ASSUMED OXYGEN-CONSUMPTION BASED ON CALCULATION FROM DYE DILUTION CARDIAC-OUTPUT - AN IMPROVED FORMULA

This study was performed because of observed differences between dye d ilution cardiac output and the Fick cardiac output, calculated from es timated oxygen consumption according to LaFarge and Miettinen, and to find a better formula for assumed oxygen consumption. In 250 patients who underwent left and right heart catheterization, the oxygen consump tion VO2 (ml.min(-1)) was calculated using Ficks principle. Either pul monary or systemic flow, as measured by dye dilution, was used in comb ination with the concordant arteriovenous oxygen concentration differe nce. In 130 patients, who matched the age of the LaFarge and miettinen population, the obtained values of oxygen consumption VO2(dd) were co mpared with the estimated oxygen consumption values VO2(lfm), found us ing the LaFarge and Miettinen formulae. The VO2(lfm) was significantly lower than VO2(dd); -21.8 +/- 29.3 ml.min(-1) (mean +/- SD), P<0.001, 95% confidence interval (95% CI) -26.9 to -16.7, limits of agreement (LA) -8-.4 to 36.9. A new regression formula for the assumed oxygen co nsumption VO2 (ass) was derived in 250 patients by stepwise multiple r egression analysis. The VO2(dd) was used as a dependent variable, and body surface area BSA (m(2)), Sex (0 fro female, 1 for male), Age (yea rs), Heart rate (min(-1)) and the presence of a left to right shunt as independent variables. The best fitting formula is expressed as: VO2( ass)=(157.3 x BSA + 10.0 x Sex-10.5 x ln Age + $.) ml.min(-1), where ln Age=the natural logarithm of the age. This formula was validated pr ospectively in 60 patients. A non-significant difference between VO2(a ss) and VO2(dd) was found; mean 2.0 +/- 23.4 ml.min(-1). P=0.771, 95% Cl=-4.0 to +8.0, LA -44.7 to +48.7. In conclusion, assumed oxygen cons umption values, using our new formula, are in better agreement with th e actual values than those found according to LaFarge and Miettien's f ormulae.