Effects of prone and supine position on sleep characteristics in preterm infants
Kazuya Goto MDDepartment of Pediatrics, Oita Medical University, Idaigaoka 1-1, Hasama-machi, Oita Gun, 879-5593 Oita, Japan.
The purpose of this study was to address the influence of sleep position on sleep characteristics in preterm infants. We studied 16 infants at a mean post-conceptional age of 36.5 weeks. Infants were successfully recorded with videopolysomnograph in the supine and prone position. Between the two positions, there were no significant differences in percentage of active sleep and quiet sleep (QS), the occurrence of arousal, and the incidence of apnea. The first QS after the feeding was longer in the prone position. The sleep position could affect sleep characteristics but not respiratory characteristics in preterm infants.
The Task Force by The American Academy of Pediatrics in 19961 recommended that, in addition to full-term infants, asymptomatic preterm infants sleep in the non-prone sleeping position to prevent sudden infant death syndrome (SIDS). However, the precise effect of sleeping position on sleep characteristics have never been addressed in preterm infants.2,3 The present study was conducted to evaluate the effects of sleeping position on sleep characteristics in preterm infants with a post-conceptual age (PCA) of around 36 weeks.
MATERIALS AND METHOD
Sixteen healthy preterm infants, with a gestational age (GA) of 32.2 ± 3.0 weeks and birth weight 1733 ± 135 g, were studied at a PCA of 36.5 ± 0.6 weeks. Polysomnography combined with time-lapse video recording (videopolysomnography (VPSG)) were made in the nursery. All preterm babies were dressed during the recording. The recordings lasted for 6 hours, usually from 11.00 till 17.00 h. After the first feeding, each infant was randomly assigned to the supine or prone position and the position was reversed after the second feeding. Polysomnographic recordings were obtained with an ambulatory digital sleep recorder (Embla). The following variables were recorded simultaneously: four scalp electroencephalograms, two electrooculograms, a chin electromyogram, electrocardiogram, thoracic respiratory movement, and oxygen saturation. The data were viewed and analyzed by the Embla software. A time-lapse video recorder enabled us to observe the behavior of infants.
Each 30 s epoch of the recordings was classified as either awake (W), active sleep (AS), indeterminate sleep (IS), quiet sleep (QS) and periods of out-of-crib/out of view/intervention. A 1-min moving average of states was used. Arousal was defined by the occurrence of body movement ≧ 10 s, and/or cry and/or eye opening ≧ 5 s according to the arousal study in infants.4 Arousal time lasting for 60 s or more was defined as an awakening.
We compared the following sleep measures between two sleep positions in each infant: (i) total sleep time (TST); (ii) AS, IS, and QS percentage of TST; (iii) the number of awakenings per 100 min during AS + IS and QS; (iv) the ratio of total awakening time over the TST; (v) the number of arousals per 100 min of AS + IS, and QS. We also measured the following values during first sleep cycle after feeding: (i) length of AS and QS; (ii) the number of awakenings per 100 min of AS and QS; (iii) the number of arousals per 100 min of AS and QS.
Statistical analysis was performed with the paired student’s t test, Mann-Whitney U test, and Wilcoxon’s signed rank sum test. Significance was accepted at P < 0.05.
Table 1 shows the sleep characteristics of the supine and prone positions. There were no significant differences in the percentage of each sleep state and the number of arousals between the supine and the prone position. However, the number of awakenings and the ratio of total awakening time to TST were significantly higher in the supine compared to the prone position.
Table 1. .
Comparison of sleep characteristics between the prone and supine position
The noticeable differences between the two positions were found in the first QS. The duration of the first QS was significantly longer in the prone position. In addition, the prone position was associated with less awakening in the first QS in comparison with the supine position. Apnea index of AS + IS, and QS did not show any significant differences between the two positions in both the TST and the first sleep cycle.
Previous studies on the effect of position on sleep suggested that infants would spend less time awake and more time in QS in the prone position.2,3 In accordance with these results, we have found increased QS in prone position but only in the first sleep cycle.2,3 We have also found that both the number of awakenings and the total awake time were significantly less in the prone position. However, there were no changes in total percentage of AS, IS, and QS between the two sleep positions.
Several factors are important when comparing differences of the data in the literature and our own findings. First of all, most of the subjects in the earlier studies were full-term infants. In addition, the infants were clothed during sleep in the present study, while preterm and full-term infants were unclothed during recording in other studies. Sleep behavior could be affected by the clothing in addition to the sleeping position.
It also remained unclear why the effects of the position were limited to the first sleep cycle in this study. Various physiological changes induced by feeding might also interact with body position, metabolic rate, and sleep architecture.
Although changes in sleep behavior caused by the prone position have been causally related to SIDS, we cannot conclude that all changes in sleep behavior caused by the prone position are related to the pathophysiology of SIDS. The advantage and disadvantage of the sleep-maintaining effect caused by the prone position need further study.
In conclusion, this study showed that sleep in preterm infants is influenced by the sleep position, although the degree of influence seems to be less in preterm infants than in full-term infants. These influences should still be considered particularly in the aspects of neurobehavioral development.