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Post mortem interval


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PM Interval

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Post mortem interval

  2. 2. Post Mortem Interval • Post-mortem interval (PMI) or Time since death(TSD) is the time period between death and examination of the body. • Important because: CREDIBILITY OF SUSPECT: one can check the credibility of suspects statement. MOMENT OF CRIME: it informs when crime was committed.
  3. 3. VITAL LEADS TO THE PATIENTS: it gives police a vital leads and starting points for their enquiries. EXCLUDE SUSPECTS: if a suspect was not in the city during the time of death, he can excluded. CHECKS ALIBI: it can confirm or disprove an alibi.
  4. 4. • Estimation of post-mortem interval or time since death is an important goal in medico legal investigation. • Determination of the time of death is important in both criminal and civil cases. - in criminal cases it is important to catch the killer. -in civil cases it may become important in deciding i)who inherit the property. ii)whether at the time of death insurance policy was in force . • It is also of crucial importance for forensic investigators, especially when they are gathering evidence that can support or deny the stated actions of suspects in a crime.
  5. 5. • After death, many changes begin to take place in the body due to physical ,metabolic, autolysis, physiochemical and biochemical process. • These changes progress in an orderly manner until the body disintegrates. • The measurement of these changes along with time is used for estimating time since death.
  6. 6. DETERMINATION OF PMI • What Time Did the Person Die? – Best estimate; offered with a reasonable degree of medical and scientific certainty. – Impossible to be 100% accurate. – UNLESS a witness (who doesn’t lie) is present at the time of death, it generally is an estimate of time (2-4 hour window is the usual).
  7. 7. Historical Background •Methods for estimating the post-mortem interval date back to the ancient Greeks and Egyptians during the third and forth centuries . They understood that dead bodies cooled and became stiff over a period of time after death. • Warm and not stiff: Dead not more than a couple of hours • Warm and stiff: Dead between a couple of hours and a half day • Cold and stiff: Dead between a half day and two days • Cold and not stiff: Dead more than two days
  8. 8. Indications of Death • Indications of death: – Unconsciousness – Loss of all reflexes – No reaction to painful stimuli – Muscular flaccidity – Cessation of heart beat and respiratory movement – Eye signs: • Loss of corneal and light reflexes • Mid-dilated position of the pupils • Irregular size and shape of the pupils • Eyelids usually closed incompletely • Tache noire: where the sclera remains exposed, two triangles of discoloration appear at each side of the cornea, either brown or black.
  9. 9. IMMIDIATE CHANGES • Bichat, concept of tripod of life, A)Insensibility and lose of movement-cessation of CNS function. B)Cessation of respiration C)Cessation of circulation Other changes-stature, immediately after death body lengthen by 2-3cm.
  10. 10. EARLY CHANGES A)Change in skin- becomes ashy-white,pale and loses elasticity within a few minutes of death. B)Changes in the eye- a)Dilate and fixed pupils. -Normal size during life-1-8mm. -pupil reacts to atropine and pilocarpine for about 2hrs after death(till molecular death)
  11. 11. b) Absence of corneal and light reflex- c)Opacity of the cornea- -Cornea becomes opaque about 6hrs after death(time period up to which cornea can be harvested for transplantation) -Tache noires(black spot)-if the eyelids remain open after death, desiccation of sclera occures giving rise to triangular shaped discoloured area, initialy yellow in colour but as dust settles in becomes dark red or black.
  12. 12. d)Flaccidity of the eyeball- -Eyes look sunken and are softer after death due fall of intraoccular prassure(IOP) -Normal IOP during life is between 10-20 mm Hg  1 hour after death-12 mmHg  2hrs after death-10mmHg  3 hrs after death-8.5mmHg  8hrs after death-5mmHg -Absence of intraocular fluid suggests more than 4 days. -IOP gives a rough of PMI
  13. 13. e)Retinal vessels-  Segmentation of the retinal blood columns (Kevorkian sign) accrues immediately after death.  Colour of retina-become pale after death, and become more and more pale as time of death increase.  Disk outline become hazy after few hrs.
  14. 14. • Following death many physiochemical changes occur to the body Algor Mortis: Body temperature after Death Livor Mortis: Discoloration after Death Rigor Mortis: Stiffness after Death Decomposition • Putrefaction and Autolysis
  15. 15. Algor Mortis • Algor Mortis (Body Cooling,chill of deth) – Cooling of the body occurs after death since all metabolism comes to a stop. – During life heat is constantly transferred from one body part to another by conduction as well as convection(through blood flow). – -There is some production of heat during initial period after somatic death due to ATP molecule breakdown(up to 2hrs) and anaerobic glycolysis(much longer) – Rectal temperature fall or not at all during first 2 hrs. – Cooling occurs from surface to the surroundings. – -Core temperature is the temperature of vicera,it is slightly increased as compred to the body surface temperature. – Core temperature is a better guide to TSD than surface temperature. – Body cooling is inaccurate in obtaining time of death.
  16. 16. • Site for core body temperature- Rectal temperature –best method- Insert a thermometer 8-10 cm in rectum and left for 2-3min. Other sites: auditory meatus , nostrils or under the liver, brain. Things to be recorded- i)Temp of body ii)Temp of environment iii)Time of recording iv) at least 5 reading at the interval of half hours to calculate the rate of fall.
  17. 17. Calculation of time since death – At 70°F – 75°F, the body cools 2.5°F to 2.0°F for first hour, – then 1.5°F to 2.0°F for next twelve hours, – then 1.0°F for next 12 hours. Time since death = 98.6°F – Rectal Temp (°F)/ 1.5 or(37.2-rectal temp )/0.6 • The rectum should be checked before insertion of the thermometer (May have been a sexual assault) – Patient may not die immediately after assault. • This may change time of death by several hours. • Thumb rules Time since death = 37°C – Rectal temperature (C) + 3
  18. 18. • Henssge’s nomogram method-
  19. 19. Factors affecting Rate of Cooling • Body weight: – Larger bw: slower cooling – Smaller bw: faster cooling • Edema: – slower cooling rate. • Surface area of the body: – Larger surface area  speeds up cooling rate. – Children have an increased surface area which allows for rapid heat loss.
  20. 20. • Clothing and emaciation • Environmental Temperature: – Higher humidity: rapid cooling rate – Rapid air velocity: rapid cooling rate • Water: – Rapid cooling rate: – More rapid in flowing water than still water • If there is a fulminating infection, e.g. septicemia, the body temperature may continue to rise for some hours after death.
  21. 21. Post mortem lividity(livor mortis) • Livor mortis- Suggilation ,vabices, hypostasis, staining, darkening of death. • Purplish-blue discoloration due to the settling of blood by gravitational forces within dilated, toneless capillaries of the skin • Livor mortis can be seen as early as 30 minutes after death. Since lividity results from the heart stopping, it may begin appearing antemortem in decedents who die as a result of cardiac failure. This stains the surrounding tissue.
  22. 22.  Post mortem lividity commences with in an hour after death.  Present as mottled patches in dependent parts with in 1-3 hours  Patches gradually increase in size and coalesce in about 2-6 hours .  Lividity is fully developed and fixed i.e. becomes unchangeable in about 6-8 hours.  Finally disappears when putrefaction sets in >8hrs  Pressure of thumb- Blanches (Not fix) TSD <8hours.  Pressure of thumb- Does not blanches (Fix) TSD >6hours
  23. 23. Rigor mortis • After death muscles are initially flaccid and can be moved easily. • The flaccidity is followed by increasing stiffness or rigidity of the muscles. • Joints are frozen. • The rigidity will gradual subside and the body will be flaccid again.
  24. 24. – Chemical changes causes muscle mass to become rigid; looks like body is frozen in place (fixed) – Small muscles go into rigor first – Rigor usually occurs from head to toe
  25. 25. Order of appearance and disappearance – • Heart (left chamber in 1 hour) • Eye lids ,Face muscles(2-3hrs) • Neck and trunk (3-4hrs) • Upper extemities (6hrs) • lower extermities(9hrs) • Small muscle of finger and toes( last to be affected 11- 12 hours) • It passes off in same order of appearance • It takes 12 hr to develop from head to foot , persists for another 12 hr and takes 12 hr to pass off. • In summer 18- 36 hr and In winter 24- 48 hr. • This is dependent on environmental temperatures • Fully flaccid body by 36 hours.
  26. 26. • Rigor is accelerated by – Prior exercise – Convulsions – Electrocution – Hyperpyrexia – Hot environmental temperatures – Age (does not form well in children) – Strychnine poisoning • Rigor is inhibited by – Hypothermia – Cold environment
  27. 27. Factors affecting timing of RM • Environmental temperature: – Cold and wet  onset slow, duration longer – Hot and dry  onset fast, duration shorter • Muscular activity before death: – Muscles healthy and robust, at rest before death  slow onset, duration longer – Muscles exhausted/ fatigued  onset rapid, esp in those limbs being used (eg in someone running at time of death, lower limbs develop RM faster than upper limbs) – Increase activity (convulsions, electrocution, lightning)  rapid onset & short duration
  28. 28. • Age: – Extremes of age  rapid onset • Health: • Cause of death: – Asphyxia, pneumonia, nervous de’s with muscle paralysis & dehydration  slow onset – Septicemia & poisoning  rapid onset, may even be absent, especially in limbs affected by septicemia – Emaciated or died of wasting disease  rapid onset, short duration
  29. 29. RM: time estimation Warm Flaccid Death < 3 hrs Warm Stiff 3-8 hrs Cold Stiff 8-36 hrs Cold Flaccid Death > 36 hrs
  30. 30. Postmortem Decomposition • The disintegration of body tissues after death • Tissue components leak and release hydrolytic enzymes • Bacteria and other microorganisms thrive on the organic material of the body • Two parallel process of decomposition occur: – Autolysis: Self-dissolution by body enzymes released from disintegrating cells – Putrefaction: Decomposition changes produced by the action of bacteria and microorganisms
  31. 31. • The normal final sign of death. • Starts immediately after death at the cellular level • Becomes visible in 48-72 hrs. • Its onset may be sped up or delayed by several factors mainly: – Temperature • The ambient temperature can speed up or slow down this process • A fever prior to death can speed up putrefaction – Humidity • One week in air equals two weeks in water and eight weeks in soil
  32. 32. • The 1st visible sign of putrefaction is green or greenish red discoloration of the skin of the anterior abdominal wall – Normally starts in the right iliac fossa. • The Next phase: – Gas formation – Blisters containing red fluid appear on the skin, mistaken as bleeding • Humidity, temperature, bacterial activity  body proteins break into polypeptides & amino acids • Brain & Epithelial tissues are the 1st to be affected by putrefaction • Heart, Uterus & Prostate may survive for longer periods. • Military Plaques: nodules in heart (epi/endocardial) • Marbling: bacteria colonize venous system  hemolysis  stain.
  33. 33. The decomposition of a body can be divided into several stages, even if the duration of each stage may vary a lot: • 2 - 3 days: green staining begins on the right side of the abdomen. – Body begins to swell. • 3 - 4 days: staining spreads. – Veins go "marbled" - a brownish black discoloration • 5-6 days: abdomen swells with gas. – Skin blisters • 2 weeks: abdomen very tight and swollen. • 3 weeks: tissue softens. Organs and cavities bursting. Nails fall off • 4 weeks: soft tissues begin to liquefy. Face becoming unrecognizable • 4 - 6 months: formation of adipocere, if in damp place. – This is when the fat goes all hard and waxy. • A body without a coffin will be decayed within 12 years.
  34. 34. Marbling (Arborization)
  35. 35. Influences on Putrefaction  A high environmental humidity will enhance putrefaction.  The rate of putrefaction is influenced by the bodily habits of the decedent; obese individuals putrefy more rapidly than those who are lean.  Putrefaction will be delayed in deaths from exsanguination (bleeding to death) because blood provides a channel for the spread of putrefactive organisms within the body.  Conversely, putrefaction is more rapid in persons dying with widespread infection, congestive cardiac failure or retention of sodium and salts.  It tends to be more rapid in children than in adults, but the onset is relatively slow in unfed new-born infants because of the lack of commensal bacteria.
  36. 36. • Heavy clothing and other coverings, by retaining body heat, will speed up putrefaction. • Rapid putrefactive changes may be seen in corpses left in a room which is well heated, or in a bed with an electric blanket. • Injuries to the body surface promote putrefaction by providing portals of entry for bacteria and the associated blood provides an excellent medium for bacterial growth.
  37. 37. Electrical contractility of muscle • During supravital period electrical contractility of muscle can be used to calculate TSD up to 2-3 hrs.
  38. 38. Bone marrow cell change • Bone marrow is aspirated from the sternum • Deposited on glass slide, smear made and stained by cytochemical stains like PAS,peroxidase,sudan black. • INTERPRETATION 1 hr- no appreciable change 1-2 hrs-occasional pyknotic erythroblasts are seen,budding of nucleus.
  39. 39. -3hrs-pyknotic erythroblasts are more common. -6hrs-early neutrophil lysis by vacuolation of the cytoplasm . 7hrs-myelocyte lysis. 9-12 hrs-advance neutrophils lysis. 12 hrs-all myelocyte lise.
  40. 40. Nasal ciliary motility • Nasal cilia maintain motility up to 18 hrs after death.
  41. 41. Stomach Emptying as a measure of time since a death- • Average meal last for 2-3 hrs. • Vegitable meal- 4-6 hrs. • Farinaceous meal- 6-7 hrs. • Stomach empting starts within 10 min of swallowing. • Light meal-1- 2 hrs. • Medium meal- 3-4 hrs. • Heavy meal- 5-6 hrs. • Meal reaches to ileocaecal valve between 6 and 8 hrs. • Movement of food distal to stomach- • Hepatic flexure-6hrs • Splenic flexure-9-12 hrs • Pelvic colone -12-18 hrs
  42. 42. • Conclusion: 1. If undigested stomach contents are present, then death occurred 0 to 2 hrs after last meal. 2. If stomach is empty but food is found in the small intestine, then death occurred at least 4 to 6 hrs after a meal. 3. If the small intestine is empty and wastes are found in the large intestine, the death occurred 12 or more hours after a meal.
  43. 43. Postmortem chemistry(Thanatochemistry) BLOOD Carbohydrates: Glycolysis in the PM period occures at a rate of 12.8mg/100ml/hrs. Blood glucose levels are not useful PMI indicator because of several variables like , DM,cause of death(increase glucose levels in asphyxia,co poisoning ,increased ICP)
  44. 44. Lactic acid: • During life-plasma and RBC levels -1mEq/L • 1hr after death-20 mEq/L • 12-24 hrs after death-50-75mEq/L Nitrogenous compound: -Creatinine, NPN,and total soluble protein all increase linearly with PMI. Amino acid nitrogen: -Up to 10 hrs after death-<14mg% -48 hrs >=30mg% -no further increase after that.
  45. 45. Enzymes: all increase after death. Acid phosphatase -within 48 hrs levels increase 20 times. Alkaline phosphatase -increases with PMI Normal ante mortem range-1.5-4BU. 10 hrs after death-5.3 BU 18 hrs after death-9BU 48hrs after death-30 BU Amylase: After 2 days levels are 3-4 times that of normal ante mortem levels.
  46. 46. Electrolytes: -Na levels-falls at rate of 0.90mEq/l/hr Cl levels-falls at rate of 0.97mEq/l/hr -k levels-incresed to18mEq/L after 1 hr,due to its release from cells.Thereafter continues to increased gradually. Ca-levels are constant upto 10hrs. Thereafter increase P-Both organic and inorganic P increase after death.After 18 hrs inorganic P increases to 20mEq/L
  47. 47. CSF Carbohydrates: Glucose-decreases rapidly after death Lactic acid- increases sharply and regularly upto 10 hrs ,thereafter continues to increase but at lower rate. Inositol- normal level during life1.7±0.45mg% -increases regularly after death ,up to 72mg% Electrolytes: Inorganic sulphates-stable up to 3 days after death Potassium-increases in proportion up to 70 hrs after death.
  48. 48. Vitreous Variation between two eyes may be upto 10%. Carbohydrates: Glucose- normal vitreous glucose level are approximately half of the serum level. With increasing PMI there is a consistent decrease in level. Within 4-5 hrs levels are zero in non diabetics. Lactic acid- normal-80-160mg%, after 20 hrs increase to 210-260mg% Electrolyte- calcium,-normal levels are 54.0-95.5mg/l,post-mortem change not significant. Chloride-normal levels are 114mmol/l,change are insignificnts
  49. 49. Potassium- most usefull indicator -During life k con is low in vitreous humour(5.8mmol/l)but much higher in peripheral tissues like retina. -After death k from peripheral tissues starts diffusing in the vitreous increasing its concentrtion. TSD(in hrs)=7.14x(k ion con in mmol/l)_39.1 (Sturner’s formula) TSD(in hrs)=5.26x(k ion con in mmol/l)-30.9 (Madea’s formula) TSD(in hrs)=4.32x(k ion con in mmol/l)-18.35 (James formula) Hypoxanthine show linear rise up to 120 hrs. Na- Decreases 0.9 mmol/l/hr
  50. 50. Pericardial fluid – Not useful -Potassium increase at rate of 0.30mmol/hrs -Sodium decrease at rate of 0.37mmol/hrs in first 85 hrs after death. Synovial fluid- K+ > 2X in first 2 days. Muscle Enzymes- -Myofibrillar protease increases linearly -Creatinine phosphokinase decreases linerly
  51. 51. Entomoogy of the cadaver • Within minutes of death, certain insects arrive to lay their eggs on the warm body, attracted by the smell of the first stages of decomposition. • The eggs will hatch and feed on the tissues. • Blowflies are a common example. • Flesh flies are another example. • Blowflies are attracted to two gases of decomposition: – Putrescine – Cadaverene As the corpse progresses through the stages, other kinds of insects will arrive. – Tiny wasps come to lay their eggs on maggots already present in the body – Cheese skippers arrive once putrefaction is underway; they are attracted by the seepage of body fluids. – Mites and beetles feed on dry tissues and hair
  52. 52. 1. <8 hours after death—blowfly eggs can be found in the moist, warm areas of a corpse 2. Within 20 hours—1st of their 3 larva stages 3. 4th or 5th day—3rd of their 3 larva stages 4. 8 to 12 days—larvae migrates to a dry place 5. 18 to 24 days— Early pupa; immobile; changes from light brown to dark brown 6. By the 21st-24th day the pupa cases will split open and adult blowflies will emerge.
  53. 53. The Scene Of Death Cell phone record- death must have occurred between last call attended and first call unattended. Milk bottles- number uncollected milk bottles at door step indicate number of days person is dead. Newspapers- earlist newspaper uncollected at door step gives the possible date of death.
  54. 54. Stopped wrist watch- in cases of drowning ,fall from height, blunt trauma etc where weapon struck watch and stopped, it may rarely give exact time of death. Dates on uncollected mail. Sales receipts and date slips of paper in deceased’s pockets. Statement from neighbours –when they last saw the deceased. State of food on the table- fully completed , half eaten etc. State of dress –whether the person was in normal dress or night dress . Corpse lying on grass –look at grass underneath the corpse. - The state of drying ,yellowness etc can indicate time of death.
  55. 55. Radio carbon dating • Half life of C-14 is 5730 years.knowing the ratio of c-14/c-12 in body can give time of death. • Lesser c-14 means more time o death and vice versa. • Can only date bodies more than 100 years virtually useless for medico legal purposes.
  56. 56. Miscellaneous methods Brain RNA: Brain RNA degrades in a linear fashion after death,18s r RNA is more stable than beta-actin m RNA in the post-mortem period. their ratio can be used to predict TSD. Flow cytometry: DNA start degrading immediately after death, number of cells with degraded DNA would increases as PM interval increases. Histologic changes in the skin: • <6hrs-epidermis,dermis,hair follicles ,sweat, and sebaceous glands appear normal for 6hrs after death. • After this period degenerative changes began.
  57. 57. • 6-9 hrs-degeneration starts in the dermis. • 18hrs-dermis begins to disintegrate. • >18hrs-hair follicles ,sweat and sebaceous glands start showing degeneration. Melatonin: is secreted into the blood by the pineal body. Its synthesis increases vastly in night time and decreases in day is not influenced by environmental factors except light. If the melatonin levels in post-mortem blood , urine , serum are high, it can be said that the individual died in night time if low, in day time.
  58. 58. • Strontium-90: strontium-90 is an artificial nuclear fission product of the atmospheric atomic bomb testing between 1945-1979. • It was spread through out the atmosphere in the following years. • Strontium-90 is an analogue to calcium and therefor deposited in human bones. • Its half life 28.1years. • During life strontium-90 is continuously being inheld but after death it degrade continuously. • Residual strontium-90 in bones is determined,it indicates TSD just like in radiocarbon dating
  59. 59. THANKS