Sleeping body temperatures in 3-4 month old infants

Temperature threshold in the screening of bacterial infections in young infants with hypothermia

BACKGROUND

Young infants with hypothermia presenting to the emergency department (ED) are at risk for serious bacterial infections (SBI), however there is no consensus temperature to prompt evaluation for SBI among these children. We sought to statistically derive a temperature threshold to guide detection of SBI in young infants with hypothermia presenting to the ED.

METHODS

We performed a cross-sectional study of infants ≤90 days old presenting to four academic paediatric EDs in the United States of America from January 2015 through December 2019 with a rectal temperature of ≤36.4°C. Our primary outcomes were SBI, defined as urinary tract infection (UTI), bacteraemia and/or bacterial meningitis, and invasive bacterial infections (IBI, limited to bacteraemia and/or bacterial meningitis). We constructed receiver operating characteristic (ROC) curves to evaluate an optimally derived cutpoint for minimum ED temperature and presence of SBI or IBI.

RESULTS

We included 3376 infants, of whom SBI were found in 62 (1.8%) and IBI in 16 (0.5%). The most common infection identified was Escherichia coli UTI. Overall, cohort minimum median temperature was 36.2°C (IQR 36.0°C-36.4°C). Patients with SBI and IBI had lower median temperatures, 35.8°C (IQR 35.8°C-36.3°C) and 35.4°C (IQR 35.7°C-36.3°C), respectively, compared with those without corresponding infections (both p<0.05). Using an outcome of SBI, the area under the ROC curve (AUROC) was 61.0% (95% CI 54.1% to 67.9%). At a cutpoint of 36.2°C, sensitivity was 59.7% and specificity was 59.2%. When using an outcome of IBI, the AUROC was 65.9% (95% CI 51.1% to 80.6%). Using a cutpoint of 36.1°C in this model resulted in a sensitivity of 68.8% and specificity of 60.1%.

CONCLUSION

Young infants with SBI and IBI presented with lower temperatures than infants without infections. However, there was no temperature threshold to reliably identify SBI or IBI. Further research incorporating clinical and laboratory parameters, in addition to temperature, may help to improve risk stratification for these vulnerable patients.

Distal skin vasodilation in sleep preparedness, and its impact on thermal status in preterm neonates

OBJECTIVE

Prior to sleep onset in human adults, distal body temperatures change progressively from wakefulness levels (low skin temperatures and a high core temperature) to sleep levels (high skin temperatures and a low core temperature) due to distal skin vasodilation and greater body cooling. It is not known whether this sleep preparedness exists in preterm neonates, even though sleep has a key role in neonatal health and neurodevelopment. The present study's objectives were to determine whether sleep preparedness (as observed in adults) can be evidenced in preterm neonates, and to assess repercussions on thermal stress.

METHODS

During a 12-h night-time polysomnography session, skin temperatures (recorded with an infrared camera), sleep, and wakefulness episodes were measured in 18 nine-day-old preterm neonates.

RESULTS

Fifteen wakefulness episodes were considered. Our results highlighted significant pre-sleep distal skin vasodilation (mainly at the foot: an increase of 0.38 °C in the 20 min preceding sleep onset) for the first time in preterm neonates. This vasodilation occurred even though (1) most factors known to influence pre-sleep vasodilation in adults were not present in these neonates, and (2) the neonates were nursed in a nearly constant thermal environment. The vasodilatation-related increase in body heat loss corresponded to a 0.15°C/h fall in mean body temperature (calculated using partitional calorimetry).

CONCLUSION

Compensation for this body heat loss and the maintenance of body homeothermia would require a 4% increase in metabolic heat production. In neonates, this type of energy expenditure cannot be maintained for a long period of time.

Neuronal noise as an origin of sleep arousals and its role in sudden infant death syndrome

In addition to regular sleep/wake cycles, humans and animals exhibit brief arousals from sleep. Although much is known about consolidated sleep and wakefulness, the mechanism that triggers arousals remains enigmatic. Here, we argue that arousals are caused by the intrinsic neuronal noise of wake-promoting neurons. We propose a model that simulates the superposition of the noise from a group of neurons, and show that, occasionally, the superposed noise exceeds the excitability threshold and provokes an arousal. Because neuronal noise decreases with increasing temperature, our model predicts arousal frequency to decrease as well. To test this prediction, we perform experiments on the sleep/wake behavior of zebrafish larvae and find that increasing water temperatures lead to fewer and shorter arousals, as predicted by our analytic derivations and model simulations. Our findings indicate a previously unrecognized neurophysiological mechanism that links sleep arousals with temperature regulation, and may explain the origin of the clinically observed higher risk for sudden infant death syndrome with increased ambient temperature.

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.

Evaluation of the thermal insulation of clothing of infants sleeping outdoors in Northern winter

It is a common practice in Northern countries that children aged about 2 weeks to 2 years take their daytime sleep outdoors in prams in winter. The aim was to evaluate the thermal insulation of clothing of infants sleeping outdoors in winter. Clothing data of infants aged 3.5 months was collected, and sleep duration, skin and microclimate temperatures, humidity inside middle wear, air temperature and velocity of the outdoor environment were recorded during sleep taken outdoors (n = 34) and indoors (n = 33) in families' homes. The insulation of clothing ensembles was measured by using a baby-size thermal manikin, and the values were used for defining clothing insulation of the observed infants. Required clothing insulation for each condition was estimated according to ISO 11079. Clothing insulation did not correlate with ambient air temperature. The observed and required insulation of the study group was equal at about -5 °C, but overdressing existed in warmer and deficiency in thermal insulation in colder temperatures (r (s) 0.739, p < 0.001). However, even at -5 °C a slow cooling (ca. 0.012 °C/min) of mean skin temperature (T (sk)) was observed. When the difference between observed and required insulation increased, the cooling rate of T (sk) increased linearly (r (s) 0.605, p < 0.001) and the infants slept for a shorter period (r (s) 0.524, p = 0.001). The results of this study show the difficulty of adjusting systematically the optimal thermal insulation for outdoor sleeping infants during northern winter. Therefore, the necessity for guidelines is obvious. The study provides information for adequate cold protection of infants sleeping in cold conditions.

Infants sleeping outdoors in a northern winter climate: skin temperature and duration of sleep

AIM

The aim of the study is to describe the relationships among thermal environment, skin temperatures and infants' daytime outdoor sleep duration in northern winter conditions.

METHODS

This study is a cross-over observational study. Skin temperatures of three-month-old infants were recorded from seven skin sites continuously throughout outdoor (n = 34) and indoor sleep (n = 33) in the families' homes. The duration of the sleep was observed, and temperature and the air velocity of the environment were recorded.

RESULTS

Skin temperatures increased towards the end of indoor sleeping, whereas they decreased during outdoor sleeping. The cooling rate of mean skin temperature (T(sk)) increased in lower outdoor temperatures (r(s) = .628, p < 0.001) in spite of increased clothing. On some occasions, cold extremities were observed, suggesting slight deviations from thermoneutrality. Sleep time was 92 min longer in outdoors than in indoors. However, outdoor sleep duration was shortened when the cooling rate of T(sk) increased (r(s) = 0.611, p < 0.001).

CONCLUSION

The longest sleep was recorded outdoors when the cooling rate of T(sk) was minimal. Restriction of movements by clothing probably increases the length of sleep, and a cold environment makes swaddling possible without overheating. A decrease in ambient temperature increased the cooling rate, suggesting that the cold protection of the clothing compensated only partly for the increased heat loss.

Assessment of fever in African children: implication for malaria trials

We evaluated methods for assessing body temperature by comparing subjective assessment of fever by parents and doctors with objective axillary, tympanic, and rectal measurements of body temperature in 1000 children < or = 10-years-old who presented at outpatient clinics with recent history of fever. Sensitivity of subjective assessment of fever were higher at thresholds of > or = 38.3 degrees C with specificity as low as 60%. Axillary methods showed better specificity at fever thresholds of > 38.0 degrees C with maximum sensitivity of 63% at thresholds of > or = 37.5 degrees C. Bland-Altman analysis showed wide limits of agreement between objective methods of measurements: -1 degrees C to 3 degrees C for comparison of rectal and axillary, -1 degrees C to 2 degrees C for rectal and tympanic, and -1 degrees C to 2 degrees C for tympanic and axillary measurements. A choice of method to measure body temperature for diagnosis of fever in African children should be informed by a trade-off between its specificity and sensitivity that considers thresholds > 38.0 degrees C.

Airway covering during bed-sharing

BACKGROUND

Parent-infant bed-sharing is a common practice in Western post-industrial nations with up to 50% of infants sleeping with their parents at some point during early infancy. However, researchers have claimed that infants may be at risk of suffocation or sudden infant death syndrome related to airway covering or compression in the bed-sharing environment. To further understand the role of airway covering and compression in creating risks for bed-sharing infants, we report here on a sleep-lab trial of two infant sleep conditions.

METHODS

In a sleep-lab environment 20 infants aged 2-3 months old slept in their parents' bed, and in a cot by the bed, on adjacent nights. Infants' oxygen saturation and heart rate were monitored physiologically while infant and parental behaviours were recorded via ceiling-mounted infra-red cameras. Infants served as their own controls. Continuous 8-h recordings were obtained for covering of infant external airways, levels of infant oxygen saturation, infant heart rate, evidence of parental compression/overlying of infant, circumstances leading up to potential infant airway obstruction, and parental awareness of and responses to infant airway covering.

RESULTS

The majority of infants (14/20) spent some part of the bed night with their airways (both mouth and nose) covered, compared with 2/20 on the cot night; however, no consistent effect on either oxygen saturation levels or heart rate was revealed, even during prolonged bouts of airway covering. All cases of airway covering were initiated by parents; 70% were terminated by parents, the remainder by infants. Seven bouts of potential compression were observed with parental limbs resting across infant bodies for lengthy periods, however, in only two cases was the full weight of a parental limb resting on an infant, both events lasting less than 15 s, both being terminated by infant movement.

CONCLUSION

Although numerous authors have suggested that bed-sharing infants face risks because of airway covering by bed-clothes or parental bodies, the present trial does not lend support to this hypothesis.

Long-range correlations in rectal temperature fluctuations of healthy infants during maturation

Background

Control of breathing, heart rate, and body temperature are interdependent in infants, where instabilities in thermoregulation can contribute to apneas or even life-threatening events. Identifying abnormalities in thermoregulation is particularly important in the first 6 months of life, where autonomic regulation undergoes critical development. Fluctuations in body temperature have been shown to be sensitive to maturational stage as well as system failure in critically ill patients. We thus aimed to investigate the existence of fractal-like long-range correlations, indicative of temperature control, in night time rectal temperature (T_rec) patterns in maturing infants.

Methodology/Principal Findings

We measured T_rec fluctuations in infants every 4 weeks from 4 to 20 weeks of age and before and after immunization. Long-range correlations in the temperature series were quantified by the correlation exponent, α using detrended fluctuation analysis. The effects of maturation, room temperature, and immunization on the strength of correlation were investigated. We found that T_rec fluctuations exhibit fractal long-range correlations with a mean (SD) α of 1.51 (0.11), indicating that T_rec is regulated in a highly correlated and hence deterministic manner. A significant increase in α with age from 1.42 (0.07) at 4 weeks to 1.58 (0.04) at 20 weeks reflects a change in long-range correlation behavior with maturation towards a smoother and more deterministic temperature regulation, potentially due to the decrease in surface area to body weight ratio in the maturing infant. α was not associated with mean room temperature or influenced by immunization

Conclusions

This study shows that the quantification of long-range correlations using α derived from detrended fluctuation analysis is an observer-independent tool which can distinguish developmental stages of night time T_rec pattern in young infants, reflective of maturation of the autonomic system. Detrended fluctuation analysis may prove useful for characterizing thermoregulation in premature and other infants at risk for life-threatening events.

Thermal insulation and SIDS-an investigation of selected 'Eastern' and 'Western' infant bedding combinations

BACKGROUND

Differences in the incidence of SIDS between 'Western' and 'Eastern' countries has been attributed to cultural practices, which may affect the infants care and thermal environment.

AIM

The purpose of this work was to estimate for selected 'commonly' used bedding, sleep positions and practices in Japan, Korea and New Zealand, the intrinsic 'dry' thermal resistance of bedding. Insulation levels are also discussed in the context of published information about the thermal environment in which the bedding is likely to be used.

METHOD

Selected Japanese, Korean and New Zealand bedding was loosely tucked over an infant manikin in the lateral, prone and supine sleep positions. Thickness in use was measured, and intrinsic 'dry' thermal resistance estimated using the Wilson Laing model which accommodates the effect on insulation of the three-dimensional arrangement of bedding combinations during use.

RESULTS AND DISCUSSION

Thickness of under- and upper-bedding varied among countries with thickness and estimated 'dry' thermal resistance of the upper-bedding affected by the type/combination of bedding and the infants sleep position. Insulation levels are discussed in relation to environmental conditions within and among countries and between seasons. Further information on thermal environments, bedding combinations used and care practices within both Asian and Western countries is needed.

CONCLUSIONS

'Eastern' infants appear likely to be generally covered in bedding combinations of greater insulation than those used to cover 'Western' infants in comparable seasons. Differences existed between insulation of the Japanese and Korean bedding combinations investigated. Lower rates of SIDS apparent in 'Asian' populations do not appear attributable to use of lower levels of bedding insulation only.

Infant Weight and Gestational Age Effects on Thermoneutrality in the Home Environment

OBJECTIVE

To describe infant temperature in the home environment and explore factors, particularly weight and gestational age at birth, associated with maintenance of thermal neutral temperatures in the home.

DESIGN

Continuous abdominal skin temperature was recorded at 1-minute intervals for a 24-hour period in both full-term and preterm infants, using a two-group exploratory design.

SETTING

Infants were studied in the home environment.

PATIENTS/PARTICIPANTS

Twenty-four preterm and 16 full-term infants were studied at approximately 44 weeks postconceptional age.

MAIN OUTCOME MEASURES

Abdominal skin temperature was coded as within, over, or under the thermal neutral zone, and the percentage of time in these thermal conditions was calculated.

RESULTS

Regression analysis was conducted, and weight, gestational age, and weight by gestational age interaction were found to be statistically significant predictors of percent of time over and under the thermal neutral zone. Smaller preterm infants were overheated, whereas heavier preterm infants were underheated. Smaller full-term infants were underheated, and heavier full-term infants were overheated.

CONCLUSION

Thermal care of infants in the home may be influenced by parental perception of thermal vulnerability relative to weight and gestational age at birth.

Overnight deep body temperature and urinary cortisol excretion in infants from economically deprived areas

OBJECTIVES

To assess the pattern of postnatal physiological maturation in economically deprived infants by measuring the age-related changes in deep body temperature during night-time sleep.

SETTING

Inner city Leicester, UK.

PARTICIPANTS

Forty-eight infants aged 6-21 weeks from economically deprived areas and 87 control infants from more affluent areas.

OUTCOME MEASURES

Average deep body temperature between 2 and 4 h after bedtime, overnight and early morning urinary cortisol excretion.

RESULTS

Both groups showed a decline in overnight deep body temperature with age that averaged 0.030 degrees C per week (SE = 0.003). Over the age range studied, the average age-adjusted overnight temperature in the infants from deprived homes was 0.090 degrees C (SE = 0.028) higher than that for the affluent group (P = 0.001). Deprived infants had on average 51% higher overnight urinary cortisol and 80% higher morning cortisol. The differences remained when the effects of room temperature, clothing, smoking, birthweight and gestational age were taken into account.

CONCLUSION

These indicators of postnatal physiological maturation suggest that infants from economically deprived homes mature less quickly. This might increase their vulnerability to illness.

Scrotal temperatures do not differ among young boys wearing disposable or reusable diapers

BACKGROUND/AIMS

This study investigated the effect of specific, commonly used diaper types on scrotal temperatures in normal healthy, young boys. These included both modern disposable and reusable diapers as well as various types of protective outer coverings that are in common use in both North America and Europe

METHODS

Scrotal and skin surface temperatures were continuously monitored in healthy, young males using a computerized data-logging system based on temperature probes specifically designed for paediatric studies. These systems could be used either tethered to the PC or made completely portable depending upon the age and activity of the child being measured. Based on our results from several pilot studies, it became clear that the best way to determine if disposable and reusable diapers differ with regard to their impact on scrotal temperatures is to run these comparisons under controlled laboratory conditions where "diaper type" was the primary variable. A 2-h time period was chosen to ensure that sufficient time had elapsed for thermal equilibrium to be established under the diapers. We also felt it necessary to study the impact of urination and simulated this condition over the last 15 min using standardized methods. In addition to the skin surface temperatures, we also measured the temperature of the tympanic membrane using an infrared thermometer as an estimate of "core" temperature for each individual at various times during the session.

RESULTS AND CONCLUSIONS

In this study, we have clearly shown that scrotal temperatures are the same whether the child is wearing disposable or reusable cloth diapers with a protective cover. The only situation in which scrotal temperatures were found to be lower is when the cloth diaper is used alone without a protective cover but this is not representative of how these products are actually used. We also found that on average scrotal temperatures are significantly lower than core for each diaper type. Occasionally, we did see individuals in which the maximal scrotal temperatures approached core temperatures but in every case the thermal sensors were soiled by a bowel movement. We also found that skin surface temperatures increased not only when covered by a diaper but also due to the thermal insulation provided by outer garments and blankets.

Central and peripheral temperature change in normal infants

The purpose was to explore the relationship between the fall in rectal temperature seen in normal infants after being put down to sleep and the concomitant rise in peripheral shin temperature. In this observational study 21 normal infants had continuous overnight peripheral shin and central rectal temperature recorded, for three nights at 2 weeks, 6 weeks, 3 months and 5 months of age. Parents documented the start and end of feed/nappy changing episodes during the night. All recordings were made in the infants' own home. A strong inverse linear correlation (median r2 = 0.95, lower quartile 0.92, upper quartile 0.97) was seen between rectal temperature and shin temperature on falling to sleep when put down on 106 (65%) of 161 nights. On many other nights a significant nonlinear association was present. It was not possible to exclude the process of being put down to sleep as a confounding variable in this strong association. However, a similar inverse relationship between shin and rectal temperature was seen overnight during 111 of 121 (92%) feed/nappy changing episodes. If causal, the development in early infancy of an inverse relationship between shin and rectal temperature may be important for cardiovascular homeostasis. Further sleep laboratory work including video recording is required to separate the peripheral and central temperature changes that take place on falling to sleep from those associated with removal of clothing during a nappy change.

Deep body temperature changes in twins

Twins show differences in physiological maturity within and between twin sets; where one infant is 5-weeks later than its sibling; while one pair may both be slow but develop together. Zygosity, birth weight and sex may be contributory but not causative factors. How vulnerability to illness may be affected, is discussed.

Assessment of infant physiology and neuronal development using magnetic resonance imaging

Previous work has demonstrated both that there are substantial individual differences in the rate of physiological development,and that infants with risk factors for Sudden Infant Death Syndrome (SIDS) develop more slowly, suggesting that their increased vulnerability may be due to delayed neuronal development associated with compromised development in fetal or early neonatal life. This project aims to test the hypothesis that individual differences in the rate of physiological development of infants correlate with measurable differences in the rate of brain development as assessed by magnetic resonance imaging (MRI). Sixty infants were recruited to this study in three different groups that are known to have differing rates of physiological development. MRI was performed successfully in 49 cases at 6 weeks of age without sedation. Forty-one of these cases had full follow-up (15 normal; 19 IUGR; 11 'high risk'). Postnatal physiological development was assessed by measuring age-related deep body temperature patterns during sleep. Neuronal development was assessed by subjective analysis of MRI images and objective measurements relating to myelination using T1 and diffusion weighted (23 cases) MRI images. As expected the normal group acquired the adult temperature pattern earlier, but this was not statistically significant. All MRI scan appearances were within normal limits. Ranking cases subjectively in order of maturity revealed no significant pattern. The normal group had a significantly higher myelination score than the IUGR and 'high risk' groups (P = 0.001). This trend was also shown by the diffusion weighted myelination score but did not reach statistical significance. No significant differences were seen in both the subjective and objective MRI measurements and development of nocturnal temperature patterns. The results suggest there may be differences in neurodevelopment between the different groups at 6 weeks of age but these are not linked to late development of temperature patterns. It is therefore unlikely that this related to a global delay in maturation.

Gender-related differences in rectal temperature in human neonates

The aim of this study was to examine the gender-related differences in human neonates' body temperature. Rectal temperatures of 101 newborns (52 girls and 49 boys) were measured using a calibrated glass-mercury thermometer five times during their first 5 days of life. Results show that the temperature of males, averaged over 5 days, was significantly lower (37.068 degrees C) than that of females (37.168 degrees C). This result suggests that gender-dependent differences in baseline body temperature are present at birth.

Biological rhythm development in preterm infants: does health status influence body temperature circadian rhythm?

Twenty-six preterm infants, postconceptional age from 28 to 35 weeks and postnatal age approximately 14 days, were included in a study of the development of temperature circadian rhythm. Insulated abdominal skin temperature and incubator air temperature were recorded continuously at 1-min intervals for 24 hr. Using cosinor analysis, cycle mesor, amplitude, and acrophase were determined. Initial results from regression analysis did not confirm a predicted linear relationship between postconceptional age and amplitude; however, dividing the sample according to health status into sick (N = 15) and not sick (N = 11) groups revealed differing regression models. For not sick infants, amplitude increased with postconceptional age (R(2) =.405), whereas no relationship was found between postconceptional age and cycle amplitude in sick infants (R(2) =.069). These results indicate that healthy preterm infants demonstrate emergence of circadian temperature rhythm. Implications include potential time-based periods of vulnerability, overheating and hyperthermia, and management of incubator operation.

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.

Night-time non-nutritive sucking in infants aged 1 to 5 months: relationship with infant state, breastfeeding, and bed-sharing versus room-sharing

AIM

Epidemiological studies suggest that pacifier use may be protective against SIDS but little is known of the relationship between pacifier use and other forms of non-nutritive sucking (NNS) in infancy, or of patterns of NNS during the night, when most SIDS deaths occur. We report the first longitudinal study of NNS by direct overnight observations in healthy infants in a sleep laboratory.

METHODS

Healthy, breast fed term infants (n = 10) were enrolled at birth, and sequential overnight polygraphic and infrared video recordings of infants with their mothers performed at monthly intervals from 1 to 5 months. Each month, mother baby pairs were randomized to 1 night bed-sharing (BN) then 1 room-sharing (RN), or vice versa. 'Episodes' of pacifier, own digit and mother's digit sucking (> 1 min) were identified and compared with state-matched control periods without sucking or feeding before and after each such episode.

RESULTS

329 episodes of NNS were identified in 749 h of video recording. The prevalence of pacifier sucking decreased with age, whilst digit sucking increased. Routine pacifier users rarely sucked their digits. There were temporal differences throughout the night in the distribution of different types of sucking and in infant state during and around sucking episodes. Sleeping in the 'non-routine' location was associated with a larger percentage of nights with sucking episodes and increased sleep latency. Bed sharing (routinely or on a given night) was associated with less sucking behavior and more breastfeeding. Non-nutritive sucking was not, however, associated with decreased total time breastfeeding per night or number of feeds per night.

CONCLUSION

Patterns of NNS during the night change with age and are affected by maternal proximity. Digit sucking has state modulating effects, and may be suppressed by pacifier use. Thus any benefits of pacifier use must be set against the potential loss of a self-directed ability to modulate state during the night, and possible shortening of breastfeeding duration.

Is baby too warm? The use of infant clothing, bedding and home heating in Victoria, Australia

Overheating of infants has been associated with a raised risk for sudden infant death syndrome (SIDS). Data on the use of heating, bedding and clothing and other measures affecting the thermal environment of 4 week old infants were collected at a home interview for infants of women born in Australia (Anglo-Celtic background), in Southern Europe, in Asia and of women who had a planned out-of-hospital birth. These groups have different risks of SIDS not explained by the classic social and perinatal risk factors nor associated with the currently promoted 'new' risk factors. Thermal insulation of the infant's bedding and clothing and excess thermal insulation (for any observed room temperature) were calculated. Bed sharing differed significantly between the groups as did the use of a sheepskin, tucking in firmly, the closing of doors and windows and the use of heating in the infant's room. After stratifying by bed sharing practice and season of interview, it was found that bed sharing infants had more thermal insulation than those sleeping alone irrespective of season of interview. Infants sleeping alone in the Asian-born and Southern European-born groups were kept warmer than infants in the other two groups. Cultural factors appear to affect the thermal environment in which infants are raised. Some bed sharing infants in all four groups were inappropriately warm, particularly in colder weather, but this was more likely in the Asian-born (low risk) group than in the home birth (high risk) group. These results do not explain the differences in SIDS incidence between the groups.

Effects of temperature on sleep in the developing rat

In altricial species, such as humans and rats, much of the development of autonomic systems occurs postnatally. Consequently, vulnerabilities exist early in postnatal development when immature autonomic functions are challenged by external factors such as variations in ambient temperature (Ta). Ta profoundly influences sleep/wake state structure in adult animals and humans, and exposure to excessive warmth has been implicated as a risk factor in sudden infant death syndrome. To better understand the relationship between temperature and sleep during development, we investigated the effect of Ta variation on sleep/wake state structure and sleep intensity in developing rats. In this experiment, sleep intensity was measured by the intensity of slow-wave activity during slow-wave sleep. Neonatal Long-Evans hooded rat pups were surgically prepared for chronic sleep/wake state and brain temperature (Tbr) recording. Two-hour recordings of sleep/wake state and Tbr were obtained from rats on postnatal day 12 (P12), P14, P16, P18, and P20 at a Ta of either 28.0-30.0, 33.0-35.0, or 38.0-40.0 degrees C. Ta significantly influenced sleep/wake state structure but had little, if any, effect on sleep intensity in developing rats.

Consequences of getting the head covered during sleep in infancy

OBJECTIVE

To study the consequences of getting the head covered by bedding (fiber quilt) on carbon dioxide (CO2) accumulation around the face, behavior, and physiologic responses during prone and supine sleep in infants to add understanding to why victims of sudden infant death syndrome are often found under the bedding. METHPDOLOGY: Of 33 healthy term, usually nonprone sleeping infants, behavior and computerized polysomnography were successfully recorded for 30 during prone and supine sleep at 21/2 months and for 23 prone and 25 supine at 5 months.

RESULTS

For both ages and body positions, covering the head resulted in significant CO2 accumulation around the face, fewer apneas (3 to 10 seconds), shorter duration of apneas after sighs, higher heart and respiratory rates, and peripheral skin temperature. Differences were generally greater at 21/2 than at 5 months. While covered, the prone position was associated with higher CO2 levels close to the face, slightly higher transcutaneous PCO2, and higher heart rates and peripheral skin temperatures than the supine position. In the supine position 23% were able to remove the cover from the head at 21/2 and 60% at 5 months, whereas only 1 infant of 5 months managed to remove the cover when prone.

CONCLUSIONS

The observed responses are consistent with a potential for distress when the head is covered, particularly when placed prone. Probably most important with respect to sudden infant death syndrome is the infants' inability to remove the bedding from the head upon awakening from prone sleep.

Behaviour and physiological responses during prone and supine sleep in early infancy

AIMS

To study the effect of prone and supine sleep on infant behaviour, peripheral skin temperature, and cardiorespiratory parameters to aid understanding of why prone sleeping is associated with an increased risk of sudden infant death syndrome.

METHODS

Of 33 enrolled infants, 32 were studied at 2.5 and 28 at 5 months of age. A computer aided multichannel system was used for polysomnographic recordings. Behaviour was charted separately.

RESULTS

Prone REM (active) sleep was associated with lower frequencies of short arousals, body movements and sighs, and a shorter duration of apnoeas than supine REM sleep at both ages. At 2.5 months there were less frequent episodes of periodic breathing during prone sleep in non-REM (quiet) and REM sleep. Heart rate and peripheral skin temperature were higher in the prone position during both sleep states at both ages.

CONCLUSIONS

The observation of decreased variation in behaviour and respiratory pattern, increased heart rate, and increased peripheral skin temperature during prone compared with supine sleep may indicate that young infants are less able to maintain adequate respiratory and metabolic homoeostasis during prone sleep.

Interactions between infant care practices and physiological development in Asian infants

Asian infants are less likely to suffer cot death despite apparently higher prevalence of some risk factors. This paper compares the development of night time body temperature patterns in a small sample of Asian babies with the pattern already established for white infants, where babies who develop an adult-like night time temperature pattern later than usual share characteristics with victims of SIDS. The Asian infants had similar body temperature patterns to whites, but tended to develop the adult-like pattern later, not earlier as might have been expected. More Asian infants than white in our sample slept in the parental bed, and, before the adult-like body temperature patterns appeared, co-sleeping infants had higher body temperatures than those in their own cots. Asian infants slept in significantly warmer rooms than whites, but under similar amounts of bedding. These studies do not therefore reveal any physiological difference between Asians and whites which might account for low vulnerability to cot death, indeed, if anything the reverse.

Body temperature changes before minor illness in infants

This study aimed to examine the overnight temperature pattern of babies during the prodromal phase of minor illnesses. The overnight rectal temperature pattern of 123 babies was recorded weekly from about 6 to at least 16 weeks old, while parents maintained detailed records of signs of illness. By analysis of patterns of signs and visits to the general practitioner, 86 periods of minor illness were identified, mostly upper respiratory tract infections, though it was not usually possible to identify the infection by conventional virology. Data were analysed separately for babies who had developed an adult-like night time temperature pattern and those who had not. In both groups, obvious signs of illness were preceded by a disturbance of night time temperature pattern. Temperature was significantly raised over control weeks, though few babies were clinically febrile. The greatest temperature disturbances were seen in the three days before illness, though some disturbances were seen up to seven days before. A similar disturbance of temperature was seen the night after diphtheria, pertussis, and tetanus immunisation, and individual responses to natural infection and immunisation were well correlated, suggesting that the temperature change is more a function of the host response than the infecting agent.

How much wrapping do babies need at night?

In a longitudinal, population based study, overnight temperature recordings were made in the bedrooms of 152 babies aged 3-18 weeks and the insulation provided by their bedclothing was assessed. Outdoor temperatures for the study nights were also available. Parents applied more insulation on colder nights with lower bedroom temperatures than on warmer nights (mean 8.5 tog at 15 degrees C minimum bedroom temperature falling to 4.0 tog at 25 degrees C). For a particular temperature they also applied 2 tog more insulation in winter than in summer. The amounts of bedclothing used in the home were compared with insulation levels predicted to achieve thermo-neutrality over a similar range of environmental temperature from heat balance studies in young infants. They corresponded closely. The average amount of bedclothing chosen for babies in Avon allows them to remain in thermoneutral conditions throughout the night. These values are proposed as broad guidelines for the thermal care of young babies at night.

Factors affecting the development of night time temperature rhythms

The rectal temperature of 26 infants between 6 and 16 weeks old was monitored continuously for one night each week. Rectal temperature always decreased with sleep but the minimum temperature attained changed with age. Some time between 8 and 16 weeks old the minimum sleeping rectal temperature decreased abruptly from around 36.8 degrees C to around 36.4 degrees C. This change was complete within one week and did not normally revert unless the infant became ill. Some infants changed as early as 8 weeks old, others not until 16 weeks. Breast fed infants changed significantly earlier than bottle fed infants. Girls changed significantly earlier than boys. First born infants changed significantly earlier than second or subsequent infants. Early changes were significantly more likely to be sleeping lateral or supine, and to have older mothers. They tended to come from more affluent families. There was no association between the time of change and the thermal environment in which the infant slept or the number of episodes of minor illness in the early weeks of life.

Oscillations of body temperature at night

There is increasing evidence that overheating is a contributing factor for some cot deaths. One hypothesis is that infant thermoregulation is closely related to respiratory control. To test this hypothesis it was necessary to determine the normal pattern of body temperature in the developing infant. A system has been designed and built to record continuously temperature signals from ambient, rectal, and various skin site sensors. Overnight studies were performed on 30 infants aged between 2 and 26 weeks in a hospital ward. Various time and frequency domain analyses of the temperature data have been developed. Analysis of body temperature rhythms has confirmed patterns during sleep which mature with age. In addition a periodic oscillation of body temperature has been found with a cycle of approximately one hour. This oscillation may reflect sleep state and its further study may give an insight into control of infant thermoregulation and the integration of this control with that of breathing and the cardiovascular system.

A probability nomogram to predict rectal temperature in children

The relationship between rectal and peripheral-site temperature was investigated to achieve two objectives: 1) to evaluate a prevailing practice of intersite adjustment by use of an invariant temperature difference; and 2) to develop a statistical method for intersite temperature predictions in the individual child, especially for fever as defined by rectal measurement. Rectal, oral, axillary, left abdomen skin, and forehead skin temperatures (degrees F) were measured with an electronic thermometer in 257 children. Objective 1 was not achieved because a simple temperature difference between a peripheral site and the rectal site could not be used to predict rectal temperature reliably. For objective 2, intersite differences met three statistical criteria so that normal distribution theory could be used to derive the probabilities for occurrence of each difference. Accordingly, cumulative probability nomograms were constructed to estimate rectal-site fever from measurements at peripheral sites. This nomogram method produces a clinically reliable prediction of rectal-site fever from temperature measurement at peripheral sites, especially the oral and axillary sites. These predictions offer useful assessments of febrile illness severity when rectal temperature is not available.

Combined effect of infection and heavy wrapping on the risk of sudden unexpected infant death

Three methods were used to investigate the role of infection in sudden unexpected infant death (SUD): (i) microbiological comparison of SUD victims and matched, live, community controls; (ii) postmortem classification of the contribution of infection to death; and (iii) case-control analysis of the relative risk associated with both infection and heavy wrapping. Limited sampling from the upper respiratory tract and gut in SUD victims and controls showed no significant excess of viral infection in the SUD victims (odds ratio = 1.98, 95% confidence interval (CI) 0.9 to 4.5). At postmortem examination, infection explained death in 3/95 babies and may have contributed to death in 37/95. Over 70 days of age, the combined presence of viral infection and wrapping in excess of 10 togs produced an odds ratio of SUD of 51.5 (95% CI 5.64 to 471.48) compared with wrapping of less than 6 togs. Viral infection was not a major risk factor as long as babies were lightly wrapped. In heavily wrapped babies the presence of a viral infection greatly increased the risk of SUD.

HomeLog: long-term recording of infant temperature, respiratory and cardiac signals in the home environment

There is increasing evidence that overheating is a contributing factor for some cot deaths. The authors' hypothesis is that infant thermoregulation is closely related to respiratory control. HomeLog is a system built to investigate the developing thermal, respiratory and cardiac behaviour of infants in the home environment over several weeks. HomeLog is based on a modified laptop computer. Signals recorded include body temperature (from rectal and various skin sites), ambient temperature, thoracic impedance, abdominal movement and electrocardiogram (ECG). Continuous night-time recordings have been made for up to 6 weeks from infants between 1 and 4 months of age, in their own cots, in their own homes. Various time and frequency domain analyses of the breathing and temperature data have been developed. Analysis of breath rate variability and of body temperature fluctuations has confirmed sleep/wake changes. In addition, a periodic oscillation of body temperature every 1-2 h has been found, which closely matches oscillations of breath rate variability.

Axillary and rectal temperature measurements in infants

Rectal and axillary temperatures were measured during the daytime in 281 infants seen randomly at home and 656 at hospital under 6 months old, using mercury-in-glass thermometers. The normal temperature range derived from the babies at home was 36.7-37.9 degrees C for rectal temperature and 35.6-37.2 degrees C for axillary temperature. Rectal temperature was higher than axillary in 98% of the measurements. The mean (SD) difference between rectal and axillary temperatures was 0.7 (0.5) degrees C, with a range of 3 degrees C. When used in hospital to detect high temperature, axillary temperature had a sensitivity of 73% compared with rectal temperature. This is too insensitive for accurate detection of an infant's high temperature. Rectal temperature measurement is safer than previously suggested: perforation has occurred in less than one in two million measurements. If an infant's temperature needs to be taken, rectal temperature should be used.

Sleeping position and rectal temperature

The effects of sleeping position upon body temperature were assessed by continuous monitoring of rectal temperature in 137 babies sleeping at home under conditions chosen by their parents. There were three groups of subjects: (1) normal babies aged 12-22 weeks whose temperature rhythms were developed, (2) normal babies aged 6-12 weeks who were developing their night time temperature rhythms, and (3) babies the night after diphtheria, pertussis, and tetanus immunisation, whose temperature rhythms were disturbed. Sleeping in the prone position was not associated with higher rectal temperatures at any time of night in young babies, nor did it exaggerate the disturbance of rectal temperature rhythm after immunisation. In older normal babies the prone position did not disturb rectal temperature in the first part of the night, though prone sleepers warmed a little faster prior to walking, especially in warm conditions. Prone sleepers were, however, born earlier in gestation and tended to be of lower birth weight. Normal babies can therefore thermoregulate effectively whatever their sleeping posture, even in warm conditions, though the prone position may make it slightly more difficult to lose heat. It is difficult to see how the prone position, even interacting with warm conditions, could induce lethal hyperthermia in otherwise normal babies. Perhaps the prone position is associated with other risk factors for sudden infant death syndrome.

Development of night time temperature rhythms over the first six months of life

Continuous recordings of night time rectal temperature were made at regular intervals over the first six months of life in 49 babies. In the first two weeks of life rectal temperature changed little overnight, but by 6 weeks of age rectal temperature at bedtime was significantly higher than later in the night. By around 12 weeks of age sleeping deep body temperature fell below 36.5 degrees C, and by 16 weeks of age all babies exhibited a consistent rhythm of rectal temperature. This fell by about 0.8 degrees C within two hours of bedtime, and then remained low until an hour or two before waking. As babies got older the mean interval between bedtime and first disturbance of parents got longer. Sleeping rectal temperature fell below 36.5 degrees C at about the time babies slept for seven hours. From 6 weeks of age, as individual baby's rectal temperatures fell more with sleep, sleep got longer.

Rectal temperature of normal babies the night after first diphtheria, pertussis, and tetanus immunisation

Continuous rectal temperature recordings were made from 32 babies the night after their first diphtheria, pertussis, and tetanus immunisation and compared with recordings made before immunisation. Tog values of clothes and wrapping and room temperatures were also recorded. We found that immunisation the day before disturbs the normal night time rhythm of deep body temperature. The rectal temperature of immunised babies was significantly higher than non-immunised babies from two hours into the night. We also found that there were considerable individual variations in the extent of disturbance of temperature rhythm. They were not correlated with thermal environment. There is no reason to suppose that these mild physiological responses to immunisation are in any way harmful.

Factors influencing the body temperature of 3-4 month old infants at home during the day

Continuous recordings of rectal temperature were made from 40 normal infants, aged 3-4 months, at home during two days of normal activities. We found that the rectal temperature of a normal, healthy baby may vary from 36.0 degrees C at night to 37.8 degrees C during active periods of the day. During daytime sleep rectal temperature fell, but to a lesser extent, and for less time than during night time sleeps. Feeds raised the temperature unless the baby slept, when they reduced the rate of fall of temperature. Bottle feeds affected temperature more quickly than breast feeds. The changes in temperature during sleep and after feeds were independent of the room temperature or thermal insulation of clothing and wrapping.

Use of thermographic imaging to study babies sleeping at home

Two 3 month old infants sleeping under different thermal conditions were found to maintain similar deep body temperatures. Thermographic imaging suggested that though the uncovered head is the main source of heat transfer, other parts of the body such as the hands may be used when necessary.

Disturbed nights and 3-4 month old infants: the effects of feeding and thermal environment

Parents completed a prospective diary of a night's sleep for 87, 3-4 month old infants at home whose body temperatures were continuously recorded. We found that about half of the babies disturbed their parents in the night. Breast fed babies were more likely to wake parents in the middle of the night. The babies who disturbed their parents in the middle of the night were significantly more heavily wrapped in significantly warmer rooms. We suggest that discomfort from efforts at active thermoregulation in warm environments may lead some babies to disturb their parents at 'unsocial hours'.

Review of the epidemiology of sudden infant death syndrome and its relationship to temperature regulation

Infants dying suddenly and unexpectedly now account for 20% of all infant deaths in England and Wales, and the incidence shows no sign of falling. Recent work relating sudden infant death to a raised environmental temperature and a raised body temperature, implicates fever as a possible contributory cause of death; some infants may be unable to control their febrile response to infection, or to thermoregulate effectively, when well wrapped and heated. Death might then result from apnoea, occurring in a critical sleep state. These ideas have increased the interest in describing the normal practices of parents in caring for the environment of their infants in health and disease, and the effect of their behaviour on the child's temperature. Studies of these areas depend on collecting and interpreting data from young children during their day to day lives, and present a challenge of great relevance to primary care research.