A gas measurement module configured to be inserted into a respiratory circuit that is in fluid communication with an airway of a subject, the gas measurement module comprising: a chamber having a first opening and a second opening, wherein the chamber is configured to form a flow path between the first opening and the second opening such that if the gas measurement module is inserted into the respiratory circuit, gas from the airway of the subject is transported through the flow path; an infrared source configured to emit infrared electromagnetic radiation along an optical path that passes through the flow path formed by the chamber; a movable filter member including a first filter element configured to filter electromagnetic radiation in a first wavelength band and a second filter element configured to filter electromagnetic radiation in a second wavelength band; a photosensitive detector held at a fixed position along the optical path to receive infrared electromagnetic radiation that has been filtered by the filter member and has passed through the flow path formed by the chamber, and to generate output signals that convey information related to one or more parameters of the received infrared electromagnetic radiation; and an actuator configured to actuate the filter member between a first position and a second position, wherein at the first position the first filter element is positioned in the optical path, and wherein at the second position the second filter element is positioned in the optical path; characterized in that the gas measurement module further comprises one or more of (i) a gate positioned to selectively block the optical path, wherein the electromagnetic radiation is blocked by said gate from becoming incident on the filter member as filter member is being actuated between the first position and the second position,, (ii) a switch configured to selectively connect the photosensitive detector with a processor, wherein the switch is configured to selectively disconnect the photosensitive detector from the processor if the filter member is between the first position and the section position, and to connect the photosensitive detector with the processor if the filter member is at the first position or the second position, and (iii) one or more controllers that control the infrared source and/or the actuator, wherein the infrared source is controlled to emit the electromagnetic radiation in pulses that are coordinated with the filter member being positioned at a position corresponding to a filter element (44, 46).. a chamber having a first opening and a second opening, wherein the chamber is configured to form a flow path between the first opening and the second opening such that if the gas measurement module is inserted into the respiratory circuit, gas from the airway of the subject is transported through the flow path; an infrared source configured to emit infrared electromagnetic radiation along an optical path that passes through the flow path formed by the chamber; a movable filter member including a first filter element configured to filter electromagnetic radiation in a first wavelength band and a second filter element configured to filter electromagnetic radiation in a second wavelength band; a photosensitive detector held at a fixed position along the optical path to receive infrared electromagnetic radiation that has been filtered by the filter member and has passed through the flow path formed by the chamber, and to generate output signals that convey information related to one or more parameters of the received infrared electromagnetic radiation; and an actuator configured to actuate the filter member between a first position and a second position, wherein at the first position the first filter element is positioned in the optical path, and wherein at the second position the second filter element is positioned in the optical path; (i) a gate positioned to selectively block the optical path, wherein the electromagnetic radiation is blocked by said gate from becoming incident on the filter member as filter member is being actuated between the first position and the second position,, (ii) a switch configured to selectively connect the photosensitive detector with a processor, wherein the switch is configured to selectively disconnect the photosensitive detector from the processor if the filter member is between the first position and the section position, and to connect the photosensitive detector with the processor if the filter member is at the first position or the second position, and (iii) one or more controllers that control the infrared source and/or the actuator, wherein the infrared source is controlled to emit the electromagnetic radiation in pulses that are coordinated with the filter member being positioned at a position corresponding to a filter element (44, 46)..