A computer program for the multivariate and graphical monitoring of acid-base data in an intensive care unit

Monitoring the arterial acid-base status of ICU patients is done by measuring and calculating the acid-base variables pH, the partial pressure of carbon-dioxide (PCO2) and the bicarbonate-ion concentration ([HCO-3]). Univariate normal reference ranges exist for these values. However, it is well known that an exact linear relationship exists between pH, the logarithm of PCO2 and the logarithm of [HCO-3] values. We developed a computer program for the multivariate evaluation and graphical monitoring of these values in an intensive care setting that takes this intrinsic two-dimensionality into account. A composite index is introduced for the monitoring of all three laboratory values. Moreover, using this index, a multivariate statistical reference region based on an unselected population of ICU patients was derived.