Types of death: Asphyxia Flashcards
Asphyxia definition
Asphyxia derives from Greek, meaning ‘absence of
pulsation’
Forensic use means ‘ Interference with oxygenation’
Interference from environmental down to cellular
level.
Anything that interferes with oxygen transfer can be
called asphyxia;
Terms like hypoxia and anoxia should be used
Examples of asphyxia
Absence or reduction of oxygen tension in the atmosphere;
Obstruction of external respiratory passage- mouth and nose;
Blockage of internal respiratory passages.
Restriction of respiratory movements
Disease of the lungs that reduces gas exchange;
Reduction in heart function.
Reduced ability of the blood to transport O2.
Inability of tissues to utilise O2
Mechanical asphyxia
Broad term used to cover a wide range of different asphyxial
situations.
External pressure on the chest, neck or other areas of the body
to make respiration difficult or impossible.
Classic signs of asphyxia: Petechial Hemorrhages
Small pin-point collections of blood lying in the skin, sclera or conjunctivae
and under the thoracic serous membranes (pleura, pericardium).
1-2 mm in size.
Caused by the rupture of thin-walled venules, especially in the lax tissue.
May disappear with lengthening post-mortem interval
Significance of Petechiae
Not always as an indicator to asphyxia.
Position of the body after death as well as an enumerable number of other factors can lead to the appearance of
petechiae.
Typically, petechiae are used in
conjunction with other evidence to indicate asphyxia.
Classic sign of asphyxia: Congestion and Oedema
Result of obstructed venous return (blood drainage).
When neck is compressed, the face, lips and tongue become swollen and reddened.
Hypoxia causes tissues swelling
Increased vascular permeability-flow of water out of blood vessel
Froth may emerge from mouth and nostrils
Classic sign of asphyxia: Cyanosis
Greek word for “Dark Blue.”
Normal pink colour of well oxygenated skin may change to blue when oxygen is lacking.
Constriction of the neck traps blood in the veins with decreased
oxygenated hemoglobin, which leads to the bluish colour.
Suffocation
Broad term encompassing many different types of asphyxia.
Refers to death caused by reduction of O2 conc. in the respired
atmosphere.
Physical replacement of O2 by other gases such as CO or CO2
Smothering
This term refers to death from mechanical occlusion of the
mouth and nose.
Smothering agent: Fabric, Impervious sheet, hand, Sand, Mud, Flour
Death may occur either by occluding substance pressing down on the facial orifices, or by the passive weight of the head pressing down.
Deliberate homicide is seen usually in the old, debilitated and infants.
Pressure marks are rarely distinguished from normal
postmortem changes.
Extremely hard to prove intent
E.g. Smothering of babies; accidental or intentional
Overlaying of infants
Is a form of mechanical asphyxia.
Accidental smothering by rolling over it in bed.
Hazard of death reported to be greater in infants less than 5
months.
Infant’s airway is obstructed, thorax and abdomen compressed and
neck circulation impaired.
Autopsy findings usually negative.
Plastic bag suffocation
Common form of suicide but can be accidental or homicidal.
This type of suffocation involves the creation of a local hypoxic environment
within a plastic bag securely fastened around the neck.
Rapid and leave no visible signs.
Petechial haemorrhage is often not seen.
Chocking
Blockage of internal airways.
Occurs between pharynx and the bifurcation of the trachea.
Death can result from pure hypoxia from occlusion of airway with congestion and cyanosis or from neurogenic cardiac arrest.
Vagal stimulation and rapid death
Sometimes food and F.B. can cause death by distension of food pipe or
stimulation of larynx, pharynx mucosa.
Death is rapid.
Overactivity of parasympathetic nervous system.
No signs of asphyxia seen.
Common in old persons and mentally retarded children.
Traumatic asphyxia
Refers to the mechanical fixation of the chest.
Restricted respiratory movements thus preventing inspiration.
Occurs in conditions such as:
Chest is compressed by an object so that expansion is
prevented
Collapse of an excavation, other industrial accidents
Crushing in crowds
Trapping between vehicle and a wall etc.
Mechanism of Death by fatal pressure on the neck
Physiological and Anatomical factors:
1. Airway occlusion:
Direct compression of larynx or trachea.
Closure of pharynx by the root of the tongue
- Occlusion of the neck veins:
Responsible for classical sign of congestion, cyanosis,
swelling and petechie above the line of constriction.
Ext. Jugular Veins more vulnerable - Compression of the Carotid arteries:
Deep seated so need considerable pressure.
Occlusion results in immediate unconsciousness.
Permanent brain damage results if compressed for >4-5
minutes. - Nerve effects:
Pressure on the baroreceptors
