[Gasometric values reported in healthy subjects from the Mexican population: review and analysis]

We do not know the normal relationship between altitude and PaCO2 in Mexico. We collected and analyzed the reports of reference values for gasometry in Mexico City (2240 m above sea level and a mean barometric pressure of 585 Torr) and other places in the country. The reports include arterial, capillary and expired gases in children and adults, with measurements done in resting and exercising subjects, breathing room air and 100% oxygen. In Mexico City we found 18 studies in normal subjects reporting a mean PaCO2 ranging from 25.5 to 38.4 Torr. Averaging arterial studies from children and adults, adjusting for the number of subjects studied, and discarding data with mean pH below 7.37 or above 7.43 (suggesting non steady state), 10 studies with a total of 581 subjects have the following average values (Torr, means and SD): PaCO2 = 31.1 +/- 2.6, PaO2 = 67.7 +/- 2.6, calculated PAO2 and P(A-a)O2 73.6 +/- 3.3 y 6.1 +/- 3.7 respectively. The PaCO2 found was much lower than that reported for native Peruvians in the Andes who have a mean PaCO2 of 37.8 Torr at an altitude of 2390 m, and a mean PaCO2 of 33.0 Torr only at 4860 m above the sea level. On the other hand, the average values in Mexico are similar to those found in North Americans who have a mean PACO2 of 33.1 Torr at 2131 m of altitude, a mean PACO2 of 30.7 at 2371 m and a mean PaCO2 of 31 Torr at 2238 m. Normal values for gasometry in Mexico are scarce and some of the existing ones are erroneous probably due to lack of adequate calibrations and to poor quality control. Values of PaCO2 in Mexico are more similar to those found in the USA than to those found in Peruvian natives.