I. Immediate Cause
i) External haemorrhage – Loss of more than 1/3rd of the total volume of body blood at a time may cause death due to circulatory failure. External haemorrhage is more and rapid in case of incised wounds of arteries.
ii) Internal haemorrhage – Depending on the site of internal haemorrhage, the quantity which may cause death varies. Thus, when it is inside the abdominal cavity, haemorrhage of 1 litre may not cause death. When it is in the pericardial sac 100 ml bleeding may also be compatible with life. But when it is in the pons or base of brain, bleeding of only a few drops may cause quick death.
b) Injury to the vital organs like brain, heart, lungs, liver or kidneys may cause immediate or rapid death.
c) Vagal shock from injury may cause rapid death.
d) Primary or neurogenic shock – Excessive and extensive pain as in cases of burns, may cause death within a few minutes to a few hours, due to neurogenic shock.
e) Secondary or hypovolumic shock – This may occur due to loss of blood in case of mechanical injuries and due to loss of fluid in case of burning and scalding (through blister formation). Death may occur within about 48 hrs.
i) Air – when some big veins or subcutaneous veins are injured, air may be sucked in them. Ordinarily, about 100 ml. of air, when enters the circulation, may cause death. But in case of patent foramen ovale or ventricular septal defect, 8 ml. of air in the circulation may cause death. Lung is a good barrier to the passage of air to different vital organs. But in cases of Auricular or Ventricular septal defects air in rt. side of heart (coming here through veins) can reach different vital organs without any barrier. During P.M. examination air bubbles may be seen in arterioles and capillaries at different places and froth may be present in the chambers of the heart.
ii) Fat embolism – due to, injury to subcutaneous fatty tissue with rupture of veins there; fracture of femur causing fat containing bone marrow emboli ; fatty abortifacient fluid entering the system through a ruptured vein in the uterus ; wrongful I. V. injection of oily preparation meant for I. M. injection.
iii) Thrombus formed inside an injured vessel may act as an embolus and may be taken to a distant place due to atrio-ventricular septal defect or may be obstructed by lung. Death may occur in either case.
g) Asphyxia – May occur as in case of choking due to inhalation of blood in cut throat injury.
II. Delayed Causes
a) Infection – like, tetanus, peritonitis, septicaemia, meningitis, encephalitis, pneumonitis etc
b) Complications of injuries, like, stricture of oesophagus, diaphragmatic hernia, paraplegia due to spinal injury.
c) Mismatched blood transfusion.
III. Immediate or delayed – Due to wrong treatment or neglect in the treatment.