Involvement of cough reflex impairment and silent aspiration of oral bacteria in postoperative pneumonia: a model of aspiration pneumonia

Postoperative pneumonia (PP) occurs in elderly subjects whose cough reflex (CR) is impaired postoperatively. This finding indicates that silent aspiration of oral bacteria may be involved in PP. This study aimed to clarify the involvement of CR impairment and silent aspiration of oral bacteria in PP. Intraoperative bronchial aspirates (BA) from 22 subjects aged over 60 years undergoing lung resection were cultured anaerobically on blood agar plates. The CR of all subjects was measured on 1st postoperative day. Eleven subjects showed impaired CR, whereas 11 showed normal. The bacterial amounts in intraoperative BA of subjects with postoperatively impaired CR were found to be higher than those with normal CR. PP occurred in 2 out of 11 subjects with impaired CR but not in 11 subjects with normal CR. These results suggest that impairment of the CR and silent aspiration of oral bacteria may be associated with the development of PP in elderly subjects.