnea. Theophylline was administered as aminophylline, 8 mg/kg per rectum every 12 hours for two doses and 4 mg/kg every 12 hours for a total of two or five days (short and long courses). The tcPO₂, heart rate (beat-to-beat), and thoracic impedance were continuously monitored during each of three 4-hour study periods: 12 hours before theophylline administration, 12 hours after initiation of theophylline therapy, and 24 to 48 hours after discontinuing the drug's use. Plasma levels were measured by a radioimmunoassay developed in our laboratory. Polygraphic recordings were analyzed without knowledge of treatment for frequency of apneic spells, mean duration of apneas, total duration of hypoxemia (tcPO₂ ≤40 torr), total duration of hyperoxemia (tcPO₂ ≥100 torr), basal tcPO₂, heart rate, and respiratory rate.

In each case during theophylline use, cardiorespiratory patterns were altered, respirations were more regular, apneic spells were reduced, PO₂ was stabilized with less hypoxia and hyperoxia, and bradycardic episodes were decreased. There was considerable variation in the response of the ten infants and a significant difference in the frequency of return of symptoms between those receiving short-term therapy and those receiving the longer course.