Novel, adjustable, clinical bymixer measures mixed expired gas concentrations in anesthesia circle circuit.

UNLABELLED: We have introduced a novel, parallel design into a new clinical bymixer (patent pending), named for the bypass of a constant fraction of total flow through a mixing chamber. Over a wide range of tidal volumes (300-1200 mL), frequency (6-20 breaths/min), and PCO(2) (6-50 mm Hg), the bymixer provided accurate measurement of mixed expired gas fractions in the ventilation circuit compared with an expired gas collection in a metabolic lung bench setup (average slope, 1.00; average y intercept, -0.01; average coefficient of determination, R(2) = 0.9988). Simple changes in mixing chamber volume provided adjustable bymixer response times. The fast bymixer response (time constant, 6.4 s) should allow measurements to be updated every 20 s (where 95% response occurs by three time constants). The new clinical bymixer is constructed from standard anesthesia circuit components, attaches easily to the anesthesia machine inspired outlet and expired inlet ports, is simple to clean and sterilize, and has no reservoir to trap condensed water vapor from expired gas. The new clinical bymixer may facilitate indirect calorimetry (CO(2) elimination, VCO(2), and oxygen uptake, VCO(2)) during anesthesia and the noninvasive detection of metabolic upset (e.g., onset of anaerobic metabolism) and critical events (e.g., pulmonary embolism). IMPLICATIONS: A new clinical bymixer (inline mixing chamber) provides a fast response and accurate measurements of mixed expired gas fractions in the anesthesia circle circuit. A novel parallel design facilitates adjustable response, easy cleaning, and construction from standard airway circuit components. The new clinical bymixer may facilitate widespread introduction of indirect calorimetry during anesthesia.