Trends in sudden infant death. Infant respiratory death rates mirror sudden infant deaths.
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Delimitation of the sudden unexplained infant death syndrome (SIDS) is difficult as the diagnosis is made by exclusion. The difficulties in the differential diagnosis are concentrated on interpretation of the significance of positive viral and bacterial findings, inflammatory changes in the respiratory organs, heart and central nervous system together with malformations. Classification of SIDS appears, therefore, to vary according to time and place. New techniques, e.g. DNA analysis, have explained the etiology in a few per cent of the cases but have not yet solved the riddle of SIDS. The article reviews hypotheses about apnoea, arrhythmia, overheating and inefficient surveillance of the infant. It is emphasized that assessment of risk factors for SIDS requires valid epidemiological investigations where the basis for the diagnosis is a uniform classification of SIDS infants as compared with other groups of sudden death in infancy. An investigation of this nature has been initiated in the Nordic countries. It is important to examine and treat infants with abnormal sleep apnoea but generalized employment of monitoring has not reduced the number of unexplained infantile deaths.
The 155 cases of SIDS investigated at the Institut für Rechtsmedizin of the Medizinische Hochschule in Lübeck (northern part of the Federal Republic of Germany) between 1971 and 1981 have been analysed retrospectively under epidemiological aspects. The incidence was 2.17 cases of SIDS/1,000 live-born babies, 63.9% were male, 79.3% of the infants died during the first 6 months of life with a clear peak in the 2nd month. There was no seasonal accumulation; 68.4% of the infants died between 8.00 p.m. and 8.00 a.m., in 75% the socio-economic factors were inconspicuous, but we observed a significantly higher incidence of infants from mothers younger than 25 years. In 58% of our cases no signs of illness or changed behaviour had been observed during the 48 h before death. The results of our study are compared with the literature and discussed with special regard to a possible prevention.
Infants who have had bronchopulmonary dysplasia (BPD) are at an increased risk of sudden infant death syndrome. Because failure of the cardiorespiratory response to hypoxia is suggested to play a key role in sudden infant death syndrome, we tested the hypothesis that infants who have had BPD have a reduced respiratory chemoreflex response to hypoxia. We examined the reflex respiratory responses to breath-by-breath alternations in fractional inspired oxygen concentration in eight infants who had had BPD (mean gestation = 27 wk, mean postnatal age = 93 d) who were no longer on supplemental oxygen and compared the responses with those of 12 preterm infants who had not required supplemental oxygen or been mechanically ventilated since birth (mean gestation = 30 wk, mean postnatal age = 38 d). For test runs we alternated fractional inspired oxygen concentration through two gas delivery lines between 0.21 and 0.16 on a breath-by-breath basis, and for control runs we alternated the inspirate between the two gas lines with a fractional inspired oxygen concentration of 0.21 in each. Respiration was measured using inductance plethysmography infants with BPD showed no significant differences between test and control responses for any respiratory variable. In contrast, all respiratory variables in the preterm infants showed test responses significantly greater than control. We speculate that the "blunted" chemoreflex respiratory response seen in infants with BPD may predispose them to subsequent respiratory failure, but we do not known which component of the chemoreflex is impaired.
Strategies involving 14 sources were used to locate 230 parents of sudden infant death syndrome infants who died in Southern California between 1989 and 1992 and 255 parents of healthy, living infants matched by birth hospital, birth date, race and sex. The sample consisted of adults of reproductive age residing in Southern California. After an event of sudden infant death, many parents moved without a forwarding address; only their names, last known address, and the infant's race, birth date, and sex were available. There was no access to birth certificates, obstetric or pediatric medical records, parents' Social Security numbers, or parents' birth dates. The most successful tracking sources for case parents were the Department of Motor Vehicles, postal service, reverse directory and neighbors, private investigator, and California Medicaid services. For control parents, the post office, Department of Motor Vehicles, and Folks Finders proved the most helpful. Using a combination of the 14 sources achieved an adequate sample size.
Infants epidemiologically at high risk for SIDS demonstrate a variety of abnormalities in sleep-state organization, maturation, and sleep-state modulation of cardio-respiratory control mechanisms. These involve both the REM and quiet-sleep states and are seen in twins who have had no evidence of clinical cardio-respiratory compromise during infancy as well as in near-miss infants who have suffered serious cardio-respiratory failure. Although these infants have higher levels of REM sleep around 40 weeks, of special concern is the decrease in the maturation of the quiet system, which becomes evident after 44 weeks, and the reported quiet-sleep abnormalities in reflex control of respiration and arousal. The source of these abnormalities is environmental rather than genetic and most likely occurs prenatally. During the critical period for SIDS, infant sleep begins to coalesce from a series of naps to more prolonged night time sleep periods that last up to 8 hours. We believe that the ability to maintain physiologic homeostasis during prolonged sleep is a challenge facing infants who are epidemiologically at risk for sudden infant death. The challenge facing sleep research is the more complete understanding of the relationship between prolonged inhibition, homeostasis, arousal, and development.
Longitudinal day-to-day recordings of symptoms in the siblings of Sudden Infant Death Syndrome (SIDS) infant show a wide variety of symptoms varying with season and days of years. Implications are discussed.
The QT interval was measured in 12 normal and 7 aborted sudden infant death syndrome (SIDS) infants in rapid eye movement (REM) and quiet sleep at monthly intervals through the age of 4 months. An accuracy of better than 2 msec was assured by high resolution of the digitized signal and calibration of each QT measurement with an accurately generated time code. In contrast to current speculations, the QT index was significantly smaller in the infants with aborted SIDS than in the normal infants in both REM and quiet sleep (P less than 0.05). In addition, as in normal infants, the QTc was smaller in REM than in quiet sleep (P less than 0.01). Although these results offer no support for the hypothesis that SIDS results from prolongation of the QT interval, they suggest that aborted SIDS infants have a functional abnormality in the autonomic nervous system.
Ventilatory and heart rate responses to hypercapnia and hypoxia were measured in the following three groups: group I, controls (n equals 15); group II, parents of threatened sudden infant death syndrome (SIDS) infants (n equals 10); and group III, parents of SIDS infants (n equals 17). We found significantly reduced heart rate responses to carbon dioxide and hypoxia in group II (1.4 plus or minus 1.9 percent and 16.0 plus or minus 4.0 percent; mean plus or minus SEM) compared with controls (7.1 plus or minus 1.4 percent and 26 plus or minus 2.4 percent; P less than .025). Ventilatory responses to hypoxia in groups II and III were not significantly different from controls. Two group II mothers had a greatly reduce ventilatory response to carbon dioxide. Four other parents in group II had abnormally low heart rate responses to hypoxia or carbon dioxide. We concluded that parents of threatened SIDS infants had reduced heart rate responses to carbon dioxide and hypoxia and may have reduced ventilatory responses to carbon dioxide.
To gain insight into the role of the vagus nerve in sudden infant death syndrome (SIDS), 180 infants ranging in age from 1 to 66 weeks were examined with respect to cardiac response to ocular compression. There were 35 near-miss infants, 76 normal siblings of SIDS victims, and 69 normal control infants. Asystoles within the control group ranged from 0.3 to 1.8 seconds. Ten of 35 (28%) near-miss infants and 10/76 (13%) siblings had asystoles greater than 2.0 seconds when first tested. When statistically compared, the near-miss infants were significantly different from both the control infants and the siblings (Kruskal-Wallis procedure: P less than .01, and P less than .05, respectively). It is concluded that in the first year of life a significant number of near-miss infants have an exaggerated cardiac response to ocular compression. Furthermore, the presence of prolonged asystoles in certain siblings indicates that vagal hypersensitivity, as manifested by ocular compression, may be, in part, hereditary.
Twenty-nine near miss for sudden infant death syndrome and thirty normal infants between the ages of 3 weeks and 6 months were monitored polygraphically for 24 hours. The distribution of sleep and abnormal respiratory events were analyzed for both groups. On the basis of mixed and obstructive apnea, 12-hour nocturnal segments (8 PM to 8 AM) consistently distinguished near miss from normal infant groups between the ages of 3 weeks and 4.5 months. Daytime naps do not provide statistical differences sufficient to differentiate between the two groups. During sleep, abnormal respiratory events are more likely to occur between 1 AM and 6 AM, at least 40 minutes after sleep onset. Respiratory pauses show a significant increase just prior to waking (a strong respiratory stimulus). Any impairment of the arousal threshold during sleep will place near miss infants at increased risk.
In recent years the study of infant care practices within the sleeping environment has proved to be the single most important set of observations for reducing the risk of Sudden Infant Death Syndrome (SIDS). To further reduce the number of deaths and resolve the debate on safe infant care practice, a closer scrutiny of this environment is required. However, anecdotal observation from uncontrolled death-scene investigations and a reluctance to diagnose SIDS because of adverse social conditions or circumstantial evidence at the time of death is undermining future research. To investigate SIDS now means investigating the wider umbrella of all Sudden Unexpected Deaths in Infancy (SUDI) because of the potential for misdiagnosis. In trying to find out why SIDS infants die we have increasingly been forced to search for why infants survive in the first few months of life and it is this comparative component of epidemiological observation that has saved so many lives. A death-scene investigation is vital to any planned future investigation of SIDS but equally essential is a sleep-scene investigation of surviving infants to put any findings into context. SIDS infants are no longer scattered across the social strata and the cot is not the only environment in which they are found, social deprivation and use of the parental bed are now more discernable. Future studies should therefore reflect these changes with a second control group of surviving infants more closely matched to the type of environment in which SIDS infants might be found.
Three hundred six infants were referred for evaluation of "near-miss" sudden infant death syndrome (SIDS) from 1973 to 1980. Following the hospitalization and medical evaluation, there were 156 infants (115 term and 41 preterm) for whom there was no explanation for the presenting event and who were considered near-miss infants; 88% of these infants were seen during the first 3 months of life. A repeat near-miss event was reported in 63% (term) and 83% (preterm) infants. Twelve percent of term infants and 17% of the preterm infants had ten or more repeat events. A home apnea/cardiac monitor was prescribed for 88% of the infants for an average duration of 5.6 months in term infants and 3.5 months in preterm infants. Monitoring had been discontinued in 69% of the infants by 7 months of age. One full-term infant was later a SIDS victim. The risk of a repeat near-miss event is concluded to be sufficiently great to demand immediate hospitalization, medical evaluation, home monitoring when there is no specific treatment, and close clinical follow-up. Follow-up studies are needed to determine whether there is any long-term morbidity for infants who have had near miss events.