Higher rectal temperatures in co-sleeping infants

Hyperthermia and Heat Stress as Risk Factors for Sudden Infant Death Syndrome: A Narrative Review

BACKGROUND AND OBJECTIVES

Heat stress and hyperthermia are common findings in sudden infant death syndrome (SIDS) victims. It has been suggested that thermal stress can increase the risk of SIDS directly via lethal hyperthermia or indirectly by altering autonomic functions. Major changes in sleep, thermoregulation, cardiovascular function, and the emergence of circadian functions occur at the age at which the risk of SIDS peaks-explaining the greater vulnerability at this stage of development. Here, we review the literature data on (i) heat stress and hyperthermia as direct risk factors for SIDS, and (ii) the indirect effects of thermal loads on vital physiological functions.

RESULTS

Various situations leading to thermal stress (i.e., outdoors temperatures, thermal insulation from clothing and bedding, the prone position, bed-sharing, and head covering) have been analyzed. Hyperthermia mainly results from excessive clothing and bedding insulation with regard to the ambient thermal conditions. The appropriate amount of clothing and bedding thermal insulation for homeothermia requires further research. The prone position and bed-sharing do not have major thermal impacts; the elevated risk of SIDS in these situations cannot be explained solely by thermal factors. Special attention should be given to brain overheating because of the head's major role in body heat losses, heat production, and autonomic functions. Thermal stress can alter cardiovascular and respiratory functions, which in turn can lead to life-threatening events (e.g., bradycardia, apnea with blood desaturation, and glottal closure). Unfortunately, thermal load impairs the responses to these challenges by reducing chemosensitivity, arousability, and autoresuscitation. As a result, thermal load (even when not lethal directly) can interact detrimentally with vital physiological functions.

CONCLUSIONS

With the exception of excessive thermal insulation (which can lead to lethal hyperthermia), the major risk factors for SIDS appears to be associated with impairments of vital physiological functions when the infant is exposed to thermal stress.

The influence of bed-sharing on infant physiology, breastfeeding and behaviour: A systematic review

This review aimed to better understand the underlying physiology of the risks and benefits of bed-sharing. Eight databases were searched using terms relating to adult-infant/baby, bed-sharing/co-sleeping combined with outcome terms for physiology, sleep, cardiovascular, respiratory, temperature and behaviour. Of 836 papers identified, 59 papers representing 48 cohorts met inclusion criteria. Objective data using various methodologies were available in 27 papers and subjective data in 32 papers. Diverse measures were reported using variable definitions of bed-sharing. Identified physiological and behavioural differences between bed-sharing and cot-sleeping included increased behavioural arousals, warmer in-bed temperatures and increased breastfeeding duration in bedshare infants as well as differences in infant overnight sleep architecture, cardiorespiratory control and cortisol responses to stress. We concluded that many differences are context-specific, and dependent on the subjective view of the parents and their cultural values. Objective risk arises if the infant is unable to mount an appropriate physiological or behavioural response to their micro-environment. More studies in the bed-sharing setting are needed to identify infant risk, the potential benefits of a safer environment, and how bed-sharing interacts with infant care practices other than sleep.

Parent-child bed-sharing: The good, the bad, and the burden of evidence

The practice of parent and child sharing a sleeping surface, or 'bed-sharing', is one of the most controversial topics in parenting research. The lay literature has popularized and polarized this debate, offering on one hand claims of dangers, and on the other, of benefits - both physical and psychological - associated with bed-sharing. To address the scientific evidence behind such claims, we systematically reviewed 659 published papers (peer-reviewed, editorial pieces, and commentaries) on the topic of parent-child bed-sharing. Our review offers a narrative walkthrough of the many subdomains of bed-sharing research, including its many correlates (e.g., socioeconomic and cultural factors) and purported risks or outcomes (e.g., sudden infant death syndrome, sleep problems). We found general design limitations and a lack of convincing evidence in the literature, which preclude making strong generalizations. A heat-map based on 98 eligible studies aids the reader to visualize world-wide prevalence in bed-sharing and highlights the need for further research in societies where bed-sharing is the norm. We urge for multiple subfields - anthropology, psychology/psychiatry, and pediatrics - to come together with the aim of understanding infant sleep and how nightly proximity to the parents influences children's social, emotional, and physical development.

Thermoregulatory effects of swaddling in Mongolia: a randomised controlled study

OBJECTIVE

To investigate thermal balance of infants in a Mongolian winter, and compare the effects of traditional swaddling with an infant sleeping-bag in apartments or traditional tents (Gers).

DESIGN

A substudy within a randomised controlled trial.

SETTING

Community in Ulaanbaatar, Mongolia.

SUBJECTS

A stratified randomly selected sample of 40 swaddled and 40 non-swaddled infants recruited within 48 h of birth.

INTERVENTION

Sleeping-bags and baby outfits of total thermal resistance equivalent to that of swaddled babies.

OUTCOME MEASURE

Digital recordings of infants' core, peripheral, environmental and microenvironmental temperatures at 30-s intervals over 24 h at ages 1 month and 3 months.

RESULTS

In Gers, indoor temperatures varied greatly (<0->25°C), but remained between 20°C and 22°C, in apartments. Despite this, heavy wrapping, bed sharing and partial head covering, infant core and peripheral temperatures were similar and no infants showed evidence of significant heat or cold stress whether they were swaddled or in sleeping-bags. At 3 months, infants in sleeping-bags showed the 'mature' diurnal pattern of a fall in core temperature after sleep onset, accompanied by a rise in peripheral temperature, with a reverse pattern later in the night, just before awakening. This pattern was not related to room temperature, and was absent in the swaddled infants, suggesting that the mature diurnal pattern may develop later in them.

CONCLUSIONS

No evidence of cold stress was found. Swaddling had no identifiable thermal advantages over sleeping-bags during the coldest times, and in centrally heated apartments could contribute to the risk of overheating during the daytime.

TRIAL REGISTRATION NUMBER

ISRTN01992617.

Parent-infant bed-sharing behavior : Effects of feeding type and presence of father

An evolutionarily informed perspective on parent-infant sleep contact challenges recommendations regarding appropriate parent-infant sleep practices based on large epidemiological studies. In this study regularly bed-sharing parents and infants participated in an in-home video study of bed-sharing behavior. Ten formula-feeding and ten breast-feeding families were filmed for 3 nights (adjustment, dyadic, and triadic nights) for 8 hours per night. For breast-fed infants, mother-infant orientation, sleep position, frequency of feeding, arousal, and synchronous arousal were all consistent with previous sleep-lab studies of mother-infant bed-sharing behavior, but significant differences were found between formula and breast-fed infants. While breast-feeding mothers shared a bed with their infants in a characteristic manner that provided several safety benefits, formula-feeding mothers shared a bed in a more variable manner with consequences for infant safety. Paternal bed-sharing behavior introduced further variability. Epidemiological case-control studies examining bed-sharing risks and benefits do not normally control for behavioral variables that an evolutionary viewpoint would deem crucial. This study demonstrates how parental behavior affects the bed-sharing experience and indicates that cases and controls in epidemiological studies should be matched for behavioral, as well as sociodemographic, variables.

A mitochondrial DNA polymorphism associated with cardiac arrhythmia investigated in sudden infant death syndrome

AIM

Long QT syndrome (LQTS) has been shown to be the cause of death in some cases originally diagnosed as sudden infant death syndrome (SIDS). Such cardiac arrhythmias have also been noted in families with mitochondrial disease, and studies indicate that mitochondrial disease could be involved in SIDS. This makes the mtDNA polymorphism T3394C interesting, as a previous study has shown it to be associated with electrocardiographic (ECG) changes after exercise in a family with LQTS, where some members harboured a KCNH2 mutation.

SUBJECTS

A total of 245 SIDS cases and 176 control cases.

METHODS

DNA was prepared from blood/tissue samples. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were performed to search for the mtDNA polymorphism and KCNH2 mutation. Differences were confirmed by sequencing.

RESULTS

The T3394C polymorphism was found in 3 pure SIDS cases (1.5%), 2 borderline SIDS cases (4.4%), 1 case of explained death (1.6%) and 2 living control cases (1.8%) (p = 0.62). The KCNH2 mutation was not found in cases or controls.

CONCLUSION

The mtDNA polymorphism studied was found in a small number of SIDS cases and the frequency did not differ statistically from control subjects, making an association with increased SIDS risk unlikely.

Inappropriate mediastinal baroreceptor reflex as a possible cause of sudden infant death syndrome – Is thorough burping before sleep protective?

Despite extensive research, a link between the assumed mechanisms of death and known risk factors for sudden infant death syndrome (SIDS) has not yet been established. Modifiable risk factors such as prone sleeping position, nicotine exposure and thermal stress and non-avoidable risk factors like male gender and some risky socio-economic conditions could be detected, but the etiology of SIDS remains unknown. In many SIDS cases histopathological findings suggest an involvement of vital autonomic control functions and unidentified trigger factors seem to play a role. From a hypothetical point of view, a developmental sympatheticovagal imbalance of the cardiovascular reflex control could cause a predisposition for SIDS. An assumed gastroesophageal trigger impulse is possibly developed during the first weeks of life and could lead to the infant's vagal reflex death. Air swallowed during feeding escapes through the esophagus while the infant is sleeping. The temporarily bloated esophagus exerts pressure on neighboring mediastinal baroreceptors, which is potentially misinterpreted as a rise in arterial pressure. The following cardiodepressoric baroreceptor reflex could lead to arterial hypotension, bradycardia and cardiac arrest. Sleeping in prone position may create an increased thoracic pressure on mediastinal baroreceptors, causing a more pronounced vagal reflex and an increased likelihood of SIDS. Prone position in connection with soft objects in the infant's sleeping environment potentially generates an increased oculobulbar pressure, resulting in an additional cardiodepressoric condition (Aschner-Dagnini phenomenon). From the sixth month of life onwards the sympatheticovagal balance seems to have matured sufficiently to compensate the life-threatening challenges in most infants. Insufficient postprandial burping could either create another independent modifiable risk factor or present the missing link to a common trigger mechanism for SIDS. Further investigations may possibly lead to the explicit recommendation to burp all infants sufficiently and repeatedly before sleep.

Co-sleeping, an ancient practice: issues of the past and present, and possibilities for the future

Co-sleeping-infants sharing the mother's sleep space-has prevailed throughout human evolution, and continued over the centuries of western civilization despite controversy and blame of co-sleeping mothers for the deaths of their infants. By the past century, "crib death" was recognized, later identified as Sudden Infant Death Syndrome (SIDS), and generally found to occur more frequently during bed sharing. Pediatricians warned parents of the dangers of SIDS and other risks of bed sharing, and the frequency of bed sharing decreased markedly over the years. However, during recent decades, bed sharing began to increase, though major issues were raised, including: whether bed sharing actually exacerbates or is protective against the occurrence of SIDS, whether the practice facilitates breast feeding, whether bed sharing is beneficial for an infant's development, and other concerns. Dissention may soon be diminished by use of a crib which opens at the mother's bed-side and is becoming a popular approach to mother-and-infant closeness through the night.

The Controversy About What Constitutes Safe and Nurturant Infant Sleep Environments

In 1999, the U.S. Consumer Product Safety Commission stated that cribs provide the safest sleep environment for infants. Scientific data fails to support that statement and controversy continues in the scientific, medical, and parenting communities. Recent data demonstrate that cribs may represent the most unsafe sleep. This article seeks to inform health care professionals of the issues involved in the controversy and to offer guidelines for educating parents about safe and unsafe sleep practices.

An 8 year study of risk factors for SIDS: bed-sharing versus non-bed-sharing

BACKGROUND

It is unclear if it is safe for babies to bed share with adults. In Ireland 49% of sudden infant death syndrome (SIDS) cases occur when the infant is bed-sharing with an adult.

OBJECTIVE

To evaluate the effect of bed-sharing during the last sleep period on risk factors for SIDS in Irish infants.

DESIGN

An 8 year (1994-2001) population based case control study of 287 SIDS cases and 831 controls matched for date, place of birth, and sleep period. Odds ratios and 95% confidence intervals were calculated by conditional logistic regression.

RESULTS

The risk associated with bed-sharing was three times greater for infants with low birth weight for gestation (UOR 16.28 v 4.90) and increased fourfold if the combined tog value of clothing and bedding was > or =10 (UOR 9.68 v 2.34). The unadjusted odds ratio for bed-sharing was 13.87 (95% CI 9.58 to 20.09) for infants whose mothers smoked and 2.09 (95% CI 0.98 to 4.39) for non-smokers. Age of death for bed-sharing and sofa-sharing infants (12.8 and 8.3 weeks, respectively) was less than for infants not sharing a sleep surface (21.0 weeks, p<0.001) and fewer bed-sharing cases were found prone (5% v 32%; p = 0.001).

CONCLUSION

Risk factors for SIDS vary according to the infant's sleeping environment. The increased risk associated with maternal smoking, high tog value of clothing and bedding, and low z scores of weight for gestation at birth is augmented further by bed-sharing. These factors should be taken into account when considering sleeping arrangements for young infants.

Why babies should never sleep alone: a review of the co-sleeping controversy in relation to SIDS, bedsharing and breast feeding

There has been much controversy over whether infants should co-sleep or bedshare with an adult caregiver and over whether such practises increase the risk of SIDS or fatal accident. However, despite opposition from medical authorities or the police, many western parents are increasingly adopting night-time infant caregiving patterns that include some co-sleeping, especially by those mothers who choose to breast feed. This review will show that the relationships between infant sleep patterns, infant sleeping arrangements and development both in the short and long term, whether having positive or negative outcomes, is anything but simple and the traditional habit of labelling one sleeping arrangement as being superior to another without an awareness of family, social and ethnic context is not only wrong but possibly harmful. We will show that there are many good reasons to insist that the definitions of different types of co-sleeping and bedsharing be recognised and distinguished. We will examine the conceptual issues related to the biological functions of mother-infant co-sleeping, bedsharing and what relationship each has to SIDS. At very least, we hope that the studies and data described in this paper, which show that co-sleeping at least in the form of roomsharing especially with an actively breast feeding mother saves lives, is a powerful reason why the simplistic, scientifically inaccurate and misleading statement 'never sleep with your baby' needs to be rescinded, wherever and whenever it is published.

Bed-sharing and the infant's thermal environment in the home setting

AIMS

To study bed-sharing and cot-sleeping infants in the natural setting of their own home in order to identify differences in the thermal characteristics of the two sleep situations and their potential hazards.

METHODS

Forty routine bed-sharing infants and 40 routine cot-sleeping infants aged 5-27 weeks were individually matched between groups for age and season. Overnight video and physiological data of bed-share infants and cot-sleeping infants were recorded in the infants' own homes including rectal, shin, and ambient temperature.

RESULTS

The mean rectal temperature two hours after sleep onset for bed-share infants was 36.79 degrees C and for cot-sleeping infants, 36.75 degrees C (difference 0.05 degrees C, 95% CI -0.03 to 0.14). The rate of change thereafter was higher in the bed-share group than in the cot group (0.04 degrees C v 0.03 degrees C/h, difference 0.01, 0.00 to 0.02). Bed-share infants had a higher shin temperature at two hours (35.43 v 34.60 degrees C, difference 0.83, 0.18 to 1.49) and a higher rate of change (0.04 v -0.10 degrees C/h, difference 0.13, 0.08 to 0.19). Bed-sharing infants had more bedding. Face covering events were more common and bed-share infants woke and fed more frequently than cot infants (mean wake times/night: 4.6 v 2.5).

CONCLUSIONS

Bed-share infants experience warmer thermal conditions than those of cot-sleeping infants, but are able to maintain adequate thermoregulation to maintain a normal core temperature.

Randomized controlled trial of kangaroo care: cardiorespiratory and thermal effects on healthy preterm infants

PURPOSE

To determine the safety and effects on healthy preterm infants of three continuous hours of kangaroo care (KC) compared to standard NICU care by measuring cardiorespiratory and thermal responses.

DESIGN

Randomized controlled trial-pretest-test-posttest control group design.

SAMPLE

Twenty-four healthy preterm infants (33-35 weeks gestation at birth) nearing discharge. Eleven of the infants received KC; 13 received standard NICU care.

MAIN OUTCOME VARIABLES

Heart rate, respiratory rate, oxygen saturation, and abdominal skin temperature were manually recorded every minute. Apnea, bradycardia, periodic breathing, and regular breathing were captured continuously on a pneumocardiogram printout. Three consecutive interfeeding intervals (three hours each) on one day constituted the pretest, test, and posttest periods.

RESULTS

Mean cardiorespiratory and temperature outcomes remained within clinically acceptable ranges during KC. Apnea, bradycardia, and periodic breathing were absent during KC. Regular breathing increased for infants receiving KC compared to infants receiving standard NICU care.

Factors relating to the infant's last sleep environment in sudden infant death syndrome in the Republic of Ireland

AIM

To identify risk factors for sudden infant death syndrome (SIDS) in the sleeping environment of Irish infants.

METHODS

A five year population based case-control study with parental interviews conducted for each case and three controls matched for age, place of birth, and last sleep period. A total of 203 SIDS cases and 622 control infants born 1994-98 were studied.

RESULTS

In a multivariate analysis, co-sleeping significantly increased the risk of SIDS both as a usual practice (adjusted OR 4.31; 95% CI 1.07 to 17.37) and during the last sleep period (adjusted OR 16.47; 95% CI 3.73 to 72.75). The associated risk was dependent on maternal smoking (OR 21.84; 95% CI 2.27 to 209.89), and was not significant for infants who were > or =20 weeks of age (OR 2.63; 95% CI 0.49 to 70.10) or placed back in their own cot/bed to sleep (OR 1.07; 95% CI 0.21 to 5.41). The use of pillows, duvets, and bedding with tog value > or =10 were not significant risk factors when adjusted for the effects of confounding variables, including maternal smoking and social disadvantage. However, the prone sleeping position remains a significant SIDS risk factor, and among infants using soothers, the absence of soother use during the last sleep period also significantly increased the SIDS risk (OR 5.83; CI 2.37 to 14.36).

CONCLUSION

Co-sleeping should be avoided in infants who are <20 weeks of age, or whose mothers smoked during pregnancy. The prone position remains a factor in some SIDS deaths, and the relation between soother use and SIDS is a complex variable requiring further study.

Sudden infant death syndrome--a defect in circulatory control?

The majority of Sudden Infant Death Syndrome (SIDS) infants die during sleep and especially during the overnight sleep period. Recent evidence from SIDS cases, which occurred while on a cardiorespiratory monitor at home, has suggested that the mechanism of death involves circulatory failure, with the development of a shock like state, associated with a progressive bradycardia in the presence of continued breathing movements. In this paper we explore the circulatory effects of sleep and in particular the down regulation of the baroreceptor reflex, associated with a reduction in vasomotor tone and a fall in central venous return, cardiac output and blood pressure. This sequence of events would be exacerbated by many of the known SIDS risk factors, namely the prone sleeping position, overheating and co-sleeping. Poor central venous return,with diminished cardic distension could induce a progressive bradycardia as occurs in adults with neuro-cardiogenic syncope. Alternatively a reduced cardiac output could result in the rapid onset of severe hypoxia through poor lung perfusion. The effects of sleep on circulatory control deserve further study in infants.

Triadic bed-sharing and infant temperature

The effects on infants of sleeping with their parents is currently the subject of much debate. One concern regarding infants who sleep in their parents' bed involves the possibility of overheating. Previous research reported a significantly greater core temperature of 0.1 degrees C among a cohort of bed-sharing infants compared with a matched cohort of infants sleeping alone. This paper presents a preliminary analysis of the overnight rectal temperature of 12 of the 20 infants who were monitored sleeping alone and with their parents on separate nights at the University of Durham Parent-Infant Sleep Lab. No significant differences were found in all night rectal temperature, or temperature from 2 h after sleep onset between bed-sharing and cot sleeping nights. These preliminary analyses suggest a night-time difference in rectal temperature between routine bed-sharers and routine cot sleepers, however, these findings will be further explored in the full analyses for this study.

Prone versus supine sleep position: a review of the physiological studies in SIDS research

A number of physiological studies, published over the last 10 years, have investigated the links between prone sleeping and sudden infant death syndrome (SIDS). This review evaluates those studies and derives an overview of the different affects of sleeping prone or supine in infancy. Generally, compared with the supine, the prone position raises arousal and wakening thresholds, promotes sleep and reduces autonomic activity through decreased parasympathetic activity, decreased sympathetic activity or an imbalance between the two systems. In addition, resting ventilation and ventilatory drive is improved in preterm infants, but in older infants (>1 month), there is no improvement in ventilation, and in 3-month-old infants, the position is adverse in terms of poorer ventilatory drive (in active sleep only). The majority of findings suggest a reduction in physiological control related to respiratory, cardiovascular and autonomic control mechanisms, including arousal during sleep in the prone position. Since the majority of these findings are from studies of healthy infants, continued reinforcement of the supine sleep recommendations for all infants is emphasized.

Preterm infant temperature circadian rhythm: possible effect of parental cosleeping

The purpose of this study was to describe the circadian rhythm of abdominal skin temperature and explore factors related to the timing of circadian rhythm acrophase. Thirty-four preterm infants (gestational age 26 to 33 weeks) were studied in the home environment at 44 to 46 weeks postconceptional age. Insulated abdominal skin was monitored continuously, and parents recorded sleep/wake activity over a 24-h period. Circadian rhythm was analyzed using cosinor analysis. Using MANCOVA, the effects of cosleeping, feeding method, night feeding, hospital stay, time home, and illness on acrophase were determined. Infants demonstrated evidence of developing circadian rhythm of temperature. Cosleeping and length of hospital stay were significantly related to acrophase. The mean acrophase for cosleeping infants was 07:44 (95% confidence interval = 05:12, 11:08), whereas that for non-cosleeping infants was 22.05 (95% confidence interval = 17:31, 01:42). Proximity with parents during nighttime hours may serve to entrain preterm infant circadian rhythm.

Changes in the epidemiological pattern of sudden infant death syndrome in southeast Norway, 1984-1998: implications for future prevention and research

AIM

To look for changes in risk factors for sudden infant death syndrome (SIDS) after decrease and stabilisation of the SIDS rate.

METHODS

Questionnaires were distributed to parents of 174 SIDS infants, dying between 1984 and 1998, and 375 age and sex matched controls in southeast Norway.

RESULTS

The proportion of infants sleeping prone has decreased, along with the decrease in SIDS rate for the region during the periods studied, but over half of the SIDS victims are still found in the prone position. As the number of SIDS cases has decreased, additional risk factors have become more significant. Thus, after 1993, a significantly increased risk of SIDS is seen when the mother smokes during pregnancy. After 1993, young maternal age carries an increased risk. Maternal smoking and young maternal age are associated with each other. For SIDS victims, an increase in the number of infants found dead while co-sleeping is seen, and the age peak between 2 and 4 months and the winter peak have become less pronounced.

CONCLUSION

Changes in risk factor profile following the decrease in SIDS rate in the early 1990s, as well as consistency of other factors, provides further clues to SIDS prevention and to the direction of further studies of death mechanisms.

Increased facial temperature as an early warning in Sudden Infant Death Syndrome

The promotion of supine sleeping position in young infants has resulted in significant declines in the incidence of Sudden Infant Death Syndrome although little is understood in terms of mechanisms. We hypothesize that supine sleeping position promotes appropriate thermal regulation via the face and head which is the major source of infant heat loss. By facilitating temperature regulation, the supine position ensures that the centre for thermoregulation in the hypothalamus does not become dysfunctional due to local temperature fluctuations. Because these hypothalamic, thermoregulatory neurones are synaptically linked to those regulating respiration in the medulla, adequate temperature control by the infant maintains normal respiration. In contrast, an increase in face and head temperature over and above core temperature would suggest thermoregulatory stress and an increased likelihood of respiratory apnoea.

Review of risk factors for sudden infant death syndrome

Sudden infant death syndrome (SIDS) accounts for the largest number of deaths during the first year of life in developed countries. The possible causes of SIDS are numerous and, to date, there is no adequate unifying pathological explanation for SIDS. Epidemiological studies have played a key role in identifying risk factors, knowledge of which has underpinned successful preventive programmes. This review critically assesses information on the main risk factors and causal hypotheses put forward for SIDS, focusing on research published since 1994. The overall picture that emerges from this review is that affected infants are not completely normal in development, but possess some inherent weakness, which may only become obvious when the infant is subjected to stress. Initially there may be some minor impairment or delay in development of respiratory, cardiovascular or neuromuscular function. None of these is likely to be sufficient, in isolation, to cause death and, provided the infant survives the first year of life, may no longer be of any significance. However, when a compromised infant is confronted with one or more stressful situations, several of which are now clearly identified as risk factors, and from which the majority of infants would normally escape, the combination may prove fatal.

Thermal stress in sudden infant death: Is there an ambiguity with the rebreathing hypothesis?

OBJECTIVE

To assess the role of thermal stress in the cause of sudden infant death syndrome (SIDS), and to compare risk factors with those of rebreathing.

METHODOLOGY

Analysis of publications concerning the epidemiology and physiology of thermal stress in SIDS.

RESULTS

A strong association between thermal regulation and ventilatory control was found, specifically for prolonged apnea. Infections, excessive room heat and insulation, and prone sleeping produce significantly increased odds ratios for SIDS. Although some of the risk factors for rebreathing could be explained by the effects of thermal stress, several factors for thermal stress could not reasonably be explained by the rebreathing hypothesis.

CONCLUSIONS

Although the risk of thermal stress is widely accepted abroad, it has received relatively little attention in the United States. The incidence of SIDS in the United States can likely be further reduced by educating the public against the dangers of overheating, as an integral part of the back-to-sleep campaign.

Effect of prone sleeping on circulatory control in infants

BACKGROUND

The mechanism of death in sudden infant death syndrome (SIDS) remains unclear. Progressive bradycardia is the pre-eminent terminal event, suggesting that circulatory failure might be a crucial factor. Vasomotor tone regulates the circulatory system by controlling blood volume distribution while maintaining venous return and blood pressure.

AIM

To examine whether prone sleeping, the most consistently identified risk factor for SIDS, has a measurable influence on vasomotor/circulatory control.

METHODS

44 full term infants (mean age, 7.9 weeks) were studied during an overnight sleep. Recordings were made while the infants were horizontal and asleep in the supine and prone positions, and repeated after a head up tilt to 60 degrees, maintained for 30 minutes, while in both sleep positions. Blood pressure, heart rate, anterior shin, and anterior abdominal wall skin temperatures were measured.

RESULTS

Systolic blood pressure was lower, but peripheral skin temperature and heart rate were higher during sleep, while horizontal, in the prone rather than the supine position. After tilting, there was a greater reduction in blood pressure and a greater increase in peripheral skin temperature and heart rate when in the prone position. Anterior abdominal wall skin temperature did not vary in either sleeping positions while horizontal or tilted.

CONCLUSION

Prone sleeping has a measurable effect on circulatory control, with a reduction in vasomotor tone resulting in peripheral vasodilatation, a higher peripheral skin temperature, a lower blood pressure, and a higher resting heart rate. Because vasomotor tone is crucially important in circulatory control this could be a factor in increasing the risk of SIDS.

Increased infant axillary temperatures in non-REM sleep during mother-infant bed-sharing

This study addressed the effect of mother-infant bed-sharing on infant body temperature and possible mediating mechanisms. Axillary temperatures were recorded for the entire night in 26 infants on both a bed-sharing night and a solitary sleeping night, accompanied by polysomnography and video-taping to allow assignment of sleep stages and behavioral analysis. All infants were approximately 3 months old, healthy, Latino and breast-feeding; 16 of the infants bed-shared since birth while the others routinely slept alone. Bed-sharing was associated with a significantly increased mean axillary temperature compared to solitary sleeping in both routine bed sharers and routine solitary sleepers. This increase was expressed only in non-REM sleep, with no differences during REM sleep or waking. The increase in temperature during bed-sharing may be related to an increased frequency of transient, movement-associated arousals during bed-sharing.