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  • Title: In vivo oxygen dissociation curves in transfused and untransfused newborns with cardiopulmonary disease.
    Author: Wilkinson AR, Phibbs RH, Heilbron DC, Gregory GA, Versmold HT.
    Journal: Am Rev Respir Dis; 1980 Oct; 122(4):629-34. PubMed ID: 6159811.
    Abstract:
    We used a new, rapidly responding in vivo catheter oximeter to continuously measure arterial oxygen saturation (Sao2) in 34 newborns with cardiopulmonary disease. The Sao2 was compared with the oxygen tension (Pao2) of blood sampled through the catheter in 2 groups. We evaluated the oxygen dissociation curves of 24 untransfused infants whose hemoglobin F (HbF) concentration was greater than or equal to 80%. We also examined the Sao2 curves of 20 extensively transfused infants who had greater than or equal to 80% hemoglobin A (HbA). We found a wide variation in Sao2 at levels of arterial Po2 between 30 and 90 mmHg. Although the oxygen dissociation curve of the transfused group was significantly to the right of the untransfused group, there was considerable overlapping between the 2 curves. This dispersion reflected the wide range of clinical states encountered in newborns with cardiopulmonary disease, and the changes in blood oxygen affinity. In some newborns, when Pao2 was less than 50 mmHg, Sao2 could be > 90% whereas in others, Sao2 could be < 75%. When both Pao2 and Sao2 were low, Sao2 reflected arterial oxygen contents more precisely because of the shape of the individual oxygen dissociation curves in both groups. Opinions vary as to the safe upper limit of Pao2 at which retrolental fibroplasia does not occur. The Sao2 at 2 upper limits of Pao2 (100 and 80 mmHg) was estimated by probit analysis of simultaneous measurements of Pao2 and in vivo Sao2. In both the untransfused and extensively transfused groups of newborns, Pao2 was < 100 mmHg when Sao2 was < 96%. The Pao2 was < 80 mmHg, when the Sao2 was < 92%, if the HbF was greater than equal to 80%, and when Sao2 was < 91%, if HbA was greater than equal to 80%, (95% confidence limits). The findings suggested a caveat against the practice of calculating Sao2 from measurements of pH, Pao2, and Paco2. This can be quite inaccurate when taking samples of arterial blood from newborns.
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