The association between the prone sleeping position and sudden infant death syndrome (SIDS): an editorial overview

Prevalence and associated factors of supine sleep position in 3-month-old infants: findings from the 2015 Pelotas (Brazil) Birth Cohort

BACKGROUND

Non-supine infant sleep position is an important modifiable risk factor for sudden unexpected death in infancy. The aim of this study was to assess the prevalence of supine sleep position and associated factors among 3-month-old infants from a birth cohort in the city of Pelotas, southern Brazil.

METHODS

The present study evaluated longitudinal data from the 2015 Pelotas Birth Cohort. Study outcome was supine infant sleep position, defined as the appropriate position, among 3-month-old children. Demographic, socioeconomic, behavioral, and health characteristics collected at birth and at the 3-month follow-up were investigated as possible associated factors. The prevalence of each associated factor was investigated, and crude and hierarchical adjusted analyses were performed using Poisson regression.

RESULTS

Among the 4108 infants assessed in this study, 2274 (55.4%) slept in supine position at 3 months and only 66 (1.6%) in prone position. Maternal white skin color, higher family income and maternal schooling, advanced maternal age, maternal cohabiting with a partner, receiving counseling from health care professionals and non-bed-sharing were associated with higher prevalence of infants sleeping in supine position at 3 months. All these variables remained associated in our hierarchical adjusted analyses except maternal cohabitation with a partner. Participants with white mothers were more likely to sleep in supine position (PR: 1.23; 95%CI: 0.75-0.89) compared to participants with black mothers. Those belonging to the richest quintile were more likely to sleep in supine position (PR: 1.49; 95%CI: 1.35-1.65) compared to those who belong to the poorest. Mothers aged 31-36 years were more likely to choose supine sleep position (PR: 1.65; 95%CI: 1.42-1.92) compared to mothers younger than 19 years.

CONCLUSIONS

The findings of the present study showed the influence of maternal age, socioeconomic status, and counseling on infant sleep habits as predictors of choice of infant sleep position in a Brazilian population. It is recommended to implement informative campaigns and public policies to at-risk population and to improve recommendations from health care professionals.

Why is a prone sleeping position dangerous for certain infants?

The prone (face down) sleeping position is known to be associated with a significantly increased risk of sudden and unexpected death in infancy (sudden infant death syndrome or SIDS), however, the reasons for this are unclear. Suggested mechanisms have involved suffocation from occlusion of the external airways by soft bedding/pillows or from flattening of the nose with backward displacement of the tongue, rebreathing of carbon dioxide, blunting of arousal responses with decreased cardiac responses to auditory stimulation, diaphragmatic splinting or fatigue, lowering of vasomotor tone with tachycardia, nasopharyngeal bacterial overgrowth, overheating, alteration of sleep patterns, compromise of cerebral blood flow and upper airway obstruction from distortion of nasal cartilages. Recent studies have, however, shown a significant reduction in substance P in the inferior portion of the olivo-cerebellar complex in SIDS infants which is crucial for the integration of motor and sensory information for the control of head and neck movement. This deficit may explain why some infants are not able to move their faces away from potentially dangerous sleeping environments.

Novel strategies to prevent stillbirth

This article reviews three new and emerging risk factors for stillbirth that may be modifiable or might identify a compromised fetus. We focus on fetal movements, maternal sleep, and maternal diet. Recent studies have suggested than a sudden increase in vigorous fetal activity may be associated with increased risk of stillbirth. We review the papers that have reported this finding and discuss the implications as well as potential future directions for research. There is emerging literature to suggest that maternal sleep position may be a risk for stillbirth, especially if the woman settles to sleep supine. This risk is biologically plausible. How this knowledge may be utilized to assist stillbirth reduction strategies is discussed. Finally, we examine the somewhat limited literature regarding maternal diet and pregnancy outcome. Introducing probiotics into the diet may prove useful, but further work is required. The possible next steps for research are considered, as well as some potential intervention strategies that may ultimately lead to stillbirth reduction.

Candidate gene variants of the immune system and sudden infant death syndrome

BACKGROUND

Sudden infant death syndrome (SIDS) causes early infant death with an incidence between 0.5 and 2.5 cases among 1000 live births. Besides central sleep apnea and thermal dysregulation, infections have been repeatedly suggested to be implicated in SIDS etiology.

METHODS

To test the risk contribution of common genetic variants related to infection, we genotyped 40 single-nucleotide polymorphisms (SNPs) from 15 candidate genes for association with SIDS in a total of 579 cases and 1124 controls from Germany and the UK in a two-stage case control design.

RESULTS

The discovery-stage series (267 SIDS cases and 303 controls) revealed nominally significant associations for variants in interleukin 6 (IL6) (rs1880243), interleukin 10 (IL10) (rs1800871, rs1800872), and mannose-binding lectin 2 (MBL2) (rs930506), and for several other variants in subgroups. Meta-analyses were then performed in adding genotype information from a genome-wide association study of another 312 European SIDS cases and 821 controls. Overall associations were observed for two independent variants in MBL2: rs930506 in a co-dominant model (odds ratio (OR) = 0.82, p = 0.04) and rs1838065 in a dominant model (OR = 1.27, p = 0.03).

CONCLUSION

Our study did not replicate published associations of IL10 variants with SIDS. However, the evidence for two independent MBL2 variants in the combined analysis of two large series seems consistent with the hypothesis that infection may play a role in SIDS pathogenesis.

Review of external ocular compression: clinical applications of the ocular pressure estimator

PURPOSE

The authors have previously validated an Ocular Pressure Estimator (OPE) that can estimate the intraocular pressure (IOP) during external ocular compression (EOC). The authors now apply the OPE in clinical states where EOC is clinically important. The original work is described for two periods of risk: during sleep and during the digital ocular massage (DOM) maneuver used by surgeons after trabeculectomy to keep the operation functional. Other periods of risk for external ocular compression are then reviewed.

METHODS

The first protocol estimated the IOP in the dependent eye during simulated sleep. Subjects had their IOPs initially measured in an upright-seated position, immediately upon assuming a right eye dependent side sleeping position (with nothing contacting the eye), and then 5 minutes later while still in this position. While maintaining this position, the fluid filled bladder of the OPE was then placed between the subject's closed eye and a pillow during simulated sleep. The IOP was continuously estimated in this position for 5 minutes. The subjects then had the IOP measured in both eyes in an upright-seated position. The second protocol determined if a larger vertical cup-to-disc ratio was more common on the side that patients reported they preferred to sleep on. The hypothesis was that chronic asymmetric, compression induced, elevations of IOP during sleep would be associated with otherwise unexplained asymmetry of the vertical cup-to-disc ratio. The third protocol assessed the IOP during DOM. The OPE was used to characterize the IOP produced during the DOM maneuver of five glaucoma surgeons. After this, 90 mmHg was chosen as a target pressure for DOM. The surgeons were then verbally coached during three additional compressions. After a 5-minute period, the surgeons were asked to reproduce this targeted IOP during subsequent compressions.

RESULTS

The mean IOP during the "sleep session" was 22±5 mmHg (SEM). The mean peak pressure was 40±11 mmHg (SEM) and the mean trough pressure was 15±2 mmHg (SEM). There was a 78% agreement between the eye that was reported to be dependent during sleep and the eye with the larger vertical cup-to-disc ratio, for eyes with at least a 0.10 cup-to-disc ratio difference, P=0.001, n=137. The OPE estimated an average induced IOP during typical DOM of 104±8 mmHg (SEM), with each compression having an average range of 17±3 mmHg (SEM). After coaching, and a 5-minute waiting period, the average induced IOP reduced to 95±3 mmHg (SEM) with a reduced average range of IOP to 11±1 mmHg.

CONCLUSION

The OPE was successfully used to estimate the IOP while subjects experienced EOC during normal sleep postures. These EOC-induced elevations of IOP were considerable, and likely contribute to significant ocular pathology, not only for glaucoma, but for retinal vascular occlusive diseases, retinal vascular leakage, and the induction of the ocular-cardiac reflex in infants, as well. The correlation of a larger vertical cup-to-disc ratio in patients with a sleep posture preference suggests a causal relationship, since patients with other conditions known to be associated with cup-to disc ratio asymmetry were excluded from this study. The OPE is a useful device to teach DOM to surgeons and patients for home use.

Socioeconomic position and factors associated with use of a nonsupine infant sleep position: findings from the Canadian Maternity Experiences Survey

OBJECTIVES

With a focus on socioeconomic position, we examined the association between maternal education and nonsupine infant sleep position, and examined patterns of effect modification with additional sociodemographic, maternal, infant, and health services predictors.

METHODS

Data were from the Maternity Experiences Survey, a national population-based sample of 76 178 new Canadian mothers (unweighted n = 6421) aged 15 years or older interviewed in 2006-2007. Using logistic regression, we developed multivariate models for 3 maternal education strata.

RESULTS

Level of maternal education was significantly and inversely related to nonsupine infant sleep position. Stratified analyses revealed different predictive factors for nonsupine infant sleep position across strata of maternal education. Postpartum home visits were not associated with use of this sleep position among new mothers with less than high school completion. Adequacy of postpartum information regarding sudden infant death syndrome was not associated with nonsupine infant sleep position in any of the educational strata.

CONCLUSIONS

These findings suggest a need to revisit Back to Sleep health promotion strategies and to ensure that these interventions are tailored to match the information needs of all families, including mothers with lower levels of formal education.

Scientific consensus forum to review the evidence underpinning the recommendations of the Australian SIDS and Kids Safe Sleeping Health Promotion Programme--October 2010

This paper summarises a 1-day scientific consensus forum that reviewed the evidence underpinning the Australian SIDS and Kids Safe Sleeping Health Promotion Programme. The focus was on each of the potentially modifiable risk factors for sudden unexpected deaths in infancy, including sudden infant death syndrome (SIDS) and fatal sleeping accidents. In particular infant sleeping position, covering of the face, exposure to cigarette smoke, room sharing, unsafe sleeping environments, bed sharing, immunisation, breastfeeding, pacifier use and Indigenous issues were discussed in depth. The participants recommended that future 'Reducing the Risk' campaign messages should focus on back to sleep, face uncovered, avoidance of cigarette smoke before and after birth, safe sleeping environment, room sharing and sleeping baby in own cot.

Sudden infant death syndrome and prone sleeping position

In this review, we describe the epidemiological work conducted by ourselves and others on prone sleep position and sudden infant death. What we have learned since 1990 is that the prone sleep position was a major component of a casual pathway that was operating in over half of the SIDS deaths that were occurring in developed countries at the end of the 1980. It has been estimated that advice to place infants supine to sleep may have saved in the order of 850 infants annually in Australia and other countries. The story of the SIDS epidemic is an example of the contribution that epidemiology can make to the understanding and prevention of an important public health problem.

Current recommendations on infants' sleeping position are being followed-initial results of a population-based sentinel study on risk factors for SIDS, 1996-2006, in Hamburg, Germany

Sudden infant death syndrome (SIDS) is a target for public health care in Germany. The aim of this study was to monitor data on risk-related behavior in the population of Hamburg, Germany, in order to respond to changes quickly and to estimate the effectiveness of prevention activities. Data have been gathered using the sentinel system with repeated surveys (1996, 1998, 2001, and 2006) in pediatric practices, thus allowing an estimate of the prevalence of risk factors in an urban population, both transversally and vertically. From 1996 to 2007, the SIDS rate in Hamburg fell from 0.9/1,000 live births to 0.1. The prevalence of infants sleeping prone declined from 8.1% in 1996 to 3.5% in 2006. In this small subgroup, up to 81.7% (2006) of the caretakers were well aware of the risk of sleeping prone. The prevalence of infants sleeping on their sides fell from 55.3% in 1998 to 10.6% in 2006. The sentinel setting is suitable for gathering risk-related data on SIDS. Despite the fact that, so far, no nationwide back-to-sleep campaign has been instituted in Germany, local campaigns have proved successful in reducing prone sleeping for infants. Moreover, the substantial reduction of side sleeping within a short time span going along with a reduced SIDS rate is an indicator of the effectiveness of prevention activities on a local basis.

Implementation of the SIDS guidelines in midwifery practice

The literature suggests that midwives strongly influence parenting practices immediately after birth and during early postnatal management of the newborn. Midwives must therefore be aware of the current evidence and public health recommendations for reducing the risk of Sudden Infant Death Syndrome (SIDS) and provide consistent information about use of the supine position. Midwives must also include information about environmental factors that are also known to increase the risk of SIDS such as exposure to cigarette smoke, covering the infant's face during sleep and other potential unsafe sleeping practices such as co-sleeping and bed sharing with their infant. The position midwives use to settle infants and place them for sleep is an important example for parents. The position favoured by midwives when placing a newborn to sleep will have a significant impact on parental practice after discharge home. A standardised evidenced based approach to the SIDS Guidelines immediately after birth will facilitate consistency in practice and uniformity in the message parents are given about safe sleeping practices for their newborn infant.

Sudden infant death syndrome: overview and update

The past decade and a half has seen marked changes in the epidemiology of sudden infant death syndrome (SIDS). The avoidance of certain risk factors such as sleeping prone and cigarette smoke exposure has resulted in the death rate falling dramatically. Careful evaluation of environmental factors and endogenous characteristics has led to a greater understanding of the complexities of the syndrome. The development and implementation of death scene and autopsy protocols has led to standardization in approaches to unexpected infant deaths with increasing diagnoses of accidental asphyxia. Despite these advances, there is still confusion surrounding the diagnosis, with deaths being attributed to SIDS in many communities and countries where death scene investigations and autopsies have not been conducted. The following review provides a brief overview of the historical background, epidemiology, pathology, and pathogenesis of SIDS. Contentious issues concerning the diagnosis and current problems are discussed. Despite calls to abandon the designation, SIDS remains a viable term for infants who die in their sleep with no evidence of accident, inflicted injury, or organic disease after a full investigation has been conducted according to standard guidelines.

Intrathoracic petechiae in sudden infant death syndrome: relationship to face position when found

Previous studies have not addressed the relationship of intrathoracic petechiae (IP) to the position of the face when a caretaker finds a victim of sudden infant death syndrome (SIDS). The aims of this retrospective study were to determine (1) the rate of the facedown position in SIDS (not to be confused with the prone body position), (2) if the facedown position occurred more frequently among SIDS victims with intrathoracic petechiae than those without petechiae, and (3) if the facedown position occurred more frequently among cases with more severe petechial hemorrhage of the thymus. We selected 199 SIDS cases from the San Diego SIDS Research Project database and grouped them as IP-present and IP-absent. Each case was analyzed with regard to the face position when found unresponsive or dead. Among these 199 cases, 37% were found face-down, which represents 51% of the 142 cases found prone. The two groups were similar with respect to age, sex, and rate of premature birth. Thirty-nine percent (39%) of the IP-present group and 9% of the IP-absent group were found in the facedown position (P = 0.057; 95% confidence interval for the difference = 0.3%, 40%). Cases were also grouped by severity of thymic petechiae and analyzed regarding face position. Neither age nor the facedown position was associated with greater severity of thymic petechiae. The wide confidence interval yielded by our analysis of IP limits our ability to clarify the precise pathophysiologic role of external oronasal obstruction in SIDS. While it remains possible that a subset of SIDS cases occur as a result of external obstruction, we are unable to generalize its importance. Internal airway obstruction and rebreathing with terminal gasping, both of which have been documented in sudden infant death, remain other possible scenarios leading to the production of IP.

Gastric aspiration and sleeping position in infancy and early childhood

Concern has been expressed that the recommendation of supine sleeping position for infants would result in an increase in deaths due to gastric aspiration. A review of 196 cases of infant and early childhood death in children under 3 years of age, occurring over a 9-year period (September 1989 to August 1998) was undertaken to ascertain how many cases of significant gastric aspiration had occurred. Extensive and widespread filling of the airways/alveoli with gastric contents was found in three infants/young children aged 5, 6 and 30 months, respectively. In each instance the body had been found lying face down (prone), with the face in a pool of vomitus in at least one case. No cases of significant gastric aspiration were found in infants who had been found lying on their sides or backs (supine). In addition, no significant increase in numbers of infant and early childhood deaths in South Australia due to gastric aspiration over this time could be demonstrated. Concerns that the supine rather than the prone position is more likely to result in significant gastric aspiration are not supported by this study.

Infant sleep position. Nursing practice and knowledge

PURPOSE

(1) to examine the extent to which maternal/child health nurses caring for children accept the American Academy of Pediatrics recommendations on infant sleep position, (2) to determine if nurses are practicing according to the AAP recommendations, and (3) to determine the type of bedding utilized in the two institutions for infants.

METHODS

Descriptive survey using 103 nurses in 2 institutions, and an observational assessment of nurses' practice.

RESULTS

Findings revealed that 97% of the nursing staff were aware of the AAP recommendations, although only 67% agreed with the recommendations. The observational component of the investigation evaluated the sleep position during hospitalization of 206 infants < 6 months old on both the pediatric and maternity units of the two institutions. Fifty-five percent of the infants were observed to be in the side-lying position, 29% in the recommended supine (back) position, and 16% in the prone (abdomen) sleeping position. The recommended firm bedding was observed with 63% of the infants, whereas the remainder of the infants were observed to be on foam mattresses, extra blankets, or gel packs.

CLINICAL IMPLICATIONS

Because side sleeping position was observed in the majority of infants, and one-third of the nurses queried disagreed with the AAP recommendations, education of nurses about Sudden Infant Death Syndrome prevention through "Back to Sleep" is still necessary.

Sudden infant death syndrome: a hypothesis

A study of the strikingly low incidence of sudden infant death syndrome in Eastern countries revealed significant differences in infant handling thought to have an etiological bearing; therefore this writer suggested that adoption of certain Eastern methods of nursing may reduce the incidence of sudden infant death syndrome. A dramatic fall in incidence has resulted from implementing one of the suggestions made by the writer in 1983, namely the abandonment of the prone position, after initial opposition. The present hypothesis sets out to give a scientific explanation for this fall, and is a unified hypothesis explaining certain puzzling and disparate features of sudden infant death syndrome such as the remarkable winter incidence, age incidence, and the occurrence of sudden infant death syndrome during sleep, and is based on a postulated disturbance in thermoregulatory function (a unique hypothermia). Recommendations are made for evolving a test for sudden infant death syndrome-proneness and a possible method of treatment of a fatality within a short time frame.

Sudden infant death syndrome — a ‘diagnosis’ in search of a disease

Although Sudden Infant Death Syndrome (SIDS) is the major cause of death in infants aged between 1 week and 1 year in Western countries, it is one of the most enigmatic conditions encountered in paediatric forensic practice. SIDS has been recognized since Biblical times, and yet the definition continues to be debated and the aetiology remains obscure. In addition, there are no accepted pathognomonic features at post-mortem and the diagnosis is still one of exclusion. Emery once asked whether the term 'SIDS' is in reality more of a 'diagnostic dustbin' into which are placed a variety of unrelated entities.(1) To a certain extent this is true, as it is now recognized that a range of disorders can result in the sudden and unexpected death of an infant in a cot. It is also likely that the aetiology of SIDS is heterogeneous and that the term SIDS is not so much a diagnosis but a term covering a variety of mechanisms which result in a common lethal outcome. There are a number of controversies in the SIDS field which complicate the use of the term and which confound the assessment of causes and mechanisms of sudden infant death.

Accidental death or sudden infant death syndrome?

OBJECTIVE

To describe the reasons why it is difficult to decide whether to attribute some infant deaths to accidents or to SIDS.

METHODOLOGY

To extract from infant deaths data in South Australia those where the cause of death is debatable.

RESULTS

The risks associated with rocking cradles, bed sharing, bedclothes, couch sleeping, unsafe cots or beds and the prone position are presented.

CONCLUSIONS

Uniform worldwide death scene investigations for all infant deaths should help identify unsafe sleeping conditions for infants.

Has changing diagnostic preference been responsible for the recent fall in incidence of sudden infant death syndrome in South Australia?

OBJECTIVE

An apparent decrease in deaths attributed to sudden infant death syndrome (SIDS) has been noted in a number of diverse geographical areas during the past several years. At the same time the definition of SIDS has been in a state of flux and some observers have raised the possibility that the fall in SIDS deaths is due to diagnostic transfer rather than to a genuine decrease in numbers. The present study was undertaken to investigate this possibility.

METHODOLOGY

All sudden and unexpected deaths in infants under 1 year of age in South Australia during a 10 year period from 1984 to 1993 were reviewed.

RESULTS

The number of deaths due to SIDS fell from 40 in 1984 to 17 in 1993, with a maximum of 52 cases per year in 1987. In contrast, the number of cases of sudden death not due to SIDS remained under 10 per year. The overall infant death rate also fell, while the total number of births per year remained relatively unchanged.

CONCLUSIONS

The lack of major change in sudden infant death rates from other causes, combined with the fall in SIDS deaths, is not supportive of diagnostic transfer being a major determinant of the declining SIDS death rate. Therefore, other factors are likely to be responsible for the falling SIDS rate in this population.

Carbon dioxide concentrations in the environment of sleeping infants

In 22 infants continuous measurements were made of the concentration of carbon dioxide (CO2) in inspired air during sleep. Evidence was found of CO2 enrichment of inspired air in certain environmental conditions. The levels achieved were not sufficiently high to acutely endanger an infant. Carbon dioxide concentrations as high as 2-3% were observed in the prone position when the infant's head was under a blanket and when the lower face was obscured by bedding. Sleeping prone on a sheepskin also resulted in an increased concentration of CO2 but to a lesser extent than being under a blanket. In awake infants the presence of a pacifier also promoted an excess of CO2 in the inspired air, both in the prone and supine positions. The physiological and clinical implications of these findings, in relation to the Sudden Infant Death Syndrome (SIDS), are unknown and warrant investigation.

Impaired ventilation in infants sleeping facedown: potential significance for sudden infant death syndrome

Although accidental suffocation has been suggested as a cause of sudden infant death syndrome in infants who are found prone with their faces straight down, the occurrence and effects on breathing of this position in living infants are unknown. We studied prone sleeping infants to see whether they will sleep with their faces straight down; whether they can spontaneously change from this position; the way that thermal stimuli or bedding softness influences this change; and whether rebreathing or airway obstruction occurs. We studied 11 healthy infants, aged 0.2 to 6 months, while they slept on soft and on firm bedding. Most infants slept facedown spontaneously or when turned to this position. All could turn their heads readily but slept facedown for variable periods. All infants put their faces straight down more often after cold than after warm stimuli. Obstructive apnea occurred only once, but rebreathing occurred in all subjects. When the infants were in the facedown position, inspired carbon dioxide was three times greater on soft than on hard bedding. End-tidal carbon dioxide partial pressure rose in all subjects while they were in the facedown position; in one infant, high end-tidal carbon dioxide partial pressure and desaturation occurred without signs of arousal. We conclude that infants sleeping facedown may occasionally have significant asphyxia; this sleep position may have a role in some infant deaths diagnosed as sudden infant death syndrome.

Rebreathing expired gases from bedding: a cause of cot death?

The reported association of cot death and sleeping prone could be due to rebreathing of expired gases. A mechanical model simulating the respiratory system of an infant, exhaling warm humidified air with an end tidal carbon dioxide of 5%, has been used to investigate this. Some commonly used bedding materials caused an accumulation of carbon dioxide of 7% to over 10% with the model lying face down. This phenomenon persisted even with the head inclined at 45 degrees, but only on very soft materials, and could be a cause of cot death in a baby unresponsive to asphyxial blood gas changes. A coir fibre mattress allowed complete dispersal of exhalate as did a rubber sheet between any mattress and the covering sheet.