Asphyxia from bardale book

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Asphyxia - The Essentials of Forensic Medicine and Toxicology (Bardale/Reddy, 36th Edition)

Definition

Asphyxia is a condition caused by interference with respiration, or due to lack of oxygen in respired air, due to which the organs and tissues are deprived of oxygen (together with failure to eliminate CO2), causing unconsciousness or death.

Key point: Asphyxia indicates a mode of dying, rather than a cause of death.

Physiological Background

Young/middle-aged adults: arterial PO2 = 90-100 mm Hg (12-13.5 KPa)
Persons >60 years: 60-85 mm Hg (8-10 KPa)
In severe/fatal asphyxia: falls to 20-40 mm Hg (3-5 KPa) - hypoxia even though Hb is 90% saturated
Brain = 1.4% of body weight but uses 20% of total oxygen
In total brain ischemia:
- Cerebral cortex function ceases after 8-15 seconds
- Brainstem ganglia ceases after 25-30 seconds
- Irreparable damage to cortex after ~3 minutes
- Basal ganglia after 6-7 minutes
- Vagal center after 9-10 minutes
Thumb rule: Breathing stops within 20 seconds of cardiac arrest; heart stops within 20 minutes of stopping of breathing
If heart continues for several minutes after breathing stops, lung weight may increase to 450-500 g

Types and Causes of Asphyxia

1. Mechanical

Air passages are blocked mechanically:

(a) Smothering - closure of external respiratory orifices (nose/mouth) by hand, cloth, mud
(b) Hanging, strangulation, throttling - external pressure on the neck closing air passages
(c) Choking - foreign bodies in larynx/pharynx
(d) Drowning - air passages filled with fluid
(e) Traumatic asphyxia - external compression of chest and abdomen interfering with respiratory movements

2. Pathological

Entry of oxygen to lungs is prevented by disease:

Diseases of the lungs: pneumonia, edema, emphysema, laryngeal spasm
Diseases of the blood: CO poisoning, met-hemoglobinemia

3. Environmental/Toxic

Lack of oxygen in environment (confined space)
Toxic gases displacing oxygen (CO2, H2S, methane)
Cyanide poisoning (prevents cellular use of oxygen)

4. Positional/Postural

Body position preventing adequate respiration (e.g., prone position with restraint)

Stages of Asphyxia (Classic 4-Stage Description)

Stage	Duration	Features
1. Dyspnoea (Engorgement)	~1 min	Rapid breathing, congestion, cyanosis begins, increased BP and HR
2. Convulsions	~1 min	Violent muscular movements, BP at maximum, loss of consciousness
3. Exhaustion (Apnoea)	~1 min	Respiratory movements cease, BP falls, reflexes lost
4. Terminal Gasping	~1 min	Irregular gasping, cardiovascular collapse, death

Total duration roughly 4-5 minutes in complete obstruction.

Signs and Symptoms of Asphyxia

External Signs (Post-mortem)

Cyanosis - Bluish discoloration of lips, nail beds, face. Due to accumulation of deoxygenated Hb (>5 g/dL deoxyHb)
Petechial hemorrhages (Tardieu's spots) - Small pinpoint hemorrhages on:
- Conjunctivae and sclerae
- Skin of face and neck
- Pleural and pericardial surfaces (internally)
- Due to rupture of small capillaries from increased venous pressure
Congestion of face - Plethoric (bloated/swollen) appearance
Fluidity of blood - Post-mortem blood remains fluid (fibrinolysis activated)
Frothy fluid - at nose and mouth (especially in drowning)

Internal Signs

Congestion of viscera - Lungs, liver, spleen, brain engorged with blood
Petechiae on pleura (Tardieu's spots), pericardium, thymus
Pulmonary edema - Lungs heavy, waterlogged, frothy
Right heart dilation - Right side of heart distended with dark fluid blood
Cyanosis of organs - Dark bluish discoloration

Tardieu's Spots

Petechial hemorrhages found on the visceral pleura and pericardium, first described by Tardieu (1855)
Also seen on conjunctivae, face, and under scalp
Caused by rupture of capillaries due to increased venous pressure from obstructed venous return during asphyxial struggle
Significance: Classic sign of asphyxia, but NOT pathognomonic - can also occur in:
- CPR, violent coughing, vomiting
- Septicemia, blood dyscrasias
- Sudden natural deaths (especially cardiac)
In putrefied bodies, presence under eyelids and conjunctivae still suggests mechanical asphyxia

Post-mortem Appearances in Asphyxia (Summary)

Feature	Finding
Face	Congested, cyanosed, swollen
Petechiae	Conjunctivae, sclerae, skin of face
Blood	Dark, fluid, does not clot
Lungs	Congested, edematous, heavy; pleural Tardieu's spots
Heart	Right side dilated; left side contracted
Brain	Congested, edematous
Abdominal organs	Congested

Absence of Asphyxial Signs

Asphyxial signs may be absent in:

Foetal hypoxia
Sudden blockage of trachea by food
Plastic bag pulled over the head
Victim entering a space devoid of oxygen
When death occurs very rapidly

In such cases, cause of death is given as "consistent with asphyxia."

Delayed Deaths Following Asphyxia

Higher cortical centers suffer first from hypoxic injury, followed by basal ganglia, then vital centers. Delayed deaths may follow due to:

Anoxic cerebral damage with unconsciousness
Hypostatic pneumonia
Massive subcutaneous and mediastinal emphysema from tracheal/laryngeal lacerations
Occlusion of airway due to edematous/hemorrhagic swelling of pharyngeal tissues or aryepiglottic folds
Pneumonia

When death occurs hours, days, or weeks after the asphyxial episode, the proximate cause of death is the traumatic incident.

- The Essentials of Forensic Medicine and Toxicology, 36th Edition (Bardale), pp. 143 onward

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