Inspired oxygen and Cape Bristol ventilators.

The Cape Bristol ventilator is a volume-preset machine which utilises oxygen from a flowmeter and air-entrainment attachment to provide a known inspired oxygen level. The level can be calculated from the oxygen flow rate and the patient's minute ventilation using a nomogram supplied by the manufacturers. Serious discrepancies between predicted and measured inspired oxygen levels delivered by these machines can occur and the advisability of using air entrainment devices in high oxygen dependent patients is questioned. Modification to the Cape Bristol ventilator to limit these errors are discussed and the more frequent use of oxygen monitors recommended.