[Barometric pressure and respiratory quotient for estimating the alveolar-arterial oxygen gradient].
OBJECTIVE
To evaluate how they influence in the calculatión of the alveolar-arterial oxygen difference (AaPO2) the measurement of the barometric pressure (Pb) and respiratory quotient (R), in patients with chronic respiratory disease.


METHODS
Prospective study of 39 patients with chronic respiratory disease in stable situation. We calculate: 1. AaPO2 (PAO2 - PaO2) through the equation of the alveolar air [PAO2 = PIO2 - PaCO2 [FiO2 + (1 - FiO2)/R)], assuming Pb = 760 mmHg and R = 0.8 and 2. Real AaPO2, with the figures measured of Pb and R.


RESULTS
The values of AaPO2 and real AaPO2 were (mean +/- SD) 27.85 +/- 9.32 mmHg and 34.23 +/- 11.17 mmHg, respectively (p = 0.000). The figure of real AaPO2 is greater than AaPO2 in 34 patients, of those which in 21 cases (53.8%) is > or = 5 mm Hg and in 8 cases (20.5%) is > or = 10 mmHg.


CONCLUSIONS
The traditional calculation of AaPO2 minimizes the severity of the pulmonary disease and it can contribute, in part, to the mistakes in the physiopathologic classification of the origin of the respiratory insufficiency (hipoxemia caused by alveolar hypoventilation and hipoxemia caused by alveolar hipoventilation complicated by other abnormalities of gas exchange).
Maya Martínez
M
M
Servicio de Neumología, Hospital Clínico Universitario, Valencia.
Carrión Valero
F
F
Díaz López
J
J
Marín Pardo
J
J
D000368:Aged; D001158:Arteries; D001784:Blood Gas Analysis; D005260:Female; D006801:Humans; D008173:Lung Diseases, Obstructive / Q000097:blood* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood* / Q000502:physiology*; D011312:Pressure; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000503:physiopathology*
D010100:Oxygen
Presión barométrica y cociente respiratorio en el cálculo del gradiente alveolo arterial de O2.