Define asphyxia
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Here is a comprehensive definition of asphyxia:
Asphyxia
Asphyxia (also called asphyxiation) is a condition arising from interference with respiration that results in simultaneous hypoxia (oxygen deficiency) and hypercapnia (carbon dioxide accumulation) in the body, leading to generalized oxygen deprivation of the tissues.
Core Definition
At its most basic level, asphyxia represents a failure of gas exchange — oxygen cannot reach the tissues and carbon dioxide cannot be eliminated. This differs from simple hypoxia (low O₂ alone) because asphyxia characteristically involves the combined buildup of CO₂ alongside the loss of O₂.
In the context of fetal/neonatal medicine, asphyxia is defined as persistently impaired gas exchange leading to hypoxemia, hypercapnia, and fetal acidosis. Severe fetal acidemia is defined as an umbilical arterial pH < 7.00 and is associated with increased risk of adverse neurologic outcome. — Creasy & Resnik's Maternal-Fetal Medicine
Pathophysiology
When the airway is occluded (a common mechanism):
- Acute hypercapnia and hypoxia develop simultaneously
- Respiratory stimulation becomes pronounced — violent respiratory efforts ensue
- Blood pressure and heart rate rise sharply; catecholamine secretion increases
- Blood pH drops (acidosis)
- Respiratory efforts eventually cease, blood pressure falls, and the heart slows
- At this stage, the individual can still be revived by artificial respiration, though ventricular fibrillation is a serious risk (due to hypoxic myocardial damage combined with high circulating catecholamines)
- Without intervention, cardiac arrest occurs within 4–5 minutes
— Ganong's Review of Medical Physiology
Types of Asphyxia
| Type | Mechanism |
|---|---|
| Mechanical / Physical | Airway obstruction by a foreign body, compression of the chest, or external neck compression |
| Positional | Body positioned such that respiration is mechanically impaired (e.g., prone restraint) |
| Traumatic | Large compressive force applied to the chest/upper abdomen → venous hypertension in the SVC → petechiae, facial cyanosis, subconjunctival hemorrhage, neurologic symptoms |
| Strangulation | External compression of the neck (manual, ligature, or hanging) |
| Drowning | Asphyxia caused by immersion; ~10% of drownings involve fatal laryngospasm without water entering the lungs |
| Chemical | A chemical agent prevents oxygen from reaching cells (e.g., carbon monoxide, cyanide) |
| Fetal / Perinatal | Interrupted placental or umbilical blood flow → impaired gas exchange → hypoxic-ischemic encephalopathy |
Clinical Consequences
- CNS: Brain damage is the primary and most feared consequence; cerebral edema often complicates resuscitation after prolonged asphyxia
- Cardiac: Ventricular fibrillation risk; cardiac arrest within minutes if untreated
- Neonatal: Perinatal asphyxia is a leading cause of hypoxic-ischemic encephalopathy (HIE), intellectual disability, and cerebral palsy
Key Distinction
| Term | Meaning |
|---|---|
| Asphyxia | Oxygen not reaching the airways/lungs (gas exchange failure) |
| Hypoxia | Low O₂ in blood or tissue |
| Hypoxemia | Low O₂ partial pressure in blood |
| Ischemia | Reduced blood flow to tissues |
Asphyxia leads to both hypoxia and hypercapnia, whereas isolated hypoxia (e.g., altitude sickness, anemia) does not necessarily involve CO₂ retention.
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