Head turning and face-down positioning in prone-sleeping premature infants

The effect of positioning on preterm infants' sleep-wake states and stress behaviours during exposure to environmental stressors

Previous studies separately examined the effects of positioning or environmental stressors on preterm infants' sleep and stress. Since positioning and environmental stressors occur simultaneously during infant hospitalization exploring these variables in the same study may offer new insights. A quasi-experimental study by one-group interrupted time-series design. In the current study, a total of 22 preterm infants were enrolled. Each infant was moved to either the supine or prone position for an hour at a time. Infants were videotaped and the sleep-wake states, stress behaviours and environmental conditions (light, noise and stimulation/handling) were recorded during the observation period. A total of 80 observations from 22 infants were accrued. In the supine position, preterm infants demonstrated more frequent waking states after adjusting for various environmental stressors (p < .01). These infants demonstrated more frequent stress behaviours in the supine position after adjusting for various environmental stressors (p < .01). These results suggest that the prone position is a more favourable position for facilitating sleep and reducing stress for preterm infants exposed to varying environmental stressors. Preterm infants present different stress behaviours in response to varying types of environmental stimuli.

The physiological determinants of sudden infant death syndrome

It is well-established that environmental and biological risk factors contribute to Sudden Infant Death Syndrome (SIDS). There is also growing consensus that SIDS requires the intersection of multiple risk factors that result in the failure of an infant to overcome cardio-respiratory challenges. Thus, the critical next steps in understanding SIDS are to unravel the physiological determinants that actually cause the sudden death, to synthesize how these determinants are affected by the known risk factors, and to develop novel ideas for SIDS prevention. In this review, we will examine current and emerging perspectives related to cardio-respiratory dysfunctions in SIDS. Specifically, we will review: (1) the role of the preBötzinger complex (preBötC) as a multi-functional network that is critically involved in the failure to adequately respond to hypoxic and hypercapnic challenges; (2) the potential involvement of the preBötC in the gender and age distributions that are characteristic for SIDS; (3) the link between SIDS and prematurity; and (4) the potential relationship between SIDS, auditory function, and central chemosensitivity. Each section underscores the importance of marrying the epidemiological and pathological data to experimental data in order to understand the physiological determinants of this syndrome. We hope that a better understanding will lead to novel ways to reduce the risk to succumb to SIDS.

Prematurity and sudden infant death syndrome: United States 2005-2007

OBJECTIVE

In 1987, the sudden infant death syndrome (SIDS) rate in the United States was 1.2 per 1000 live births. By the year 2005, the SIDS rate had dropped more than half to approximately 0.5 per 1000 live births. In 1987, the risk of SIDS was 2.32 times greater for extremely premature infants compared with term infants. The objective of this analysis was to determine if with the falling SIDS rate there has been a change in the risk for SIDS among preterm infants.

STUDY DESIGN

Data were obtained from the United States Linked Infant Birth and Death Certificate Public User Period files for the years 2005 to 2007. The adjusted odds ratios (ORs) for postneonatal out-of-hospital death by gestational age were determined by logistic regression modeling.

RESULT

Over the 3-year period, there were 5203 postneonatal out-of-hospital deaths attributable to SIDS; 2010 attributable to other sudden deaths; 1270 attributable to suffocation in bed; and 3681 attributable to other causes. The adjusted OR for SIDS among the most preterm infants (24 to 28 weeks gestation) was significantly increased compared with term infants, OR(adj)=2.57 (95% confidence interval=2.08, 3.17), as were the adjusted ORs for the other causes of sudden infant death.

CONCLUSION

Despite the marked drop in the incidence of SIDS since 1987, the risk for SIDS among preterm infants remains elevated. Other causes of sudden infant death for which SIDS is often mistaken reflect similar levels of increased risk among preterm infants.

The effects of nicotine on the alpha-7 and beta-2 nicotinic acetycholine receptor subunits in the developing piglet brainstem

Exposure to cigarette smoke is a major risk factor for sudden infant death syndrome (SIDS). We tested the hypothesis that nicotine increases expression of the nicotinic acetylcholine receptor (nAChR) subunits alpha7 and beta2 in a piglet model. Piglets exposed to 2mg/kg/day nicotine for 14 days postnatally (n=14) were compared to non-exposed controls (n=14), (equal gender proportions). Immunohistochemistry was performed to identify and quantify changes in, alpha7 and beta2 nAChR subunits in 8 nuclei of the medulla at both the rostral and caudal levels. Compared to controls, nicotine exposed piglets had decreased alpha7 in the rostral dorsal motor nucleus of the vagus (rDMNV) (p=0.01), and increased beta2 in the caudal DMNV (cDMNV) (p=0.05), caudal nucleus of the spinal trigeminal tract (cNSTT) (p=0.03) and caudal nucleus of the solitary tract (cNTS) (p=0.04). Analysis by gender showed that in the control group, compared to males, females had higher beta2 in the caudal hypoglossal (cXII) (p<0.01) and caudal inferior olivary (p=0.04) nuclei, while in the nicotine group females had higher beta2 in the cDMNV (p=0.02). Compared to control males, nicotine exposed males had lower beta2 in the cXII (p<0.01). Overall, changes in alpha7 were specific to nicotine exposure with no gender differentiation. Changes in beta2 were more widespread but showed gender-specific effects. These findings provide evidence that early postnatal exposure to nicotine significantly affects nAChR subunit expressions in the developing brainstem.

Habituation of arousal responses after intermittent hypercapnic hypoxia in piglets

RATIONALE

Clinical studies have demonstrated arousal deficits in infants suffering obstructive sleep apnea, and some infant deaths have been attributed to such an arousal deficit.

OBJECTIVES

To evaluate whether arousal deficits can be induced by intermittent asphyxia during normal development.

METHODS AND MEASUREMENTS

Young piglets were exposed to intermittent hypercapnic hypoxia for 4 days from age 9.55 +/- 0.5 days. Arousal responses were compared between control animals and animals exposed to intermittent hypercapnic hypoxia. Outcome measures included time to arouse after onset of the respiratory stimulus and frequency of arousals during recovery.

MAIN RESULTS

Arousal deficits emerged after successive exposures to hypercapnic hypoxia on Day 1, and were exacerbated on Day 4, although after overnight recovery, the deficit only became evident during the second and subsequent episode of hypercapnic hypoxia. On Day 1, time to arouse increased from 16.9 +/- 7.1 seconds in the first epoch to 41.7 +/- 28.6 seconds in the fourth epoch (p = 0.004 between cycles, one-way analysis of variance). In the recovery periods after hypercapnic hypoxia, there were 64% fewer arousals than baseline on Day 1 and 90% fewer arousals on Day 4. Respiratory effort, measured by VT across 10 breaths before the arousal, increased from 25.7 +/- 7.6 on Day 1 to 29.1 +/- 6.8 ml/kg on Day 4 (p < 0.001, two-way analysis of variance, Day 4 vs. Day 1, respectively).

CONCLUSIONS

These studies demonstrate that acute and chronic arousal deficits can be induced by intermittent asphyxia, on a background of otherwise normal postnatal development.

Sudden infant death syndrome among extremely preterm infants: United States 1997-1999

BACKGROUND

Preterm infants have been reported to be at higher risk than term infants for sudden infant death syndrome (SIDS). Reasons for this higher risk are not clear.

OBJECTIVE

The objective of this study was to analyze medical and demographic characteristics among infants 24 to 32 weeks gestation to identify characteristics more prevalent among infants dying of SIDS in the postneonatal period than among infants of similar gestation who survived or who died of other causes in the postneonatal period.

DESIGN/METHODS

United States linked birth and death certificate period data for 1997 to 1999 were used for this analysis. The population used was limited to infants 24 to 32 weeks gestation weighing 500 to 2500 g. SIDS deaths were limited to the postneonatal period and compared to survivors and infants dying in the postneonatal period of other causes.

RESULTS

There were 469 postneonatal SIDS deaths with complete data (rate=2.2/1000 live births surviving > or =28 days); 3950 other postneonatal deaths (rate=18.7/1000) and 206,640 survivors. Compared with survivors, infants dying of SIDS were more likely to be born to mothers with <12 years of education (odds ratio=2.5, 95% confidence interval (95% CI=1.8, 3.3); be born to mothers < or =17 years of age (OR=2.0, 95% CI=1.4, 2.8); and be born to mothers with >3 previous pregnancies (OR=2.6, 95% CI=1.9, 3.5). Compared with infants dying in the postneonatal period of other causes, these same demographic factors continued to be significant risk factors for SIDS. There were no medical risk factors such as breech presentation, abruptio placenta, Apgar score <4 at 5 minutes, or mechanical ventilation for >30 minutes after birth, for which infants dying of SIDS were at greater risk than survivors or infants dying of other causes.

CONCLUSIONS

Risk factors for SIDS among infants 24 to 32 weeks gestation appear to be more associated with sociodemographic characteristics than medical characteristics. This suggests that for the immediate future, the risk for SIDS among very preterm infants will be best addressed through further modification of the environment and parent behavior.

Birth weight- and gestational age-specific sudden infant death syndrome mortality: United States, 1991 versus 1995

OBJECTIVE

To estimate the changes in birth weight- and gestational age-specific sudden infant death syndrome (SIDS) mortality rates since the publication of the sleep-positioning recommendations by the American Academy of Pediatrics Task Force on Infant Positioning and SIDS.

METHODS

This is a historical cohort study using US vital statistic linked birth and infant death certificate files for the years 1991 and 1995. SIDS deaths were identified as any death attributed to International Classification of Diseases, Ninth Revision code 7980, occurring between the 28th and 365th days of life.

RESULTS

There were 4871 deaths attributed to SIDS in 1991 for a postneonatal mortality rate of 1.2/1000 postneonatal survivors compared with 3114 deaths in 1995 for a rate of.8/1000. This represents a 33% drop in the postneonatal SIDS mortality from 1991 to 1995. Between 1991 and 1995, SIDS rates declined 38%, 38%, 35%, and 32% for birth weight groupings of 500 to 999 g, 1000 to 1499 g, 1500 to 2499 g, and >/=2500 g, respectively. There were no SIDS deaths attributed to infants weighing <500 g. The SIDS rates declined 27%, 21%, 40%, and 23% for gestational age groups of <29 weeks, 29 to 32 weeks, 33 to 36 weeks, and >/=37 weeks. The rate of decline did not differ significantly across birth weight- or gestational age-specific categories. There was a significant increase in the black:non-black postneonatal SIDS mortality ratio from 2.00 to 2.28, reflecting a smaller decline in birth weight- and gestational age-specific mortality for blacks than observed for the non-black population.

CONCLUSION

Postneonatal SIDS mortality decreased significantly across all broad birth weight and gestational age categories. If the decline in the prevalence of prone positioning that has been reported since 1992 has occurred across all birth weight and gestational age, these data support the hypothesis that supine or side sleep positioning is effective in preterm/low birth weight infants as well as term infants.