The maturation of respiratory control is an important part of the discharge-planning pathway. Clinicians typically assess this maturation through clinical observation of infants in the hospital, the times for which can range from 1 to 21 days.6
However, many of these observation times are the same regardless of the characteristics of the infant or when this observation period occurs. Our study of more than 1400 premature infants suggests that a large number of infants do not have future apnea or bradycardia events once they are otherwise ready for discharge on the basis of other physiologic characteristics. Younger gestational age, older chronologic age at the time of observation, and site of care were associated with lower success rates. We found higher success rates when we restricted the analysis to infants who were off methylxanthines for 3 or 5 days. These data suggest that guidelines on the basis of patient characteristics, such as gestational age, chronologic age, and days off of methylxanthines, would optimize the discharge planning of premature infants and discontinuation of home monitoring by primary care physicians.
suggests that apnea and bradycardia are more common in premature infants than in healthy term infants or infants with idiopathic apnea and that this risk remains elevated until 43 weeks' PMA. Much of the earlier work on the epidemiology of apnea and bradycardia within premature infants centers on the effect of gestational age on the timing of the last apnea or bradycardia event. Darnall et al6
examined 91 infants with a gestational age of less than 32 weeks who were born between 1992 and 1993. These infants had their last apnea event at an average PMA of 37.7 ± 0.3 weeks. Infants with a gestational age of 28 weeks or less had their last event ~2 weeks later than older infants. Similar results were found in a single-center study4
of 226 infants with a gestational age between 24 and 28 weeks. In this study, ~20% of infants with a gestational age of 26 weeks or less had an apnea event at 40 weeks' PMA or later. Severe events resolved at an earlier PMA than self-resolved events, similar to our study results. Our data also suggest that gestational age may influence the resolution of apnea or bradycardia events once the infants are ready for discharge because younger infants, especially those with a gestational age of less than 26 weeks, were more likely to have a future event than infants of older gestational ages.
The PMA of the last event also may be an important factor in the epidemiology of apnea and bradycardia. Apnea and bradycardia events were common several days or weeks after the last event if the last event occurred at a PMA of 36 weeks or older, regardless of the gestational age of the infant. Compared with term infants, prematurely born infants have a blunted response to a hypercapnea challenge,16
a diminished glossopharyngeal muscular contraction in response to periodic breathing,17
and a higher percentage of swallowing events that result in apnea when attempting to oral feed.18
These physiologic responses mirror infants born at term as the premature infant matures.18,19
Infants with persistent apnea or bradycardia may have delayed maturation of these physiologic skills or, as suggested by , increased severity of common complications of prematurity that may influence the resolution of apnea or bradycardia events.
Our study found inter-NICU differences in the success rates of various observation time periods, similar to previous work20
that found wide inter-NICU variations in the time to the last apnea or bradycardia events. Our results suggest that the case mix of the NICU may influence the success rates of various observation time periods because NICUs with a larger percentage of infants observed after 38 weeks' PMA had lower overall success rates. Accounting for process differences between NICUs reduced inter-NICU variation in success rates by 50% to 90%. These results emphasize the importance of processes of care in understanding differences in inter-NICU outcomes.
Finally, these data show the difficulty in applying statistics for diagnostic tests to the care of an individual patient. For each observation time, the EIR of the observation interval was much lower than the success rate of the test. This fact occurred because more than 75% of the infants did not have a future apnea or bradycardia event once they met other criteria for discharge. For a clinician observing a specific newborn, the more relevant statistic is the success rate if the apnea or bradycardia recurrence in their NICU was similar to those units included in this study. However, the EIR can be used to generate NICU-specific success rates when the overall recurrence risk of apnea or bradycardia differs from those units included in this study.
There are several limitations to this study. First, all events were captured through a nursing report in the medical chart, which were standardized between the multiple sites in the KPMCP health care system. Short, spontaneously resolving events may have been missed if the nurse was distracted when the event occurred.21
have used a similar data-collection methodology. Nursing records should, however, capture all events that required respiratory intervention by a health care provider. When we only examined these events, we found similar results to the data that used all events. Also, we only were able to use events after discharge that resulted in a visit to a health care provider. Short, self-limited events or obstructive events without apnea may have been missed.5
As a result, when a health care provider decided to discharge a patient may marginally affect these results for those infants discharged relatively soon after their last apnea or bradycardia event. This study also used information from a limited number of NICUs because of the difficulty in collecting detailed data on respiratory maturity from a large number of premature infants with complete postdischarge data. The statistical power provided by this cohort is important to understanding the relationship between gestational age, PMA of the last event, and the future risk of apnea or bradycardia. Finally, the clinical relevance of a 95% or 98% success rate threshold is not certain in the context of apnea or bradycardia.