New indices of arterial oxygen status: an experience on 168 subjects.

We investigated the repeatability and the clinical usefulness of assessing several parameters related to oxygen status in arterial blood. pH, PaCO2, PaO2, oxygen saturation, total hemoglobin concentration, and fractions of carboxy- and methemoglobin were measured in arterial blood. Applying a new algorithm, other parameters were calculated from the above mentioned, among which total oxygen concentration, half saturation tension, 2,3-DPG concentration, uncompensated mixed venous oxygen tension, and cardiac oxygen compensation factor. In 12 subjects we performed three simultaneous determinations of these indices with a good repeatability of the measures. Then, we examined the same parameters in 92 subjects with normal PaO2, 52 patients with respiratory failure (38 normocapnic and 14 hypercapnic), 9 of which were monitored to follow the behaviour of the measures with time according to variations of the clinical status, and in 12 subjects before and after exercise. We found that important alterations in oxygen transport and delivery may be present even when oxygen tension in arterial blood is normal. Furthermore, oxygen status of arterial blood in respiratory failure may be affected by several factors, whose knowledge is essential for a proper treatment. Our data suggest that such an approach to the evaluation of oxygen status offers interesting clinical perspectives.