Expansion
Pulmonary damage from free radicals, plus central nervous system toxicity at high pressure
Expansion
Pulmonary (Lorrain Smith effect)
- Reactive oxygen species overwhelm antioxidant defences
- Tracheobronchitis within 12 to 24 hours at 100 per cent oxygen
- Diffuse alveolar damage resembling ARDS with prolonged exposure
- Generally considered safe below about 60 per cent for prolonged periods
Central nervous system (Paul Bert effect)
- Occurs above about 1.6 atmospheres partial pressure, so only in hyperbaric or diving conditions
- Twitching, nausea, visual disturbance and convulsions
Other
- Absorption atelectasis, from nitrogen washout
- Retinopathy of prematurity, from vasoproliferation after hyperoxia in the neonate
- Bronchopulmonary dysplasia in preterm infants
- Blunted hypoxic drive and worsened V/Q matching in chronic hypercapnia
The practical conclusion is to titrate oxygen to a target saturation rather than giving the maximum available: usually 94 to 98 per cent, or 88 to 92 per cent in those at risk of hypercapnic respiratory failure.