Livor Mortis

When cardiac activity stops, the hydrostatic pressure of the liquid blood causes it to settle and distend the dependent capillary bed. (The color of the dependent part will depend on the skin pigment and any additional compounds in the blood that may affect color, such as carbon monoxide, cyanide, or cold, but it is generally dark blue or purple).

Livor begins at or very soon after death since it is a function of blood flow and, therefore, cardiac activity. However, stasis can occur to some extent in shock and some degree of lividity can be present even while a person is technically alive. It is readily recognizable in 2-4 hours and becomes complete or fixed in 8-12 hours. Although it does not actually disappear, it becomes less distinguishable with changes in body coloration with continued decomposition. Although it is a simple process of settling, there are factors that will accelerate or retard the onset of visible livor, and the "disappearance" rate is similarly variable.

Livor will not usually develop where there is pressure from clothing or objects so important information regarding whether a patient was clothed for a period of time after death or if his position was changed can be gained from a careful inspection of livorfs distribution. Generally, time of death can, at best, be supported from observation of livor and comparison with the accelerating or decelerating factors affecting that scene.

A variation of livor is the phenomenon referred to as Tardieu spots. When the accumulated area engorged with blood is large, gravity can cause capillaries in the small area to rupture so that larger, usually circular or rounded areas of skin hemorrhage occur. Although there have been some statements as to a minimum time required to develop Tardieu spots, it seems to depend more on the weight of blood in an area coupled with the time the pressure is in effect.

These have to be differentiated from the much smaller petechial hemorrhages more suggestive of asphyxia. Size is important since these areas are usually 4-5 mm or larger in diameter, whereas petechiae are usually 1 mm or smaller in diameter.

From "Estimation of Time of Death" by Patricia J. McFeeley, M.D.