The objective of the present proposed study is to discover whether, in the nursery setting, administration of low concentration inhaled CO2 (0.8%) for a prolonged period (3 days) can make breathing more regular with less apneic time than that observed with administration of theophylline. The hypothesis to be tested is that inhalation of low concentration CO2 (0.8%) will reduce apnea more effectively and will have fewer adverse side effects than theophylline.

1. To discover whether, in the nursery setting, continuous administration of a low concentration of inhaled CO2 (0.8%) for a prolonged period (3 days) can make breathing in preterm infants more regular with less apneic time than that observed with theophylline.
2. To discover whether inhalation of low CO2 decreases apneas, particularly prolonged apneas (>20 seconds), more effectively than theophylline.
3. To discover whether short term (during hospitalization) and long term (2 years) adverse side effects are less pronounced with CO2 than with theophylline.

Inclusion Criteria:

• Infants between 27 and 32 weeks gestational age hospitalized in the neonatal intensive or intermediate care units
• Significant apnea, defined as 5 or more self-resolved apneas, or 2 or more apneas requiring intervention over a 12 hr period

Exclusion Criteria:

• Already on methylxanthine treatment
• On supplemental oxygen, nasal continuous positive airway pressure (CPAP)
• Had major congenital anomalies, sepsis, or other known causes of apnea