ASPHYXIA - FMT (Exam-Oriented for WBUHS Professional Exam)

1. DEFINITION

Key point (exam favourite): "Asphyxia indicates a mode of dying rather than a cause of death."

• The Essentials of FMT 36th ed., p. 143

2. IMPORTANT PHYSIOLOGICAL FACTS (Frequently Asked in Short Notes)

3. TYPES AND CAUSES OF ASPHYXIA

(1) Mechanical Asphyxia

• (a) Smothering - closure of external respiratory orifices (nose and mouth) by hand, cloth, mud
• (b) Hanging / Strangulation / Throttling - external pressure on neck occluding air passages
• (c) Choking - foreign bodies in larynx or pharynx
• (d) Drowning - air passages filled with fluid
• (e) Traumatic Asphyxia - external compression of chest/abdominal walls preventing respiratory movements

(2) Pathological Asphyxia

• Bronchitis, acute oedema of glottis, laryngeal spasm, tumors, abscess
• Paralysis of respiratory muscles (e.g., acute poliomyelitis)

(3) Toxic Asphyxia

• CO poisoning - reduces hemoglobin's capacity to bind oxygen
• Cyanide poisoning - blocks enzymatic utilization of O2 by tissues
• Opium, barbiturates, strychnine - paralyze respiratory center
• Gelsemium - paralyzes muscles of respiration

(4) Environmental Asphyxia

• Insufficient O2 in enclosed spaces (disused refrigerator, trunk)
• Irrespirable gases (sewer gas, CO, CO2)
• High altitude

(5) Traumatic Asphyxia (causes)

• Pulmonary thromboembolism (femoral vein thrombosis from lower limb injury)
• Pulmonary fat embolism (fracture of long bones)
• Pulmonary air embolism (incised wound of internal jugular vein)
• Bilateral pneumothorax (chest wall or lung injuries)

(6) Postural Asphyxia

(7) Iatrogenic Asphyxia

4. PATHOLOGY OF MECHANICAL ASPHYXIA

Pathophysiology of Neck Compression:

1. Compression of neck → occlusion of jugular veins → venous drainage from head blocked
2. Arterial supply via carotid and vertebral arteries continues
3. Impaired oxygenation → reduced O2 content of arterial blood
4. Reduced O2 tension → capillary dilatation
5. Stasis of blood in dilated capillaries and venules → capillo-venous engorgement
6. Blood stasis → congestion of organs, diminished venous return → anoxia → more capillary dilatation (vicious cycle)

5. CARDINAL SIGNS OF ASPHYXIA

A. Petechial Hemorrhages (Tardieu Spots)

• Fine pin-point hemorrhages, usually dark red/brownish-red
• Described by Tardieu (1855) - called Tardieu spots - seen in the subpleural and subpericardial surfaces, beneath conjunctivae, sclera, eyelids, face and scalp
• Mechanism: Sudden, sharp rise in intravascular pressure → rupture of capillaries
• Seen in strangulation, throttling, smothering (neck compression types)
• Seen in subpleural areas (especially Tardieu spots on lung surface and heart)
• NOT specific to asphyxia - also seen in whooping cough, eclampsia, septicemia, and any cause of raised venous pressure

Exam key: Tardieu spots are most characteristic of strangulation (throttling). They are present in subconjunctival and subpleural regions.

B. Cyanosis

• Definition: >5 g/100 mL of whole blood in the form of reduced hemoglobin
• Seen on skin (hypostatic livid stains), lips, ears, tip of nose, fingernails, cheeks
• Internal: lungs, liver, spleen, kidneys, meninges
• Essential cause: Diminished oxygen tension in blood + rise in proportion of reduced hemoglobin
• Methemoglobin and sulfhemoglobin also cause cyanosis
• When head is lower than body: marked congestion, cyanosis, and petechial hemorrhages are common

C. Congestion and Oedema

• Congestion - passive engorgement of organs due to venous stasis
• Oedema of lungs, brain - from anoxia-induced capillary damage

D. Fluidity of Blood

• Blood remains fluid due to release of fibrinolysin from endothelium (defense mechanism against stagnation/slowing of blood flow)
• Blood is dark blue and remains fluid for 4-6 hours until postmortem clotting
• Important: Right-sided heart dilatation and blood fluidity are now considered obsolete signs - seen in any type of congestive death including primary heart failure

6. THE ASPHYXIAL TRIAD (Asphyxial Stigmata)

1. Cyanosis
2. Petechial (Tardieu) hemorrhages - facial, palpebral, bulbar (conjunctival), subpleural
3. Visceral congestion (particularly lungs, liver, brain)

Exam key: Asphyxia is NOT a pathological entity and cannot be clearly recognized from morbid anatomical findings alone. The triad is NOT pathognomonic.

7. STAGES OF ASPHYXIA (Four Classical Stages)

Total duration of death from asphyxia: approximately 4-5 minutes Note: Death can occur in any stage - e.g., vagal inhibition in stage 1, or sudden tracheal blockage before stages develop.

8. HISTOLOGICAL SIGNS OF ASPHYXIA

1. Partial disruption of alveolar septa with distinctive hemorrhage within alveoli and intra-alveolar oedema fluid
2. Brick-red discoloration of nerve cells in cerebral cortex (in stained neurological sections); pallor and vacuolar degeneration of Purkinje cells in cerebellum
3. Vacuolar degeneration of liver cells in prolonged suffocation

9. ABSENCE OF CLASSIC SIGNS

• Sudden blockage of trachea by food (rapid vagal inhibition)
• Plastic bag pulled over head
• When victim enters a space devoid of oxygen
• Deaths in infants (difficult to demonstrate)

10. DELAYED DEATHS FOLLOWING ASPHYXIA

• Higher cortical centers suffer first from hypoxic injury → basal ganglia → vital centers
• Delayed deaths follow periods of unconsciousness from anoxic cerebral damage → hypostatic pneumonia
• Other causes of delayed death:
  • Massive subcutaneous and mediastinal emphysema from tracheal/laryngeal lacerations
  • Occlusion of airway due to oedematous/hemorrhagic swelling of pharyngeal tissues or aryepiglottic folds
• When death occurs hours, days or weeks after the asphyxial episode, the proximate cause remains the traumatic incident

11. TRAUMATIC ASPHYXIA (Crush Asphyxia)

• Heavy weight pressing on chest or upper abdomen making respiration impossible
• Common causes: Person pinned under vehicle (jack slips), cave-in burial (head above ground), crowd crush
• Autopsy findings:
  • Congestion of head, neck, upper trunk with numerous petechiae in these areas
  • Petechiae in sclerae, conjunctivae, periorbital skin
  • Retinal hemorrhages may be present
  • Internally: often no evidence of trauma despite heavy weight on chest

12. POSITIONAL ASPHYXIA

• Occurs when body position prevents normal breathing
• Common in persons incapacitated by drugs/alcohol
• Found face-down or head-down with neck flexed
• Autopsy: features of asphyxia; no other cause of death found
• Important in medico-legal context (custody deaths)

13. MEDICOLEGAL IMPORTANCE

14. KEY EXAM-FOCUSED POINTS (WBUHS Pattern)

Commonly Asked Long Questions:

• "Describe the signs and symptoms of asphyxia. How will you differentiate asphyxia from other causes of death?" - Include all cardinal signs, stages, and stigmata.
• "What is asphyxia? Classify it. Describe the autopsy findings in mechanical asphyxia."

Commonly Asked Short Notes:

• Tardieu spots - subpleural/subpericardial/subconjunctival petechial hemorrhages described by Tardieu 1855; caused by sudden rise in intravascular pressure; NOT pathognomonic
• Cardinal signs of asphyxia - Petechiae, Cyanosis, Congestion, Fluidity of blood
• Stages of asphyxia (4 stages, ~4-5 min total)
• Cyanosis threshold - >5 g/100 mL reduced hemoglobin
• Obsolete signs - right-sided cardiac dilatation and blood fluidity (not specific)
• Traumatic asphyxia - crush asphyxia; congestion above level of compression

Critical "Must Know" One-Liners:

• Asphyxia = mode of dying, NOT cause of death
• Thumb rule: breathing stops in 20 seconds of cardiac arrest; heart stops in 20 minutes of respiratory arrest
• Brain uses 20% O2 despite being only 1.4% body weight
• Cortex irreversible damage: 3 min; Basal ganglia: 6-7 min; Vagal center: 9-10 min
• Tardieu spots most marked in: throttling > strangulation > smothering
• Throttling is always homicide
• In putrefied bodies, petechiae under eyelids = evidence of mechanical asphyxia
• Delayed death: proximate cause is still the traumatic asphyxial episode