Excessive airway pressure during anaesthesia. Hazards, effects and prevention

The modern continuous flow anaesthetic machine supplies gases under high pressure directly to the patient's trachea. Accidental obstruction to the outflow of expired gases is not uncommon, and may lead to the application of excessive pressure to the patient's airways with potentially disastrous results. The ways in which obstruction to outflow may occur, and the factors which affect the subsequent rise in intrapulmonary pressure are enumerated. The effects of a substained elevation of airway pressure on cardiac output are discussed and an outline is given of the sequence of events which lead from alveolar rupture to the development of mediastinal emphysema and tension pneumothorax. Finally, suggestions are made for ways in which the patient can be protected from excessive airway pressure, by routine use of a pressure-limiting reservoir bag in conjunction with a suitable pressure-limiting valve on all anaesthetic breathing attachments.