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 data sets of arterial pH, PCO2, and BE values from intensive care patients 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 collected in a respiratory intensive care unit (ICU) of a University Hospital, 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 are similar for all 3 data sets, but the representations of the three distributions in the new chart are highly dissimilar, both in shape and in location.

CONCLUSIONS

PCA can be used to derive a patient-based reference region for arterial pH, PCO2, and BE values. Furthermore, the new chart may be useful for the graphical monitoring of acid-base data because distances between consecutive observations are faithfully represented.