14.8 Flashcards
Define asphyxia
- A deficiency ofoxygen (hypoxia/anoxia)
- not enough O2 in enviroment
- can’t get into lungs
- can’t get to cells
- etc
Classification of hypoxia
Hypoxic hypoxia
- not enough O2 in blood
- Low arterial oxygen pressure (PaO2)
- Hypoventilation during anaesthesia
- Low inspired oxygen: High altitude/ SCUBA diving
- Lung pathology (COPD) and Cyanotic congenital heart disease
Anemic hypoxia
- no or little blood
- not enough blood to carry O2 (blood loss)
- enough blood but functionality is lacking
- Blood loss with low Hb
- Carbon monoxide poisoning – loss of Hb function (Hb will rather bind to CM than to O2)
Stagnation hypoxia
- Pooling of blood in the vascular system
- Heart failure and cardiogenic shock
- Myocardial infarction
- Venous infarction
Cytotoxic / histotoxic hypoxia
- Cell / tissue toxic
- Blockage of cells from accepting O2 in the last steps of Oxidative Phosphorylation to produce ATP.
- Cyanide poisoning
- Hydrogen sulfide poisoning
Classification of asphyxia
1. ENVIRONMENTAL SUFFOCATION: (Versmoring)
- Decreased oxygen tension in the environment
- = Low barometric pressure (don’t have normal atmospheric pressure {1})
- Displacement by inert/ non-toxic gasses (N2; CO2)
- airplane that suddenly decompresses
2. SMOTHERING: (Versmoring)
- Mechanical obstruction of external airways (mouth and nose).
- cloth, plastic bag
3. CHOKING: (Verstikking)
- Mechanical obstruction of internal airways (mouth, pharynx,
trachea).
- food bolus or FB in airway (can’t choke with hands around neck!)
4. External pressure on the neck
- Manual strangulation = Force exerted by hands on the neck (with hands around neck)
- Ligature strangulation = Force exerted by ligature on neck
- Hanging = Force exerted by ligature on the neck by applying body mass
- Neck holds = Neck holds are used by law enforcement agencies to subdue violent individuals.
5. Restriction of respiratory movements
- pressure applied to chest
- Traumatic/ mechanical asphyxia
- Positional asphyxia
- Paralysis of respiratory muscles
6. Drowning
- Inhalation of fluid (not just water!)
7. Toxic gasses
- Inhalation CO/ H2S/ HCN
8. (Aspiration of stomach contents)
- Choking!
Environmental suffocation
- Decreased or inadequate oxygen in the atmosphere due to environmental conditions.
Actual reduction of oxygen in the environment:
- Shipwreckswhereoxygenreactswithmetalstoformrust.
- Siloswherefungiconsumeoxygenfortheirownmetabolicprocesses.
- FiresconsumeoxygenandproduceCO2andCO(andothertoxicgases).
Displacement of oxygen by inert gasses:
- SiloswherefungiproduceCO2=Carbondioxidenarcosis
- Shipwrecks where N2 accumulates from the metabolic processes of micro-organisms = Nitrogennarcosis
Consumption of available oxygen:
- Closed chambers – children playing hide-and-seek in an old freezer.
- Defective SCUBA apparatus
Reduction of oxygen pressure:
- Decompression with a drop in barometric pressure think airplane decompression.
- accident / homicide
Smothering
- Mechanical obstruction of external airways = mouth and nose
- Examples:
• Persons becoming entrapped/buried in the sand.
• Plastic bag secured over the head.
• Occluding the mouth and the nose by duct tape.
• Smothering with a pillow or other bedding
• Closing the mouth and the nose with the assailant’s hands and fingers. - Accident/homicide/suicide
- Minimal findings at autopsy.
- SIDS is NOT caused by smothering (diagnosis of exclusion) {sudden infant death syndrome; not the same as cot syndrome}
Gagging
- Permeable material may become impermeable due to saliva and result in smothering – a sock stuffed into the mouth, with the mouth then covered by duct tape.
- An object placed in the mouth may also result in obstruction due to swelling/edema of the tissues or displacement of the object into the pharynx
Choking
- Mechanical obstruction of the internal airways between the pharynx and bifurcation of the trachea.
- Examples:
• Foreign objects: Teeth; food; marbles; beans. Children, elderly, psychiatric patients, those with a decreased level of consciousness, Parkinson’s Disease and acute alcohol intoxication.
• Bolus deaths = “Café coronary {looks like cardio infarction}”
• Acute obstructive lesions:
➡️Allergies – is anaphylaxis an unnatural cause of death?
➡️Acute epiglottitis (Haemophilus influenza type B) – not an unnatural cause of death. - Rarely homicides: when gagging becomes choking.
- Most cases of choking are accidental.
- Post-mortem findings:
• Foreign objects in the airway
• Use a scalpel to cut open the airway
• Edema/ inflammation with acute obstructive lesions • ‘Asphyxia’ signs often absent
• Small particles of food in the airways?
Fatal pressure to neck
- Manual strangulation (with hand)
- Ligature strangulation
- Hanging
- Neck holds
Mechanisms of death
Compression of neck veins:
- Compression of the internal and external jugular veins.
- Especially potent if carotid arteries are still patent.
- Stagnant hypoxia.
- ‘Asphyxia’ signs above the level of obstruction.
- 2 kg necessary to obstruct the veins.
Compression of the carotid arterial system
- Less common than veins.
- Hypoxic hypoxia. (Can’t get O2 to brain)
- Bilateral compression: almost immediate loss of consciousness
- 5 kg necessary to obstruct the arteries.
- Occlusion of vertebral arteries is very rare.
Airway obstruction
- Direct force on the larynx/trachea or
- Lifting of the tongue and larynx with obstruction of the pharynx
- Hypoxic hypoxia.
- 15 kg necessary to obstruct the trachea.
Neurogenic stimulation
- Stimulation of baroreceptors (carotid sinus and body)
- Reflex arch:
• n Glossopharyngeus: Afferent (sensory)
• n Vagus: Efferent
- Parasympathetic effect: bradycardia – cardiac arrest
- Similar mechanism with bolus death
- Alcohol and drugs may predispose
- More common in hanging and manual strangulation, than in ligature strangulation
- Blows to the neck may stimulate sinus
Combination of mechanisms
- Changes in the grip on the neck may result in more than one mechanism playing a role
Manual strangulation (with the hands)
- Pressures of the hands, forearms, or legs on the neck will occlude the blood vessels, airways or stimulate the carotid body and sinus.
- Stagnant hypoxia, ischaemic hypoxia and hypoxic hypoxia.
- Domestic murders;
- Sexually- associated murders;
- Children
- Seldom done by women (except on children) or one man throttling another man
- Throttling is a dynamic process – the hands change grip continuously
- Suicide is not possible, as the loss of consciousness would result in the release of the pressure on the neck.
- Virtually all cases are homicides.
- A higher percentage of victims are women.
Manual strangulation postmortem findings
- Local skin contusions:
- Produced by the fingers of the assailant, and to a lesser extend the victim.
• Differ in size;
• Round to oval-shaped;
• Mostly on the side of the neck and the underside of the chin;
• May indicate left/right-handedness. - Abrasions on the neck:
- Produces by the nails of the victim and to a lesser extent, the assailant.
• Curved if static or linear if associated with movement (scratch mark)
• Examine nails and collect nail scrapings/clippings - The face appears congested and cyanotic.
- Petechial haemorrhages of the sclerae and the conjunctivae.
- Damage to underlying structures
• Hemorrhage in soft tissue and muscles of neck;
• Damage to vascular structures;
• Fractures of hyoid bone and cartilage structures (men > women/ adults > children);
• Haemorrhages in the thyroid- and submandibular glands.
Neck Holds
- Force exerted by arm on neck.
- Usually used by police forces and security agencies to subdue a victim.
Types:
- Bar arm hold
• The forearm is placed across the neck.
• The free hand then grips the wrist of the arm around the neck, pulling the arm backward.
• Pushing on the trachea.
• Displacing the tongue upwards into the oropharynx.
• Hypoxic hypoxia.
- Carotidsleeper
• An arm is placed around the front of the neck.
• Cradling the midline of the neck the antecubital fossa.
• The free hand then grips the wrist of the arm around the neck.
• Pulling it backwards.
• Creating a pincer effect by the forearm
and the arm.
• Compression of the carotid arteries with preservation of the airways.
• Stagnant and Ischaemic hypoxia within 10 – 15 seconds
Ligature strangulation
- Pressure on the neck, is applied by a ligature, tightened by a force other than the body weight.
• Rope, belt, thin bamboo stick, scarf.
• May be twisted > 1 time around neck.
• May be knotted.
• May cut into skin if very thin.
• May be wound up with stick (Spanish windlass). • Multiple twists and knots sometimes in suicide.
• Body mass plays no role. - Occlusion of the carotid arteries with subsequent ischaemic hypoxia.
- Homicide > accidents > suicides
- Damage to neck structures < manual strangulation
- ‘Asphyxia’ signs
• Often prominent above the ligature;
• Petechia, edema, cyanosis.
• Sometimes bleeding from ear and nose;
• Sometimes no changes (? Vaso-vagal inhibition)
Ligature strangulation postmortem findings
- Local findings
Ligature mark:
• Impression contusion/abrasion of ligature.
• Soft material may not cause any skin damage.
• Ligature may be deeply embedded due to edema.
• Usually encircles the neck.
• Runs horisontally.
• Low in the neck: at or below laryngeal prominence.
• Sometimes cross-over point in ligature.
- Scratch marks on the neck caused by the victim.
Hanging
- Type of ligature strangulation where the weight of the body tightens a noose around the neck compressing the vessels and airways.
- Not necessary for the body to be free hanging, standing, sitting or even lying down – 5kg is sufficient to compress the carotid arteries.
- Almost all hanging are suicides, occasional accidental hangings, rarely murder.
- Nooses are created from whichever material is available: nylon rope, electric cords, ties, shoelaces, sheets, belts, dog chains.
- Damage to neck structures less than in manual strangulation.
- Hypostasis of arms and legs in the gravity-dependent areas.
- ‘Asphyxia’ signs
• Usually none (vasovagal inhibition)
• Sometimes petechiae; edema, congestion, cyanosis
