Bymixer provides on-line calibration of measurement of CO sub(2) volume exhaled per breath

• Published in: Annals of biomedical engineering 1997-01, Vol.25 (1), p.164-171
• Main Authors: Breen, Peter H, Serina, Eugene R
• Format: Article
• Language: English
• Subjects: Anesthesia; Carbon dioxide; Carbon monoxide; Chambers; Circuits; Devices; Regression; Sampling; Ventilation
• ISSN: 0090-6964; 1573-9686
• DOI: 10.1007/BF02738547

The measurement of CO sub(2) volume exhaled per breath ( V CO 2 , br ) can be determined during anesthesia by the multiplication and integration of tidal flow ( V . ) and P CO 2 . During side-stream capnometry, P CO 2 must be advanced in time by transport delay (TD), the time to suction gas through the sampling tube. During ventilation, TD can vary due to sample line connection internal volume or flow rate changes. To determine correct TD and measure accurate V CO 2 , br during actual ventilation, TD can be iteratively adjusted (TD sub(ADJ)) until V CO 2 , br /tidal volume equals P CO 2 measured in a mixed expired gas collection ( P E [macr] CO 2 ) (J. Appl. Physiol. 72:2029-2035, 1992). However, ( P E [macr] CO 2 ) is difficult to measure during anesthesia because CO sub(2) is absorbed in the circle circuit. Accordingly, we implemented a bypass flow-mixing chamber device (bymixer) that was interposed in the expiration limb of the circle circuit and accurately measured ( P E [macr] CO 2 ) over a wide range of conditions of ventilation of a test lung-metabolic chamber (regression slope=1.01; R super(2)=0.99). The bymixer response (time constant) varied from 18.1c0.03 sec (12.5 l/min ventilation) to 66.7c0.9 sec (2.5 l/min). Bymixer ( P E [macr] CO 2 ) was used to correctly determine TD sub(ADJ) (without interrupting respiration) to enable accurate measurement of V CO 2 , br over widely changing expiratory flow patterns.