Maverick Story's - December 25, 2024

Estimation of the time of death for Autopsy Examinations

December 25, 2024

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Need for Autopsy in every death –

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Estimation of the time of death for Autopsy Examinations

Estimation of time, since death, is an essential, although is often found to be complicated, intrigue while compiling a forensic investigation pertinent to death. It is noteworthy that Post-Mortem Interval (PMI) is the time period between the death of an individual, and subsequent examination of its body by a forensic scientist while conducting the autopsy.

All bodies undergo various physical, metabolic, physiochemical, biochemical and autolytic changes in a sequential manner until it disintegrates to its skeletal form. Such patterned changes can help deduce appropriate PMI ranges. Cadaveric physical changes are sometimes influenced by a number of

extraneous factors like age, sex, nutrition, health condition of deceased, climatic conditions of the area, time of collection of body fluid etc, making such estimations unrealistic for forensic purposes. Body fluids like vitreous humor, pericardial fluid, cerebrospinal fluid, synovial fluid etc., remain stable for a longer period of time and doesn’t contaminate or disintegrate quickly after death.

Of all these fluids, vitreous humor is the most investigated body fluid for estimation of PMI as the same can be collected and isolated very easily while it remains well protected anatomically from contaminations and putrefactions. It can be found well preserved even in cases of severe head trauma.

Changes in the chemical analytes of vitreous humor –

Levels in the chemical components changes in human vitreous humor in a sequential manner which facilitates PMI estimations. Potassium, glucose, urea, creatinine, calcium, sodium, chloride, lactate, creatine, urea and hypoxanthine are some of the investigated vitreous analytes that vary in their concentration levels with varying extents of PMI. During life-time, the concentration of Potassium remains lower in vitreous humor, but is found to be in higher proportions in the peripheral eye tissue like choroid, vitreous layer and retina. An abrupt increment has been observed in the concentration of potassium in vitreous fluid after death, as sodium Potassium – ATPase pump disintegrates to allow potassium ions to leak through the membrane to attain equilibrium.

Various scientist has found a statistically significant correlation between potassium concentration and PMI in vitreous humor. Some have found a linear increase in potassium level with increase in death duration; correlation between vitreous potassium and death interval in the first 12 hours has been found which becomes significantly stronger afterwards; hypoxanthine (Hx) is another analytic constituent of vitreous fluid formed as a degradation product of adenosine monophosphate (AMP); Hx level increases with post mortem in a linear fashion under hypoxic conditions and thus, has been widely employed for time since forensics; death timings in the linear correlation between levels of potassium and hypoxanthine with PMI intervals is elementary temperature dependent.

Similarly, Glucose level has also been found to decrease with PMI, though it was not found to be a reliable indicator of PMI as its level may depend upon ante-mortem metabolic and physiological state of the deceased.

Effect of temperature, sex, age and eye difference on analytes used for PMI estimations –

Much of a sex differences have not been observed in levels of vitreous electrolytes or sodium / potassium ratio; on the contrary findings have been reported with respect to the effect of temperature, age of deceased and side difference of eyes on concentration of post mortem analytes. Some studies carried out by the eminent scientist Pounder has demonstrated no difference in the concentration of electrolytes between right and left eyes.

It was scientist Rognum, and Zilg, who have established that concentration of various analytes varies significantly with temperature. Zilg, reported that age of deceased has a decisive role in electrolyte levels in body fluids after death. Approximately 16% of variation observed in potassium concentration is due to age differences.

In a recent study carried out in India, it has been concluded that age, sex, cause of death, season of death and refrigeration of sample does not influence vitreous chemistry or its potassium levels. Thus, conflicting results of vitreous chemistry and its relation with post mortem interval among different studies may be due to certain discrepancies in vitreous humor aspiration techniques, selection of cases, age and health status of deceased, variations in methodology including sample storage, pre-treatment methods, analytical procedures and instruments used to perform the experiments.

Estimation Errors and Efficacies of PMI estimations from Vitreous Humor –

In a major survey study carried out across several autopsied bodies with known time of death, established the fact that:

Potassium content in the vitreous humor was significantly correlated with death interval (with

standard error of estimate of ±2.9 hours).

The mean overestimation of TSD varied from 18.6 ± 9.5 hours to 30.5 ± 21.4 hours.

The levels of Sodium (Na), Potassium (K) and Chloride Levels (Cl) in vitreous humor has been ascertained to be within the first 36 hours of the death, with a mean age of 36.4 ± 15.6 years.

Amongst all the chemical components of vitreous humor; Potassium is considered to be the most extensively studied analyte for PMI estimations for forensic purposes. PMI estimated from vitreous analytes depicts a time interval since death, and not any precise or accurate TSD as which has more medicolegal importance. However, when vitreous potassium is combined with other analytes like glucose and hypoxanthine, it can produce some more reliable results than using potassium alone. Concurrent use of different analytical techniques like NMR, CIA, GC-MS may help in some authentic PMI estimations within specific thresholds/ranges acceptable by the courts of law.

However, this is needed to be used with caution as – the estimation from vitreous humour and other body fluids, the best time since death can be just a corroborative evidence, as wide range of over-estimations can be used for forensic purposes where very narrow ranges of estimates are considered more reliable and authentic for deciding the cases demanding such expert opinions.