A multi-dimensional analysis of three chemical quantities in the blood

A three-dimensional model for the analysis of the three quantities pH, pCO2 and base excess (BE), as measured in arterial blood, is presented. Whereas the conventional analysis of these quantities relies on reference regions as established from the univariate distributions, treating the quantities as uncorrelated, the present model estimates the parameters of the three-dimensional reference region from a sample of observations, based on the assumption that the observations inside the reference region follow a multi-dimensional Gaussian distribution. For observations outside the reference region, reference directions are established, corresponding to the conventionally defined specific states of acid-base disturbances. This leads to a new classification model, the results of which are compared to those of the conventional model.