[Pulmonary oxygen transfer under a respirator in anesthesia and resuscitation]

The resistance of the passage of oxygen from air to blood is estimated in measuring P(A-a)O2. This index varies with FIO2. P(a/A)O2, the index proposed by GILBERT and KEIGHLEY [18], expresses PaO2 as a percentage of PAO2. This index would be independent of FIO2. Two groups are studied. Patients of the first group (n = 22) are artificially ventilated in intensive care for severe parenchymal lesion. Those of the second group (n = 25) have no notable history of pulmonary disease and are anaesthetized and hooked up to a respiratory for surgery. Blood gases are measured and the transfer indices calculated for increasing FIO2 (0.4, 0.6, 0.8 and 1). Under conditions of anaesthesia, the effect of thermic decrease on PaCO2 is dampened by maintaining a constant PACO2 during measurement. P(a/A)O2 does not vary significantly as a function of FIO2 in the intensive care group, whereas the results observed in the anaesthetized patients are substantially dispersed. Factors which are susceptible to affect oxygen transfer as well as the effects of FIO2 increase are discussed. P(a/A)O2 stability observed in intensive care is probably related to the predominant effect of venous admixture, which is hardly affected by variations in FIO2. In anaesthesia, resistance to the transfer of oxygen appears to be linked mainly to changes in the distribution of the ventilation/perfusion ratio (reduction in CRF; pharmacological effect of oxygen on pulmonary vascular reactivity). These phenomena lead to alveolar instability and a variable shunt effect.(ABSTRACT TRUNCATED AT 250 WORDS)