Objective: To determine if oxygen consumption (V over dot O-2) calcula
ted using the Fick relationship (calculated V over dot O-2) determines
total body V over dot O-2 accurately and precisely enough to employ t
his method during clinical assessment of oxygen transport. Design: Met
hods comparison, using repeated measures during four physiologic state
s: normal heart/normal lungs, heart failure/normal lungs, normal heart
/acute lung injury, heart failure/acute lung injury. Settings: Univers
ity research laboratory. Subjects: Thirteen adult Yucatan pigs. Interv
entions: Oleic acid-induced acute lung injury; heart failure was induc
ed with a continuous infusion of esmolol. Measurements and Main Result
s: Calculated V over dot O-2 was determined by multiplying thermodilut
ion cardiac output by the arterial-venous oxygen content difference in
anesthetized, spontaneously breathing animals. Conditions were tightl
y controlled so that calculated V over dot O-2 would be as accurate as
possible. ''True'' V over dot O-2 was measured simultaneously with a
water sealed spirometer (spirometry V over dot O-2). Calculated V over
dot O-2 and spirometry V over dot O-2 were determined and analyzed du
ring the four physiologic states listed above. Pooled data also were e
valuated. Mean spirometry V over dot O-2 and calculated V over dot O-2
differed significantly during all four physiologic states and when da
ta were pooled (spirometry V over dot O-2 273 +/- 70, calculated V ove
r dot O-2, 178 +/- 58 mL/min; p < .01). Calculated V over dot O-2 cons
istently underestimated spirometry V over dot O-2, as demonstrated by
the large, positive bias in pooled data (95 +/- 59 mt of oxygen/min) a
nd in the four physiologic states. Linear regression of data from all
four states yielded slopes that were indistinguishable from 1, but y i
ntercepts that varied from -152 to +182. For pooled data, the followin
g equation was used: calculated V over dot O-2 = 0.5 x (spirometry V o
ver dot O-2 + 46); r(2) = .35. Precision in pooled data was 22% of the
mean spirometry V over dot O-2. Data analysis for the four physiologi
c states demonstrated results similar to those results obtained when d
ata were pooled. Conclusions: Even in a tightly controlled, clinical s
imulation in the laboratory, calculated V over dot O-2 from the Fick r
elationship systematically underestimated V over dot O-2 measured with
a water-sealed spirometer. If true V over dot O-2 changes, the magnit
ude and direction of change will be reflected by calculated V over dot
O-2 but with similar to 20% error in the absolute value. Heart failur
e, acute lung injury, and their combination did not affect the accurac
y of calculated V over dot O-2. Therefore, calculating V over dot O-2
using the Fick relationship is too inaccurate to be used for research
purposes. Because assessment of the directional change of V over dot O
-2 may be clinically useful, calculated V over dot O-2 can be employed
with discretion during clinical oxygen transport evaluation, bearing
in mind the calculation's inherent imprecision.