How good are you at estimating time of patient's death?
Simple external body changes can help a GP estimate how long a body has been dead, says Dr Anthony Busuttil
long a body has been dead, says Dr Anthony Busuttil
Whenever a doctor is asked to confirm that death has supervened, quite frequently he or she will also be asked their opinion about the time at which death has occurred. This boils down to an estimation of the so-called post-mortem interval (PMI), namely the period elapsed between the time that death has actually occurred and the time the dead body was found.
In line with the myth that television dramas perpetuate, the questioner frequently expects that the doctor will always be able to pronounce on this matter sagely and convincingly. This cannot be further from the truth.
Even those forensic medics who carry out these estimates regularly and are armed with various scientific observations and measurements cannot pronounce accurately and with full conviction on the time of death, often producing what can only be described as no more than an educated guess. Indeed, if they are at all experienced, they will know to restrict their answers to a range of times rather than to an actual and specific time of death.
It is unlikely that a family practitioner will be asked to quantify the PMI in bodies who have been dead for 24 hours or longer. By this time some putrefactive changes will be evident, particularly if the death has taken place in a warm room, if the body was covered with bedclothes or an electric blanket, or if the person had been lying close to a heat source such as an electric heater or a radiator.
The earliest changes of putrefaction are the presence of greenish discolouration of skin over the lower abdominal wall, mainly towards the right (due to the reaction between putrefactive nitrogen- and sulphur-containing gases produced by the colonic bacteria and myoglobin and haemoglobin), and marbling of the subcutaneous veins due to haemolysis of the blood within them and consequent staining of their walls by haemoglobin. If these changes are well established, it can be safely stated that the body has been dead for more than 18 hours.
If these changes are not present then the signs to look for are:
· Drying of the cornea and tarsal conjunctiva
· Cooling of the skin
· Development of muscular rigidity
· Passive gravity-mediated sedimentation of blood after death towards the dependent parts of the body.
If the eyes are open at death there will be drying of the tarsal conjunctiva and cornea and increasing opacification of the cornea within about 10 minutes of death. It takes up to about 45-60 minutes if the eyes were closed. There is gradual loss of palpable tension in the eyeball after about eight to 10 hours.
To identify a loss of warmth of the body, feel
the exposed parts with the back of the hand, feel the armpits and then feel the dependent and covered parts of the body. The greater the degree of the cooling of the skin the more time has elapsed since death.
Assuming the patient was neither pyrexial nor hypothermic before death the rate of cooling as a quick rule of thumb is at about 1.5°C per hour in the first six hours. Cooling will commence once the body's exothermic metabolism has wound down completely and will be found in the exposed body parts, particularly in the face (the hands of the deceased are not good indicator sites). It will be delayed on the back and in skin folds.
Post-mortem cooling depends heavily on the level of the ambient temperature, on local humidity, on the mode of death (active and violent as opposed to very slow and gradual), on the amount of insulation of the body by clothes, bedding and by fat, on the surface area of the body, and on many other variables.
Useful broad rules of thumb are the following:
· If the face is cold but everywhere else is warm, death was two to three hours earlier;
· If the body is generally cold even in insulated and covered areas, death occurred 10 to 12 hours previously.
Rigor mortis develops as all types of muscle use up their ATP content and lactic acid accumulates within them due to anaerobic myofibre respiration. It is not usually present at death, but its development is orderly and predictable (see table below).
Blood starts to sediment gravitationally towards the dependent parts of the body and results in a purplish-red discolouration of these areas, producing a livid, purplish staining. This starts within two to three hours of death as mottled patches, which coalesce in three to six hours.
Lividity cannot be shifted: the skin cannot be made to re-blanch and lose its acquired colour by externally applied pressure (with a finger, for example) after six to eight hours. This phenomenon is often referred to as fixation of the lividity. This sedimentation is internal and external, universal and not localised, and can thus be easily distinguished from bruising.
Finally, it is useful to note that the development of peripheral cyanosis below the fingernails and toenails (and central cyanosis in the lips) due to accumulation of deoxygenated haemoglobin is not a useful PMI marker.
Anthony Busuttil is regius professor of forensic and clinical medicine, University of Edinburgh