Journal of Applied Physiology, Vol 68, Issue 2 787-791, Copyright © 1990 by American Physiological Society
Alveolar dead space does not affect indirect Fick cardiac output determinations
J. M. Badgwell and J. E. Heavner
Department of Anesthesiology, Texas Tech University, Health Sciences Center, Lubbock 79430.
We examined the influence of three variables (different breathing circuits,
breath selected for analysis, and alveolar dead space ventilation) on the
accuracy of noninvasive cardiac output determinations with the Fick CO2
(indirect) equation. We compared noninvasive determinations with invasive
thermodilution measurements over a wide range of cardiac outputs in 17
2-mo-old pigs anesthetized with halothane and nitrous oxide and paralyzed
with either pancuronium or d-tubocurare. We found that rebreathing and
nonrebreathing circuits provide accurate cardiac output determinations and
that the optimal breath for analysis with either the rebreathing or
nonrebreathing technique appears to depend on the cardiac output. When
alveolar dead space was increased by using positional changes and the
intracardiac administration of glass beads, there was still a good
correlation between noninvasive and invasive cardiac output determinations.
We conclude that both rebreathing and nonrebreathing techniques of indirect
Fick cardiac output determinations correlate well with thermodilution
measures over a wide range of cardiac outputs and alveolar dead space/tidal
volume fractions.
