DESIGN AND REPRESENTATION OF MULTIVARIATE PATIENT-BASED REFERENCE REGIONS FOR ARTERIAL PH, PCO2 AND BASE EXCESS VALUES

Objectives: To determine and compare the shape and location of three d ata sets of arterial pH, PCO2, and BE values from intensive care patie nts in a new acid-base chart for the purpose of deriving multivariate reference regions. Design and Methods: The new chart is constructed by applying a statistical technique called principal component analysis (PCA). Three different data sets, each comprised of 1500 arterial pH, PCO2, and BE values, were subjected to PCA. The 3 data sets were colle cted in a respiratory intensive care unit (ICU) of a University Hospit al, in a general ICU of a District Hospital, and in a neonatal ICU of a Children's Hospital. Results: The outlines of the resulting charts a re similar for all 3 data sets, but the representations of the three d istributions in the new chart are highly dissimilar, both in shape and in location. Conclusions: PCA can be used to derive a patient-based r eference region for arterial pH, PCO2, and BE values. Furthermore, the new chart may be useful for the graphical monitoring of acid-base dat a because distances between consecutive observations are faithfully re presented.