Der Anaesthesist
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The decrease of functional residual capacity during anaesthesia makes mechanical ventilation mandatory. Volume- and pressure-controlled modes should both be possible. Ventilator-assisted spontaneous respiration is rarely indicated during general anaesthesia, and this mode is therefore unnecessary for anaesthesia machines. ⋯ For easier management, fresh-gas-flow-compensated circle systems facilitating adjustment of tidal volume after changes of fresh gas flow are desirable. Precautions aimed at the prevention of ventilation with hypoxic gas mixtures are still insufficient: the oxygen failure devices (nitrous oxide flow shutoff valve) are only effective if oxygen pressure from the gas supply is low. Distinct improvements have been achieved with oxygen ratio systems, preventing the administration of hypoxic gas mixtures at fresh gas flows higher than 1 l/min.