Continuous Fick cardiac output compared to continuous pulmonary artery electromagnetic flow measurement in pigs

A system for continuous Fick cardiac output measurement (CFCO) is described and compared to continuous electromagnetic pulmonary artery flow (EMCO) and intermittent thermodilution (TDCO) measurements. Oxygen consumption was determined from continuous respiratory gas exchange analysis and arterio-venous oxygen difference from fiberoptic oximetry. A computer calculated cardiac output and other variables every 20 s. Seven pigs were monitored for a total of 10 h, during which cardiac output was manipulated by obstructing venous return or infusing epinephrine. 1748 pairs of EMCO and CFCO values were compared. The best correlation was obtained when CFCO was advanced 20 s with respect to EMCO (R = .89, CFCO = .99 EMCO + .16). TDCO was compared to EMCO during periods of steady state (R = .85, TDCO = .89 EMCO + 1.25, N = 139). TDCO was also compared with simultaneous CFCO (R = .87, TDCO = .89 CFCO + 1.01, N = 251). CFCO is recommended as a reliable standard of continuous cardiac output measurement. It is not a real time measurement; the technique has a time lag of approximately 20 s which is the result of the time constant of the VO2 measurement. Sources for error are discussed with suggestions for improving quality control.