['Anesthesia ventilators use oxygen or oxygen/air mixtures to drive the bellows during controlled ventilation. As a practitioner may find himself in a situation that the only available oxygen source is a compressed oxygen cylinder, it is important to know the oxygen consumption of anesthesia ventilators during controlled ventilation.', 'We tested the Datex-Ohmeda 7900 ventilator mounted on an Excel 210 anesthesia machine under a variety of conditions. For comparison, we also tested the Ohmeda 7800 and the Dräger AV-2 ventilator under control conditions. All experiments were performed using a test lung.', 'The oxygen consumption of the AV-2 and the Datex-Ohmeda ventilators averaged 302 +/- 17 L x hr(-1) and 564 +/- 68 to 599 +/- 56 L x hr(-1), respectively (P < 0.01 AV-2 vs 7800 and 7900). When using an E-type cylinder, this would result in a mean time to alarm of 93 min and 54 to 57 min, respectively. Decreased lung compliance increased the oxygen consumption to 848 +/- 16 L x hr(-1).'] Do contemporary anesthesia ventilators incur a significant `` oxygen cost ''?