Mathematical arterialization of venous blood in emergency medicine patients

Abstract

Arterial punctures represent a painful and unpleasant experience. Acid-base and oxygenation status can be assessed from peripheral venous blood, but agreement with arterial values is not always clinically acceptable. This study evaluates a method for mathematically transforming peripheral venous values into arterial values in emergency medicine patients. Paired arterial and peripheral venous samples were analysed in groups A (47 patients) and B (101 patients), corresponding to the clinical need for arterial blood sampling (A) and without (B). Venous values were input into the mathematical arterialization method and the values of arterial pH, PCO2 and PO2 were calculated and compared with the measured values. The calculated and measured arterial pH and PCO2 values correlated well with the correlation coefficients (r ) of group A, pH 0.94, PCO2 0.97; group B, pH 0.87, PCO2 0.83; and Bland-Altman limits of agreement well within the limits of acceptable laboratory and clinical performance. The calculated values of arterial PO2 followed a set of predefined rules relating calculated and measured PO2 levels in all cases. The method represents an improvement on the use of venous blood alone where the correlation coefficients were as follows: group A, pH 0.85, PCO2 0.88; group B, pH 0.79, PCO2 0.59; and limits of agreement for PCO2 at the border of (group A) or beyond (group B) acceptable clinical limits. Application of the mathematical arterialization method may reduce the pain associated with assessment of acid-base and oxygenation status, maximize the information obtained from peripheral venous blood and allow venous measurements to be presented as more commonly interpreted arterial values.