Evaluation of univariate ranges with a multivariate standard

A re-appraisal of the tri-axial chart for monitoring arterial acid-base values

“…Only a single value needs to be set to monitor the complete acid-base status. The abnormality index takes into account the dependencies between the variables and is therefore to be preferred over setting limits for the variables separately [1]. Therapeutic actions after an alarm can then still be based on the original values.…”

“…In general, monitoring involves setting lower and upper limits for the variable in question. When monitoring the acid-base status with arterial pH, arterial carbon dioxide partial pressure (PaCO2) and actual arterial bicarbonate-ion concentration (a[HCO~]), however, the simultaneous use of lower and upper limits assumes the variables to be independent of each other, which may lead to false positive and false negative observations [1]. Moreover, the linear relationship between the variables makes separate monitoring of all three variables illogical [2].…”