Abstract
In order to elucidate the relationship between roentgenographic infiltrates and gas exchange disturbance in pneumonia of the aged, we investigated 48 subjects with pneumonia who had their chest roentgenogram and arterial blood gas examined simultaneously. The aged group consisted of 27 subjects (male:female=14:13, mean age=76.3 years) with the age of 65 years or above, while the young group consisted of 21 subjects (male:female=16:5, mean age=44.0 years). The area of total lung field (TL) and that of pneumonic infiltrates (PI) on a chest film of posterior-anterior view were measured using a digitizer (MITABLET-II, Graphtec Co.) and the size of pneumonic infiltrates (SI, SI=100×PI/TL (%)) was calculated. There was a significant correlation between SI and PaO2 (r=-0.499, p<0.01) in the aged as well as in the young. When the regression equation of the aged was compared with that of the young, PaO2 level of pneumonia among the elderly was much lower than that of the young for a given SI. With regard to the relationship between SI and AaDO2, significant correlation also existed both in the aged (r=0.476, p<0.01) and in the young. When the regression equations were applied to estimate the magnitude of gas exchange disturbance, AaDO2 level of pneumonia of the aged was higher than that of the young for a given SI. In order to verify the accuracy of SI measured with eyes, we examined correlation of measured area with eyes and a digitizer. The correlation was highly significant (r=0.963, p<0.01) to confirm the accuracy of measurement with eyes. In 21 subjects whose chest films were available both on posterior-anterior (PA) and lateral view, we compared the data obtained with unidirectional (SI on PA view) measurement with that of bidirectional (summed SI on PA and lateral view) measurement. The correlation was highly significant (r=0.983, p<0.01), so that little difference should be expected between both measurements except for a case with pneumonia of left lingular lobe. Through these observations, we conclude as follows. (1) In pneumonia of the aged, the most common disorder of gas exchange is deoxygenation accompanied by increase of AaDO2, which might be caused by ventilation-perfusion mismatching. (2) Early oxygen administration should be recommended in pneumonia of the elderly, considering the tendency that PaO2 level of pneumonia in the aged is much lower than that of the young for a given SI and that the aged patients are susceptible to respiratory failure.
