Patent ID: 8701659

Claim:
A patient ventilation system comprising: a breathing circuit comprising an inspiration channel and an expiration channel adapted for connection to a patient; a flow regulating and gas mixing arrangement connected to said breathing circuit that delivers a gas mixture comprising oxygen and at least a second gas to the patient via the expiratory channel; a control unit configured to control operation of said flow regulating and gas mixing arrangement; a gas identification unit configured to initiate an attempt to identify said second gas by actively measuring a first value dependent on a characteristic of said second gas that distinguishes said second gas from gases other than said second gas; said control unit being configured to monitor said attempt by said gas identification unit to identify said second gas and, if said attempt fails to identify said second gas, in response to said attempt failing to identify said second gas, to cause said flow regulating and gas mixing arrangement to, at least temporarily, change a concentration of said second gas in said gas mixture; and said gas identification unit being configured, after said change in concentration, to initiate a subsequent attempt to identify said second gas by actively measuring a second value dependent on said characteristic of said second gas and to identify said second gas from said second value alone or in combination with said first value.