Is overheating a factor in some unexpected infant deaths?

Development of behavioral responses to thermal challenges

Body temperature regulation involves the development of responses to cold and warm challenges. Matching our understanding of the development of body temperature regulation to warm challenges with that of cold challenges will enhance our understanding of the ontogeny of thermoregulation and reveal different adaptive specializations. Warm and cold thermoregulation are important processes, and they include direct thermal effects on offspring, as well as indirect effects on them, such as those imposed by thermally associated alterations of maternal behavior. The present paper is a selective review of the existing literature and a report of some new empirical data, aimed at processes of mammalian development, especially those affecting behavior. We briefly discuss the development of body temperature regulation in rats and mice, and thermal aspects of maternal behavior with emphasis on responses to high temperatures. The new data extend previous analyses of individual and group responses in developing rodents to warm and cool ambient temperatures. This literature not only reveals a variety of adaptive specializations during development, but it points to the earlier appearance in young mammals of abilities to combat heat loss, relative to protections from hyperthermia. These relative developmental delays in compensatory defenses to heating appear to render young mammals especially vulnerable to environmental warming. We describe cascading consequences of warming-effects that illustrate interactions across levels of physiological, neural, and behavioral development.

Camera-Based, Non-Contact, Vital-Signs Monitoring Technology May Provide a Way for the Early Prevention of SIDS in Infants

Sudden infant death syndrome (SIDS) is the unexplained death, usually during sleep, of a baby younger than 1-year-old. Even though researchers have discovered some factors that may put babies at extra risk, SIDS remains unpredictable up until now. One hypothesis is that impaired cardiovascular control may play a role in the underlying mechanism of SIDS. A reduction of heart rate variability (HRV) and progressive decrease in heart rate (HR) have been observed in infants who have later succumbed to SIDS. Many clues indicated the heart could be the final weakness in SIDS. Therefore, continuous monitoring of the dynamic changes within the heart may provide a possible preventive strategy of SIDS. Camera-based photoplethysmography was recently demonstrated as a contactless method to determine HR and HRV. This perspective presents a hypothesis that a camera-based, non-contact, vital-sign monitoring technology, which can indicate abnormal changes or a sudden loss of vital signs in a timely manner, may enable a crucial and low-cost means for the early prevention of SIDS in newborn infants.

Heat stress and sudden infant death syndrome--stress gene expression after exposure to moderate heat stress

The aim of the present study was to investigate stress gene expression in cultured primary fibroblasts established from Achilles tendons collected during autopsies from sudden infant death syndrome (SIDS) cases, and age-matched controls (infants dying in a traumatic event). Expression of 4 stress responsive genes, HSPA1B, HSPD1, HMOX1, and SOD2, was studied by quantitative reverse transcriptase PCR analysis of RNA purified from cells cultured under standard or various thermal stress conditions. The expression of all 4 genes was highly influenced by thermal stress in both SIDS and control cells. High interpersonal variance found in the SIDS group indicated that they represented a more heterogeneous group than controls. The SIDS group responded to thermal stress with a higher expression of the HSPA1B and HSPD1 genes compared to the control group, whereas no significant difference was observed in the expression of SOD2 and HMOX1 between the two groups. The differences were related to the heat shock treatment as none of the genes were expressed significantly different in SIDS at base levels at 37 °C. SOD2 and HMOX1 were up regulated in both groups, for SOD2 though the expression was lower in SIDS at all time points measured, and may be less related to heat stress. Being found dead in the prone position (a known risk factor for SIDS) was related to a lower HSPA1B up-regulation in SIDS compared to SIDS found on their side or back. The study demonstrates the potential usefulness of gene expression studies using cultured fibroblasts established from deceased individuals as a tool for molecular and pathological investigations in forensic and biomedical sciences.

Accidental overheating of a newborn under an infant radiant warmer: a lesson for future use

A fully functional radiant warmer induced rapid and continuous increases in regional skin temperatures, heart rate, mean arterial blood pressure and respiratory rate in a newborn patient without corrective action. We report this case of passive overheating to create awareness of the risks associated with regulating radiant heat output based upon a single servo-controlled temperature.

Heart rate variability in sleeping preterm neonates exposed to cool and warm thermal conditions

Sudden infant death syndrome (SIDS) remains the main cause of postneonatal infant death. Thermal stress is a major risk factor and makes infants more vulnerable to SIDS. Although it has been suggested that thermal stress could lead to SIDS by disrupting autonomic functions, clinical and physiopathological data on this hypothesis are scarce. We evaluated the influence of ambient temperature on autonomic nervous activity during sleep in thirty-four preterm neonates (mean ± SD gestational age: 31.4±1.5 weeks, postmenstrual age: 36.2±0.9 weeks). Heart rate variability was assessed as a function of the sleep stage at three different ambient temperatures (thermoneutrality and warm and cool thermal conditions). An elevated ambient temperature was associated with a higher basal heart rate and lower short- and long-term variability in all sleep stages, together with higher sympathetic activity and lower parasympathetic activity. Our study results showed that modification of the ambient temperature led to significant changes in autonomic nervous system control in sleeping preterm neonates. The latter changes are very similar to those observed in infants at risk of SIDS. Our findings may provide greater insight into the thermally-induced disease mechanisms related to SIDS and may help improve prevention strategies.

Sudden twin infant death on the same day: a case report and review of the literature

Sudden infant death syndrome (SIDS) is a major contributor to infant mortality. The cause of death is unknown: suggested possibilities include cardiovascular disease, anaphylactic shock, and suffocation. The occurrence of simultaneous sudden infant death syndrome is uncommon, such cases being extremely rare in forensic pathologic practice. We report two 10-week-old male twins who appeared well at the time of their evening feeding, yet died while sleeping on their backs. Both infants had petechial hemorrhages on the visceral pleura, epicardial surface of the heart, and thymus gland. Microscopic examination revealed pulmonary edema, intra-alveolar hemorrhage, and minor lymphocytic infiltration, again in both infants. In this report, we discuss the risk factors for SIDS, which should be considered individually or in combination as possible causes of death.

What is the mechanism of SIDS? Clues from epidemiology

The cause of sudden infant death syndrome (SIDS) is unknown. Many mechanisms have been postulated, although thermal stress, rebreathing of expired gases and infection/inflammation seem the most viable hypotheses for the causation of SIDS. Deaths from SIDS have reduced dramatically following the recommendation not to place infants to sleep prone. Epidemiological data have shown that prone sleeping position is more risky in winter, colder latitudes, higher altitudes, if the infant is unwell or has excessive bedding or clothing. This suggests prone sleeping position involves either directly or indirectly a thermal mechanism. SIDS caused by an infective/inflammatory mechanism might be associated with deaths occurring during the night. Rebreathing of expired gases, airway obstruction, long QT syndrome and other genetic conditions may explain a small number of sudden unexpected deaths in infancy.

Activation of 5-HT1A receptors in medullary raphé disrupts sleep and decreases shivering during cooling in the conscious piglet

Activation of 5-HT1A receptors in the medullary raphé decreases sympathetically mediated brown adipose tissue (BAT) thermogenesis and peripheral vasoconstriction when previously activated with leptin, LPS, prostaglandins, or cooling. It is not known whether shivering is also modulated by medullary raphé 5-HT1A receptors. We previously showed in conscious piglets that activation of 5-HT1A receptors with (±)-8-hydroxy-2-(dipropylamino)-tetralin (8-OH-DPAT) in the paragigantocellularis lateralis (PGCL), a medullary region lateral to the raphé that contains substantial numbers of 5-HT neurons, eliminates rapid eye movement (REM) sleep and decreases shivering in a cold environment, but does not attenuate peripheral vasoconstriction. Hoffman JM, Brown JW, Sirlin EA, Benoit AM, Gill WH, Harris MB, Darnall RA. Am J Physiol Regul Integr Comp Physiol 293: R518–R527, 2007. We hypothesized that, during cooling, activation of 5-HT1A receptors in the medullary raphé would also eliminate REM sleep and, in contrast to activation of 5-HT1A receptors in the PGCL, would attenuate both shivering and peripheral vasoconstriction. In a continuously cool environment, dialysis of 8-OH-DPAT into the medullary raphé resulted in alternating brief periods of non-REM sleep and wakefulness and eliminated REM sleep, as observed when 8-OH-DPAT is dialyzed into the PGCL. Moreover, both shivering and peripheral vasoconstriction were significantly attenuated after 8-OH-DPAT dialysis into the medullary raphé. The effects of 8-OH-DPAT were prevented after dialysis of the selective 5-HT1A receptor antagonist WAY-100635. We conclude that, during cooling, exogenous activation of 5-HT1A receptors in the medullary raphé decreases both shivering and peripheral vasoconstriction. Our data are consistent with the hypothesis that neurons expressing 5-HT1A receptors in the medullary raphé facilitate spinal motor circuits involved in shivering, as well as sympathetic stimulation of other thermoregulatory effector mechanisms.

Activation of 5-HT1A receptors in the paragigantocellularis lateralis decreases shivering during cooling in the conscious piglet

Activation of 5-HT1A receptors in the medullary raphé decreases sympathetic outflow to thermoregulatory mechanisms, including brown adipose tissue (BAT), thermogenesis, and peripheral vasoconstriction when these mechanisms are previously activated with leptin, prostaglandins, or cooling. These same mechanisms are also inhibited during rapid eye movement (REM) sleep. It is not known whether shivering is also modulated by medullary raphé neurons. We previously showed in the conscious piglet that activation of 5-HT1A receptors with 8-OH-DPAT (DPAT) in the paragigantocellularis lateralis (PGCL), a medullary region lateral to the midline raphé that contains 5-HT neurons, decreases heart rate, body temperature and muscle activity during non-rapid eye movement (NREM) sleep. We therefore hypothesized that activation of 5-HT1A receptors in the PGCL would also attenuate shivering and peripheral vasoconstriction during cooling. During REM sleep in a cool environment, shivering, carbon dioxide production, and body temperature decreased, and ear capillary blood flow and ear skin temperature increased. Shivering associated with rapid cooling was attenuated after dialysis of DPAT into the PGCL. In animals maintained in a continuously cool environment, dialysis of DPAT into the PGCL attenuated shivering and decreased body temperature, but there were no significant increases in ear capillary blood flow or ear skin temperature. We conclude that both naturally occurring REM sleep and exogenous activation of 5-HT1A receptors in the PGCL are associated with a suspension of shivering during cooling. Our data are consistent with the hypothesis that 5-HT neurons in the PGCL facilitate oscillating spinal motor circuits involved in shivering but are less involved in modulating sympathetically mediated thermoregulatory mechanisms.

A Clinical Report of Adverse Health Effects Due to Bed Sharing in Two Children with Spinal Cord Injury and Traumatic Brain Injury

This paper explores the possibility that bed sharing may carry particular risks for children with special healthcare needs (CSHCN). Two cases of CSHCN who may have sustained adverse health effects from bed sharing are described. These two case reports indicate that CSHCN may be particularly susceptible to risks associated with bed sharing. Healthcare providers for CSHCN may need to inquire about patients' sleeping arrangements and, when bed sharing is acknowledged, provide counseling regarding the potential risks and benefits. They may need to monitor more closely for adverse events when bed sharing is a factor and should consider reporting health problems that may have occurred in concurrence with bed sharing.

Inhibitory effects of hyperthermia on mechanisms involved in autoresuscitation from hypoxic apnea in mice: a model for thermal stress causing SIDS

The physiological mechanisms that might be involved in an association between heat stress and sudden infant death syndrome (SIDS) are obscure. We tested the hypothesis that a combination of acute hypoxia and elevated body temperature (T(B)) might prevent autoresuscitation from hypoxic apnea (AR). We exposed 21-day-old mice (total = 216) to hyperthermia (40.5-43.5 degrees C), hypoxia, or a combination of the two. Neither hyperthermia alone (40.5-42.5 degrees C) nor hypoxia alone was found to be lethal, but the combination produced failure to AR during the first hypoxic exposure with increasing frequency as T(B) increased. The ability to withstand multiple hypoxic exposures was also reduced as T(B) increased. In contrast, heat stress causing moderate T(B) increase (40.5 degrees C) had no effect on survival. Increased T(B) (43.5 degrees C) reduced gasping duration and number of gasps. It increased heart rate during anoxia but did not alter gasping rate. Furthermore, the oxygen-independent increase in heart rate observed before gasping failure was usually delayed until after the last gasp in hyperthermic animals. Mild dehydration occurred during T(B) elevation, but this did not appear to be a primary factor in AR failure. We conclude that a thermal stress, which by itself is nonlethal, frequently prevents AR from hypoxic apnea. This may be due, at least in part, to decreased gasp number and duration as well as to hyperthermia-related asynchrony of reflexes regulating heart and gasping frequencies during attempted AR.

Sudden infant death—focus subject of medico-legal research

The compilation of research activities concerning SID in the field of legal medicine could only choose those out of a great abundance of high-quality examinations which represent applied research. By this they have contributed either to the clarifying of the aetiology which has not been cleared up or to the prophylaxis. For this looking through in a widest sense the basic approach was to consider SID being the result of an intrinsic and/or extrinsic disturbance of the modulation of respiratory regulation of the infant. This namely means a metabolic disturbance of respiratory neurons. One must not share this opinion even if it is given a certain plausibility by newer physiological examinations. But this also means that some examinations did not receive the acknowledgement which they would have received if there had been an immunological approach. The compilation was completely done without a presentation of the primary crisis intervention and the long-term care as being a fundamental medico-legal approach. Altogether may be summarized that legal medicine has completely fulfilled its duty to take care of the problem SID and that the examinations did not remain without success.

Heat stress and sudden infant death syndrome incidence: a United States population epidemiologic study

OBJECTIVES

To determine the role of heat stress in sudden infant death syndrome (SIDS) by examining the SIDS rates during periods of extreme environmental temperatures in a period when most infants were placed prone for sleep.

DESIGN

A retrospective study of SIDS rates and mortality rates attributable to excessive environmental heat in relationship to climatologic temperature was performed. Data were collected for each of 454 counties in 4 states (Arkansas, Georgia, Kansas, and Missouri) from May 1 to September 30, 1980, and were then summed to yield the mortality rates for each 5 degrees F (2.8 degrees C) temperature range.

RESULTS

chi2 analyses revealed significant relationships for heat-related mortality rates and both the maximal daily temperature and mean daily temperature but demonstrated no such relationships for SIDS rates. No association between SIDS rates and heat-related mortality rates was found with Spearman's ranked correlation, for either the maximal daily temperature or the mean daily temperature.

CONCLUSIONS

On the basis of our findings of no significant association between SIDS and either measure of temperature during periods of high heat stress-related death rates, it seems unlikely that the heat stress associated with the combination of prone sleep positions and elevated environmental temperatures has a significant role in the development of SIDS.

Peripheral chemoreceptor activity in sleeping neonates exposed to warm environments

In neonates, it is often assumed that ventilatory control and heat stress interact. Thus the two factors have been implicated in various pathologies (apnoea, sudden infant death syndrome). However, little is known about the mechanisms of this interaction, and the influence of sleep is still debated. This study aimed at determining the influence of warm exposure on the decrease in ventilation during a hyperoxic test (HT), which is considered to be a measure of peripheral chemoreceptor activity. The test was performed in active (AS) and quiet sleep (QS) in 12 neonates exposed to thermoneutral or warm environments. The HT consisted of 30 s of inspired, 100% O(2). The ventilatory response was assessed in terms of a response time, defined as the time elapsing between HT onset and the first significant change in V(E). Our results show that, in both thermal conditions, the fall in V(E) was higher in AS than in QS. Warm exposure significantly enhanced the ventilatory response in AS (-27.5 +/- 8.7% vs. -38.3 +/- 8.8%, P < 0.01) but not in QS. A thermometabolic drive or inputs from thermoreceptors could be involved in the reinforcement of peripheral chemoreceptor activity in AS in warmer environments, which could contribute to an increasing risk of apnoea in neonates with altered chemoreceptor function. Since hypothalamic structures are involved in thermoregulatory, sleep processes and (probably) in respiratory control, it could well be the principal site where this interaction occurs.

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.

SIDS: more facts and controversies

A more robust theory of the causation of sudden infant death syndrome (SIDS) is needed. The asphyxial theory of SIDS, which encompasses the prone sleeping position, relies on contradictory pathological evidence and fails to explain infants with SIDS who are found in the supine or lateral position. Many of the risk factors for SIDS point to an infective cause. The relative risks of these infection-related factors differ from study to study, as does the relative risk of prone sleeping position. I present the case for an infection model for SIDS causation, which has largely been neglected by mainstream SIDS researchers.

Simultaneous sudden infant death syndrome: a proposed definition and worldwide review of cases

Epidemiologic studies of sudden infant death syndrome (SIDS), the leading cause of death of infants during the postperinatal period (7-365 days), have mainly focused on the deaths of single infants. Simultaneous sudden infant death syndrome (SSIDS), the death of a pair of twins occurring at the same time, has received limited attention within the medical community. To the authors' knowledge, this article is the first to describe the 41 SSIDS cases cited in the world literature from 1900 to 1998 by the location of death, a summary of the circumstances surrounding the deaths, and evaluation of these cases in terms of a proposed definition of SSIDS. This evaluation critiques whether the 41 pairs of SSIDS cases adhere to a newly proposed definition of SSIDS. Twin infant deaths must meet all three criteria to be considered SSIDS. The study found that only 12 pairs of twins met all three criteria (29.2%), nine pairs met two criteria (21.9%), alternative cause of death was offered in five pairs of twins (12.1%) and in the remaining 15 pairs (36.6%), only limited information was available; therefore, no conclusions could be reached.

The effect of bacterial enterotoxins implicated in sids on the rabbit intestine

The aim of this project was to characterise the type of damage caused to the intestine of the infant rabbit by bacterial enterotoxins implicated in sudden infant death syndrome (SIDS). Samples of the duodenum, jejunum, ileum, caecum and large intestine exposed to the toxins for up to 6 hours were examined by scanning (SEM) and transmission electron microscopy (TEM). The damage was quantitatively assessed (% villi damaged) by SEM and qualitatively by SEM and TEM. Clostridium perfringens enterotoxin, staphylococcal enterotoxin B and Clostridium difficile toxin A + toxin B combined all caused severe damage to the villi in the small intestine (80-90% damage). Clostridium difficile toxin B caused only slight damage (17% to the jejunum, 26% to the caecum). Clostridium perfringens alpha-toxin caused moderate damage to the small intestine (duodenum 34%, caecum 35%), and Escherichia coli STa caused significant damage to the small (53-70%) and large intestine (51%). The level of toxin damage increased with time, the small intestine being more susceptible generally to damage than the large intestine. Each toxin differed in its ability to damage the villi, microvilli, enterocytes and lamina propria.

Sedation with promethazine profoundly affects spontaneous airway protection in sleeping neonatal piglets

1. Phenothiazine use in infants has been implicated in apparent life-threatening events, sleep apnoea and Sudden Infant Death Syndrome. 2. The aim of this study was to investigate the cumulative effects of a commonly used antihistamine medication containing promethazine on airway protective mechanisms and cardiorespiratory responses in 42 healthy neonatal piglets (21 naturally sleeping, 21 sedated sleeping). 3. Sedated piglets were given 1.5 mg/kg, p.o., promethazine 2 h prior to each recording session. Control animals slept naturally with no sedative given. On three consecutive days in all piglets, physiological recordings were made during sleep; on at least one of these days, simultaneous physiological and radiological observations were made. 4. Following sedation, sleep time and time in active sleep were increased significantly (P < 0.01). The spontaneous occurrence of swallowing, arousal, body movement, gastrooesophageal reflux and apnoea was compared between naturally and sedated sleeping piglets. Sedation with promethazine significantly decreased the spontaneous occurrence of swallowing (P < 0.05) and arousal (P < 0.05) and increased the occurrence of both central (P < 0.05) and obstructive sleep apnoea (P < 0.0001). 5. By the third day, a cumulative effect of promethazine was seen; the rate of swallowing and body movement significantly decreased (P < 0.01). 6. In summary, a low dose of promethazine profoundly altered sleep characteristics, airway protective mechanisms and cardiorespiratory responses in normal healthy sleeping piglets. Continued use of promethazine over several days may attenuate airway protective mechanisms to a potentially life-threatening degree. Our findings support continued caution in the use of promethazine-containing medications for the sedation of infants.

Influence of core temperature on autoresuscitation during repeated exposure to hypoxia in normal rat pups

Failure to autoresuscitate by hypoxic gasping during prolonged sleep apnea has been suggested to play a role in sudden infant death. Furthermore, thermal stress brought about by a contribution of infection, overwrapping, or excessive environmental heating has been shown to be associated with an increased risk of sudden infant death, particularly in prone sleeping infants. The present experiments were carried out on newborn rat pups to investigate the influence of "forced" changes in core temperature on their time to last gasp during a single hypoxic exposure and on their ability to autoresuscitate during repeated exposure to hypoxia. On day 5 or 6 postpartum the pups were placed in a temperature-controlled chamber regulated to 33, 35, 37, 39, or 41 degrees C and exposed to a single period of hypoxia (97% N(2)-3% CO(2)) and their time to last gasp was determined, or they were exposed repeatedly to hypoxia and their ability to autoresuscitate from primary apnea was determined. Increases in core temperature brought about by changes in ambient temperature from 33 to 41 degrees C decreased the time to last gasp after a single hypoxic exposure and decreased the number of successful autoresuscitations after repeated hypoxic exposures. Thus our data support the hypothesis that forced changes in core temperature brought about by changes in ambient temperature influence protective responses in newborns that may prevent death during hypoxia, as may occur during single or repeated episodes of prolonged sleep apnea.

Sleeping position in infants over 6 months of age: implications for theories of sudden infant death syndrome

The aim of this study was to determine the prevalence of prone and supine sleeping in infants aged 0-12 months and relate this to changes in the number of cases of sudden infant death syndrome (SIDS) since 1985. Seventy-two babies, 38 male and 34 female, were followed for the first 18 months of life with regular home visits and sleeping position was recorded. In addition, data on the number of cases of SIDS in England and Wales between 1985 and 1995 were analysed. All babies slept supine for the first 5 months of life, but once they could turn over in their cots (mean age 7.34 months, range 5-11 months) the majority slept prone. By 11 months of age, 53 regularly slept prone (73%), 95% CI +/- 19.8%), while 11 slept supine, three adopted the side position and five varied from night to night. The number of cases of SIDS in infants aged 7-11 months has fallen significantly (P<0.0001) in a period in which the prevalence of prone sleeping, in that age group, has not changed. The most plausible explanation for this paradoxical result is that supine sleeping in the first 5 months of life reduces the absolute risk of SIDS in the second 6 months of life even though most babies are then sleeping prone. It is suggested that reduced exposure to nasopharyngeal bacterial superantigens in babies sleeping prone might explain this effect.

Dew-point hygrometry system for measurement of evaporative water loss in infants

Evaporation of water from the skin is an important mechanism in thermal homeostasis. Resistance hygrometry, in which the water vapor pressure gradient above the skin surface is calculated, has been the measurement method of choice in the majority of pediatric investigations. However, resistance hygrometry is influenced by changes in ambient conditions such as relative humidity, surface temperature, and convection currents. We have developed a ventilated capsule method that minimized these potential sources of measurement error and that allowed second-by-second, long-term, continuous measurements of evaporative water loss in sleeping infants. Air with a controlled reference humidity (dew-point temperature = 0 degree C) is delivered to a small, lightweight skin capsule and mixed with the vapor on the surface of the skin. The dew point of the resulting mixture is measured by using a chilled mirror dew-point hygrometer. The system indicates leaks, is mobile, and is accurate within 2%, as determined by gravimetric calibration. Examples from a recording of a 13-wk-old full-term infant obtained by using the system give evaporative water loss rates of approximately 0.02 mgH2O.cm-2.min-1 for normothermic baseline conditions and values up to 0.4 mgH2O.cm-2. min-1 when the subject was being warmed. The system is effective for clinical investigations that require dynamic measurements of water loss.

Overheating alone can trigger malignant hyperthermia in piglets

Seven out of eight piglets which were susceptible to malignant hyperthermia (MHS) died when subjected to a heat challenge which was well tolerated by controls. The piglets which succumbed developed the classical clinical and biochemical changes of malignant hyperthermia before they died. These results show that overheating alone can trigger malignant hyperthermia in susceptible animals. Because the biochemical basis of malignant hyperthermia is similar in both humans and pigs, these observations suggest that overheating can also trigger malignant hyperthermia in humans. The susceptibility to overheating in malignant hyperthermia susceptible humans and animals probably explains why the myopathy which predisposes to this condition has also been reported to predispose to heat-stroke and the sudden infant death syndrome. In view of this, particular care to prevent overheating should be taken in infants of parents who are susceptible to malignant hyperthermia.

Pathophysiology of overheating in a piglet model: findings compared with sudden infant death syndrome

OBJECTIVE

To examine the nature of hyperthermia-induced pathophysiological changes in an animal model including effects on lung compliance.

METHODOLOGY

Piglets were randomly assigned to heated or non-heated groups. Heated animals were warmed to 4 degrees C above normal body temperature while sedated and breathing spontaneously. Cardiorespiratory variables were recorded serially and haematological assessments and blood cultures taken at 0 and 6 h. After 6 h the animals were killed and a limited postmortem was performed. Control animals had all procedures without heating.

RESULTS

Heated piglets developed tachycardia, hypotension and a metabolic acidosis in addition to tachypnoea, hypocapnic alkalosis and a neutrophil leucocytosis. Rectal temperature after death fell at the same rate in both groups. Lung histology revealed an excess of lung haemorrhage and alveolar oedema in the heated group. No significant group differences in dynamic lung compliance were demonstrated.

CONCLUSIONS

The pathological changes that occur during hyperthermia are non-specific but not incompatible with those found in sudden infant death syndrome. There was no confirmation of the thesis that hyperthermia causes death by altering lung compliance.

Clothing and bedding and its relevance to sudden infant death syndrome: further results from the New Zealand Cot Death Study

As part of a large nationwide case-control study covering a region with 78% of all births in New Zealand during 1987-90, the clothing and bedding of infants dying of sudden infant death syndrome (SIDS) and that of an appropriate control group were recorded. Cases consisted of 81% (n = 393) of all cases of SIDS in the study area and 88.4% (n = 1592) of 1800 control infants randomly selected from the hospital births and who completed a home interview. Use of a wool 'waterproof' underblanket was associated with a significantly reduced risk of SIDS (adjusted OR 0.44; 95% CI: 0.26-0.73) while sheepskin use was not. Firm tucking was identified as contributing to a reduced risk of SIDS even after adjusting for potentially confounding variables (adjusted OR 0.63, 95% CI: 0.46-0.86). Sixty case infants (15.6% of cases) were found dead with the head covered but there were no equivalent data for controls. Having been found previously completely covered by bedding was equally common in cases and controls (28.8% cases and 30.6% of control infants). Other differences of bedding and clothing between cases and controls were small; mattress characteristics were not studied. The exact methods in which babies are cared for are important and this study suggests that infants are at lower risk of SIDS when firmly tucked in and when sleeping on a 'waterproof' wool underblanket.

Hypothalamic dysthermia in persons with brain damage

Brain injury causing dysthermia has appeared to be not uncommon in institutionalized people with mental retardation. We sought to determine the characteristics and risks of patients of one institution. Of 1100 residents surveyed over 10 years 92 were reported to have unexplained high or low body temperatures, and 48 were monitored. Core temperatures were taken by non-invasive thermometers recording continuously for 24 h. Results were related to clinical conditions and aetiologies of mental retardation. Twenty-one per cent of the residents monitored showed hyperthermia, often related to prenatal metabolic or chromosomal abnormalities. Forty-two per cent had hypothermia, related to other causes of brain injury. Seventy-five per cent had abnormal patterns, including flat or exaggerated rhythms, reversed day-night cycle, unusual fluctuations, or sleep phase delay. Sixty-two per cent of 21 deaths to date have occurred in hypothermic patients. Occasional discrepancies between history of dysthermia and monitored results are best explained by fluctuations of temperature control over several days, probably due to changes in timing of hypothalamic rhythmicity. This could be better delineated by longer periods of monitoring.

Ethnic differences in infant-rearing practices and their possible relationship to the incidence of sudden infant death syndrome (SIDS)

The aetiology of sudden infant death syndrome (SIDS) is still uncertain, although associations with overheating and the prone sleeping position have been reported. In the UK, the incidence of SIDS is considerably lower in infants of Asian origin, but as yet no explanation for this has been suggested. We have studied a group of 202 white and 172 Asian multiparous mothers attending an antenatal clinic to compare the sleeping position and home environment of infants in each ethnic group. We found that significantly more white infants (31%) than Asians (11%) were placed in the prone position at night and that 94% of Asian infants slept in their parents' bedroom, compared with 61% of whites. These observations demonstrate marked differences in the infant rearing practices favoured by Asians and whites and lend support to the concept that the prone position and separate bedrooms may be contributors to the development of sudden infant death.

Thermal environment and sudden infant death syndrome: case-control study

OBJECTIVE

To compare the thermal environment of infants who died of the sudden infant death syndrome with that of age matched control infants.

DESIGN

Case-control study. Infants who died were matched with two controls, one for age and one for age and birth weight. Thermal measurements were conducted at the death scene for cases and at the scene of last sleep for control infants, who were visited unexpectedly within four weeks of the index infant's death on a day of similar climatic conditions. A follow up questionnaire was administered to parents of cases and controls.

SETTING

The geographical area served by the professional Tasmanian state ambulance service, which includes 94% of the Tasmanian population.

SUBJECTS

41 infants died of the sudden infant death syndrome at home; thermal observations at death scene were available for 28 (68%), parental questionnaire data were available for 40 (96%). 38 controls matched for age and 41 matched for age and birth weight.

RESULTS

Cases had more excess thermal insulation for their given room temperature (2.3 togs) than matched controls (0.6 togs) (p = 0.009). For every excess thermal insulation unit (tog) the relative risk of the sudden infant death syndrome was 1.26 (95% confidence interval 1.05 to 1.52). The average thermal bedding value calculated from parental recall was similar to that observed by attendant ambulance officers (mean difference = 0.4 tog, p = 0.39). Cases were more likely to have been found prone (odds ratio 4.58; 1.48 to 14.11). Prone sleeping position was not a confounder or effect modifier of the relation between excess thermal insulation and the syndrome.

CONCLUSIONS

Overheating and the prone sleeping position are independently associated with an increased risk of the sudden infant death syndrome. Further work on infant thermal balance and sudden infant death is required and guidelines for appropriate infant thermal care need to be developed.

A review of epidemiological studies of sudden infant death syndrome in southern New Zealand

The rate of sudden infant death syndrome (SIDS) in Southern New Zealand has been very high with an apparent real increase in incidence from the early 1970s. Recent research is reviewed and the results of specific interventions aimed at preventing SIDS summarized. The intervention consisted of strongly advising new parents that their babies sleep on their back or side and that they avoid over-heating, especially during infections. For the Otago area, child-care practice has been documented and prone sleeping of 1 month old babies has declined from 41.8% in 1986 to 2.4% in 1989-90. There is also evidence that parental control of infants' thermal environment has improved, maternal smoking during pregnancy has slightly decreased and the number of babies breast fed at 1 month of age has increased by 11%. In Southern NZ there has been a decline in post-neonatal SIDS mortality from 6.3 deaths per 1000 live births 1979-84 to 1.3 per 1000 live births in 1990. There are grounds for supposing that the intervention has been causative of this change, a possibility being addressed by on-going studies.

Home environmental temperatures in an Irish infant population

In this study the ambient temperature in which thirty-three Irish infants, within six weeks of birth, were nursed was documented. The study was conducted from October to March and a total of 1,250 individual room temperatures were recorded with a mean of 19.3 degrees C and a range of 8 degrees C, to 28 degrees C. The highest ambient temperature occurred from 1800 to 2100 hours and the lowest from midnight to 0300 hours. There was no central heating in 60% of the homes in this study. Comparing the various methods of home heating we found that houses with a coal fire and back boiler had the greatest range of temperatures recorded (from 10 degrees C to 23.5 degrees C) and also the lowest mean temperature recorded (17.14 degrees C). There was little relationship found between the ambient temperature and the amount of clothing and bedding used and some infants were heavily clothed despite a high ambient temperature. The purpose of this paper is to provide background data on which to base future studies examining the effects of varying ambient temperatures and amounts of clothing on an infant's physiological homeostasis.

How mothers keep their babies warm

Details of room temperature, clothing, and bedding used by night and by day and in winter and in summer were recorded for 649 babies aged 8 to 26 weeks. Room temperature at night was significantly related to outside temperature and duration of heating. Total insulation was significantly related to outside temperature and to minimum room temperature, but there was wide variation in insulation at the same room temperature. High levels of insulation for a given room temperature were found particularly at night and in winter, and were associated with the use of thick or doubled duvets and with swaddling. At least half the babies threw off some or all of their bedding at night, and at least a quarter sweated. Younger mothers and mothers in the lower social groups put more bedclothes over their babies, and the latter also kept their rooms warmer. Many mothers kept their babies warmer during infections.

Sudden infant deaths and cold weather: was the rise in infant mortality in 1986 in England and Wales due to the weather?

Using the daily number of deaths due to sudden infant death syndrome in England and Wales from 1979 to 1985, and the daily temperature recorded at the London Weather Centre, two models were constructed, one including a temperature term and one without it, and the models used to predict the mortality in 1986. It was found that the model using temperature had a slightly better predictive power and successfully accounted for the increased mortality in February 1986. Thus, we conclude that the excess mortality of February 1986 was associated with the unusually cold weather during that month.

Interaction between bedding and sleeping position in the sudden infant death syndrome: a population based case-control study

OBJECTIVE

To determine the relation between sleeping position and quantity of bedding and the risk of sudden unexpected infant death.

DESIGN

A study of all infants dying suddenly and unexpectedly and of two controls matched for age and date with each index case. The parents of control infants were interviewed within 72 hours of the index infant's death. Information was collected on bedding, sleeping position, heating, and recent signs of illness for index and control infants.

SETTING

A defined geographical area comprising most of the county of Avon and part of Somerset.

SUBJECTS

72 Infants who had died suddenly and unexpectedly (of whom 67 had died from the sudden infant death syndrome) and 144 control infants.

RESULTS

Compared with the control infants the infants who had died from the sudden infant death syndrome were more likely to have been sleeping prone (relative risk 8.8; 95% confidence interval 7.0 to 11.0; p less than 0.001), to have been more heavily wrapped (relative risk 1.14 per tog above 8 tog; 1.03 to 1.28; p less than 0.05), and to have had the heating on all night (relative risk 2.7; 1.4 to 5.2; p less than 0.01). These differences were less pronounced in the younger infants (less than 70 days) than the older ones. The risk of sudden unexpected death among infants older than 70 days, nursed prone, and with clothing and bedding of total thermal resistance greater than 10 tog was increased by factors of 15.1 (2.6 to 89.6) and 25.2 (3.7 to 169.0) respectively compared with the risk in infants of the same age nursed supine or on their side and under less than 6 tog of bedding.

CONCLUSIONS

Overheating and the prone position are independently associated with an increased risk of sudden unexpected infant death, particularly in infants aged more than 70 days. Educating parents about appropriate thermal care and sleeping position of infants may help to reduce the incidence of the sudden infant death syndrome.

C-reactive protein and prealbumin in suspected sudden infant death syndrome

This study investigated the levels of C-reactive protein (CRP) and prealbumin in 87 infants suspected of dying from sudden infant death syndrome (SIDS). These proteins change rapidly, within 24 hr, in patients who have an acute phase response, especially a response resulting from bacterial infection. In addition, prealbumin is sensitive to a recent reduction of protein or calorie intake. Eighty patients were determined to have typical SIDS. Only four of these had a minimal increase in CRP (0.8-2 mg/dl), and in none could an explanation be found. Seven patients were uncovered who had a significant infection, four of whom had prominent CRP elevations. Prealbumin was not decreased in the SIDS population. We conclude that there is no evidence that the acute inflammatory response is activated in infants dying of SIDS. An elevation of CRP above 2 mg/dl should prompt additional studies to find the cause. There is also no evidence of a recent, significant decrease in nutrition in these patients.

Child care practices and the sudden infant death syndrome

Southern New Zealand has one of the highest reported rates of the sudden infant death syndrome (SIDS) in the world. Data were collected on 49 infants who died from SIDS in the Dunedin and Invercargill Health Districts of southern New Zealand. Forty-two of the families were interviewed at home following the loss of their infant. In the week prior to death, 17 infants (40%) had an upper respiratory tract infection, although in 11 of these infants their infection had apparently resolved at least 24 h prior to death. Thirty infants (71%) had their faces down into the bedding or their heads covered with bedding. Thirty-four infants (81%) were found dead in the prone position, whereas 49% of New Zealand infants aged 3 months would be expected to sleep prone. Sleep position and the terminal position of the head in relation to SIDS requires further study.

Malignant hyperthermia

Malignant hyperthermia is a hereditary trait characterized by hypercatabolic reactions induced by anesthetic drugs, or physical or emotional stress. Patients must be treated quickly and efficiently in order to prevent irreversible organ damage and death.

Sudden infant death syndrome and environmental temperature: an analysis using vital statistics

We examined the relation between the daily numbers of deaths ascribed to sudden infant death syndrome (SIDS) (n = 6226) and daily temperature in England and Wales over the five year period 1979-83. When the data were filtered to remove the dominant seasonal trend, and residual autocorrelation, we found a significant negative correlation of deaths with both the level and rate of change of temperature four to six days earlier, irrespective of age at death. Place of usual residence was obtained for 909 SIDS cases occurring during the unusually severe winter of 1981-82, and, using space-time clustering techniques, we confirmed previous findings of the lack of 'epidemicity' for this condition. These results are compatible with several previous hypotheses of the relation between the weather and SIDS and directly incriminate drops in temperature in the occurrence of the condition.

Death-scene investigation in sudden infant death

We conducted death-scene investigations in 26 consecutive cases in which a presumptive diagnosis of sudden infant death syndrome (SIDS) was made and the infants were brought to the emergency room of the Kings County Hospital Center between October 1983 and January 1985. In six cases, we observed strong circumstantial evidence of accidental death. In 18 other cases, we discovered various possible causes of death other than SIDS, including accidental asphyxiation by an object in the crib or bassinet, smothering by overlying while sharing a bed, hyperthermia, and shaken baby syndrome. This study suggests that many sudden deaths of infants have a definable cause that can be revealed by careful investigation of the death scene and that the extremely high rate of SIDS (4.2 per 1000 live births) reported in the population of low socioeconomic status served by Kings County Hospital Center should be questioned.

Dress and care of infants in health and illness

The mothers of 199 infants (mean age 36.7 days) were interviewed to determine how the infant was dressed and wrapped, and how the mother would deal with illness. These data were related to measures of the infant's toe and underarm temperatures and demographic information about the family. The data did not support the hypothesis that infants with particular types of clothing or bedding were at risk of overheating and shows that most mothers dress their infants appropriately. Mothers' ideas about management of illness were often inappropriate particularly in lower socioeducational groups.

Sudden infant death. Overheating and cot death

Four risk factors for overheating were sought in the histories of 34 cot-death victims in Oxford and Scarborough. 19 babies were unusually hot or sweating when found dead; 14 died in an unusually warm environment; 17 had evidence of a terminal infective illness; and 24 were excessively clothed or overwrapped. 3 babies had all four risk factors, 8 had three, 17 had two, and 4 had one risk factor. Only 2 had no risk factor; both had had very low birthweights. In 6 of 15 babies (40%) whose rectal temperature was recorded after death the temperature was above 37 degrees C, the highest being 42 degrees C. If parents could be educated to anticipate the dangerous situations preceding febrile apnoea, many cot deaths could probably be avoided.

Unexplained protracted infant deaths

Seven unexplained, protracted infant deaths with similar clinical, biochemical and laboratory characteristics are described, being similar to other groups reported previously. Although autopsy examination frequently revealed extensive tissue damage, a primary cause of death could not be elucidated. It is argued that this condition represents a protracted form of conventional cot death and should be considered in any severely shocked infant where the cause is not readily identifiable. Many of the clinical and pathological manifestations are similar to those described in endotoxic shock and a small intestinal mucosal abnormality on histology of unknown pathogenesis was common.