Cot deaths in Edinburgh: infant feeding and socioeconomic factors

Vitreous humor endogenous compounds analysis for post-mortem forensic investigation

The chemical and biochemical analysis of bodily fluids after death is an important thanatochemical approach to assess the cause and time since death. Vitreous humor (VH) has been used as a biofluid for forensic purposes since the 1960s. Due to its established relevance in toxicology, a literature review highlighting the use of VH with an emphasis on endogenous compounds has not yet been undertaken. VH is a chemically complex aqueous solution of carbohydrates, proteins, electrolytes and other small molecules present in living organisms; this biofluid is useful tool for its isolated environment, preserved from bacterial contamination, decomposition, autolysis, and metabolic reactions. The post-mortem analysis of VH provides an important tool for the estimation of the post-mortem interval (PMI), which can be helpful in determining the cause of death. Consequently, the present review evaluates the recent chemical and biochemical advances with particular importance on the endogenous compounds present at the time of death and their modification over time, which are valuable for the PMI prediction and to identify the cause of death.

Review of Postmortem Interval Estimation Using Vitreous Humor: Past, Present, and Future

For decades, forensic scientists have sought a means of estimating the postmortem interval using laboratory analyses. The best known of these attempts uses a linear regression formula based on the increasing concentration of potassium ions in vitreous humor following death. Like all laboratory analyses, the determination of a potassium concentration is subject to pre-analytical, analytical, and post-analytical errors. Any error is magnified when entered into a regression formula that itself is subject to statistical variation, typically with a 95% confidence interval. Estimating the postmortem interval based solely on the concentration of potassium in vitreous humor proved too simplistic for accurate modeling of the myriad factors that influence postmortem changes. Research continues, using more complicated algorithms involving multivariate ion and chemical analyses and genomic sequencing of the postmortem biome. However refined estimates of the postmortem interval based on laboratory analysis become, sound medical practice will still require the integration of scene findings and information concerning the last time that a given decedent was known to be alive with the results of postmortem examination and laboratory analyses into a medical opinion concerning the postmortem interval.

A new model for the estimation of time of death from vitreous potassium levels corrected for age and temperature

Analysis of potassium concentration in the vitreous fluid of the eye is frequently used by forensic pathologists to estimate the postmortem interval (PMI), particularly when other methods commonly used in the early phase of an investigation can no longer be applied. The postmortem rise in vitreous potassium has been recognized for several decades and is readily explained by a diffusion of potassium from surrounding cells into the vitreous fluid. However, there is no consensus regarding the mathematical equation that best describes this increase. The existing models assume a linear increase, but different slopes and starting points have been proposed. In this study, vitreous potassium levels, and a number of factors that may influence these levels, were examined in 462 cases with known postmortem intervals that ranged from 2h to 17 days. We found that the postmortem rise in potassium followed a non-linear curve and that decedent age and ambient temperature influenced the variability by 16% and 5%, respectively. A long duration of agony and a high alcohol level at the time of death contributed less than 1% variability, and evaluation of additional possible factors revealed no detectable impact on the rise of vitreous potassium. Two equations were subsequently generated, one that represents the best fit of the potassium concentrations alone, and a second that represents potassium concentrations with correction for decedent age and/or ambient temperature. The former was associated with narrow confidence intervals in the early postmortem phase, but the intervals gradually increased with longer PMIs. For the latter equation, the confidence intervals were reduced at all PMIs. Therefore, the model that best describes the observed postmortem rise in vitreous potassium levels includes potassium concentration, decedent age, and ambient temperature. Furthermore, the precision of these equations, particularly for long PMIs, is expected to gradually improve by adjusting the constants as more reference data are added over time. A web application that facilitates this calculation process and allows for such future modifications has been developed.

Sudden unexpected death in infancy and socioeconomic status: a systematic review

This paper aimed to systematically review observational studies documenting the relation between sudden unexpected death in infancy and socioeconomic status. A search of two electronic databases (Medline 1966 to November 2002; Embase 1981 to November 2002) yielded 52 case-control or cohort studies meeting the inclusion criteria. An increased risk of sudden unexpected death in infancy was reported in 51 studies and 32 of 33 studies reporting graded measures of socioeconomic status showed a dose-response relation of sudden death with socioeconomic status. Of the 10 studies in which adjustment was made for maternal smoking, socioeconomic status retained an independent effect on infant death in nine. The effect of socioeconomic status was also independent of birth weight in 10 of 11 studies and independent of sleeping position in two. The included studies reported a significant association of socioeconomic status with sudden unexpected death in infancy with risk of infant death increasing with greater exposure to adverse social circumstances. The findings support a significant role for adverse social circumstances in the pathways to sudden unexpected death in infancy.

Human postmortem interval estimation from vitreous potassium: an analysis of original data from six different studies

The investigation of the postmortem interval (PMI) by determining potassium levels in the vitreous humor (KV) has been a subject of forensic pathology research for more than a quarter of a century. The numerous studies to date have yielded a variety of linear or piecewise-linear relationships between KV and PMI, i.e., different estimated intercepts and slopes of regression line(s) as well as different reliabilities of these estimates. This lack of agreement is due in part to the variable numbers of cases reported from study to study, differing observed ranges of KV and PMI, and the unaccommodated effects of factors on potassium concentration, including age of subject, amount of urea nitrogen, ambient temperature, and presence of illness. Original data from six of these studies, for a total of 790 cases, are reanalyzed together. The relationship between KV and PMI is not completely linear, and the residual variability of KV as a function of PMI is not constant. Thus, two main assumptions of the simple linear model, linearity and constant variance, are not supported by the data. It is clearly problematic to report statistical summaries such as the slope of an estimated regression line and the reliability of that estimate based on a model with faulty assumptions. Yet even after rescaling the data in an attempt to achieve linearity in the KV-PMI relationship and to stabilize residual variation, the relationship continues to be non-linear and its variability unstable. A new approach is developed for modeling KV and PMI that accommodates non-linearities and changing residual variability. A local regression model, specifically a loess smooth curve, is fitted separately to the data from each of the six studies. The loess smooth curve adapts locally to the changing and possibly non-linear relationship between KV and PMI across their observed ranges. The data from all six studies are then combined to yield a single loess curve with 95% confidence bands. The estimated loess curve and confidence bands are used in an inverse prediction method to construct low, middle and high PMI estimates at given values of KV. The reliability of estimated PMI decreases as KV increases. Although the confidence bands surrounding the overall curve widen in the extreme high end due to there being fewer available data in that region, PMI estimates are more precise over the entire range of KV and PMI than those obtained from any single study alone. A cross-validation procedure provides an independent check of the predictive performance of the method.

Sudden infant death syndrome: does winter affect poor and rich babies equally?

STUDY OBJECTIVE

The aim was to investigate whether the winter increase in risk of sudden infant death was similar across social classes.

DESIGN

This was an unmatched case-control study using routine data.

SETTING

Cases and controls were selected from files holding routine birth and death certificate data for England and Wales for 1986.

SUBJECTS

Cases were deaths in the first year of life occurring in the summer or the winter of 1986 with mention of sudden infant death or SIDS in the death certificate. Controls were a 1% random sample of all children born in the same year. Only children whose parents were married or living together at the time of birth registration were included.

MAIN RESULTS

Data on age and season of death for cases, and on date of birth, social class of father, and birth weight were abstracted from the file. Season of birth and birth weight were treated as confounding variables. The increase in risk of SIDS in winter was calculated for each age group and social class. The winter increase in SIDS was more marked among the higher social classes for all ages, but not to a statistically significant degree: the p values for heterogeneity were 0.26 for age 0-3 months, 0.42 for 4-7 months, and 0.41 for 8-12 months.

CONCLUSIONS

There is no direct association between seasonal variation in sudden infant death and social class.

Vitreous potassium as a measure of the postmortem interval: an historical review and critical evaluation

This is an historical review of the articles published in English on the use of vitreous potassium to determine the PMI. External factors which influence the validity of the test are sampling techniques, analytical instrumentation and environmental temperature during the PMI. Internal factors that are recognized at the present time which influence vitreous potassium are the age of the individual, the duration of the terminal episode and the presence or absence of nitrogen retention.

Epidemiology of babies dying at different ages from the sudden infant death syndrome

An analysis of data from the United Kingdom multicentre study of postneonatal mortality has been made to assess whether there are causally distinct groups of babies dying from the Sudden Infant Death Syndrome (SIDS), and to develop explicit risk factor profiles for the subgroups. The 303 SIDS babies in the multicentre study were divided into four subgroups by age at death: weeks 1-7, 8-15, 16-23, and 24 or more weeks. Contrasts between these subgroups with respect to 28 epidemiological characteristics and to pathology findings were investigated. Significant contrasts in the number of previous pregnancies, duration of the 2nd stage of labour, gestational length, family finances and repair of housing were found. Overall, very strong evidence of epidemiological differences was found (chi 2(9) = 29.3, p less than 0.001), and of contrasts in the nature and degree of any acquired terminal disease. It is concluded that there are different causes of SIDS with different distributions according to age at death.

Clinical biochemistry of the neonatal period: immaturity, hypoxia, and metabolic disease

This review attempts to provide practical information on common problems in the laboratory medicine of newborn infants and also considers unresolved problems in achieving neonatal diagnoses. A common cause of upset in the newborn--intrapartum asphyxia--can now be positively diagnosed. This leaves a small group whom it is necessary to investigate because they may have metabolic disease. The initial investigation of metabolic disease at the district general hospital should be limited to the commoner conditions.

Magnesium, potassium, sodium and calcium in post-mortem vitreous humour from humans

Levels of magnesium, potassium, sodium and calcium in post-mortem vitreous humour from human controls, fire fatalities and drowning victims have been determined. The effects of time-related internal changes, external environmental parameters and different causes of death are evaluated. Despite the positive correlation and marked increase of potassium and, to a lesser extent, of magnesium and calcium with the length of the post-mortem interval, individual biological variability severely limits the usefulness of predictions of post-mortem interval based on electrolyte metal data. At best, there is only a 2/3 chance of a prediction being within 12 h of the true value. Vitreous humour metal concentrations are affected by external influences, such as the elevated temperatures of fires which increase the rate of release of intracellular magnesium and potassium. In cases where drowning is suspected, establishment or exclusion of this cause of death is not possible on the basis of vitreous humour electrolyte metal data because of possible post-immersion diffusion across the permeable membrane of the eyeball. It appears, however, that magnesium in salt-water cases and sodium in fresh-water cases are related, albeit erratically, to the length of the immersion period.

Home monitoring for central apnoea

Between July 1978 and December 1981, 64 infants thought to be at increased risk from sudden infant death syndrome (SIDS) were monitored at home for central apnoea. Twenty four of the infants had had a 'near miss' episode at age, median (range), 6 (1 to 33) weeks, and of these infants 22 had had 335 alarms for apnoea by age 6 months. Stimulation by shaking was carried out on 38 occasions and bag and mask resuscitation on one. The remaining 40 infants were siblings of SIDS victims and of these, 35 were monitored from age 1 week (usually after discharge home). Thirty four of the SIDS siblings had had 573 alarms for apnoea by age 6 months: stimulation by shaking was carried out on 32 occasions and bag and mask resuscitation on one. The duration of home monitoring was, median (range), 34 (8 to 87) weeks for 'near miss' infants and 45 (12 to 70) weeks for SIDS siblings. All infants survived. As part of an over all support system monitors were accepted and greatly appreciated by most parents, especially those with previous experience of SIDS. Home monitoring was practicable but the commitment in time and expertise was great and objective benefits to the infant remain unproved.

Cerebrospinal fluid concentrations of hypoxanthine, xanthine, uridine and inosine: high concentrations of the ATP metabolite, hypoxanthine, after hypoxia

CSF obtained for clinical purposes from newborn, children and adults has been analysed by high pressure liquid chromatography for hypoxanthine, xanthine, inosine, uridine and urate. Large rises in hypoxanthine and to a lesser extent xanthine occur for about 24 h after hypoxia. High concentrations were associated with later evidence of brain damage or subsequent death. Changes in CSF could be independent of those in plasma. Small or negligible rises were associated with localised and generalised infections including bacterial meningitis, fits, or both. Marked and rapid rises were found after death. These estimations may "predict" the extent of brain damage or brain death.

High serum thiamine and the sudden infant death syndrome

Serum thiamine concentrations in 233 infants dying from the sudden infant death syndrome were compared with those found in 46 infants dying from other explicable causes. The levels in the sudden infant death group ranged from 22- greater than 500 micrograms/1 (mean 144.3 micrograms/1) and in the controls less than 1.0-95 micrograms/1 (mean 26.5 micrograms/1). The difference was highly significant (p less than 0.001). Only 13 (5.6%) of the sudden infant death group had a serum thiamine concentrations below 50 micrograms/1 whereas four (8.7%) of the control infants had a level above 50 micrograms/1. Thiamine was measured in nine samples of human breast milk and was present in concentrations ranging from 55-366 micrograms/1 (mean 178 micrograms/1); manufactured milk based formulae contained up to 2160 micrograms/1. Absorption of thiamine in man is rate limited but it appears that in infants dying from the sudden death syndrome the vitamin may be freely absorbed leading to very high serum levels.

An epidemiological and sociological study of unexpected death in infancy in nine areas of southern England. I: Epidemiology

An epidemiological survey of unexpected deaths in infancy covering nine areas of southern England is reported. The areas include specially deprived inner city areas of London, inner and outer suburbs of London, rapidly developing and new towns and their surrounding country districts and a coastal resort. The report is based on 308 cases and 236 controls.

Theepidemiological patterns found in respect of time of death, age, sex and season are similar to those reported by previous studies. The characteristic ‘cot death’ age distribution cannot be explained by the inclusion of older infants whose respiratory passages are obstructed by bedding or infection. Possible explanations for a substantial outbreak in one area are considered. Well recognized differences between cases and controls in respect of age of parents, parity, prematurity, twinning, hospital admission and clinic attendance were found to persist and to be essentially similar in all areas despite there being significant differences between the populations. Sociological differences between cases and controls were largest in the most socially deprived areas, illustrated by an illegitimacy rate of 27 per cent in inner north London.

Bottle feeding was only significantly associated with unexpected death when the standard of the home was excellent. Where the homes were poor more cases than controls were breast fed.