Similarities between lethal asphyxia in postneonatal rats and the terminal episode in SIDS

Review of autopsies of stillborn infants with retroplacental hematoma or hemorrhage

Intrathoracic petechiae are a potential marker of acute asphyxia in stillborn infants. Retroplacental hematoma (RPH) is a cause of acute asphyxia. The histological features of RPH can be timed using criteria for intrauterine duration of fetal death. Autopsies of stillborn infants of >26 weeks in gestation with RPH were evaluated for gross or microscopic evidence of petechiae. Placental gross and microscopic features were recorded. Eleven controls from other mechanisms of death were randomly selected. Intrathoracic petechiae were present in all 17 infants with RPH of >50% of the placental area, in 3 of 7 infants with <50% area RPH, and in 2 of 11 infants with other diagnoses. The placenta demonstrated basal plate neutrophils in all cases of RPH (N  =  21). Early coagulation necrosis in the villi overlying the RPH was present in 5 of 13 cases after 4 to 24 hours, and complete coagulation necrosis was present in 3 of 4 cases after 24 hours. Infants with RPH underlying >50% of the placenta demonstrate intrathoracic petechiae, but controls and infants with smaller RPH do so much less frequently. This is consistent with the hypothesis that intrathoracic petechiae are a marker for intrauterine asphyxia. Basal plate neutrophils are a useful early marker of retroplacental hemorrhage. Early coagulation necrosis of the placenta over RPH begins in 4 to 24 hours but is not complete after more than 24 hours.

Effect of home monitoring on a high-risk population

A large cohort of infants (8,998) at high risk for sudden and unexpected death was followed with home cardiorespiratory monitoring over a five-year period. These infants included premature infants (23-36 weeks post-conceptual age), SIDS siblings, and infants who experienced an Apparent Life-Threatening Event. The overall SIDS rate in this high-risk population was 0.55/1,000, a rate significantly less than the 0.85 deaths/1,000 reported in the "general population" of Georgia over this same time period. In addition, we report our experience with using home monitors as a diagnostic tool, as well as how monitors can actually be cost-effective. Editorial opinions, and lay press summaries of the CHIME study (JAMA, May 2, 2001) imply that home cardiorespirtory monitors are of little value. Despite the fact that the study never made this claim, many clinicians are now referring to this study as evidence that home monitoring is ineffective and not needed. This article disputes those misconceptions about home cardiorespiratory monitors based on our experience with a large high-risk population of infants.

Epidemiology of intrathoracic petechial hemorrhages in sudden infant death syndrome

The possible effects of a wide range of sociodemographic and environmental factors on the incidence and distribution of petechiae were investigated in 485 sudden infant death syndrome (SIDS) cases from the New Zealand Cot Death Study. The number (nil, few, many) of macroscopic petechial hemorrhages in the visceral pleura, capsule of thymus, and epicardium was recorded in 458 of 474 autopsied SIDS cases. Other information was obtained from parental interview and obstetric records. Univariate analysis showed highly significant relationships (P < or = 0.005) between the frequency of petechiae at one or more sites and socioeconomic status, parity, breast feeding, age at death, time of death, sleep position, and head covering at death and lesser but significant relationships (P < or = 0.05) with Maori ethnicity, birth weight, gestation, pacifier use, and bed sharing. After multivariate analysis, significant associations remained between increased frequencies of thymic petechiae and parity (P = 0.0001), age at death (P = 0.0003), Maori ethnicity (P = 0.0019), pacifier use (P = 0.0001), and head covering at death (P = 0.0032); between increased frequencies of epicardial petechiae and head covering at death (P = 0.008) and an estimated time of death between 00:00 and 05:59 h (P = 0.056); and between increased frequencies of pleural petechiae and maternal smoking (P = 0.058) and parity (P = 0.022). There was a decreased frequency of pleural petechiae in infants placed prone for their final sleep (P = 0.058). The distribution and frequency of petechiae are affected by environmental factors, including known risk factors for SIDS, but these factors occur inconsistently across the three sites. The findings imply differences in the pathogenesis at each site but do not provide consistent support for previous theories of causation of petechiae.

Hyperthermia in sudden infant death

To determine whether preterminal hyperthermia is significantly associated with sudden infant death (SID), 140 structured interviews with parents of SID victims were compared with questionnaires filled in by a control group of parents living in the same area. All SID autopsies were performed between 1986 and 1992 at the Institute of Legal Medicine of Hannover Medical School according to the same protocol. Signs of profuse sweating (i.e. moist head, damp clothing or bedding) were present at the scene of death in 35.7% of cases. SID victims with signs of profuse sweating were more frequently found under their bedding (p < 0.001), were older (178 vs. 130 days) and the time period between when they were last seen alive and when they were found dead was longer (6.5 vs. 4.5 hours p < 0.01) compared to cases without sweating. Sweat on the head [odds ratio (OR) = 1.9; 95% confidence interval (CI) = 1.0, 3.6], and sweaty clothing and bedding (OR = 17.9; 95% CI = 8.7; 37.1) showed a significant association with the risk for SID. The pathophysiological basis for hyperthermia is SID remains to be determined. Hyperthermia could result from infection, overinsulation from excessive clothing with high environmental temperatures, covering of the infant's head or immature central thermoregulatory centres. The influence on the fatal outcome and the role in the pathogenesis of these deaths requires further research.

Intrathoracic and subconjunctival petechiae in sudden infant death syndrome (SIDS)

The frequency and density of intrathoracic and subconjunctival petechiae was studied in 250 cases of SIDS and 69 controls. The control group included 37 infants with natural and 32 infants with traumatic causes of death. Intrathoracic petechiae were found significantly more frequently in the SIDS group (91.2% SIDS; 42% controls; p < 0.001) and were present at a higher density (p < 0.001). Subepicardial and thymic petechiae were detected at high density in older SIDS infants. Subconjunctival petechiae were low in density and found only in 2.4% of the SIDS group but they were detected in 8.1% of the natural death group and 21.9% (p < 0.05) of the lethal trauma group. Subconjunctival petechiae were found at highest density in strangulation. Intrathoracic petechiae are commonly found in SIDS but are not specific for SIDS. Subconjunctival petechiae are typical but not specific for strangulation. In SIDS, subconjunctival petechiae are rare and appear at low density.

Sudden infant death syndrome prevention and an understanding of selected clinical issues

The etiology and prevention of sudden infant death syndrome (SIDS) are among the more frustrating topics in pediatrics. This article addresses several clinically relevant issues, including the relationships between apnea and SIDS, the nature of the "terminal event," effectiveness of home monitoring, the role of gastroesophageal reflux in apparent life-threatening events, and the association between the prone sleeping position and SIDS. This article is intended to provide the clinician with an awareness of the issues and the scientific basis needed to understand their contribution to SIDS.

Sudden death in infants sleeping on polystyrene-filled cushions

BACKGROUND

Infants are at risk for both the sudden infant death syndrome (SIDS) and accidental suffocation. On postmortem examination, however, it is difficult to distinguish one from the other without information from the scene of death. Healthy infants are assumed to be able to turn their heads and, if not otherwise restrained, to obtain fresh air. We assessed this assumption in an investigation of infant deaths that occurred during sleep on cushions filled with polystyrene beads.

METHODS

We obtained data on 25 deaths from the U.S. Consumer Product Safety Commission. We also used mechanical and animal models to study physiologic aspects of ventilation relevant to these results, by simulating the effects on an infant of breathing into a cushion. We measured the effects of softness, malleability (molding of the cushion about an infant's head), airflow resistance, and rebreathing of expired gases.

RESULTS

All 25 study infants were prone when found dead, and at least 88 percent were face down with nose and mouth obstructed by the cushion. SIDS was the diagnosis in 19 of the 23 infants who underwent autopsy. Our findings show, however, that the cushion would have limited movement of the infant's head to obtain fresh air, and the amount of rebreathing we estimated to have occurred in the infants was lethal in a rabbit model.

CONCLUSIONS

Accidental suffocation by rebreathing was the most likely cause of death in most of the 25 infants studied. Consequently, there is a need to reassess the cause of death in the 28 to 52 percent of the victims of SIDS who are found with their faces straight down. Safety regulations setting standards for softness, malleability, and the potential for rebreathing are needed for infant bedding.

Cerebral palsy among children born during the Dublin randomised trial of intrapartum monitoring

In a randomised trial involving 13,079 liveborn children intrapartum care by electronic fetal heart rate monitoring, with scalp blood sampling when indicated, was associated with a 55% reduction in neonatal seizures. Reassessment, when aged 4, of the 9 children in the intensively monitored group and 21 in the control group who survived after neonatal seizures showed that 3 such children in each group had cerebral palsy. A fourth child in the intensively monitored group with cerebral palsy had had transient abnormal neurological signs during the neonatal period. 8 other children in the intensively monitored group and 7 in the control group who had not had abnormal neurological signs in the neonatal period also had cerebral palsy. 16 (78%) of the total of 22 cases of cerebral palsy had not shown clinical signs suggestive of intrapartum asphyxia. Thus, compared with intermittent intrapartum monitoring, intensive monitoring has little, if any, protective effect against cerebral palsy.

Intrathoracic petechial hemorrhages: a clue to the mechanism of death in sudden infant death syndrome?

(1) Intrathoracic petechiae are characteristic of most SIDS cases, and tend to be more numerous in these cases than in deaths from other causes, including mechanical asphyxia. (2) Their localization suggests that intrathoracic negative pressure plays a role in their genesis. (3) Several human and animal studies suggest that petechiae arising from the pulmonary circulation may differ from those originating from systemic vessels in the thorax. (4) Experimental studies suggest that vigorous respiratory efforts are responsible for their formation. This would seem to exclude respiratory paralysis as a mechanism for most SIDS deaths. (5) These petechiae are not consistent with cardiac arrest or failure as the primary agonal event in SIDS. (6) The fact that petechiae are more prominent in SIDS than in other deaths adds to the evidence that SIDS is not a "wastebasket" diagnosis, despite the imperfection of existing diagnostic criteria. (7) These petechiae do not prove that the final mechanism of most SIDS deaths is upper airway obstruction. However, they do provide substantial support for that thesis.