Asphyxia Flashcards
Where did the word asphyxia come from
Greek derivation:
“absence of pulsation”
What is the forensic definition of asphyxia
Interference with oxygenation
This is the one we use
Describe the structure of the cricoid cartilage
Signet ring shaped cartilage
Describe the structures of the hard and soft palate
Hard is a bone structure
Transitions into the soft palate
This is a softer tissue - responsible for snoring
Where would a tracheostomy be placed
Gap in between thyroid and cricoid cartilages
List caused of oxygenation interference
Environmental
Obstruction of external respiratory passages - mouth & nose
Obstruction of Internal respiratory passages - pharynx, larynx, trachea, bronchi
Restriction of resp. movements
Lung disease
Heart disease
Oxygen transport issues
List some medical conditions that can lead to asphyxia
Pneumonia
Fluid on the lungs
Basically anything that interferes with gas transfer
Can also increase risk from asphyxia if chronic as less reserve/ tolerance to damage
How can direct force to the neck affect the spine
Direct force can compress neck cartilage/bone and compress/fracture into the spine at the back
Superior horns of thyroid cartilage prone to fracture
Hyoid bone also a risk
List the types of mechanical asphyxia
Environmental - e.g. CO Suffocation Traumatic (Crush) Asphyxia Choking Hanging Strangulation Inhalation
List the 4 stages of asphyxia
Struggle
Quiescence
Convulsions
Apnoea
What occurs during the struggle phase of asphyxia
Forceful respiratory effort
Associated signs may not be as enhanced in suicide (compared to homicide)
The longer you are conscious the more struggle signs
What occurs during the quiescence phase of asphyxia
The victim will fall unconscious
Can occur very quickly with some types of asphyxia
What occurs during the convulsion phase of asphyxia
Disturbance
Incontinence
Often agonal events
What occurs during the apnoea phase of asphyxia
Victim becomes lifeless and pulse is weak
What are the mechanisms of death in asphyxia
It is a complex process
O2 deprivation and CO2 accumulation
The neck pressure reduces the blood flow to the brain
Vagal inhibition can lead to reflex cardiac arrest
How does carbon monoxide poisoning cause asphyxia
CO takes the place of oxygen and interrupts its transport
There is no normal O2 circulating
What would happen if you covered the nose and mouth of someone with a tracheostomy
It would not have an effect on their breathing - e.g. they will not asphyxiate
They breathe from the trach lower down
Is death always due to a single type of asphyxia
No
Different causes can overlap and contribute to death
What is meant by overlying children
When you roll onto them or sleep on top of them
Causes asphyxia but little struggle
Longer you are conscious the more signs of asphyxia are produced - true or false
True
This is because you struggle for longer
What effect does jugular venous occlusion have
Causes venous stagnation
Blood cannot leave the head/neck
This can lead to swelling in the brain and loss of oxygen
What effect does carotid artery occlusion have
Leads to cerebral hypoxia
Oxygenated blood cannot enter the head/neck
List the general pathological signs of asphyxia
Petechial haemorrhages
Congestion
Cyanosis
Oedema
Petechial haemorrhages, congestion, cyanosis and oedema are all specific to asphyxia deaths - true or false
False
These are non specific signs - especially c,c and o
They are present in some non-asphyxia deaths and absent from some asphyxia cases
Can add weight to conclusions though
Describe the appearance of petechial haemorrhages
Pinpoint size (<1 mm)
Red colour
Can coalesce
What can distribution of petechial haemorrhages tell you
They occur upstream of the venous occlusion so tell you where this was
On which tissues will you commonly see petechial haemorrhages
Tarsal plates - eyelids Conjunctivae - usually florid Inner aspects of lip - mucosa Behind ears Facial skin - skin lax and thin
What causes congestion, cyanosis and oedema
All due to obstruction of venous return
The signs will be seen upstream of the occlusion as a result (e.g. above the ligature)
In which tissues do you often see congestion post asphyxia
Face
Tongue
Pharynx
Lungs
In which tissues do you often see oedema post asphyxia
Face
Lungs
Brain
In which part of the body are you most likely to see congestion, cyanosis and oedema
Most often apparent in the face
Above ligature around neck or due to chest compression
Occurs above the occlusion due to backpressure
What causes environmental asphyxia
This occurs when atmospheric O2 is low or absent
e.g. CO poisoning, anaesthesia, scuba, ship holds
Which structures in the neck are vulnerable to trauma
Hyoid bone Thyroid cartilage Cricoid cartilage Carotid artery Carotid bodies - may cause arrhythmia Jugular vein Vagus nerve - cardiac arrest
List causes of environmental asphyxia
Ships hold
Scuba diving (recreational or work) - equipment failure or just running out of O2
Enclosed breathing apparatus and enclosed spaces
Industrial chemicals - steal space from O2 in room and body
CO from faulty household goods like fridges
What causes petechial haemorrhages
Vein occlusion during asphyxia causes blood to back up in the venules (path of least resistance)
Venules get disrupted due to backpressure
As these are weak vessels they can rupture
They are pushed up to the skin in thin areas which causes the visible haemorrhage
The more prolonged the struggle the more petechial haemorrhage will be seen - true or false
True - in theory
The more prolonged the struggle the more prolonged the pressure to the vein which leads to more haemorrhages
Struggle also increases the stress response = higher BP = more haemorrhage
How long does it take petechial haemorrhages to form
Can take between 8-10 seconds for them to be produced
What process is essential for the formation of petechial haemorrhage
Must have some occlusion to the veins during life
What does bleeding in the middle ear suggest
Prolonged struggle
Not necessarily against assailant - maybe just fight to stay alive
During asphyxia the carotid bodies can get damaged, what effect can this have
They contribute to normal heart rhythm so irritating them may cause death via arrhythmia
During asphyxia the vagus nerve can get damaged, what effect can this have
It can cause arrhythmia as it innervates the heart
Typical signs of asphyxia are usually absent in environmental asphyxia - true or false
True
This is because death is often rapid - less struggle
More likely to just lose consciousness
Therefore the scene and circumstances are important in these cases
The term suffocation is often used to describe what
Often used as a general term for deprivation of O2, due to lack in environment or external obstruction of airways
More emotive term associated with struggle/homicide - best not to use if possible
What is homicidal soft smothering
Obstruction of the nose and mouth
Common in infants and elderly by a hand or a pillow - easier to overcome
List potential methods of suffocation
Soft smothering - hand or pillow
Plastic bag asphyxia
Overlaying of infants
Gagging
Why is CO poisoning less common these days
Gas used is now ‘cleaner’
CO monitors are now more common in homes
Which injuries can be caused by smothering
May get some bruising or laceration on lips/gums - pressed against teeth by compression or due to work of breathing creating suction effect
Can be confused with CPR artefacts
Which types of asphyxia are caused by plastic bag asphyxia
suffocation + environmental asphyxia
Bag means there is limited O2 supply and CO2 builds up- environmental
The bag can also form a seal over airway and suffocate
Which types of asphyxia are caused by overlaying of infants
suffocation + crush asphyxia
The weight of the adult crushes their chest so it cannot expand for breathing
Also a suffocation element due to smothering with bedclothes/adults clothing/ falling between mattress etc.
How does gagging cause asphyxia
secretions obstruct nasopharynx
makes it harder to breathe
The general signs of asphyxia are often absent in suffocation cases - true or false
True
Typically less struggle
Less obstruction of the blood vessels as well - responsible for many signs
Therefore scene and circumstance are important
Presence of signs would be suspicious
Which marking is better for determining ligature placement - lividity or congestion
Lividity - the line is much clearer than in congestion
Plastic bag asphyxia is a common method of suicide - true or false
True
death is usually quick
Why might someone try to keep the bag away from their face in cases of plastic bag asphyxia suicide
It is a more peaceful death if bag not on face
If the bag seals over the airway and causes occlusion it usually generates struggle/panic
However, if death is purely from lack of O2 there is less struggle - tend to fall into unconsciousness
What signs may be seen internally in cases of asphyxia due to external compression of nose and mouth (smothering)
May see internal haemorrhages at points of compression - seen on dissection
Even if lacking external signs
e.g. under the neck from fingers or on the back of the head due to pressure
What is traumatic or crush asphyxia
When there is pressure fixation of chest wall and abdomen
External forces prevent the chest moving sufficiently for proper oxygenation
Can’t draw O2 in or blow CO2 out
What can cause traumatic or crush asphyxia
Burial Trench collapse Crowds - e.g. Hillsborough Under vehicle Overlying
Which pathological signs are often seen in traumatic or crush asphyxia
Florid general signs both externally and internally - petechiae, congestion, cyanosis, oedema
Will occur at points above/below where pressure applied
Specific external & internal injuries often slight, most are quite general
Which pattern of congestion and lividity may be seen in a death from traumatic or crush asphyxia
Usually shows the point of compression as pale (contact pallor) with congestion surrounding this (e.g. above/below)
Congestion around clavicle/neck caused by chest compression - blood from head cannot drain
May also get entrapment marks - distinct pattern of crushing object
What is ‘Burking’
Burke & Hare’s method of asphyxia
Sitting on chest (traumatic/crush asphyxia)
Manual occlusion of nose and mouth (smothering)
Leaves little or no signs of trauma for receiving anatomist
Can alcohol contribute to asphyxia
Yes
As well as other depressant/sedative drugs
It reduces the struggle
Common in positional - too drunk to move out of dangerous position
What is positional asphyxia
When the body position itself obstructs the airway or impairs the act of breathing
e.g. Neck at right angle will compress the airways and obstruct
Associated with sedative intoxication - alcohol etc.
Some natural disease/disability can contribute too
Positional asphyxia is usually accidental - true or false
True
e.g. frail person cannot get self out of position unaided
Or too drunk to move
What is restraint asphyxia
When the chest, diaphragm & accessory muscles are impaired
Restraint asphyxia is a variant of which other type of asphyxia
Positional
What is restraint asphyxia associated with
Stimulant intoxication
Common in psychiatric & custody situations
Police restraint - controversial cases
What must be established in cases of positional asphyxia
Why they were in that position and why they didn’t get out of it
Natural disease, frailty, intoxication etc.?
Which groups are at higher risk of choking
Elderly, children, those with mental disabilities and underlying medical conditions (particularly with impaired swallow)
Define choking
Obstruction of upper airway, between pharynx & tracheal bifurcation by food or foreign object
e.g. food bolus, toy, dentures etc.
Which signs are seen in choking deaths
The general signs of asphyxia are variable in these cases
May see the obstructing object on dissection of neck/airways
How does choking cause death
Death is often rapid via vagal inhibition
Airway obstruction
Hanging is a common method of suicide - true or false
True
It is easily available and often lethal
What aspects of hanging put pressure on the body
The ligature - fixed or running loop puts pressure on the neck
Body weight - full or partial suspension puts pressure on the neck
How does hanging cause death
Obstruction of airway - pushes the tongue up into soft palate
Occlusion of the carotid arteries - decreases blood flow to brain
Irritation of carotid bodies - arrhythmia
Occlusion of jugular veins - causes cerebral oedema/hypoxia etc.
Vagal inhibition
General signs of asphyxia are usually absent in suicidal hangings - true or false
True
There is little struggle - resigned to fate
No defensive wounds (would be seen in homicide)
Describe the ligature mark seen if a narrow object is used for hanging
Will be a narrow and tight ligature mark
Often deeper as the pressure is more concentrated
Describe the ligature mark seen if a wide object is used for hanging
Larger and more spread out ligature mark
Will be more superficial are pressure is spread over a greater area
May not have as enhanced physical features
Describe the appearance of the ligature mark left in hangings
Will have a rising angle - under chin then at oblique angle upwards to the suspension point
Will have a spared patch at the point of suspension - less direct pressure here (usually back of neck)
May have pressure pallor directly under ligature with markings either side
You must be completely suspended of the ground in order too hang yourself - true or false
False
Can be partial or full
Just need to be suspended enough to prevent you correcting your position - just need to be there long enough to pass out
What is happening to rates of hanging
They are increasing
May be due to other methods being eradicated - e.g. car exhaust or head in oven (cleaner gas isn’t effective)
Which locations are high risk for hangings
Psych wards and prisons
Must consider items that can be used such as bedsheets/shoelaces
What can determine the choice of ligature in hanging
Availability and context are important
List features of suicidal hanging
Ligature will still be in place - can’t remove it as dead!
Absence of defensive wounds
Use of drugs or alcohol
Suicide notes or messages
Multiple methods - e.g. Plastic bag over head and hanging
Which ligature mark patterns suggest homicide
Horizontal ligature more in keeping with strangulation
Multiple marks can be suspicious - e.g. Throttled then hung
When might a horizontal ligature be seen in genuine hangings (i.e. not homicidal strangulation)
Can be seen if the point of suspension is very unusual
When can multiple ligature marks be seen in a non-suspicious case (i.e. suicide)
Can be due to ligature breaking and moving
or skin abrading through and slipping
Hanging may be used to conceal homicide - true or false
True
May be strangled and then and strung up to try and cover the true cause of death
Which fractures are common in hangings
Fracture to the great horn of thyroid cartilage
Will sit at an odd angle
Fracture to hyoid
May have haemorrhage around the fracture
Which lividity pattern is seen in hangings
Glove and stocking lividity distribution if suspended - blood pools in hands and feet
May be different if the body was moved before fixed
Which congestion pattern is seen in hangings
Will be congested above the ligature
Cervical fractures are common in hanging deaths - true or false
False
This requires a large drop (as per judicial hangings of the past)
This is hard to achieve alone
Often severs nerves - quick death
How long does death from hanging typically take
Loss of consciousness in 15-30 sec
Therefore cannot move themselves
Death in 1-2 mins
What is sexual asphyxia
Asphyxia that occurs during a sexual act
Usually an accidental hanging
What is the most common cause of sexual asphyxia
Failure of safety mechanisms
Sex devices usually have some for of safety feature to allow quick release - if these fail can lead to death
Item usually left in place (unless someone moves you)
Which groups are associated with sexual asphyxia
Young males - often a regular, secret practice
Those into masochism, pornography and transvestism
How can sexual asphyxia be differentiated from other causes
Scene is usually diagnostic - sex device present, clothing choice
Very different to most ligatures
Ligature strangulation is most associated with which manner of death
Homicide
Ligature may be held, tied or twisted by an assailant/ third party
Suicide and accident are rare
Which signs are commonly seen in ligature strangulation cases
Florid general signs - petechiae etc.
Horizontal mark of uniform depth (low level)
May be circumferential - more like a garrote
Skin bruises, scratch abrasions on hands/neck - trying to get ligature off
Deep neck muscle bruising
Hyoid & thyroid fractures
More signs as usually more struggle
What is manual strangulation
When the hands are used to strangle someone else
Also called throttling
Which signs may be seen in cases of manual strangulations
Finger pad bruises on neck Scratch or crescent abrasions from attacker's nails or victim's own (trying to get hands off) - may find DNA under nails Florid general signs - due to struggle Lack of ligature mark Deep neck muscle bruising Hyoid & thyroid fractures
Lots of struggle = lots of signs
What signs may be seen on the attacker following a manual strangulation
Scratch or crescent abrasions on their hands/arms from the victim’s nails (as they tried to get the hands off their neck)
As a result their DNA may be found under the victims nails
How long does the grip need to last in a manual strangulation case
Typically more than 30 secs
Describe the grip pattern seen in cases of manual strangulation
Shifting grips often lead to varying patterns
Sleeper holds
How can you tell that the thyroid cartilage has been fractured
If the horns are at a weird angle
Compare sides?
What is inhalational asphyxia
When there is obstruction of lower airway (below trachea) due to the inhalation of something
List common causes of inhalational asphyxia
Foreign bodies - toys, nuts, other food
Vomitus
Water - drowning
Which groups are at risk of inhalational asphyxia
Children The elderly Those with dementia Those with swallowing issues - muscular/neuro issues Alcoholics - at risk of inhaling vomit
Why is it hard to determine if vomit caused inhalational asphyxia was
Often agonal vomiting (e.g. occurred during death, not the cause) - common in drugs deaths
Or can be a PM artefact
List the structures of the respiratory system
Nasal passage Oral cavity Join to form pharynx Then larynx trachea Bronchi Bronchioles Alveoli - site of gas transfer Diaphragm
How does air enter the lungs
Movement of diaphragm causes pressure changes in the chest which draws air in through the mouth or nose (or trach if one in place)
Describe the structures in the oral cavity
Hard palate on roof of mouth - bone
Transitions to soft palate - may be responsible for snoring
Tongue is one large muscular structure
List the bony and cartilaginous structures of the neck
Hyoid bone
Thyroid cartilage - has superior and inferior horns
Cricoid cartilage
In which places can the airway be obstructed
External passages - mouth and nose
Internal passages - pharynx, larynx, trachea, bronchi
- pharynx/larynx obstructed if trach covered
How can the tongue appear in hanging victims
Often affected by congestion and oedema
Protrusion of the tongue common
