death Flashcards

Question

Putrefaction

Answer 1

- In this section we will discuss some of the changes that take place during the decomposition of tissue - Essentially the process of a complex organism becoming little more than a pile of liquid remains - Onset - Normally 2-3 days at average UK temperatures - Cold inhibits the process and heat accelerates it – As would be expected with any chemical process - Will not occur in all environments – Extreme dry, acid etc. - Can occur at different rates within the same body

Answer 2

* After 2-3 days – Note the discolouration of the lower abdomen * Friendly bacteria from intestines begin to break down haemoglobin into the blue/green substance sulphaemoglobin and other pigmented substances * Begin to break down the intestine itself * Digestive enzymes are able to leach into other parts of the body * If in the open flies begin activity

Answer 3

* After 1 weeks or so * Generalised spread of bacteria to all moist tissues * Causes discolouration that can interfere with hypostasis * Spread most efficiently through vasculature, observed as ‘marbling’ * Some early bloating * Blister formation in upper epidermis due to fluid accumulation during decomposition

Answer 4

* After 2-3 weeks or so * Gaseous by-products of bacterial activity cause swelling * Gases force liquids from body * Tissues also liquefy and are purged * Can be wrongly viewed as ante-mortem injury

Answer 5

* Time variable * Very dependent on environment and situation * Maggot or insect activity can destroy tissues as they secrete a proteolytic enzyme destroying ‘dead’ skin and tissue * If intact, skin may turn a reddish–green or even black colour * Skin slippage causes shedding of outer layers of fingers & toes * Eventually leads to skeletalisation (Dry)

Answer 6

* Adipocere * Not very useful forensically * Formed in cool, humid, anaerobic environments * Body fat can be saponified (turned to soap!) by anaerobic bacteria from around 1 month of death onwards * Can last for many years – Older material may be chalky * Mummification * May be the result of a natural process in which the body is prevented from the standard route of decomposition * Extremes of cold, salinity, acidity or extreme dryness may produce this effect * Flowing air can also accelerate the drying process

Answer 7

- Considered as the most useful single indicator of TOD during the first 24 hours post mortem - Why is this? - Only applicable in cool or temperate climates - Any thoughts as to why? - Methods based on core temperature (intra-abdominal temp) not oral or axillary temp - A variety of fun ways for this to be taken... - How to take the temperature - Requires long 10 –12” thermometer (chemical or digital) with wide range - Thermometer inserted 3 –4” and read in situ - Rectal temperature taken when appropriate - Liver temperature via abdominal stab alternative method - Other measurements - Ambient temperature including min & max if appropriate - Environmental observations e.g. Wet, dry, clothed, naked, in air or water (flowing or still) - Other pathological indicators such as blood loss, hypothermia etc. - Heat is produced by metabolism and distributed by blood – these both cease at death, but not uniformly! - Metabolism continues in organs and muscles - Heat is lost through the skin surface by: - Radiation: any process in which energy travels through a medium - Convection: the movement of molecules/heat within fluids (liquids & gases) - Evaporation: is a type of vaporisation of a liquid, that occurs only on the surface of a liquid - Heat loss is a physical process so follows physical rules

Answer 8

- The rate of body cooling is proportional to the difference between the temperature of the body surface and its surrounding” - However, Newton’s law only really refers to small inorganic (non-living) regularly shaped entities... - The human body however is a large, irregularly shaped lump of organic matter - Practical observations indicate that a sigmoid curve best describes cooling in real life situations – Why might this be?

Answer 9

- Be aware... Febrile illness can raise temp by up to 4–5 °C - Hypothermia can decrease temp by 10°C in some cases! - Initial plateau or lag phase varies in its length (0.5 – 3 h) before linear (Newtonian) cooling occurs - Many factors influence heat loss in linear phase - Surface area:volume largely dictates cooling - Conductive properties of tissues influential - Subcutaneous fat proportion - Oedema and dehydration effects - - In general, thin people cool quicker! - Heat loss from skin drives cooling - Radiation & convection - Postures exposing less skin cool slower than those in extended posture - Also affected by insulating properties of supporting surface - Affected by clothing also - Dry clothing reduces heat loss via convection conduction - Wet clothing accelerates cooling via evaporation

Answer 10

* A body will not cool if ambient temp = 37°C and will rise if >37°C * Problematic in tropical regions * Problematic in cases where the body is in the vicinity of radiators etc. * Very complex in the not unusual case of a person dying in a warm bath * The medium * If still, warm air may ‘block’ temperature differential for some time * Air movement brings fresh, cooler air in to contact with skin, promoting cooling and evaporation... even slight breeze has an effect * Bodies in closed, small spaces cool more slowly as transfer of heat is less effective * Damp air conducts heat more rapidly so will accelerate cooling * The medium in most cases is air, but can also be fluid in some cases * Water is a better conductor of heat than air * For a given environmental temp bodies cool twice as fast in still water and three times as fast in flowing water * Quite complex to account for! * So we’ve learned all these facts but how do we use them?

Answer 11

* Old rules of thumb for body cooling: * 37°C –1°C/h + 3 (to allow for plateau) * An example * Rectal temp = 32, TOD = (37 –32) + 3 = 8 hours ago * Any problems with this? * A better calculations comes from Henssge... * Method of TOD estimation using formula based on actual data, taking into account external factors e.g. Body weight, clothing, air, water * Best estimate ±2.8 h, worst ±7 h with 95% confidence

Answer 12

- Based upon the following: - T (rectum) – T (ambient) = 1.25 exp(Bt) – 0.25 exp(5Bt) - B = -1.2815 (Body Mass -0.625) + 0.0284 - t = time - A huge nightmare to actually solve - To make life easier, we can use a nomogram - Basically a very complex graph... - Assumes no fever or hyp(o/er)thermia, no external radiation etc. - Let’s have a go... o At 20:00, a naked body is discovered lying inside a building  Ambient temp = 12°C  Rectal temp = 30°C  Body weight = 80kg o What was the time of death?  According to the nomogram, the rectal temperature suggests death 10hrs ago...  That puts the TOD at around 10:00  ±2.8hrs  Death rounded to be between 07:10 and 12:50 o The nomogram also allows us to factor in a number of other variables

Answer 13

- The eye is an interesting organ - Unique biochemical structure - Isolated from main vasculature (No mixing) - Resistant to microbial contamination - Decomposes at a slower rate than many other organs - Samples can be obtained many hours after death (~120 hours) In vivo, ion gradient exist across the eye - Selective membrane permeability and active transport maintain difference - These cease after death - The levels of various ions and bio-molecules revert to unity over time - Potassium (K+) is most studied electrolyte for TOD estimation Collected with needle and small syringe - All vitreous humor collected from both eyes (average result used) - A gradient will exist across the vitreous too - Other structures must not be disturbed (e.g. retina & iris) - If vitreous humor cloudy or brown it cannot be used as it is contaminated by other eye structures or bacteria (respectively) - Using simple chemistry the concentration of K+ can be measured – How??? Data shows linear relationship for rise in vitreous [K+] against PMI, sampled to 120 hours PM - Sturners’s regression equation describing this relationship: - PMI = 7.14 [K+] -39.1 - Madea et al (1990) - PMI (±20 hours) = 5.26 [K+] – 30.9 - James et al (1997) - PMI = 4.32 [K+] – 18.35 - All based upon studies of PMI, yet all seem to over-read in real life situations... Just too many variables e.g. [Urea] concentration

death Flashcards

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