RELIABILITY OF THE ARTERIAL TO END-TIDAL CARBON-DIOXIDE GRADIENT IN MECHANICALLY VENTILATED PATIENTS WITH MULTISYSTEM TRAUMA

The accuracy and reliability of the relationship between arterial and end-tidal carbon dioxide (PETCO(2) and Paco(2)), expressed as the gradient, P(a - ET)CO2, was assessed with 171 comparisons in nine mechanically ventilated trauma patients. The P(a - ET)CO2 was 14 +/- 11 mm Hg. (mean +/- standard deviation.) The positive correlation between Paco(2) (44 +/- 10 mm Hg) and PETCO(2) (30 +/- 10 mm Hg) for the study population (reflected by r = 0.64, p = 0.001; but r(2) = 0.41) indicated statistical significance, but only 40% of the changes reflected a linear relationship. Seventyeight percent of individual patients had significant correlations of Paco(2) and PETCO(2) (p < 0.02 to p < 0.001). Changes in PETCO(2) erroneously predicted the Paco(2) changes in 27% of comparisons with 15% false decreases and 12% false increases. Trends in P(a - ET)coa magnitude are not reliable, and concordant direction changes in PETCO(2) and Paco(2) are not assured.