Arterial PCO2 in chronic metabolic acidosis

Abstract

We have re-investigated the relationship between PCO2 and [HCO3-], using our own data and data from all other studies that have reported individual paired values of PCO2 and [HCO3-]. One purpose was to determine why the regression slope has varied from study to study. The other was to determine what regression slope does, in fact, correctly describe all of the available data, and to provide confidence limits. Using 346 observations we have found that the relationship between PCO2 and [HCO3-] is curvilinear over the range of [HCO3-] from 2 to 25 mEq/liter and, therefore, that any linear regression must be an approximation whose slope will vary with the range of [HCO3-] values of the sample of data from which it was derived. The correct function is independent of the etiology or severity of acidosis.