Alveolar collapse and closure of airways: regular effects of anaesthesia.

Oxygenation is impaired in almost all subjects during anaesthesia, and hypoxaemia for shorter or longer periods is a common finding. Moreover, postoperative lung complications occur in 3-4% after elective surgery, and up to 20% in emergency operations. Rapid collapse of alveoli on induction of anaesthesia and more widespread closure of airways seem to explain the oxygenation impairment and may also contribute to postoperative pulmonary infection, Causative mechanisms to atelectasis and airway closure seem to be loss of respiratory muscle tone and gas resorption. Avoiding high inspired oxygen fractions during both induction and maintenance of anaesthesia prevents or reduces atelectasis, while intermittent 'vital capacity' manoeuvres, recruit atelectatic lung regions.