A new index for assessing arterial oxygen profile in patients with respiratory failure

A new index, termed 'useful ratio' of the blood oxygen binding curve, was derived on the basis of the characteristic features of hemoglobin oxygen (transported, reserve and practically non-usable hemoglobin oxygen). The index gives the ratio of the useful to the predicted total hemoglobin oxygen of patients. It is functionally related to the fraction of the measured transpulmonary shunt (FShunt), shows high correlation with the blood gases (pO2 and pCO2), correlates moderately with the hydrogen exponent, poorly with the oxygen affinity (P50) and the metabolic acid-base parameters (cHCO3), and does not show to be essentially related to the total oxygen concentration (cO2) and PO2(x), the new index proposed in the Oxygen Status Algorithm. Diagnostically, this index has much the same value as that of the calculated shunt (FShunt); it can be used only in diagnosing the conditions of hyperoxia, normoxia, and hypoxia and excludes detecting those of hyperoxemia, normoxemia, and hypoxemia. Simultaneous assessment of this index together with pO2(x) enhances further the diagnostics of respiratory insufficiency providing the necessary information about the mechanism of respiratory decompensation that is of importance for an efficacious treatment.