POSTMORTEM INTERVAL

Mr. Riyaz KhanVI th SemsterDept. of Forensic Medicine & Toxicology,NGMC, Kohalpur

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Postmortem intervalThe interval between death and the time of examination of a body is known as postmortem interval (PMI).

Also known as Time Since Death (TSD)

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Historical BackgroundMethods for estimating the postmortem interval first done by the ancient Greeks and Egyptians during the fourth and third centuries. They understood that dead bodies cooled and became stiff over a period of time after death.

a) Warm and not stiff: Dead not more than couple of hours

b) Warm and stiff: Dead between a couple of hours and a half day.

c) Cold and stiff: Dead between a half day and two days

d) Cold and not stiff: Dead more than two days

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Importance of PMI It is an important component of medicolegal investigations.

It helps in both civil and criminal cases. In civil cases, the time of death might determine who inherits property or whether an insurance policy was in force.

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Importance of PMI cont…In criminal cases,

1. To know when the crime was committed.2. It gives the police a starting point for their

inquiries, and allows them to deal with the information available more efficiently.

3. It might enable to exclude some suspects and the search for the likely culprits started earlier

4. To confirm or disprove an alibi5. To check on a suspect’s statements.

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Estimation of PMIFirst, all available history should be taken, and then local physical or environmental factors at the scene of crime, such as presence of fires and domestic heating, open windows, atmospheric temperature, etc. must be noted.

The range of time provided is at best an educated guess, based on knowledge and experience and subject to error.

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Changes useful for Estimating of PMI Change in the eye Algor mortis Hypostasis Rigor Mortis Putrefaction Adipocere Mummification Skeletonization

Insect activity Stomach & Intestinal

Contents Contents of urinary

bladder Bone marrow Changes Biochemical changes Circumstantial evidence

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1. Changes in the eyeWhen a dead body is still warm, not rigid, without any permanent haziness of cornea, the death of person possibly has occurred

1 hour in summer & Within last 2 hour in winter.

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2. Algor MortisCooling of dead body.The most useful single indicator of the PMI during the first 24 hour after death.

Under ideal conditions, the body will have no drop in temperature for 60-90 minutes after death followed by cooling at the rate of 0.5 OC per hour.

The body attains environmental temperature in about 16-20 hour after death.

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2. Algor mortis cont…

Measurement of body temperature by- Thanatometer Inserted 8-10 cm in rectum and left for 2-3 mins Other sites auditory meatus, nostrils or under liver.Calculated by: Thumb RulePMI = 98.6 OF – rectal temperaure(F) / 1.5

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3. HypostasisThe extent of appearance and its fixation give some idea about the time which has passed after death.

Begins immediately after death but visible after ½ to 1 hours well developed 4-5 hoursmaximum 6-12 hours

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4. Rigor mortisAppearance, distribution or its passing away are the most imp physical changes which are taken into account for estimation of PMI.

In tropical countries,begins 1-2 hdevelop from head to toe 9-12 h

In temperate countries,begins 3-4 hfully established 8-12 h

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5. PutrefactionAmong the delayed changes after death (& after rigor mortis), this change is the single best one for the purpose of estimation of PMI.1. Greenish discoloration

In summer 12-18 hIn winter 24-48 h

2) Marbled appearance 24-36 h3) Formation of foul smelling gases 18-36 h

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6. Adipocere

Shortest recorded period in winter is 3 days 22hrs and in summer 3 weeks

Whole body gets converted to adipocere in 1 year.

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7. Mummification

Complete mummification requires at least 3 months to 1 year

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8. Skeletonisation

Uncoffined bodies 1 year

This skeleton is of an adult man who had been missing for 1.5 months during the late fall in the southeastern united states. He was found in a wooded area. Although the skeleton was mostly intact, gnaw marks were evident on several ribs.

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9. Insect activityFlies lay eggs 18-36 hrs of death

Maggots or larva appear 48-72 hrs of death

Pupae develop 4-6 days

Adult flies develop 6-10 days

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10. Stomach and intestinal contentsAverage meal last for 2-3 hrsVegetable meal 4-6 hrsFarinaceous meal 6-7 hrs If the stomach is full and contains undigested food, it can be said that death occurred within 2-4 hours of eating of the last meal and if the food is digested(indistinguishable), then >4 hrs.

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11. Contents of urinary bladderThe amount of urine in the bladder may give some indication of the time of death in some cases.

If a body is found in the morning with the bladder full, then inference may be drawn that he might have died before the usual time of leaving his bed, since the first activity in the morning after leaving the bed is evacuating the bladder.

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12. Changes in the bone marrownuclei of the neutrophils in marrow start swelling

within 1 hrRound nuclei 4-5hrsoutline of the neturophils lost 10-12 hrs

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13. Biochemical changesa. Cerebrospinal fluid(CSF)

Amount of potassium increases at a constant rate in relation to temperature of the body during the first 20 hours.

b. Blood• There is progressive rise in lactic acid level by 50-75 fold in 12 to 24 hours• Amino acid nitrogen is less than 14mg/dL upto 10 hours but rises to 30mg/dL by 48 hours• Acid phosphatase increases 20 times by 48 hours• Amylase increases 3-4 times on second day

c. Vitreous Humor: Potassium concentration at the time of death is 5-8mmol and rises at 0.17-0.238mmol/1 hour.

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14. Facial hair & Nail growth1. Facial HairRate of growth of hair after shaving is 0.4mm/day.Hair does not grow after death. If the time of his last shave is known, then the time since death can be calculated.

2. NailsRate of growth of nails is 0.1mm/day

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15. Circumstantial evidencesPocket articles like letters, diary, cinema-show ticket, etc may indicate in some way the date and time upto which the person survived.

Degree of coagulation of milk, staleness of food on a table and when the neighbor saw the person etc. may be valuable.

The dress should be noted as regards to whether the person is fully dressed or in the night dress.

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In some cases, the wrist watch may stop and thus may indicate the date and exact time of death.

Some idea about the earliest period of death can be made from the newspaper present by the side of the dead body.

If a body is lying on the grass, it becomes pale due to non-exposure to sun for about 5 days.

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Some FACTS of PMI

The exact time of death cannot be fixed by any method, but only an approximate range of time of death can be given, because there are considerable biological variations in individual cases. So Never give a single estimate of the time since death.

The longer the postmortem interval, the wider is the range of estimate, i.e. the less accurate the estimate of the interval.

Thank you