Bymixer system can measure O2 uptake and CO2 elimination in the anesthesia circle circuit.
BACKGROUND
The ability to measure carbon dioxide elimination (Vco(2)), oxygen uptake (Vo(2)), and R (respiratory exchange ratio, Vco(2)/Vo(2)) during anesthesia may help the non-invasive detection of critical events (e.g., abrupt decrease in cardiac output) and metabolic upset (e.g., onset of anaerobic metabolism).


METHODS
We have developed a new clinical bymixer (inline mixing chamber) that can measure mixed inspired and expired gas fractions in the anesthesia circle circuit. The addition of a standard anesthesia gas analyzer and flowmeter, and a new airway temperature and humidity sensor, allow determinations of Vco(2) and Vo(2) at the airway opening of the circle circuit. Over a range of tidal volume and frequency, Vco(2) and Vo(2) were compared to reference values generated by the combustion of metered liquid ethanol in a new metabolic lung simulator.


RESULTS
By linear regression, bymixer-flow measurements of Vco(2) (slope = 1.02, Y-intercept = -5.31, coefficient of determination, R(2) = 0.998) and Vo(2) (slope = 1.05, Y-intercept = -4.34, R(2) = 0.993) correlated closely to the reference values generated by the metabolic lung simulator. Limits of agreement analysis generated percent errors (mean +/- 1.96 SD) of -1.2 +/- 7.2% for Vco(2) and 2.5 +/- 9.8% for Vo(2).


CONCLUSIONS
The new clinical bymixer is compact, lightweight, disposable, inexpensive, and has a fast and adjustable response time (time constant about 14 sec). Anesthesia circle circuit integrity is maintained. Bymixer-flow measurements of Vco(2) and Vo(2) are accurate and may add to clinical monitoring under anesthesia and surgery.
Rosenbaum
Abraham
A
Department of Anesthesiology, UCI Medical Center, Orange, CA 92868, USA.
Kirby
Christopher W
CW
Breen
Peter H
PH
D000465:Algorithms; D000693:Anaerobiosis; D000764:Anesthesia, Closed-Circuit; D002153:Calorimetry, Indirect; D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism*; D002302:Cardiac Output / Q000502:physiology; D003198:Computer Simulation; D003625:Data Collection; D000431:Ethanol / Q000737:chemistry; D006801:Humans; D006813:Humidity; D016014:Linear Models; D008168:Lung / Q000378:metabolism; D008953:Models, Anatomic; D010100:Oxygen / Q000032:analysis*; D010101:Oxygen Consumption / Q000502:physiology*; D012016:Reference Values; D012212:Rheology; D013696:Temperature
D002245:Carbon Dioxide; D000431:Ethanol; D010100:Oxygen