Most neonatologists include an
apnea-free period in the criteria for the discharge of preterm infants. However, the length of time one should wait after the cessation of
apnea before sending an infant home without a monitor is debated. We undertook this study in an attempt to define a minimal and safe observation period between the time of the last
apnea episode and discharge.
METHODS: We reasoned that in infants with idiopathic
apnea of prematurity, the intervals between days on which
apnea occurs gradually increase until some point at which clinically significant
apnea ceases. Therefore, knowledge about the intervals between days on which
apnea occurred just before the last
apnea would provide a reasonable estimate of the minimal safe observation interval between the last
apnea and discharge. We reviewed the charts of 266 infants born in 1993 and 1994 at </=32 weeks' gestational age or weighing </=1500 g at birth from two institutions to determine the intervals between the day on which the last
apnea occurred and the previous two days on which
apnea occurred. One hundred seventy-five infants were excluded because they never experienced
apnea, or data about the last
apnea was missing, or they were on
xanthines during the period encompassing the last 3
apnea days, or they weighed <1500 g or were <34 weeks' postmenstrual age at the time of the last
apnea. Of the 91 remaining infants, gestational age at birth,
birth weight, 1- and 5-minute Apgar scores, and discharge weight were not different between the two institutions. For each infant we determined the longest of the intervals between the 2 days on which
apnea occurred previous to the day of the last
apnea (MAXINT for maximum interval). The infants were then ordered by MAXINT and, starting at the longest MAXINT, the medical records of each infant were carefully examined for other conditions known to be associated with
apnea (eg, recovering from
anesthesia,
sepsis, chronic
lung disease, and so forth). The minimal safe observation period was then defined as the longest MAXINT in which there was at least 1 infant with no other explanation for the
apnea other than prematurity.
RESULTS: The median duration of the intervals between the 2 days on which
apnea occurred previous to the day on which the last
apnea occurred were 3. 0 and 2.0 days and the median duration of the MAXINT was 4.0 days. On careful examination of the charts, it was determined that each of 13 infants with a MAXINT preceding the day on which the last
apnea occurred of greater than 8 days had some other condition that might result in
apnea, including residual
lung disease,
sepsis, surgery, and so forth. In contrast, among the group of infants with a MAXINT of </=8 days, at least 1 infant at each MAXINT (eg, 1 to 8) had significant
apnea with no other explanation other than prematurity.
CONCLUSIONS: We conclude that otherwise healthy preterm infants continue to have
apneas separated by as many
as 8 days before the last
apnea before discharge. Conversely, infants with longer
apnea intervals often have identifiable risk factors other than
apnea of prematurity.