Comparison of two formulas to calculate alveolar oxygen tension in canine oleic acid pulmonary edema.
Alveolar oxygen tension (PAO2) is calculated by either of two mathematical formulas incorporating various respiratory variables. The first formula, Equation 1, assumes a constant RQ of 0.8; the second formula, Equation 2, uses the mixing equation and requires analysis of inspired, mixed expired, and end-tidal gas samples. We tested the consistency of these formulas before and after asymmetric oleic acid pulmonary edema, then calculated and compared venous admixture values using the PAO2 value derived from each formula. Before oleic acid, Equations 1 and 2 were similar (213 +/- 22 vs. 211 +/- 22 [SD] torr, respectively), as were venous admixture values (8.7 +/- 2.9% vs. 8.5 +/- 2.9%, respectively). After oleic acid injury, Equation 1 was significantly lower than Equation 2, thus slightly but consistently underestimating venous admixture (29.9 +/- 12.2% vs. 30.2 +/- 12.3%; p less than .01). However, the venous admixture values obtained after oleic acid injury calculated from Equations 1 and 2 correlated closely (r2 = .998; p less than .001), and the clinical differences yielded by the two formulas would be minimal. We recommend using the simpler formula (Eq. 1) when calculating PAO2.
Johnston
W E
WE
Department of Anesthesia, Wake Forest University Medical Center, Winston-Salem, NC 27103.
Vinten-Johansen
J
J
Strickland
R A
RA
Bowton
D L
DL
D000818:Animals; D004285:Dogs; D008433:Mathematics; D019301:Oleic Acid; D009829:Oleic Acids; D010100:Oxygen / Q000032:analysis*; D010313:Partial Pressure; D011650:Pulmonary Alveoli / Q000032:analysis*; D011654:Pulmonary Edema / Q000139:chemically induced / Q000378:metabolism*
D009829:Oleic Acids; D019301:Oleic Acid; D010100:Oxygen