Post Mortem Changes Flashcards
Overview of post mortem changes
Somatic (clinical) death Cooling - algor mortis - chill of death - hours Hypostatic lividity - livor mortis - darkening of death - hours Rigor mortis - stiffening of death - hours Putrefaction - weeks/months Skeletonisation - months/years
Usefulness of post-mortem changes
Confirm death
- indisputable evidence
- resuscitation is futile
Allow estimate for time of death
Produce confusing artefacts
Destroy evidence of identity, injury and disease
Have specific forensic uses - position and movement
Cellular resilience to hypoxia
Brain, spinal cord - 4 mins Peripheral nerves - 5 mins Skeletal muscle - 3 hours Blood cells - 6 hours Skin - 24 hours Bone, corneas - 48 hours
PM arefacts
Collapse/falls at time of death - strike nearby objects and ground - eyebrows, nose, chin and cheeks or back of head Resuscitation - bruising to neck, face, chest - scratch abrasions to face - mask marks - needle puncture marks - gripping of arms to move or lift patient - defibrillator burns - perforation of stomach Animals - insects - fish/crabs - rats/mice - dogs Water Fire Recovery of body
Artefacts of immersion
Entry impact Washerwoman change Gooseflesh - cutis anserina Rocks and river bed - flowing water Rocks and sea bed - tidal water Undressing by water movement Fish and crabs Recovery of body
Artefacts of fire
PM burns and tissue loss Skin splits Heat fractures Extradural haematoma Falling masonry Recovery of body
Calculating post mortem interval
Alibi and opportunity Survival period + PMI No reliable method Sources of information - corporal evidence - on body - environmental and associated evidence - anamnestic evidence - habits and activities
Ways to predict post mortem interval
Rate method
- observe or measure changes which occur at known rate
- changes initiated or stopped by specific events
- lividity, rigor, cooling, putrefaction
Concurrence method
- events which occurred at known times
- watch stopped by blow, digestion of meal
Features of cooling
Useful indicator of PMI in first 24 hours
Only in temperate in cool climates
Considerable experience required
Often inaccurate
Core temp measured rectally of by subcostal stab
Serial temp measurements preferred
Avoid rectal measurement in sexual cases
Factors affecting rate of cooling
Body size Exposed surface area Environmental temperature Drafts and humidity Clothing and coverings Immersion
Temperature changes post mortem
<5 hours = plateau effect 6-12 hours = linear ish fall in temp > 18 hours - curve levels out - slight increase due to decomposition - does not reach environmental temp Heat lost by - convection - radiation - conduction - evaporation
Issues with temperature post mortem
Unknown length of plateau - 30 mins up to 5 hours
Body temperature at time of death
- reduced by hypothermia, CCF and haemorrhage
- increased by heatstroke, septicaemia, pontine haemorrhage, strangulation, struggle
Environmental temp during cooling period
Features of a Henssge Nomogram
Based on mathematical cooling method
Allows correction
- for body weight, clothing, drafts, water
- corrective factors applied to body weight
Assumes normal temperature at death
Assumes constant environmental temperature
When Henssge Nomogram cannot be used
Strong heat source nearly - radiator, gas stove Cooling source nearby - air conditioning outlet Underlying surface conducts heat - body on metal tray or cold ground Abnormal body temp. at death Body had been moved
Cooling in water
Body cools faster in water than air
- better heat conductor
- twice as fast in still water than still air
- three times as fast in flowing water than still air
Water around UK is cold
- Tay estuary in January is 6°C
Phases of muscle tone
Primary flaccidity - collapse at death Rigor mortis Secondary flaccidity - due to putrification
Types of muscle stiffening post mortem
Rigor mortis Cadaveric spasm Heat stiffening - protein coagulation - shortening > pugilistic attitude Freezing - rigor postponed
Physiology of rigor mortis
Ca ions flood into cells
Actin-myosin links formed - stimulates contraction in life
Cannot relax - ATP energy dependent process
Links break down due to autolysis as putrefaction sets in
Affects all muscles
- voluntary skeletal muscles
- heart muscle
- involuntary smooth muscles
- iris - pupils unequal or irregular
- pilo-erector muscles in hairy skin - gooseflesh
- seminal vesicles - fluid discharge from glans penis
Features of rigor mortis
No significant shortening
Possible indicator of body position
Fully formed rigor if broken by force will not return
Partially formed rigor if broken will continue to form
Rate of rigor development
Onset/duration depend on
- environmental temperature - quicker in warmer temps
- muscle activity pre-mortem
Fully established by
- 3 hrs in 14% of cases
- 12 hrs in 98%
Rapid onset associated with short duration
Sequence of onset/passing of rigor mortis
Rigor develops simultaneously in all muscles
- smaller muscle groups are completely involved earlier than large muscles
Apparent sequence
- eyelids
- jaws and neck
- small joints of hands and feet
- medium joints of elbows and knees
- large joints of shoulders and hips
Passes off by putrefaction in same sequence
Onset of rigor mortis
Unreliable indicator of PMI Variable time course of onset and duration - first appearance on average 3 hours - fully established by 8 hours - remains for 24-36 hours - passes off over next 24-36 hours If broken by force will not reform - if partially formed will continue after being broken
Factors affecting onset of rigor
Hastened - high environmental temp - muscle activity or starvation prior to death - depletes glycogen - septicaemia - children, elderly Delayed - cold environmental temp - slow, peaceful death
Intensity of rigor
Intensity depends on physique - strong in adult males - minor in elderly Intensity should not be confused with degree of development - fixation of joints
Features of cadaveric spasm
Rare, instantaneous form of rigor Stiffening occurs at moment of death and persists into period of rigor mortis Violent death with extreme emotion Affects muscles groups -> intense grip Records last act of life - weapon in battle/suicide - weeds in drowning - vegetation in mountain fall
Rule of thumb for PMI
Warm and flaccid = dead < 3 hours
Warm and stiff = dead 3-8 hours
Cold and stiff = dead 8-36 hours
Cold and flaccid = dead > 36 hours
What is lividity
Gravitational settling of liquid blood in capillaries
Seen as purple discolouration in dependent areas
Horizontal fluid level
Contact pallor where vessels are compressed
Punctate haemorrhage within intense lividity - burst blood vessels due to high pressure
Easily confused with bruising
Poor indicator of PMI
Good indicator of body position since death
Timing of lividity
Blood begins to settle at death
Red patches often withing 30 mins - up to 2 hours
Well formed by 4 hours
Max intensity at 8-12 hours
Fixed after 12 hours
Delayed or minimal with anaemia of haemorrhage
Fixation of lividity
Fixation = no longer blanches on fingertip pressure
Fixation is relative
Movement before 6 hours - before well formed
- primary pattern is unfixed and fades away
- new secondary pattern forms
Movement after 10 hours - well formed but not fully fixed
- primary pattern fixed enough to remain
- enough fluid blood to form new secondary pattern
- gives dual distribution - front and back
Movement after 24 hours - well formed and fixed
- primary pattern fixed and remains
- not enough fluid blood to created new secondary pattern
Colour of lividity
Bright pink - refrigeration - hypothermia Cherry pink - carbon monoxide Chocolate brown - methaemoglobin (chlorate) Scarlet - cyanide
Internal lividity
Heart - mimics MI Lungs - mimics pneumonia Intestines - mimics infarction
Types of putrefaction
Maceration - sterile autolysis in foetus Wet putrefaction - commensal flora Skeletonisation Mummification - dry conditions Adipocere - wet conditions
Features of putrefaction
Destruction of tissues by body’s own bacteria and enzymes
Bacteria spread from gut and resp tract to other tissues via blood stream
Rate depends on environmental temp
- optimal at 21-38°C
Putrefactive bacteria
Most present in GIT and URT - coliforms - clostridia - anaerobic bacilli - micrococci Exogenous bacteria introduced by wounds, insects, animals Spread via bloodstream
Factors affecting rate of putrefaction
Hastened by - slow initial cooling - clothing, bedding - environmental temp - humidity - obesity - terminal septicaemia - wounds Delayed by - rapid initial cooling - refrigeration - fire - heat fixation - blood loss - embalming - immersion - burial
Sequence of putrefaction
Green discolouration of abdomen RIF - 2 days
- bacteria from large intestine closest to skin
Passage of rigor
Marbling - few days
Skin blisters and slippage
Gas production and bloating - week
- methane, H2, H2S, NH3
- ptomaines - putrescine, cadaverine
Loss of hair and nails
Liquefaction - months
Skeletonisation - years, days if warm and insects
Internal putrefaction
Discolouration of stomach and intestines
Haemolytic staining of blood vessels and airways
Heart dilated and flabby
Liver and brain softened and honeycombed by gas
Spleen softened and mushy
Uterus and prostate slow to putrefy - helps identification
Usefulness of stomach contents
Useful if time of last meal known
Food remains in stomach for 3-4 hours
Rates of emptying and digestion variable
Food may persist undigested for several days following severe trauma
Forensic entomology
Flies attracted by smell - calliphora vicina - bluebottle - lucilia caesar - greenbottle Lay eggs in moist areas - eyes, nose, mouth, perineum, wounds Young larvae feed on tissues Older larvae leave to pupate and hatch May be several generations on body Succession of beetles feed on larvae and tissues
Features of adipocere
Moist environment
Hydrolysis of fat into waxy, pale, soapy substance with sweetish rancid odour
Clostridium welchii important in process
Released fatty acids inhibit other bacteria
Takes weeks or months to develop
Seen in cheeks, breasts, buttocks
Affords degree of preservation to body
Features of mummification
Desiccation of tissues in dry, warm conditions Takes weeks Skin becomes dry, leathery and shrunken Internal organs decomposed or preserved More common in infants that adults Affords good preservation
