Analytic study of pulmonary shunt fraction with changes in inspired oxygen concentration Part 1. A review of the literature
Marukawa, S.; Iwai, S.
Masui. Japanese Journal of Anesthesiology 30(7): 681-687
1981
ISSN/ISBN: 0021-4892 PMID: 7321157 Document Number: 176950
To explain the cause of diversified changes in pulmonary shunt fraction in response to inspired O2 concentration (FIO2), previous clinical and experimental data were analyzed in the following aspects; underlying pulmonary disease, ventilation mode, low and high inspired FIO2, and alveolar (PAO2) and arterial O2 tension (PaO2). Patients who showed an increased shunt fraction when the FIO2 was increased were compared to those who showed a decreased shunt fraction. A wide discrepancy was observed in the mode of ventilation and the level of low inspired FIO2 with only a few exceptions. No significant difference was noted in underlying pulmonary disease. Without exception, PaO2 at low FIO2 was definitely lower in the decreased shunt fraction group wherein it did not exceed 93 mm Hg. PaO2 was > 100 mm Hg in the increased group. These phenomena and the unchanging, biphasic or triphasic response in shunt fraction to changes in FIO2 may be explained by the changes in shunt fraction being attributed to PaO2 rather than to PAo2 and assuming a characteristic biphasic pattern, i.e., it decreases when PaO2 is < 100-150 mm Hg and increases when PaO2 is above this level. The mechanism of the changes may be mainly based on the shape of the blood O2 content curve.